Identifying the translational gap in the evaluation of drug-induced QTc interval prolongation

AIMS

Given the similarities in QTc response between dogs and humans, dogs are used in pre-clinical cardiovascular safety studies. The objective of our investigation was to characterize the PKPD relationships and identify translational gaps across species following the administration of three compounds known to cause QTc interval prolongation, namely cisapride, d, l-sotalol and moxifloxacin.

METHODS

Pharmacokinetic and pharmacodynamic data from experiments in conscious dogs and clinical trials were included in this analysis. First, pharmacokinetic modelling and deconvolution methods were applied to derive drug concentrations at the time of each QT measurement. A Bayesian PKPD model was then used to describe QT prolongation, allowing discrimination of drug-specific effects from other physiological factors known to alter QT interval duration. A threshold of ≥10 ms was used to explore the probability of prolongation after drug administration.

RESULTS

A linear relationship was found to best describe the pro-arrhythmic effects of cisapride, d,l-sotalol and moxifloxacin both in dogs and in humans. The drug-specific parameter (slope) in dogs was statistically significantly different from humans. Despite such differences, our results show that the probability of QTc prolongation ≥10 ms in dogs nears 100% for all three compounds at the therapeutic exposure range in humans.

CONCLUSIONS

Our findings indicate that the slope of PKPD relationship in conscious dogs may be used as the basis for the prediction of drug-induced QTc prolongation in humans. Furthermore, the risk of QTc prolongation can be expressed in terms of the probability associated with an increase ≥10 ms, allowing direct inferences about the clinical relevance of the pro-arrhythmic potential of a molecule.

Comparison of the QT interval response during sinus and paced rhythm in conscious and anesthetized beagle dogs

INTRODUCTION

The aim of the present study was to compare sensitivity in detecting the drug-induced QT interval prolongation in three dog models: conscious telemetered at sinus rhythm and conscious and anesthetized dogs during atrial pacing. The test substances used represent different chemical classes with different pharmacological and pharmacokinetic profiles.

METHOD

Dofetilide and moxifloxacin were tested in all models, whereas cisapride and terfenadine were tested in the conscious telemetered and paced models. All substances were given as two consecutive 1.5-h intravenous infusions (infusions 1 and 2). The individual concentration-time courses of dofetilide, moxifloxacin, and cisapride were linked to the drug-induced effects on the QT interval and described with a pharmacokinetic-pharmacodynamic model to obtain an estimate of the unbound plasma concentrations at steady state that give a 10- and 20-ms drug-induced QT interval prolongation (CE10ms and CE20ms).

RESULTS

In the conscious telemetered, conscious paced, and anesthetized dog models, the mean CE10ms values were 1.4, 4.0, and 2.5 nM for dofetilide and 1300, 1800, and 12,200 nM for moxifloxacin. For cisapride, the CE10ms values were 8.0 and 4.4 nM in the conscious telemetered and conscious paced dog models. The drug-induced QT interval prolongation during the last 30 min of infusions 1 and 2 was comparable in the conscious models, but smaller in the anesthetized dog model. Terfenadine displayed a marked delay in onset of response, which could only be detected by the extended ECG recording.

DISCUSSION

All dog models investigated detected QT interval prolongation after administration of the investigated test substances with similar sensitivity, except for a lower sensitivity in the anesthetized dogs following moxifloxacin administration. The conscious telemetered dog model was favorable, mainly due to the extended continuous ECG recording, which facilitated detection and quantification of delayed temporal differences between systemic exposure and drug-induced QT interval prolongation.

Characterization of Dual Layered Pellets for Sustained Release of Poorly Water-Soluble Drug

The aim of this study was to develop pellet formulations that could be used to improve the dissolution and bioavailability of a poorly water-soluble model drug, cisapride. Six different types of pellets were prepared by coating sugar spheres in a fluidized bed coater. When the sugar spheres were single layered containing cisapride and solubilizer such as polysorbate 80, the resulting pellets provided an instant release of cisapride in the simulated gastric fluid. Dissolution tests carried out in the simulated intestinal fluid showed that there were negligible amounts of cisapride released, regardless of the pellet formulation. To succeed in attaining dissolution and the sustained release of cisapride at a neural pH, the single layered pellets were coated again with a coating suspension containing Eudragit RS 30D and L 30D. Scanning electron microscopy revealed that the dual layered pellets had a crack-free and spherical surface. Interestingly, the dual layered pellets provided the sustained release of cisapride in both the simulated gastric and intestinal fluids. The composition and components of the dual layers were found to be key parameters affecting the pattern of cisapride dissolution. Significant improvement in the bioavailability of cisapride was achieved when the dual layered pellets were administered orally to dogs. Overall, these results suggest that the dual layered pellets have potential as a sustained release dosage form for poorly water-soluble drugs.

Practical application of guinea pig telemetry system for QT evaluation

The purpose of this study was to evaluate a telemetry system for examining QT evaluation in the conscious free-moving guinea pig using 10 reference compounds whose effects on human QT interval are well established: 8 positive references (bepridil, terfenadine, cisapride, haloperidol, pimozide, quinidine, E-4031 and thioridazine), and 2 negative references (propranolol and nifedipine). Pharmacokinetic experiments were also performed for the 8 positive references. Telemetry transmitters were implanted subcutaneously in male Hartley guinea pigs, and the RR and QT intervals were measured. All 8 positive references prolonged QTc (QTc = k x QT/RR(1/2)) 10% or more during the 60 min observation period. When the values of the QTc changes were plotted against the serum concentrations, the resulting curves exhibited an anticlockwise hysteresis loop for all 8 references. In guinea pigs treated with haloperidol, changes of the T-wave shape from positive to flat were observed. The 2 negative references did not prolong the QTc. These findings suggest that the present telemetry guinea pig model is useful for QT evaluation in the early stages of drug development, because of the small body size of guinea pigs and their action potential configuration, which is similar to that of humans.

A novel approach to data processing of the QT interval response in the conscious telemetered beagle dog

INTRODUCTION

Drug-induced QT interval prolongation may lead to ventricular arrhythmias. The aim of the study was to optimize QT interval data processing to quantify drug-induced QT interval prolongation in the telemetry instrumented conscious dog model.

METHODS

The test substances cisapride, dofetilide, haloperidol, and terfenadine and corresponding vehicles were given to male and female beagle dogs during two consecutive 90-min intravenous infusions. Cardiovascular parameters were recorded for 24 h and exposure to the drugs was measured. The delayed response in the QT interval after an abrupt change in heart rate was investigated. Eight mathematical models to describe the QT interval-heart rate relationship were compared and different sets of covariates were used to quantify the drug-induced effect on the QT interval.

RESULTS

After an abrupt decrease in heart rate, a 75% adaptation of the QT interval was reached after 54+/-9 s. A linear model was preferred to correct the drug-induced effect on the QT interval for heart rate, vehicle effect, serial correlation, plasma concentration and time of day. All test substances significantly prolonged the QT interval.

DISCUSSION

To optimize the processing of QT interval data, the delay in QT interval response after an abrupt change in heart rate should be considered. The QT interval-heart rate relationship and vehicle response were individual-specific and corrections were therefore made individually. When estimating the drug-induced effect on the QT interval it is considered advantageous to use plasma concentration as a covariate, as well as adjusting for vehicle effect and serial correlation in measurements. The conscious dog model detected significant increases in the QT interval for all test substances investigated.

Effect of Anticholinergics (Atropine, Glycopyrrolate) and Prokinetics (Metoclopramide, Cisapride) on Gastric Motility in Beagles and Labrador Retrievers

The effect of atropine, glycopyrrolate, metoclopramide and cisapride on the antral motility was investigated in eight dogs (four Beagles and four Labradors) using passive telemetry. Both anticholinergics induced a pronounced and lasting reduction of the intensity and frequency of the contractions. A definite dose-related inhibition of the antral motility was seen in Beagles, similar for both active substances. Low doses of atropine (0.02 mg/kg BW i.m.) and glycopyrrolate (0.005 mg/kg BW i.m.) completely inhibited the gastric motility for at least 30 min, whereas higher doses (0.04 or 0.01 mg/kg BW) caused a cessation of activity for more than 3 h. In Labradors, the effects of both active substances were not so dose related and the effect of glycopyrrolate lasted at least 6 h, whereas the effect of atropine gradually decreased after 3 h. A distinct breed difference regarding the effect of the two prokinetics on the antral motility was also observed. In Beagles, the prokinetics, at a low dose (metoclopramide 0.3 mg/kg BW, cisapride 0.2 mg/kg BW), resulted in a significant increase in the amplitude integral. Higher doses (metoclopramide 0.6 mg/kg BW, cisapride 0.5 mg/kg BW) also increased the integrals of the pressure profiles, but significantly less than with the lower doses. In Labradors, both medications, mainly at higher doses, resulted in an increase of the contraction amplitudes. The low dose had no (cisapride) or only a transient effect (metoclopramide). The frequency of the antral contractions was not at all influenced by cisapride, and only in Beagles metoclopramide resulted in a dose-related increase. It is not clear if the different results in Labradors and Beagles are because of breed or body weight.

A novel predictive pharmacokinetic/pharmacodynamic model of repolarization prolongation derived from the effects of terfenadine, cisapride and E-4031 in the conscious chronic av node—ablated, His bundle-paced dog

INTRODUCTION

Terfenadine, cisapride, and E-4031, three drugs that prolong ventricular repolarization, were selected to evaluate the sensitivity of the conscious chronic atrioventricular node--ablated, His bundle-paced Dog for defining drug induced cardiac repolarization prolongation. A novel predictive pharmacokinetic/pharmacodynamic model of repolarization prolongation was generated from these data.

METHODS

Three male beagle dogs underwent radiofrequency AV nodal ablation, and placement of a His bundle-pacing lead and programmable pacemaker under anesthesia. Each dog was restrained in a sling for a series of increasing dose infusions of each drug while maintained at a constant heart rate of 80 beats/min. RT interval, a surrogate for QT interval in His bundle-paced dogs, was recorded throughout the experiment.

RESULTS

E-4031 induced a statistically significant RT prolongation at the highest three doses. Cisapride resulted in a dose-dependent increase in RT interval, which was statistically significant at the two highest doses. Terfenadine induced a dose-dependent RT interval prolongation with a statistically significant change occurring only at the highest dose. The relationship between drug concentration and RT interval change was described by a sigmoid E(max) model with an effect site. Maximum RT change (E(max)), free drug concentration at half of the maximum effect (EC(50)), and free drug concentration associated with a 10 ms RT prolongation (EC(10 ms)) were estimated. A linear correlation between EC(10 ms) and HERG IC(50) values was identified.

DISCUSSION

The conscious dog with His bundle-pacing detects delayed cardiac repolarization related to I(Kr) inhibition, and detects repolarization change induced by drugs with activity at multiple ion channels. A clinically relevant sensitivity and a linear correlation with in vitro HERG data make the conscious His bundle-paced dog a valuable tool for detecting repolarization effect of new chemical entities.

Coadministration of scrtraline with cisapride or pimozide: an open-label, nonrandomized examination of pharmacokinetics and corrected qt intervals in healthy adult volunteers

BACKGROUND

Sertraline hydrochloride is a selective serotonin reuptake inhibitor with demonstrated efficacy and safety for the treatment of the following disorders: major depressive, obsessive-compulsive, panic, premenstrual dysphoric, social anxiety, and posttraumatic stress. Although sertraline is unlikely to cause clinically significant inhibition of cytochrome P450 (CYP) 3A4 substrates, even modest concentration increases for narrow therapeutic index drugs, such as pimozide or cisapride, are potentially important.

OBJECTIVE

The goal of this study was to determine whether there is a pharmacokinetic interaction, as shown by plasma concentrations and electrocardiographic evidence of QTc intervals, between sertraline 200 mg QD and cisapride 10 mg QID, and between sertraline 200 mg QD and pimozide (single 2-mg dose).

METHODS

Patients in group A were administered cisapride on days 1 and 2 (10 mg QID), day 3 (10 mg/d), days 25 through 29 (10 mg QID), and day 30 (10 mg/d). Sertraline was administered on days 4 through 29 at a starting dose of 50 mg/d, which was titrated upward in 50-mg increments every third day to a maximum of 200 mg/d. Patients in group B were treated with 2 mg of pimozide on days 1 and 39. Sertraline was administered on days 18 through 46 at a starting dose of 50 mg/d, which was titrated upward in 50-mg increments every third day to a maximum of 200 mg/d.

RESULTS

There were 9 males and 6 females in group A (sertraline + cisapride) (mean age, 34.4 years for males, 41.7 years for females; mean weight, 78.7 kg for males, 66.6 kg for females; 14 Hispanic, 1 white), and 8 males and 7 females in group B (sertraline + pimozide) (mean age, 26.1 years for males, 33.4 years for females; mean weight, 70.8 kg for males, 61.4 kg for females; 15 Hispanic). Coadministration of sertraline and cisapride resulted in statistically significant reductions of 29% and 36% in cisapride C(max) and AUC from time 0 to 6 hours, respectively, compared with cisapride alone. Coadministration of sertraline and pimozide resulted in statistically significant increases of 35% and 37% in pimozide Cmax and AUC(0-infinity), respectively, compared with pimozide alone. No subject exhibited a prolongation of the QTc interval > or =15% with coadministration of sertraline and cisapride, or sertraline and pimozide.

CONCLUSIONS

This study found that coadministration of sertraline with cisapride resulted in decreases in cisapride concentrations, and no significant effects on QTc intervals. Coadministration of sertraline 200 mg/d and a single dose of pimozide 2 mg produced significant increases in pimozide concentrations but no prolongation of the QTc interval > or =15%. This opposite effect for pimozide compared with cisapride, as well as other previously tested CYP3A4 substrates, suggests that there are mechanisms other than CYP3A4 involved in the sertraline-pimozide interaction.

Mechanistic basis of adverse drugreactions: the perils of inappropriate dose schedules

Adverse drug reactions (ADRs) have long been recognised as a significant cause of morbidity and mortality. They account for a substantial number of clinical consultations, hospital admissions and extended duration of in-patient stay as well as mortality. By far the most common ADRs are the concentration-dependent pharmacological reactions, the majority of which ought to be preventable. As a result of high concentrations of the parent drug and/or its metabolite(s), there is an augmentation of primary pharmacological activity and/or appearance of new and undesirable secondary pharmacological activity. Typically, these high concentrations result from administration of high doses in an attempt to maximise efficacy and/or modulation of the pharmacokinetics of a drug by either genetic or non-genetic factors. High plasma concentrations of parent drug may result from inherited impairment or drug-induced inhibition of its pharmacokinetic disposition. Conversely, inherited overcapacity or drug-induced induction of the metabolism of a drug may result in low concentrations of parent drug and frequently, rapid accumulation of its metabolites. Environmental, dietary and phytochemical factors may also influence the activity of drug metabolising enzymes. As with inherited polymorphisms of acetylation and cytochrome P450-based drug metabolising enzymes, polymorphisms of other conjugation reactions, such as glucuronidation, increasingly appear to be associated with drug toxicity. Diseases of organs involved in elimination of a drug also alter its pharmacokinetics, plasma concentration and, therefore, the profile of its concentration-dependent ADRs. Inherited mutations, concurrently administered drugs or presence of certain diseases may also alter the sensitivity of some pharmacological targets, accounting for a substantial number of ADRs and interactions. When there is enhanced pharmacodynamic sensitivity, plasma drug concentrations that are apparently within the normal 'non-toxic' range give rise to ADRs. Recent advances have also provided important insights into the wider scope of drug-drug interactions. Interactions that occur at P-glycoproteins, drug transporters and efflux pumps, at various transmembrane interfaces such as the gastrointestinal wall, renal tubules, hepatobiliary border and blood-brain barrier, are beginning to explain many non-metabolic interactions. These alter the systemic exposure to drugs and have so far, begun to explain unexpected neurotoxicity and hepatotoxicity. The function of these transporters is also genetically modulated. These advances, together with continued increased awareness and education of prescribers and pharmacists, offer great opportunities for substantially minimising concentration-related ADRs.

Pro-kinetic medications as aids in imaging the small bowel by video-capsule

The m2a wireless video-capsule (Given Imaging Ltd., Israel) is a miniature ingestible camera utilized for the color imaging of the small intestine walls. Despite its diagnostic yield superiority over all other diagnostic modalities, a substantial part of the pathologies are not spotted. Considering the transmitted pictures high quality a resolution problem is ruled out, but rather it is assumed that parts of the intestinal wall surface are missed in the imaging process. Another important problem is the difficulty encountered by the capsule in crossing the antro-duodenal junction, probably due to pyloric hypomotility. Pro-kinetic drugs are capable of increasing the small intestine peristaltic wave velocity and contractile amplitude, thus assisting the video-capsule movements and widening the camera photo arc. The arc width is directly proportional to the surface imaging capacity. A specific dose range (cisapride 25-30 mg, metoclopramide 30 mg approximately) is calculated and an analysis is made of the use of these pro-kinetic drugs to increase the device diagnostic yield. It should be emphasized that: (1) despite a potential risk for complications, such as bleeding from small intestine lesions, radiological studies underline the high safety profile of metoclopramide; (2) increased capsule speed of progress is not expected to cause a loss of imaged area; (3) an oral dose below 15 mg (metoclopramide or cisapride) may not suffice to accelerate the capsule transit through the antro-duodenal junction. The concept is patent protected.

In vitro effects of cisapride, metoclopramide and bethanechol on smooth muscle preparations from abomasal antrum and duodenum of dairy cows

The objective of this study was to investigate the effects of cisapride (CIS), metoclopramide (MET) and bethanechol (BET) on contractility parameters from smooth muscle preparations of the abomasal antrum and proximal duodenum of cows. Smooth muscle preparations were harvested shortly post-mortem from 42 healthy dairy cows, and concentration-response curves were performed by cumulative application of the drugs. Cisapride and MET did not have any significant effect on the contractility parameters studied, while BET induced a significant, concentration-dependent increase in basal tone (BT), mean amplitude (Amean), and area under the curve (AUC) in smooth muscle preparations from the abomasal antrum, but not from the duodenum. The effect of BET on BT was more pronounced in specimens with longitudinal orientation while the maximal obtainable effect (Vm) in Amean was more pronounced in circular-oriented preparations. Atropine (1 x 10-5 m) significantly inhibited the effect of BET, whereas pre-incubation with hexamethonium or tetrodotoxin (TTX) had no effect, suggesting that the effect was mediated by cholinergic receptors on the smooth muscle. The results may be relevant to diseases or disorders associated with gastric emptying and gastric hypomotility. Further investigations are warranted to investigate the potential ability of BET to enhance abomasal emptying of adult dairy cows.

High performance liquid chromatographic determination, pharmacokinetic and comparative bioavailability studies of cisapride

A sensitive and specific reversed phase HPLC method was developed to quantitate plasma levels of cisapride in order to conduct comparative bioavailability studies. The drug and internal standard was extracted from plasma with heptane-isoamyl alcohol (95:5 v/v) and back extracted with sulfuric acid. The acidic layer was then re-extracted with the same extracting solvent. The separated organic layer was evaporated to dryness under nitrogen and the residue reconstituted with acetonitrile. Analysis was performed on a C-8 Sil-X-10 HPLC column, with a mobile phase of acetonitrile, water, and triethylamine (75:25:0.01) and UV detection at 215 nm. The standard curve covering the concentration range 5-160 ng/ml was linear (r(2)=0.9992), relative errors were within +/-10% and the CV% ranged from 1.34 to 11.82. The in vivo study was carried out in 12 healthy volunteers according to a single dose, two-sequence, cross over randomized design. The bioavailability was compared using the total area under the plasma level versus time curve (AUC(0-34,) AUC(0- infinity )), peak plasma concentration (C(max)) and time to C(max) (T(max)). No statistically significant difference was found between the AUC(0- infinity ) or C(max) values of the test (cisapride) and reference (Propulsid). It was, therefore, concluded that the generic cisapride was bioequivalent with the innovator formulation.

Cisapride disposition in neonates and infants: in vivo reflection of cytochrome P450 3A4 ontogeny

BACKGROUND

Cisapride, a prokinetic agent and substrate for cytochrome P450 (CYP) 3A4, has been used to treat neonates and infants with feeding intolerance and apnea or bradycardia associated with gastroesophageal reflux. At age 1 month, CYP3A4 activity has been reported to be only 30% to 40% of adult activity. This known developmental delay in the expression of CYP3A4 prompted us to conduct a classical open-label pharmacokinetic study of cisapride in neonates and young infants.

METHODS

A total of 35 infants with a postconceptional age of 28 to 54 weeks at the time of the study received a single oral cisapride dose (0.2 mg/kg) at a postnatal age of 4 to 102 days, followed by repeated (n = 7) blood sampling over a 24-hour period. Cisapride and norcisapride were quantitated from plasma by HPLC-tandem mass spectrometry and pharmacokinetic data determined (n = 32) by noncompartmental methods.

RESULTS

The pharmacokinetic parameters (mean +/- SD) were as follows: time to reach peak plasma concentration (t(max)), 4.4 +/- 2.8 hours (range, 0.9-12 hours); peak plasma concentration (C(max)), 29.3 +/- 16.6 ng/mL (range, 5.2-71.7 ng/mL); elimination half-life (t(1/2)), 10.7 +/- 3.7 hours (range, 1.9-18.1 hours); apparent total body clearance (Cl/F), 0.62 +/- 0.43 L. h(-1). kg(-1) (range, 0.2-1.9 L. h(-1). kg(-1)); and apparent volume of distribution (VD(ss)/F), 9.0 +/- 7.1 L/kg (range, 2.2-30.5 L/kg). The apparent renal clearance (CL(R)) of cisapride in infants (n = 28) was estimated to be 0.003 +/- 0.003 L. h(-1). kg(-1). Substratification of the population based on postconceptional age demonstrated the following findings for cisapride: (1) The mean (+/-SD) C(max) for cisapride was higher in the oldest postconceptional age category (44.5 +/- 19.6 ng/mL) than the middle and youngest categories (23.4 +/- 11.7 ng/mL and 30.0 +/- 17.5 ng/mL, respectively); (2) the t(max) for cisapride was shortest in the oldest postconceptional age category (2.2 +/- 1.1 hours) compared with the middle and youngest categories (4.4 +/- 3.3 hours and 5.0 +/- 2.6 hours, respectively); (3) the CL/F for cisapride in the youngest postconceptional age group was significantly lower (0.45 +/- 0.26 L. h(-1). kg(-1), P <.05) than in the middle and oldest categories (0.75 +/- 0.46 L. h(-1). kg(-1) and 0.85 +/- 0.69 L. h(-1). kg(-1), respectively); (4) a positive linear correlation was found between postconceptional age and the apparent terminal elimination rate constant (lambda(z)) for cisapride (P <.001, r(2) = 0.47) but not with CL/F. For norcisapride, the mean apparent C(max) was highest and the t(max) was shortest in the oldest postconceptional age group, although no association between postconceptional age and the norcisapride/cisapride area under the curve ratio was observed. All infants tolerated a single dose of cisapride well without significant alteration in QTc.

CONCLUSIONS

(1) In neonates and infants, cisapride absorption and metabolism to its primary metabolite, norcisapride, were developmentally dependent; (2) approximately 99% of cisapride CL/F in neonates and young infants was nonrenal in nature; (3) CL/F of cisapride in neonates and infants noted in this study was reduced compared with data from older children and adults, likely as a result of developmental reductions in CYP3A4 activity; (4) as reflected by the correlation between postconceptional age and lambda(z), a rapid increase in total CYP3A4 activity occurs in the first 3 months of life.

A comparison of the pharmacokinetics of two dosing regimens of cisapride and their effects on corrected QT interval in premature infants

OBJECTIVE

To compare the pharmacokinetics of two dosing regimens of cisapride and their effects on QT(c) interval.

DESIGN

Thirty-one pre-term infants were enrolled in two neonatal intensive care units. In 16 infants, cisapride was started at 0.2 mg/kg orally every 6 h (group A) and in 15 infants at 0.1 mg/kg orally every 3 h (group B). Electrocardiograms were performed before and after 72 h of treatment to calculate the QT(c) interval according to the Bazett formula. After 72 h of treatment, cisapride and norcisapride trough concentrations, and concentrations 1 h after the next cisapride administration were quantified in serum. A linear regression analysis was performed to analyse the effect of postnatal and postconception age.

RESULTS

At the start of cisapride treatment, mean postnatal age was 22.9+/-13.9 days (mean+/-SD) for group A and 23.3+/-15.0 days for group B, and mean postconception age was 34.0+/-1.8 weeks for group A and 33.3+/-0.8 weeks for group B. The QT(c) interval increased equally in both groups (group A: +37+/-20 ms, and group B: + 38+/-25 ms; P=0.9). Mean concentration of cisapride 1 h after administration was, as expected from the dosing regimen, significantly higher in group A than in group B (123.7+/-43.2 ng/ml versus 86.7+/-27.8 ng/ml; P=0.03).The difference in trough concentration was not significant (107.4+/-44.3 ng/ml versus 78.2+/-35.4 ng/ml; P=0.09). There was a positive correlation between QT(c) prolongation and cisapride serum concentration (peak: R(2)=0.20, P=0.015; trough: R(2)=0.24, P=0.008) and an inverse correlation between postnatal age and concentration 1 h after administration concentration of cisapride (R(2)=0.19, P=0.02). No correlation was found for postconception age.

CONCLUSION

Postnatal age has an inverse relationship with cisapride serum concentration in premature infants, whereas postconception age is not correlated. The maturation process of the biotransformation system of cisapride during the first weeks of life, triggered by birth, but independent of gestational age at birth can explain this observation. The effect of cisapride on cardiac repolarisation is positively related with the cisapride serum concentration. Administering cisapride every 3 h instead of every 6 h could be advantageous, as it is associated with lower peak cisapride serum concentrations. Further investigations are required to confirm this and its potential clinical benefit on QT(c )and arrhythmia risk.

Cisapride: a potential model substrate to assess cytochrome P4503A4 activity in vivo

OBJECTIVES

Cisapride was compared with midazolam in vivo to determine its potential applicability as a cytochrome P450 (CYP) 3A4 "probe." As well, we evaluated whether cisapride was transported by P-glycoprotein.

METHODS

Bidirectional transport assays were conducted in LLC-PK1 cells and the derivative cell line L-MDR1 to determine whether cisapride was a substrate for P-glycoprotein. A pharmacokinetic study was also conducted in 17 healthy adults (n = 8 women) who received intravenous midazolam (0.025 mg/kg), oral midazolam (0.15 mg/kg), and oral cisapride (0.07 mg/kg) in a randomized crossover design. Plasma concentrations were quantitated from repeated after-dosing blood samples by HPLC with ultraviolet detection for midazolam and HPLC with tandem mass spectrometry detection for cisapride and norcisapride. Pharmacokinetic parameters were determined by noncompartmental methods. Both linear and nonlinear regression analyses were used to examine the association between the apparent plasma clearance of midazolam and cisapride and the cisapride/norcisapride plasma concentration ratios.

RESULTS

Although not a substrate for P-glycoprotein, cisapride inhibited P-glycoprotein with an apparent inhibition constant (K(i)) of 16.1 micromol/L. Linear correlations between cisapride clearance and both intravenous and oral midazolam clearance (P =.01, r(2) = 0.43 and P =.001, r(2) = 0.46, respectively) were found. Cisapride/norcisapride plasma concentration ratios at 8 hours (P =.001, r(2) = 0.90) and 12 hours (P =.001, r(2) = 0.96), as well as cisapride plasma concentrations at these time points, were shown to accurately predict the area under the plasma concentration versus time curve for cisapride.

CONCLUSIONS

CYP3A4 activity reflected by the total body clearance after oral administration of cisapride should be independent of transport by P-glycoprotein. Concordance between the pharmacokinetics for cisapride and midazolam support the applicability of oral cisapride as a pharmacologic substrate to assess total CYP3A4 activity in vivo. Cisapride plasma concentration ratios at 8 or 12 hours after a single oral cisapride dose may prove useful as a single-point determination to reflect the area under the plasma concentration versus time curve and the plasma clearance of cisapride and, as well, total CYP3A4 activity in vivo.

Expression of the ether-a-go-go (ERG) potassium channel in smooth muscle of the equine gastrointestinal tract and influence on activity of jejunal smooth muscle

OBJECTIVE

To determine whether ether-a-go-go (ERG) potassium channels are expressed in equine gastrointestinal smooth muscle, whether ERG channel antagonists affect jejunal muscle contraction in vitro, and whether plasma cisapride concentrations in horses administered treatment for postoperative ileus (POI) are consistent with ERG channels as drug targets.

SAMPLE POPULATION

Samples of intestinal smooth muscle obtained from 8 horses free of gastrointestinal tract disease and plasma samples obtained from 3 horses administered cisapride for treatment of POI.

PROCEDURE

Membranes were prepared from the seromuscular layer of the duodenum, jejunum, ileum, cecum, large colon, and small colon. Immunoblotting was used to identify the ERG channel protein. Isolated jejunal muscle strips were used for isometric stress response to ERG channel blockers that included E-4031, MK-499, clofilium, and cisapride. Plasma concentrations of cisapride were determined in 3 horses administered cisapride for treatment of POI after small intestinal surgery.

RESULTS

Immunoblotting identified ERG protein in all analyzed segments of the intestinal tract in all horses. The selective ERG antagonist E-4031 caused a concentration-dependent increase in jejunal contraction. Clofilium, MK-499, and cisapride also increased jejunal contraction at concentrations consistent with ERG channel block; effects of E-4031 and cisapride were not additive. Peak plasma cisapride concentrations in treated horses were consistent with ERG block as a mechanism of drug action.

CONCLUSIONS AND CLINICAL RELEVANCE

The ERG potassium channels modulate motility of intestinal muscles in horses and may be a target for drugs. This finding may influence development of new prokinetic agents and impact treatment of horses with POI.

Matrix-assisted laser desorption/ionisation mass spectrometry in the study of polycondensation of Ti(OBun)4 in the presence of Si(OEt)4

The hydrolysis-polycondensation behaviour of alcoholic solutions containing Si(OEt)4 and Ti(OBun)4, in different molar ratios (Si/Ti = 10-0.2), was analysed by laser desorption/ionisation (LDI) and matrix-assisted laser desorption/ionisation (MALDI) mass spectrometry. The solutions were prepared using operating conditions usually employed in the sol-gel synthesis of SiO2-TiO2 materials. In accord with the well-known procedures for controlling the different chemical reactivities of the alkoxides, the pre-hydrolysis of the slower reacting silicon ethoxide and the chelation by acetylacetone of the faster reacting titanium butoxide were performed before mass spectrometric analysis. While LDI-MS did not provide evidence for the presence of mixed Si-Ti species in samples obtained from these reactions, MALDI-MS of samples diluted with chloroform and using 2,5-dihydroxybenzoic acid (DHB) as matrix led to detection of various oligomers with different contents of Si and Ti atoms. The results suggest that the formation of Si-Ti mixed oligomers seems to be the favoured process, especially for solutions in which one of the two components is diluted.

Cytochrome P450 Involvement in the biotransformation of cisapride and racemic norcisapride in vitro: differential activity of individual human CYP3A isoforms

Identification of the human cytochrome P450 (P450) enzymes involved in the metabolism of cisapride and racemic norcisapride [(+/-)-norcisapride] was investigated at 0.1 and 1 microM, concentrations that span the mean plasma C(max) for cisapride. Formation of norcisapride (Nor), 3-fluoro-4-hydroxycisapride (3F), and 4-fluoro-2-hydroxycisapride (4F) from cisapride and an uncharacterized metabolite (UNK) from (+/-)-norcisapride in human liver microsomes (HLMs) were consistent with Michaelis-Menten kinetics for a single enzyme (K(m), 6.0, 14.3, 13.9, and 107 microM; V(max), 1350, 696, 568, and 25 pmol/mg of protein, respectively). HLMs converted cisapride to Nor at rates that were at least 3 orders of magnitude greater than those observed for (+/-)-norcisapride conversion to UNK. The sample-to-sample variation in the rates of Nor, 3F, 4F, and UNK formation correlated strongly (r(2) > 0.796) with CYP3A4/5 activity in a panel of HLMs (n = 7) and was markedly reduced by ketoconazole, a potent CYP3A inhibitor. Ketoconazole virtually eliminated (+/-)-norcisapride conversion to UNK (94 +/- 0.5%). Studies with 10 cDNA-expressed enzymes revealed that CYP3A4 catalyzed the formation of Nor and 4F at rates >100 times those of non-CYP3A enzymes and >100- and 50-fold higher than CYP3A5 and CYP3A7, respectively. CYP3A4 was the only P450 capable of UNK formation. Therefore, CYP3A4 is the principal P450 enzyme responsible for the conversion of cisapride to Nor, 3F, and 4F and of (+/-)-norcisapride to UNK. Compared with cisapride, factors related to CYP3A4-mediated (+/-)-norcisapride metabolism (e.g., ontogeny of drug-metabolizing enzymes, inhibition, and induction) should be clinically unimportant due to the apparent lack of dependence on cytochromes P450 for elimination.

Stereoselective pharmacokinetics of cisapride in healthy volunteers and the effect of repeated administration of grapefruit juice

AIMS

To determine whether the pharmacokinetics of cisapride and its interaction with grapefruit juice are stereoselective.

METHODS

The study was a randomized, two-phase cross over design with a washout period of 2 weeks. Ten healthy volunteers were pretreated with either water or 200 ml double strength grapefruit juice three times a day for 2 days. On the 3rd each subject ingested a single 10 mg dose of rac-cisapride tablet. Double strength grapefruit juice (200 ml) or water was administered during cisapride dosing and 0.5 and 1.5 h thereafter. Blood samples were collected before and for 32 h after cisapride administration. Plasma concentrations of cisapride enantiomers were measured by a chiral h.p.l.c. method. A standard 12-lead ECG was recorded before cisapride administration (baseline) and 2, 5, 8, and 12 h later.

RESULTS

This study showed that cisapride pharmacokinetics are stereoselective. In control (water treated) subjects, the mean Cmax (30 +/- 13.6 ng ml-1; P = 0.0008) and AUC(0, infinity) (201 +/- 161 ng ml-1 h; P = 0.029) of (-)-cisapride were significantly higher than the Cmax (10.5 +/- 3.4 ng ml-1) and AUC(0, infinity) (70 +/- 51.5 ng ml-1 h) of (+)-cisapride. There was no marked difference in elimination half-life between (-)-cisapride (4.7 +/- 2.7 h) and (+)-cisapride (4.8 +/- 3 h). Compared with the water treated group, grapefruit juice significantly increased the mean Cmax of (-)-cisapride from 30 +/- 13.6-55.5 +/- 18 ng ml-1 (95% CI on mean difference, -33, -17; P = 0.00005) and of (+)-cisapride from 10.5 +/- 3.4 to 18.4 +/- 6.2 ng ml-1 (95% CI on mean difference, -11.8, -3.9, P = 0.00015). The mean AUC(0, infinity) of (-)-cisapride was increased from 201 +/- 161 to 521.6 +/- 303 ng ml-1 h (95% CI on mean difference, -439, -202; P = 0.0002) and that of (+)-cisapride from 70 +/- 51.5 to 170 +/- 91 ng ml-1 h (95% CI on mean difference, -143, -53; P = 0.0005). The tmax was also significantly increased for both enantiomers (from 1.35 to 2.8 h for (-)-cisapride and from 1.75 to 2.9 h for (+)-cisapride in the control and grapefruit juice group, respectively; P < 0.05). The t(1/2) of (-)-cisapride was significantly increased by grapefruit juice, while this change did not reach significant level for (+)-cisapride. The proportion of pharmacokinetic changes brought about by grapefruit juice was similar for both enantiomers, suggesting non-stereoselective interaction. We found no significant difference in mean QTc intervals between the water and grapefruit juice treated groups.

CONCLUSIONS

The pharmacokinetics of cisapride is stereoselective. Grapefruit juice elevates plasma concentrations of both (-)- and (+)-cisapride, probably through inhibition of CYP3A in the intestine. At present, there are no data on whether the enantiomers exhibit stereoselective pharmacodynamic actions. If they do, determination of plasma concentrations of the individual enantiomers as opposed to those of racemic cisapride may better predict the degree of drug interaction, cardiac safety and prokinetic efficacy of cisapride.

Evidence of impaired cisapride metabolism in neonates

AIMS

Cisapride has been shown to cause QTc prolongation in neonates in the absence of any of the known risk factors ascribed to children or adults (excessive dosage, drug-drug interactions). Our hypothesis was that the early neonatal liver may show defective elimination of cisapride resulting in its accumulation in the immature child. Owing to the difficulties associated with in vivo pharmacokinetic studies in a paediatric population, we explored the in vitro metabolism of cisapride by human cytochrome P450.

METHODS

Experiments were conducted with recombinant CYPs stably expressed in mammalian cells and with liver microsomes obtained from human foetuses, neonates, infants and adults. Cisapride metabolites were measured by high performance liquid chromatography.

RESULTS

The rate of biotransformation of cisapride was greater by recombinant CYP3A4 than by CYP3A7 (0.77 +/- 0.5 and 0.01 +/- 0.01 nmol metabolites formed in 24 h, respectively), whereas CYP1A1, 1A2, 2C8, 2C9 and 3A5 showed no activity. Norcisapride formation was significantly correlated with testosterone 6beta-hydroxylation, a CYP3A4 catalysed reaction (r = 0.71, P = 0.03) but not with the 16-hydroxylation of dehydroepiandrosterone, catalysed by CYP3A7 (r = 0.30, P = 0.29) by microsomes from a panel of livers from foetuses, neonates and infants. No or negligible cisapride metabolic activity was observed in microsomes from either foetuses or neonates aged less than 7 days, which contained mostly CYP3A7 and no CYP3A4. The metabolism of cisapride steadily increased after the first week of life in parallel with CYP3A4 activity to reach levels exceeding adult values.

CONCLUSIONS

The low content of CYP3A4 in the human neonatal liver appears to be responsible for its inability to oxidize cisapride and could explain its accumulation in plasma leading to the cases of QTc prolongation reported in this paediatric population.

Pharmacokinetic/pharmacodynamic assessment of the effects of E4031, cisapride, terfenadine and terodiline on monophasic action potential duration in dog

1. Torsades de pointes (TDP) is a potentially fatal ventricular tachycardia associated with increases in QT interval and monophasic action potential duration (MAPD). TDP is a side-effect that has led to withdrawal of several drugs from the market (e.g. terfenadine and terodiline). 2. The potential of compounds to cause TDP was evaluated by monitoring their effects on MAPD in dog. Four compounds known to increase QT interval and cause TDP were investigated: terfenadine, terodiline, cisapride and E4031. On the basis that only free drug in the systemic circulation will elicit a pharmacological response target, free concentrations in plasma were selected to mimic the free drug exposures in man. Infusion regimens were designed that rapidly achieved and maintained target-free concentrations of these drugs in plasma and data on the relationship between free concentration and changes in MAPD were obtained for these compounds. 3. These data indicate that the free ED50 in plasma for terfenadine (1.9 nM), terodiline (76 nM), cisapride (11 nM) and E4031 (1.9 nM) closely correlate with the free concentration in man causing QT effects. For compounds that have shown TDP in the clinic (terfenadine, terodiline, cisapride) there is little differentiation between the dog ED50 and the efficacious free plasma concentrations in man (< 10-fold) reflecting their limited safety margins. These data underline the need to maximize the therapeutic ratio with respect to TDP in potential development candidates and the importance of using free drug concentrations in pharmacokinetic/pharmacodynamic studies.

The effect of cisapride on the corrected QT interval and QT dispersion in premature infants

BACKGROUND

Cisapride is used frequently in premature neonates as a gastrointestinal prokinetic drug. Concerns exist, however, about its safety because of its effect on the QT interval. Premature infants could be at higher risk for side effects because of their immaturity. This prospective study investigated the pharmacokinetics of cisapride and its effects on corrected QT interval (QTc) and QT dispersion in premature infants.

METHODS

Electrocardiogram examination was performed just before and after 72 hours of treatment with cisapride (0.2 mg/kg per dose, four times daily) in 10 premature infants. Trough and anticipated peak plasma level of cisapride and norcisapride were quantified after 72 hours of treatment. Results were compared with a cohort of 41 term infants aged 0 to 3 months receiving cisapride treatment.

RESULTS

The QTc interval increased significantly from 423 ms to 461 ms after 72 hours of treatment (P = 0.0007). No effect was seen on QT dispersion (44.3 ms vs. 45.9 ms). The change in QTc interval was inversely related to postnatal age (R2 = 0.52; P = 0.02), whereas there was no correlation with gestational age or plasma levels of cisapride or norcisapride. Trough and anticipated peak plasma levels of cisapride and norcisapride were significantly higher in the premature infants compared with the term infants aged 0 to 3 months (P < 0.001).

CONCLUSIONS

Premature infants less than 1 month of age could be at higher risk for cardiac side effects of cisapride when used in the same dosage as in older infants. The daily dose should be reduced (0.1 mg/kg per dose, maximum four times daily), and the QTc interval should be monitored closely. The benefits and safety of cisapride in premature infants less than 1 month of age should be reconsidered.

Red wine-cisapride interaction: comparison with grapefruit juice

OBJECTIVES

Our objective was to compare the interactions of red wine and grapefruit juice with cisapride.

METHODS

The oral pharmacokinetics of cisapride, its norcisapride metabolite, and electrocardiographic QTc interval were determined over a 24-hour period after administration of cisapride 10 mg with 250 mL grapefruit juice, red wine (cabernet sauvignon), or water in a randomized 3-way crossover study in 12 healthy men.

RESULTS

The cisapride area under the concentration-time curve (AUC) and the maximum plasma drug concentration after single-dose administration (C(max)) with grapefruit juice were 151% (P <.01) and 168% (P <.001), respectively, of those with water. The increase in cisapride AUC and C(max) was variable among individuals; however, cisapride AUC and C(max) were enhanced by the same proportion. The time to reach maximum concentration after drug administration (t(max)) and the apparent elimination half-life (t((1/2)) for cisapride and the pharmacokinetics of norcisapride were not altered. Norcisapride/cisapride ratios were reduced. Cisapride AUC and C(max) with red wine were 115% (difference not statistically significant) and 107% (difference not statistically significant), respectively, of those with water. The cisapride t(max) was slightly longer. Cisapride t((1/2)) and norcisapride pharmacokinetics were not different. The norcisapride/cisapride ratio at cisapride C(max) was lower. One subject had a doubling in cisapride AUC and C(max) and a decrease in norcisapride/cisapride ratios with red wine and also had the largest interaction with grapefruit juice. QTc interval was unchanged in all treatment groups and individuals.

CONCLUSIONS

A single glass of grapefruit juice produced an individual-dependent variable increase in the systemic availability of cisapride by inhibition of intestinal cytochrome P450 3A4 (CYP3A4) activity. The identical volume of red wine caused only minor changes in cisapride pharmacokinetics despite some inhibition of CYP3A4 in most individuals. However, even this amount of red wine may cause a marked interaction similar to that for grapefruit juice in individuals with a preexisting high intestinal CYP3A4 content.

Cisapride plasma levels and corrected QT interval in infants undergoing routine polysomnography

BACKGROUND

Reported QTc prolongation associated with cardiac arrhythmia in a small number of children undergoing cisapride therapy and lack of pharmacokinetic correlation provided the impetus for this prospective study. The authors evaluated the relation between cisapride plasma concentrations, the electrocardiographic QT interval, and cardiac rhythm in infants undergoing routine 8-hour polysomnography.

METHODS

A total of 211 infants were enrolled: 84 (17 born prematurely) undergoing cisapride therapy for at least 4 days for suspected gastroesophageal reflux and 127 controls (10 born prematurely), aged between 1 week and 13.5 months. Infants underwent continuous bipolar limb lead I recording during routine 8-hour polysomnography. QT intervals and heart rate were measured at hourly intervals. The morning after polysomnography, 12-lead electrocardiography was performed (1 hour after cisapride administration). Cisapride plasma concentrations were determined immediately before and 1 to 2 hours after administration. Serum electrolyte concentrations were measured.

RESULTS

The administered cisapride dose ranged from 0.35 to 1.55 (mean, 0.81, median 0.79) mg. kg-1. d-1. Cisapride plasma concentrations were significantly higher in infants younger than 3 months of age. Cisapride-treated infants younger than 3 months of age had longer QTc intervals compared with age-matched controls. Heart rate was similar for cisapride-treated and control infants. No arrhythmia or atrioventricular conduction abnormalities were observed.

CONCLUSIONS

At comparable doses of cisapride and comparable plasma concentrations, the QTc was significantly higher in infants younger than 3 months of age. This confirms age-dependent cisapride pharmacokinetics in the first 10 to 12 weeks strongly correlated with changes in body weight and may also suggest an altered ability of infants younger than 3 months of age to metabolize cisapride. The clinical significance and risk of the increased QTc interval is unclear. Cisapride should be judiciously prescribed in infants younger than the age of 3 months and electrocardiography should be performed before and during therapy.

Study of the drug-drug interaction between simvastatin and cisapride in man

OBJECTIVE

The objective of our study was to evaluate in humans the drug-drug interaction occurring during the concomitant administration of cisapride and simvastatin, two well-known substrates of CYP3A4.

METHODS

Eleven healthy men aged between 20 years and 35 years gave their written informed consent to participate in the study. Each participant received repeated doses of cisapride and/or simvastatin. At first, subjects received cisapride alone, 10 mg every 8 h, for 3 days. Then, the drug was given at the same regimen during concomitant administration of simvastatin, 20 mg every 12 h for 4 days, starting on the night of day 3. Finally, cisapride was stopped and subjects received simvastatin (20 mg every 12 h) for four additional days.

RESULTS

Simvastatin administration caused a 14 +/- 20% increase in the AUC0-8 of cisapride. In contrast, plasma concentrations of simvastatin were unaltered by the coadministration of cisapride, whereas plasma concentrations of simvastatin acid, its active metabolite, were decreased by 33 +/- 24%.

CONCLUSION

The concomitant administration of the prokinetic agent cisapride and the 3-hydroxy-3-methylgluaryl CoA reductase inhibitor simvastatin resulted in altered pharmacokinetics of both drugs. Increased plasma concentrations of cisapride suggest that some patients may be at risk of toxicity while receiving both drugs, whereas the decrease in simvastatin acid plasma concentrations suggests that cholesterol lowering effects of simvastatin treatment may be blunted.

Design and evaluation of a two-layer floating tablet for gastric retention using cisapride as a model drug

A new kind of two-layer floating tablet for gastric retention (TFTGR) with cisapride as a model drug was developed. The in vitro drug release was determined, and the resultant buoyancy and the time-buoyancy curve were plotted. Because of the sodium bicarbonate added to the floating layer, when immersed in simulated gastric fluid (SGF) the tablet expands and rises to the surface, where the drug is gradually released. The in vitro drug release of this kind of two-layer dosage was controlled by the amount of hydroxypropylmethylcellulose (HPMC) in the drug-loading layer. Generally, the more HPMC, the slower the drug releases. Because cisapride has greater solubility in SGF than simulated intestinal fluid (SIF), its in vitro drug dissolution in SGF is faster than in SIF. One of the distinguishing characteristics of this kind of tablet is the separate regulation of buoyancy and drug release. The idea developed in this experiment can be used as a general modelfor the design of other tablets for gastric retention.

Does cisapride influence cardiac rhythm? Results of a United States multicenter, double-blind, placebo-controlled pediatric study

BACKGROUND

Major concerns about serious cardiac side effects underlie the recent decision by the FDA and Janssen Pharmaceutica (Titusville, NJ) to make cisapride available only through a limited access program. Concerns have grown despite the fact that most instances of prolonged QTc and other ventricular arrhythmias occurred while the drug was used concomitantly with contraindicated drugs. This study sought to analyze electrocardiograms (ECGs) from a multicenter pediatric study and to identify abnormalities in QTc interval associated with cisapride use.

METHODS

Children between 6 months and 4 years of age were enrolled if they manifested symptoms of gastroesophageal reflux not responding to medical therapy for at least 6 weeks. In 49 subjects, ECGs obtained before and after randomization to receive 0.2 mg/kg dose three times daily or placebo were reviewed independently and blindly by two pediatric cardiologists. Placebo and active drug groups were compared for QTc and for change in QTc from baseline values after 3 to 8 weeks of treatment.

RESULTS

Mean QTc among patients taking the drug was 408+/-18 ms. None was higher than 450 ms. Change between baseline and subsequent QTc at 3 to 8 weeks of treatment was 2+/-20 ms.

CONCLUSIONS

In our study group of children without underlying cardiac disease or electrolyte imbalance, cisapride was found to have no significant effect on cardiac electrical function compared with placebo. These results are consistent with the drug's record of exceedingly infrequent cardiac events. Because the availability of this prokinetic is threatened, its safety and the safety and efficacy of alternative treatment options (including surgery) should be studied further.

Influence of coadministration of fluoxetine on cisapride pharmacokinetics and QTc intervals in healthy volunteers

STUDY OBJECTIVE

To evaluate the effect of fluoxetine on the pharmacokinetics and cardiovascular safety of cisapride at steady state in healthy men.

DESIGN

Open-label, three-phase, sequential study.

SETTING

Clinical research center.

SUBJECTS

Twelve healthy male volunteers.

INTERVENTIONS

Each subject was treated according to the following sequence: baseline; phase 1 (days 1-6): cisapride 10 mg 4 times/day; washout (days 7-13); phase 2 (days 14-44): fluoxetine 20 mg/day; and phase 3 (days 45-52): cisapride 10 mg 4 times/day (days 45-51) plus fluoxetine 20 mg/day (days 45-52).

MEASUREMENTS AND MAIN RESULTS

Blood samples were drawn and 12-lead electrocardiograms performed at specified time points after the last morning dose of cisapride in phases 1 and 3. Blood samples also were taken before morning doses on the 3rd, 4th, and 5th days of phases 1 and 3. Electrocardiograms were done at baseline and on the last day of the washout period and phase 2. Coadministration of fluoxetine significantly decreased cisapride plasma concentrations. There were no clinically significant changes in corrected QT intervals during administration of cisapride alone or with fluoxetine. Cisapride was well tolerated when administered alone or with fluoxetine.

CONCLUSION

Cisapride can be administered safely to patients receiving low therapeutic dosages of fluoxetine.

The involvement of flavin-containing monooxygenase but not CYP3A4 in metabolism of itopride hydrochloride, a gastroprokinetic agent: comparison with cisapride and mosapride citrate

The goals of the present study were to identify the enzyme responsible for metabolism of itopride hydrochloride (itopride) and to evaluate the likelihood of drug interaction involving itopride. In human liver microsomes, the involvement of flavin-containing monooxygenase in N-oxygenation, the major metabolic pathway of itopride, was indicated by the following results: inhibition by methimazole and thiourea, heat inactivation, and protection against heat inactivation by NADPH. When the effects of ketoconazole on the metabolism of itopride, cisapride, and mosapride citrate (mosapride) were examined using human liver microsomes, ketoconazole strongly inhibited the formation of the primary metabolites of cisapride and mosapride, but not itopride. Other cytochrome P450 (CYP) 3A4 inhibitors, cimetidine, erythromycin, and clarithromycin, also inhibited the metabolism of cisapride and mosapride. In an in vivo study, itopride (30 mg/kg), cisapride (1.5 mg/kg), or mosapride (3 mg/kg) was orally administered to male rats with or without oral pretreatment with ketoconazole (120 mg/kg) twice daily for 2 days. The ketoconazole pretreatment significantly increased the area under the serum concentration curve and the maximum serum concentration of cisapride and mosapride but had no significant effect on the pharmacokinetics of itopride. In addition, itopride did not inhibit five specific CYP-mediated reactions of human liver microsomes. These results suggest that itopride is unlikely to alter the pharmacokinetics of other concomitantly administered drugs.

Stereoselective determination of cisapride, a prokinetic agent, in human plasma by chiral high-performance liquid chromatography with ultraviolet detection: application to pharmacokinetic study

We have developed a simple, sensitive, specific and reproducible stereoselective high-performance liquid chromatography technique for analytical separation of cisapride enantiomers and measurement of cisapride enantiomers in human plasma. A chiral analytical column (ChiralCel OJ) was used with a mobile phase consisting of ethanol-hexane-diethylamine (35:64.5:0.5, v/v/v). This assay method was linear over a range of concentrations (5-125 ng/ml) of each enantiomer. The limit of quantification was 5 ng/ml in human plasma for both cisapride enantiomers, while the limit of detection was 1 ng/ml. Intra- and inter-day C.V.s did not exceed 15% for all concentrations except at 12.5 ng/ml for EII (+)-cisapride, which was approximately 20 and 19%, respectively. The clinical utility of the method was demonstrated in a pharmacokinetic study of normal volunteers who received a 20 mg single oral dose of racemic cisapride. The preliminary pharmacokinetic data obtained using the method we describe here provide evidence for the first time that cisapride exhibits stereoselective disposition.

Drug interactions with cisapride: clinical implications

Cisapride, a prokinetic agent, has been used for the treatment of a number of gastrointestinal disorders, particularly gastro-oesophageal reflux disease in adults and children. Since 1993, 341 cases of ventricular arrhythmias, including 80 deaths, have been reported to the US Food and Drug Administration. Marketing of the drug has now been discontinued in the US; however, it is still available under a limited-access protocol. Knowledge of the risk factors for cisapride-associated arrhythmias will be essential for its continued use in those patients who meet the eligibility criteria. This review summarises the published literature on the pharmacokinetic and pharmacodynamic interactions of cisapride with concomitantly administered drugs, providing clinicians with practical recommendations for avoiding these potentially fatal events. Pharmacokinetic interactions with cisapride involve inhibition of cytochrome P450 (CYP) 3A4, the primary mode of elimination of cisapride, thereby increasing plasma concentrations of the drug. The macrolide antibacterials clarithromycin, erythromycin and troleandomycin are inhibitors of CYP3A4 and should not be used in conjunction with cisapride. Azithromycin is an alternative. Similarly, azole antifungal agents such as fluconazole, itraconazole and ketoconazole are CYP3A4 inhibitors and their concomitant use with cisapride should be avoided. Of the antidepressants nefazodone and fluvoxamine should be avoided with cisapride. Data with fluoxetine is controversial, we favour the avoidance of its use. Citalopram, paroxetine and sertraline are alternatives. The HIV protease inhibitors amprenavir, indinavir, nelfinavir, ritonavir and saquinavir inhibit CYP3A4. Clinical experience with cisapride is lacking but avoidance with all protease inhibitors is recommended, although saquinavir is thought to have clinically insignificant effects on CYP3A4. Delavirdine is also a CYP3A4 inhibitor and should be avoided with cisapride. We also recommend avoiding coadministration of cisapride with amiodarone, cimetidine (alternatives are famotidine, nizatidine, ranitidine or one of the proton pump inhibitors), diltiazem and verapamil (the dihydropyridine calcium antagonists are alternatives), grapefruit juice, isoniazid, metronidazole, quinine, quinupristin/dalfopristin and zileuton (montelukast is an alternative). Pharmacodynamic interactions with cisapride involve drugs that have the potential to have additive effects on the QT interval. We do not recommend use of cisapride with class Ia and III antiarrhythmic drugs or with adenosine, bepridil, cyclobenzaprine, droperidol, haloperidol, nifedipine (immediate release), phenothiazine antipsychotics, tricyclic and tetracyclic antidepressants or vasopressin. Vigilance is advised if anthracyclines, cotrimoxazole (trimethoprim-sulfamethoxazole), enflurane, halothane, isoflurane, pentamidine or probucol are used with cisapride. In addition, uncorrected electrolyte disturbances induced by diuretics may increase the risk of torsade de pointes. Patients receiving cisapride should be promptly treated for electrolyte disturbances.

Interaction of cisapride with the human cytochrome P450 system: metabolism and inhibition studies

Using human liver microsomes (HLMs) and recombinant cytochrome P450s (CYP450s), we characterized the CYP450 isoforms involved in the primary metabolic pathways of cisapride and documented the ability of cisapride to inhibit the CYP450 system. In HLMs, cisapride was N-dealkylated to norcisapride (NORCIS) and hydroxylated to 3-fluoro-4-hydroxycisapride (3-F-4-OHCIS) and to 4-fluoro-2-hydroxycisapride (4-F-2-OHCIS). Formation of NORCIS, 3-F-4-OHCIS, and 4-F-2-OHCIS in HLMs exhibited Michaelis-Menten kinetics (K(m): 23.4 +/- 8.6, 32 +/- 11, and 31 +/- 23 microM; V(max): 155 +/- 91, 52 +/- 23, and 31 +/- 23 pmol/min/mg of protein, respectively). The average in vitro intrinsic clearance (V(max)/K(m)) revealed that the formation of NORCIS was 3.9- to 5. 9-fold higher than that of the two hydroxylated metabolites. Formation rate of NORCIS from 10 microM cisapride in 14 HLMs was highly variable (range, 4.9-133.6 pmol/min/mg of protein) and significantly correlated with the activities of CYP3A (r = 0.86, P =. 0001), CYP2C19, and 1A2. Of isoform-specific inhibitors, 1 microM ketoconazole and 50 microM troleandomycin were potent inhibitors of NORCIS formation from 10 microM cisapride (by 51 +/- 9 and 44 +/- 17%, respectively), whereas the effect of other inhibitors was minimal. Of 10 recombinant human CYP450s tested, CYP3A4 formed NORCIS from 10 microM cisapride at the highest rate (V = 0.56 +/- 0. 13 pmol/min/pmol of P450) followed by CYP2C8 (V = 0.29 +/- 0.08 pmol/min/pmol of P450) and CYP2B6 (0.15 +/- 0.04 pmol/min/pmol of P450). The formation of 3-F-4-OHCIS was mainly catalyzed by CYP2C8 (V = 0.71 +/- 0.24 pmol/min/pmol of P450) and that of 4-F-2-OHCIS by CYP3A4 (0.16 +/- 0.03 pmol/min/pmol of P450). Clearly, recombinant CYP2C8 participates in cisapride metabolism, but when the in vitro intrinsic clearances obtained were corrected for abundance of each CYP450 in the liver, CYP3A4 is the dominant isoform. Cisapride was a relatively potent inhibitor of CYP2D6, with no significant effect on other isoforms tested, but the K(i) value derived (14 +/- 16 microM) was much higher than the clinically expected concentration of cisapride (<1 microM). Our data suggest that CYP3A is the main isoform involved in the overall metabolic clearance of cisapride. Cisapride metabolism is likely to be subject to interindividual variability in CYP3A expression and to drug interactions involving this isoform.

Sequential single doses of cisapride, erythromycin, and metoclopramide in critically ill patients intolerant to enteral nutrition: a randomized, placebo-controlled, crossover study

OBJECTIVE

To evaluate the comparative efficacy of enteral cisapride, metoclopramide, erythromycin, and placebo for promoting gastric emptying in critically ill patients with intolerance to gastric enteral nutrition (EN).

DESIGN

A randomized, crossover study.

SETTING

Adult medical intensive care unit at a university-affiliated private hospital and trauma intensive care unit at a university teaching hospital.

PATIENTS

Ten adult, critically ill, mechanically ventilated patients not tolerating a fiber-containing EN product defined as a single aspirated gastric residual volume >150 mL or two aspirated gastric residual volumes >120 mL during a 12-hr period.

INTERVENTIONS

Patients received 10 mg of cisapride, 200 mg of erythromycin ethylsuccinate, 10 mg of metoclopramide, and placebo as 20 mL of sterile water every 12 hrs over 48 hrs. Acetaminophen solution (1000 mg) was administered concurrently. Gastric residual volumes were assessed, and plasma acetaminophen concentrations were serially determined by TDx between 0 and 12 hrs to evaluate gastric emptying.

MEASUREMENTS AND MAIN RESULTS

Gastric residual volumes during the study were not significantly different between agents. No differences in area under the concentration vs. time curve or elimination rate constant were identified between agents. Metoclopramide and cisapride had a significantly shorter mean residence time of absorption than erythromycin (6.3+/-4.5 [SEM] mins and 10.9+/-5.8 vs. 30.1+/-4.5 mins, respectively [p<.05]). Metoclopramide (9.7+/-15.3 mins) had a significantly shorter time to peak concentration compared with erythromycin and placebo (60.7+/-8.1 and 50.9+/-13.5 mins, respectively [p<.05]). The time to onset of absorption was significantly shorter for metoclopramide vs. cisapride (5.7+/-4.5 vs. 22.9+/-5.7 mins [p<.05]).

CONCLUSION

In critically ill patients intolerant to EN, single enteral doses of metoclopramide or cisapride are effective for promoting gastric emptying in critically ill patients with gastric motility dysfunction. Additionally, metoclopramide may provide a quicker onset than cisapride.

Population pharmacokinetics of enterally administered cisapride in young infants with gastro-oesophageal reflux disease

AIMS

To investigate the pharmacokinetics of enterally administered cisapride suspension in young infants being treated for gastro-oesophageal reflux disease.

METHODS

Plasma cisapride concentrations in 49 subjects (weight: 825-5010 g; n=108 samples, median two per patient; concentration: 14.8-170 ng ml-1 ) were fitted to a one-compartment model with first-order absorption and elimination in the NONMEM program using a logarithmic transformation of the observed and predicted concentrations. Fitting was achieved using the first order conditional estimation (FOCE) method with interaction between the interpatient and intrapatient variabilities. The interpatient variance of clearance (CL/F ) and volume of distribution (V /F ) and their covariance were estimated using an exponential error model. Intrapatient (residual) variance was estimated using an additive model.

RESULTS

The clearance of cisapride was shown to be linearly related to current body weight, slope: 0.538. The typical population values of CL/F, V /F and Ka (absorption rate constant) were 0.538 l h-1 kg-1, 21.9 l, and 2.58 h-1, respectively. The population coefficients of variation (CV%) for CL/F and V/F were 34.4% and 84.3%, respectively. The squared coefficient of correlation between random effects for CL/F and V /F was 0.45. The intrapatient variance was 0.15. V /F and Ka were not influenced significantly by any patient characteristic.

CONCLUSIONS

Cisapride pharmacokinetics in infants with reflux disease were satisfactorily described by a one-compartment model. Current weight should be taken into account when calculating maintenance cisapride doses in these infants.

Repeated consumption of grapefruit juice considerably increases plasma concentrations of cisapride

BACKGROUND

Grapefruit juice increases the bioavailability of several drugs that are metabolized during first pass by CYP3A4. In this study, the effect of grapefruit juice on the pharmacokinetics of orally administered cisapride was investigated.

METHODS

In a randomized, two-phase crossover study, 10 healthy volunteers took either 200 mL double-strength grapefruit juice or water three times a day for 2 days. On day 3, each subject ingested 10 mg cisapride with either 200 mL grapefruit juice or water, and an additional 200 mL was ingested 1/2 hour and 1 1/2 hours after cisapride administration. Timed blood samples were collected for 32 hours after cisapride intake, and a standard 12-lead ECG was recorded before the administration of cisapride and 2, 5, 8, and 12 hours later.

RESULTS

The mean peak plasma concentration of cisapride was increased by 81% (range, 38% to 138%; P < .01) and the total area under the plasma cisapride concentration-time curve by 144% (range, 65% to 244%; P < .01) by grapefruit juice. The time of the peak concentration of cisapride was prolonged from 1.5 to 2.5 hours (P < .05) and the elimination half-life from 6.8 to 8.4 hours (P < .05) by grapefruit juice. ECG tracings did not show any significant differences in the QTc interval between the grapefruit juice and control phases.

CONCLUSIONS

Grapefruit juice significantly increases plasma concentrations of cisapride, probably by inhibition of the CYP3A4-mediated first-pass metabolism of cisapride in the small intestine. Concomitant use of high amounts of grapefruit juice and cisapride should be avoided, at least in patients with risk factors for cardiac arrhythmia.

No pharmacokinetic but pharmacodynamic interactions between cisapride and bromperidol or haloperidol

Pharmacokinetic and pharmacodynamic interactions between the gastrokinetic drug cisapride and the antipsychotic drugs bromperidol and haloperidol were studied in 29 schizophrenic inpatients. Fourteen patients were taking bromperidol (12-24 mg/d), and 15 were taking haloperidol (12-36 mg/d). Cisapride 10 mg/d was coadministered for 1 week, and blood sampling was performed before cisapride treatment, 1 week after starting cisapride treatment, and I week after stopping cisapride treatment. On the same days as the blood sampling, psychotic symptoms and side effects were evaluated using the Brief Psychiatric Rating Scale (BPRS) and the Udvalg for Kliniske Undersøgelser (UKU) side effect rating scale (UKU), respectively. Plasma concentrations of bromperidol, haloperidol, and their reduced metabolites were measured by high-performance liquid chromatography. The mean BPRS scores after adding cisapride were significantly higher than those before cisapride (p<0.01) and after stopping cisapride (p<0.001) in the haloperidol group in this uncontrolled study. A similar tendency was observed in the bromperidol group, although it did not reach statistical significance (p = 0.08). Cisapride coadministration caused no significant changes in the mean plasma concentrations of bromperidol, haloperidol, and their reduced metabolites or in the mean UKU score. The present study suggests that there is no significant pharmacokinetic interaction between cisapride and bromperidol or haloperidol, but cisapride appears to deteriorate psychotic symptoms by a pharmacodynamic interaction in schizophrenic patients treated with haloperidol.

Influence of grapefruit juice on cisapride pharmacokinetics

OBJECTIVE

Grapefruit juice increases the oral bioavailability of several drugs metabolized by cytochrome P450 3A4. This study investigated the influence of grapefruit juice on the pharmacokinetics of oral cisapride, a substrate of CYP3A4.

METHODS

Fourteen healthy volunteers received in random order 10 mg cisapride (Prepulsid) with 250 mL water or grapefruit juice after an overnight fast. Blood samples were taken for 25 hours and urine was collected for 36 hours after dosing. Plasma concentrations of cisapride and urinary norcisapride were measured by HPLC. The influence of grapefruit juice on pharmacokinetic parameters (mean +/- SD) was assessed with the Wilcoxon matched pairs test for 13 subjects (1 subject did not fast as instructed).

RESULTS

Grapefruit juice increased cisapride maximum measured plasma concentration (Cmax; water, 65+/-398 ng/mL; grapefruit juice, 87+/-40 ng/mL; P = .009) and area under the plasma concentration-time curve from 0 to 25 hours [AUC(0-25); water, 418+/-280 h x ng/mL; grapefruit juice, 580+/-289 h x ng/mL; P = .005] and prolonged the time to reach Cmax (water, 1.26+/-0.36 hours; grapefruit juice, 1.72+/-0.55 hours; P = .02). Half-life was not affected. Urinary norcisapride recovery was similar and thus the partial apparent metabolic clearance to norcisapride was lower (P = .046) after grapefruit juice (89.5+/-41.2 mL/min) than after water (121.5+/-54.7 mL/min). There was considerable interindividual variation in the grapefruit juice effect [range of AUC(0-25) grapefruit juice/water ratio, 0.90 to 2.65).

CONCLUSIONS

Grapefruit juice increases the oral bioavailability of cisapride, with large interindividual variation in the change in Cmax and AUC. Because cisapride has a wide therapeutic index, the interaction may not be of major clinical significance for efficacy, but further studies are necessary at steady state to rule out the possibility of side effects in susceptible individuals.

Effect of cisapride on secondary peristalsis in patients with gastroesophageal reflux disease

OBJECTIVE

Improvement of esophageal acid clearance appears to be an important effect of cisapride in the treatment of reflux disease. The mechanism underlying this effect is not clear. Esophageal peristalsis is a major component of the acid clearance process. In normal subjects secondary peristalsis is an important mechanism of esophageal acid clearance during sleep, and this response appears to be impaired in patients with reflux esophagitis. The effects of cisapride on secondary peristalsis are not known. The aim of this study was to investigate the effects of cisapride on the triggering and characteristics of secondary peristalsis in patients with reflux esophagitis.

METHODS

In 17 patients with reflux esophagitis and impaired secondary peristalsis cisapride, 10 mg q.i.d., or placebo were administered in a randomized double blind, crossover design for 4 days separated by a 4-7 day washout period. On the fourth day of treatment, primary peristalsis and secondary peristalsis in response to 10- and 20-ml air boluses were assessed.

RESULTS

Secondary peristaltic success and amplitude were greater with the 20-ml bolus than with the 10-ml bolus. However, cisapride had no effect on either secondary peristaltic success or amplitude. Cisapride also had no effect on primary peristalsis or basal LES pressure.

CONCLUSIONS

The improvement in esophageal acid clearance by cisapride is not explainable by improvement in secondary peristalsis.

Pharmacokinetics of cisapride in the horse

The purpose of this study was to determine the pharmacokinetics and absolute bioavailability of cisapride after intravenous (i.v.) and intragastric (i.g.) administration in healthy, adult horses. Five animals received single doses of 0.1 mg/kg, 0.2 mg/kg and 0.4 mg/kg cisapride by the i.g. route in an open, randomized fashion on different occasions separated by a washout period of at least 48 h. Four of these horses were also given a single i.v. dose of 0.1 mg/kg cisapride. Jugular venous blood was collected periodically up to 24 h after dosing. Plasma cisapride concentrations were measured by high-performance liquid chromatography. There was considerable inter individual variability in pharmacokinetic parameters. The mean (SD) values for systemic clearance (CI) and steady-state volume of distribution (Vss) were 494 (43.6) mL/h/kg and 1471 (578) mL/kg, respectively. Although the rate of cisapride absorption was quite rapid, only about half the i.g. dose was absorbed systemically. The average terminal half-life (t1/2) calculated over three i.g. doses was 2.06 h and that for i.v. administration was 2.12 h. The pharmacokinetics of cisapride from 0.1 mg/kg to 0.4 mg/kg were independent of the i.g. dose.

The influence of cisapride and clarithromycin on QT intervals in healthy volunteers

OBJECTIVE

Recently a few cases of long QT syndrome were reported during treatment with cisapride. In most of these cases, risk factors for cardiac arrhythmias or pharmacologic interactions might have been involved, and the role of cisapride remained unclear. Macrolides such as clarithromycin potentially interact with the metabolic elimination of cisapride and have overlapping indication areas. We therefore studied whether combined treatment with clarithromycin and cisapride leads to pharmacokinetic changes and increased QT intervals.

METHODS

The study was an open, randomized, 2-way crossover study with washout periods of 1 week. Twelve healthy volunteers were recruited. Treatments were cisapride (10 mg 4 times a day) for 10 days with concomitant clarithromycin (500 mg twice a day) from days 6 through 10, or clarithromycin (500 mg twice a day) for 10 days combined with cisapride (10 mg 4 times a day) from days 6 through 10. Frequent ECG recordings were performed for 24 hours before drug treatment (baseline). After 5 days of monotherapy and combination therapy, frequent ECG recordings and assessments of plasma drug levels were performed for 24 hours.

RESULTS

Clarithromycin alone was associated with a minimal increase in QTc intervals. Monotherapy with 10 mg cisapride 4 times a day led to a concentration-dependent QTc elevation, amounting to 6 ms during steady state. Combination of cisapride and clarithromycin caused an average QTc increase of 25 ms above pretreatment values and 3-fold increases in cisapride concentrations.

CONCLUSIONS

QTc elevations after cisapride or clarithromycin alone remained within the normal range of diurnal variation. Coadministration of cisapride and clarithromycin produced a substantial QT prolongation. The data support the recently purported interaction between cisapride and clarithromycin and thus the filed contraindication to combine these drugs.

Pharmacokinetic characteristics of cisapride in elderly patients

We demonstrated pharmacokinetic characteristics of cisapride in elderly patients (85+/-6 years) who had suffered from constipation based on intestinal motility dysfunction. After a single p.o. dose of 2.5 mg cisapride tablet on the first day, plasma unchanged cisapride concentrations were detected at 9 points within 24 hours, using high-performance liquid chromatography method. Subsequently, the patients were treated with cisapride 3 times daily during next 26 days (from the day 2 to the day 27). On the 28th day, a cisapride tablet was given once in the morning and blood samples were obtained with the same procedure as that on day 1. The obtained elimination half-life averaged 21.8+/-10.6 hours, which seems to be considerably longer than those previously reported. The area under the time-concentration curve (AUC) on the day 28 was 2.7 times larger than AUC on the day 1, suggesting that plasma cisapride concentrations can become higher than expected by physicians when given 3 times daily to extremely elderly patients. Because cisapride sometimes induces fatal ventricular arrhythmias and sudden death in a concentration-dependent manner, this medicine should be administered once or twice per day to such patients.

Comparative bioavailability of two immediate release tablets of cisapride in healthy volunteers

Relative bioavailability of cisapride was investigated after oral administration of a test versus a reference formulation of immediate release tablets of cisapride, both with 10 mg per unit. The study was conducted in a two-way cross-over design, as a single dose open-label randomised trial. The two formulations were administered in two treatment days , separated by a washout period of 6 days, in fasted subjects who received one single oral dose of 20 mg of one study medication of cisapride as two 10 mg tablets. Multiple samples were collected over 24 h post-dosing. Plasma samples were assayed for cisapride using a selective and sensitive high-performance liquid chromatography (HPLC) method with UV detection. The pharmacokinetic parameter values (mean+/-RSD%) of cisapride as the test formulation were: AUC0-infinity=329+/-20.9 ng.h/ml, Cmax=52.8+/-22.6 ng/ml, tmax=1.26+/-22.0 h and t1/2=4.08+/-15 h. Following administration of the reference formulation the values obtained for the same parameters were: AUC0-infinity=317+/-19.2 ng.h/ml, Cmax=49.2+/-21.3 ng/ml, tmax=1.38+/-30.1 h and t1/2=4.52+/-24.8 h. These results show that the two cisapride formulations can be considered as bioequivalent, with respect to the above mentioned parameters.