In Silico, Ex Vivo and In Vivo Studies of Roflumilast as a Potential Antidiarrheal and Antispasmodic agent: Inhibition of the PDE-4 Enzyme and Voltage-gated Ca++ ion Channels

The aim of the present study was to evaluate the possible gut inhibitory role of the phosphodiesterase (PDE) inhibitor roflumilast. Increasing doses of roflumilast were tested against castor oil-induced diarrhea in mice, whereas the pharmacodynamics of the same effect was determined in isolated rabbit jejunum tissues. For in silico analysis, the identified PDE protein was docked with roflumilast and papaverine using the Autodock vina program from the PyRx virtual screening tool. Roflumilast protected against diarrhea significantly at 0.5 and 1.5 mg/kg doses, with 40% and 80% protection. Ex vivo findings from jejunum tissues show that roflumilast possesses an antispasmodic effect by inhibiting spontaneous contractions in a concentration-dependent manner. Roflumilast reversed carbachol (CCh, 1 µM)-mediated and potassium (K+, 80 mM)-mediated contractile responses with comparable efficacies but different potencies. The observed potency against K+ was significantly higher in comparison to CCh, similar to verapamil. Experiments were extended to further confirm the inhibitory effect on Ca++ channels. Interestingly, roflumilast deflected Ca++ concentration–response curves (CRCs) to the right with suppression of the maximum peak at both tested doses (0.001-0.003 mg/mL), similar to verapamil. The PDE-inhibitory effect was authenticated when pre-incubation of jejunum tissues with roflumilast (0.03-0.1 mg/mL) produced a leftward deflection of isoprenaline-mediated inhibitory CRCs and increased the tissue level of cAMP, similar to papaverine. This idea was further strengthened by molecular docking studies, where roflumilast exhibited a better binding affinity (-9.4 kcal/mol) with the PDE protein than the standard papaverine (-8.3 kcal/mol). In conclusion, inhibition of Ca++ channels and the PDE-4 enzyme explains the pharmacodynamics of the gut inhibitory effect of roflumilast.

Selectivity in the impact of P-glycoprotein upon pulmonary absorption of airway-dosed substrates: a study in ex vivo lung models using chemical inhibition and genetic knockout

P-glycoprotein (P-gp) mediated efflux is recognised to alter the absorption and disposition of a diverse range of substrates. Despite evidence showing the presence of P-gp within the lung, relatively little is known about the transporter's effect upon the absorption and distribution of drugs delivered via the pulmonary route. Here, we present data from an intact isolated rat lung model, alongside two isolated mouse lung models using either chemical or genetic inhibition of P-gp. Data from all three models show inhibition of P-gp increases the extent of absorption of a subset of P-gp substrates (e.g. rhodamine 123 and loperamide) whose physico-chemical properties are distinct from those whose pulmonary absorption remained unaffected (e.g. digoxin and saquinavir). This is the first study showing direct evidence of P-gp mediated efflux within an intact lung, a finding that should warrant consideration as part of respiratory drug discovery and development as well as in the understanding of pulmonary pharmacokinetic (PK)-pharmacodynamic (PD) relationships.

Determination of loperamide in mdr1a/1b knock-out mouse brain tissue using matrix-assisted laser desorption/ionization mass spectrometry and comparison with quantitative electrospray-triple quadrupole mass spectrometry analysis

Recently matrix-assisted laser desorption/ionization mass spectrometry (MALDI MS) imaging has been used to analyze small molecule pharmaceutical compounds directly on tissue sections to determine spatial distribution within target tissue and organs. The data presented to date usually indicate relative amounts of drug within the tissue. The determination of absolute amounts is still done using tissue homogenization followed by traditional liquid chromatography-tandem mass spectrometry (LC-MS/MS). In this study, the quantitative determination of loperamide, an antidiarrheal agent and a P-glycoprotein substrate, in mdr1a/1b (-/-) mouse brain tissue sections using MALDI MS on a quadrupole time-of-flight mass spectrometry is described. 5 mg/mL α-cyano-4-hydroxycinnamic acid in 50% acetonitrile with 0.1% trifluoroacetic acid and 0.5 μM reserpine was used as the MALDI matrix. The calibration curve constructed by the peak intensities of standard samples from MALDI MS was linear from 0.025 to 0.5 μM with r² = 0.9989. The accuracy of calibration curve standards was 78.3-105.9% and the percent deviation was less than 25%. Comparison between direct MALDI tissue analysis and conventional tissue analysis using homogenization followed by electrospray LC-MS/MS was also explored.

Targeting the central nervous system: In vivo experiments with peptide-derivatized nanoparticles loaded with Loperamide and Rhodamine-123

Polymeric nanoparticles (Np) represent one of the most innovative non-invasive approaches for the drug delivery to the central nervous system (CNS). It is known that the ability of the Np to cross the Blood Brain Barrier (BBB), thus allowing the drugs to exert their pharmacological activity in the central nervous district, is linked to their surface characteristics. Recently it was shown that the biocompatible polyester poly(d,l-lactide-co-glycolide) (PLGA) derivatized with the peptide H(2)N-Gly-l-Phe-d-Thr-Gly-l-Phe-l-Leu-l-Ser(O-beta-d-Glucose)-CONH(2) [g7] was a useful starting material for the preparation of Np (g7-Np); moreover, fluorescent studies showed that these Np were able to cross the BBB. In this research, g-7 Np were loaded with Loperamide in order to assess their ability as drug carriers for CNS, and with Rhodamine-123, in order to qualitatively determine their biodistribution in different brain macro-areas. A pharmacological evidence is given that g7-Np are able to cross the BBB, ensuring, for the first time, a sustained release of the embedded drug, and that these Np are able to reach all the brain areas here examined. The ability to enter the CNS appears to be linked to the sequence of the peptidic moiety present on their surface.

Loperamide: a pharmacological review

Loperamide is an antidiarrheal medication approved for the control of diarrhea symptoms and is available without a prescription. Loperamide works by a number of different mechanisms of action that decrease peristalsis and fluid secretion, resulting in longer gastrointestinal transit time and increased absorption of fluids and electrolytes from the gastrointestinal tract. It is a phenylpiperidine derivative with a chemical structure similar to opiate receptor agonists such as diphenoxylate and haloperidol. It was designed to maintain the antidiarrheal activity of these drugs, but minimize the negative aspects associated with their effects on the opiate receptor. Because of loperamides's low oral absorption and inability to cross the blood-brain barrier, it has minimal central nervous system effects. It also has a longer duration of action than diphenoxylate. However, it has no clinically significant analgesic activity and does not decrease the pain associated with some forms of irritable bowel syndrome and diarrhea. Loperamide is metabolized by the cytochrome P450 (CYP) system and is a substrate for the CYP3A4 isoenzyme. Concurrent administration with CYP3A4 inhibitors may elevate loperamide concentrations. Common adverse reactions to loperamide include cramps and nausea. Loperamide is an effective treatment for patients with painless diarrhea and is considered to be free of abuse potential.

Tissue Distribution of Loperamide and N-Desmethylloperamide Following a Fatal Overdose

We report a case involving a fatal intoxication with loperamide (Imodium). Loperamide is a synthetic opioid of the phenyl piperidine class used as an over-the-counter antidiarrheal. It exerts its effects through interaction with micro-opiate receptors in the intestine to reduce peristalsis. Loperamide lacks the typical euphoric opiate effects when administered at recommended doses. Both loperamide and its major metabolite, N-desmethylloperamide, were isolated by liquid-liquid extraction into n-butyl chloride from alkalinized samples. Extracts were analyzed by liquid chromatography-electrospray-mass spectrometry in selected-ion-monitoring mode. Rapid separation of the drug, metabolite, and internal standard (diphenoxylate) was achieved using a high-resolution C18 column with 1.8-microm particle diameter. The mobile phase consisted of 0.1% formic acid in deionized water (60%) and acetonitrile (40%) at a flow rate of 0.5 mL/min. Heart blood concentrations for loperamide and its metabolite were 1.2 mg/L and 3.3 mg/L, respectively. In contrast, reported peak plasma concentrations of loperamide after administration of recommended daily doses of 16 mg did not exceed 0.012 mg/L in controlled trials. Because the heart blood ethanol concentration was 0.08 g/dL, the medical examiner ruled that the cause of death was loperamide and ethanol intoxication, and the manner of death as undetermined.

Validation of a liquid chromatographic-tandem mass spectrometric method for the determination of loperamide in human plasma

A sensitive and selective method based on liquid chromatography-tandem mass spectrometry (LC-MS/MS) has been developed for the quantitative determination of loperamide in human plasma. Automated solid-phase extraction (SPE) on disposable extraction cartridges (DEC) is used to isolate the compounds from the biological matrix and to prepare a cleaner sample before injection and analysis in the LC-MS/MS system. After conditioning, the plasma sample is loaded on the DEC filled with endcapped ethyl silica (C2(EC)) and washed twice with water. The analytes are therefore eluted by dispensing methanol. The eluate is then collected and added with ammonium acetate solution in order to inject an aliquot of this final extract in the LC-MS/MS system. On-line LC-MS/MS system using atmospheric pressure chemical ionization (APCI) has been developed for the determination of loperamide. The separation is obtained on a octadecylsilica based stationary phase using a mobile phase consisting in a mixture of methanol and 5mM ammonium acetate solution (25:75, v/v). Clonazepam is used as internal standard (IS). The MS/MS ion transitions monitored are m/z 477--> 266 and 316--> 270 for loperamide and clonazepam, respectively. The most appropriate regression model of the response function as well as the limit of quantitation were first selected during the pre-validation step. These latter criteria were then assessed during the formal validation step. The limit of quantitation (LOQ) was around 50 pg/ml for loperamide. The method was also validated with respect to recovery, precision, trueness, accuracy and linearity.

In Vivo Pharmacology and Antidiarrheal Efficacy of a Thiazolidinone CFTR Inhibitor in Rodents

A small-molecule inhibitor of the cystic fibrosis transmembrane conductance regulator (CFTR), 3-[(3-trifluoromethyl)phenyl]-5-[(4-carboxyphenyl)methylene]-2-thioxo-4-thiazolidinone (CFTR(inh)-172), reduces enterotoxin-induced intestinal fluid secretion in rodents. Here, we study CFTR(inh)-172 pharmacology and antidiarrheal efficacy in rodents using (14)C-labeled CFTR(inh)-172, liquid chromatography/mass spectrometry, and a closed intestinal loop model of fluid secretion. CFTR(inh)-172 was cleared primarily by renal glomerular filtration without chemical modification. CFTR(inh)-172 accumulated in liver within 5 min after intravenous infusion in mice, and was concentrated fivefold in bile over blood. At 30-240 min, CFTR(inh)-172 was found mainly in liver, intestine, and kidney, with little detectable in the brain, heart, skeletal muscle, or lung. Pharmacokinetic analysis in rats following intravenous bolus infusion showed a distribution volume of 770 mL with redistribution and elimination half-times of 0.14 h and 10.3 h, respectively. CFTR(inh)-172 was stable in hepatic microsomes. Closed-loop studies in mice indicated that a single intraperitoneal injection of 20 microg CFTR(inh)-172 inhibited fluid accumulation at 6 h after cholera toxin by >90% in duodenum and jejunum, approximately 60% in ileum and <10% in colon. No toxicity was seen after high-dose CFTR(inh)-172 administration (3 mg/kg/day in two daily doses) in mice over the first 6 weeks of life. The metabolic stability, enterohepatic recirculation, slow renal elimination, and intestinal accumulation of CFTR(inh)-172 account for its efficacy as an antidiarrheal.

LC–MS determination and bioavailability study of loperamide hydrochloride after oral administration of loperamide capsule in human volunteers

The purpose of the present study was to develop a standard protocol for loperamide hydrochloride bioequivalence testing. For this purpose, a simple rapid and selective LC-MS method utilizing a single quadrupole mass spectrometer was developed and validated for the determination of loperamide hydrochloride in human plasma, and we followed this with a bioavailability study. Methyl tert-butylether (MTBE) was used to extract loperamide hydrochloride and ketoconazole (internal standard (IS)) from an alkaline plasma sample. LC separation was performed on a Zorbax RX C18 column (5 microm, 2.1 mm x 150 mm) using acetonitrile-water-formic acid (50:50:0.1 (v/v)) as a mobile phase. The retention times of loperamide hydrochloride and IS were 1.2 and 0.8 min, respectively. Quadrupole MS detection was by monitoring at m/z 477 (M + 1) corresponding to loperamide hydrochloride and at m/z 531 (M + 1) for IS. The described assay method showed acceptable precision, accuracy, linearity, stability, and specificity. The bioavailability of loperamide hydrochloride was evaluated in eight healthy male volunteers. The following pharmacokinetic parameters were elucidated after administering a single dose of four 2mg capsules of loperamide: the area under the plasma concentration versus time curve from time 0 to 72 h (AUC72 h) 19.26 +/- 7.79 ng h/ml; peak plasma concentration (Cmax) 1.18 +/- 0.37 ng/ml; time to Cmax (Tmax) 5.38 +/- 0.74 h; and elimination half-life (t1/2) 11.35 +/- 2.06 h. The developed method was successfully used to study the bioavailability of a low dose (8 mg) of loperamide hydrochloride.

Potential roles of P-gp and calcium channels in loperamide and diphenoxylate transport

This study examined the accumulation and transport of two related systemic opioids used as antidiarrhoeal drugs and compared their rates of transport with known P-glycoprotein (P-gp) substrates used in our in vitro environment. Cellular uptake and efflux and transcellular transport were all determined using Caco-2 cells after exposure to loperamide or diphenoxylate, with or without a range of efflux inhibitors. Bidirectional transport studies of 5 microM loperamide showed efflux to be fivefold higher than influx (42 x 10(-6) compared to 8 x 10(-6) cm/s); however, this decreased to twofold at 10 microM and was abolished using 100 microM loperamide. An uptake pathway was also discovered when P-gp was inhibited which, in the presence of Ca(2+) channel blockers, was amplified, providing a potential mechanism for central nervous system effects to be increased upon blockage of L-type calcium channels, quite separate from any P-gp inhibition. Diphenoxylate transport, however, showed little sign of P-gp-mediated efflux. Diphenoxylate accumulated readily within cells, yet transport through cells was very low. Additionally, efflux inhibitors had little impact on transport or accumulation, suggesting that diphenoxylate was not a substrate for an efflux mechanism.

No effect of MDR1 C3435T variant on loperamide disposition and central nervous system effects

BACKGROUND

The MDR1 gene encodes the efflux transporter P-glycoprotein, which is highly expressed in the small intestine and in the blood-brain barrier. A major function of P-glycoprotein is to limit the absorption and central nervous system exposure of numerous xenobiotics. A genetic polymorphism in the MDR1 gene (C3435T) has been associated with changes in the intestinal expression level and function of P-glycoprotein. The aim of this study was to investigate the effect of this polymorphism on disposition and brain entry of the P-glycoprotein substrate loperamide.

METHODS

Healthy white volunteers were genotyped for the MDR1 C3435T polymorphism, and a 16-mg oral dose of loperamide was administered to 8 subjects with the 3435TT genotype and 8 subjects with the 3435CC genotype. Plasma levels of loperamide were determined by liquid chromatography-tandem mass spectrometry. Loperamide-induced respiratory depression was detected as the ventilatory response to carbon dioxide and was used as a measure of central nervous system side effects.

RESULTS

We found no significant difference in loperamide pharmacokinetics between individuals homozygous for the C and the T alleles in position 3435 of MDR1, as follows: peak plasma drug concentration, 3164 +/- 1053 pg/mL and 3021 +/- 984 pg/mL; area under the concentration-time curve from 0 to 8 hours, 14414 +/- 4756 pg. h/mL and 14923 +/- 6466 pg. h/mL; and time to peak plasma drug concentration, 3.9 +/- 1.4 hours and 3.9 +/- 2.6 hours for the MDR1 3435CC and 3435TT genotypes, respectively (P >.05, for all parameters). Hypercapnic ventilatory response changed only minimally after ingestion of loperamide (the coefficient of variation during the 0- to 8-hour period was 21% +/- 14% for the sample population), and there was no MDR1 3435 genotype-related effect on respiratory response. Carriers of the 2 major MDR1 haplotypes, MDR1*1 and MDR1*13, did not differ in their response to loperamide.

CONCLUSION

There was no association between the MDR1 C3435T variation and plasma levels or central nervous system effects of the P-glycoprotein substrate loperamide in a white study population. The MDR1 haplotype structure was quite variable and supports the use of haplotypes instead of single nucleotide polymorphisms in determining clinical consequences of genetic variation.

Wood Creosote, the Principal Active Ingredient of Seirogan, an Herbal Antidiarrheal Medicine: A Single-Dose, Dose-Escalation Safety and Pharmacokinetic Study

STUDY OBJECTIVE

To assess the safety, tolerability and pharmacokinetics of escalating single doses of wood creosote, an herbal antidiarrheal and antispasmodic agent.

DESIGN

Randomized, double-blind, placebo-controlled study.

SETTING

Clinical research center.

SUBJECTS

Forty (32 men, 8 women) healthy volunteers aged 19-42 years.

INTERVENTION

By random assignment, 22 men and 8 women received escalating single doses of wood creosote (45, 90, 135, 180, and 225 mg) and 10 men received placebo (for each of the five dose levels, 6 subjects received active substance and 2 subjects received placebo).

MEASUREMENTS AND MAIN RESULTS

Vital signs, laboratory tests, and electrocardiograms were assessed; no dose-related or clinically significant changes were noted. Serial blood samples were obtained to determine the pharmacokinetics of four major active components of wood creosote: total (conjugated plus free) guaiacol, creosol, o-cresol, and 4-ethylguaiacol. The most common adverse events were mild headache and dizziness, with no dose-related trends being apparent. Area under the concentration-time curve from time zero to infinity increased in a dose-proportional manner for total guaiacol, creosol, and o-cresol and was not assessed for total 4-ethylguaiacol owing to lack of data at the low dose level. No apparent differences by sex were noted for any of the four active components. All four components were rapidly eliminated.

CONCLUSION

Single oral doses of wood creosote up to 225 mg were safe and well tolerated in healthy men and women. Also, the doses of wood creosote were rapidly absorbed, conjugated, and eliminated. Such a rapid onset and short duration of action would appear desirable in the treatment of acute nonspecific diarrhea.

Effect of octreotide on fluid absorption and secretion by the normal human jejunum and ileum in vivo

BACKGROUND

We hypothesized that part of the non-specific antidiarrhoeal effect of octreotide is mediated by a proabsorptive or antisecretory effect on small intestinal active electrolyte transport.

METHODS

To measure the effect of octreotide on net absorption, the jejunum and ileum of normal human subjects were perfused with a balanced electrolyte solution; to measure the effect of octreotide on normal active chloride secretion, the jejunum was perfused with a bicarbonate-free solution.

RESULTS

During perfusion of a balanced electrolyte solution, octreotide increased basal net fluid absorption in the jejunum and ileum by about 40 mL/h per 30 cm. In the jejunum, octreotide markedly inhibited basal and sham feeding-stimulated active chloride secretion and inhibited water secretion by 28 and 51 mL/h per 30 cm, respectively.

CONCLUSIONS

Octreotide causes an increase in the net epithelial cell absorption rate of a balanced electrolyte solution in the normal jejunum and ileum. In the jejunum, this proabsorptive effect is mediated mainly by the reduction of normal active electrolyte secretion, rather than by stimulation of normal active electrolyte absorption. These results support the hypothesis that part of the antidiarrhoeal action of octreotide is due to its effects on active electrolyte transport mechanisms by normal epithelial cells of the small intestine.

[Physicochemical and pharmacological characteristic and clinical efficacy of an anti-irritable bowel syndrome agent, polycarbophil calcium (Polyful)]

Irritable bowel syndrome (IBS) is a functional bowel disorder characterized by abdominal pain or discomfort and abnormal defecation. Polycarbophil calcium, a water-absorbing polymer, is expected to improve stool consistency. Polycarbophil calcium decalcified under the acidic condition and then absorbed 70 times its weight of water under the neutral condition. In in situ experiments using rat jejunum and colon, polycarbophil decreased water absorption by the intestine without affecting water secretion. Polycarbophil inhibited prostaglandin E2-, 5-hydroxy-L-tryptophan- and castor oil-induced diarrhea in mice or rats. Polycarbophil calcium also inhibited sennoside-induced diarrhea in dogs. Polycarbophil increased the weight of feces in naive or low-fiber diet feeding rats. In naive dogs, polycarbophil calcium increased stool frequency, stool weight and moisture. Polycarbophil was not absorbed from the gastrointestine, not metabolized and eliminated into feces in rats and dogs. Polycarbophil calcium did not affect the absorption of coadministered drugs in dogs. In the dose-finding clinical study for IBS, polycarbophil calcium was effective both in diarrhea and constipation. In the Phase III study, polycarbophil calcium was superior to trimebutine maleate in efficacy and equal in safety. Emesis/vomiting and thirst were observed, but episodes of diarrhea or constipation by excessive action were few. Polycarbophil calcium seems promising as an anti-IBS agent.

In vitro evaluation of pectin-HPMC compression coated 5-aminosalicylic acid tablets for colonic delivery

In this study, we report pectin-HPMC compression coated core tablets of 5-aminosalicylic acid (5-ASA) for colonic delivery. Each 100 mg core tablet contained 5-ASA and was compression coated at 20 kN or 30 kN using 100% pectin, 80% pectin-20% HPMC, or 60% pectin-40% HPMC, at two different coat weights as 400 or 500 mg. Drug dissolution/system erosion/degradation studies were carried out in pH 1.2 and 6.8 buffers using a pectinolytic enzyme. The system was designed based on the gastrointestinal transit time concept, under the assumption of colon arrival times of 6 h. It was found that pectin alone was not sufficient to protect the core tablets and HPMC addition was required to control the solubility of pectin. The optimum HPMC concentration was 20% and such system would protect the cores up to 6 h that corresponded to 25-35% erosion and after that under the influence of pectinase the system would degrade faster and delivering 5-ASA to the colon. The pectin-HPMC envelope was found to be a promising drug delivery system for those drugs to be delivered to the colon.

Comparison of the intestinal absorption of quercetin, phloretin and their glucosides in rats

Absorption and metabolism of quercetin and isoquercitrin (quercetin 3-O-glucose) were investigated in rats after in situ perfusion of jejunum plus ileum (15 nmol/min) for 30 min and compared with those of phloretin and phloridzin (phloretin 2'-O-glucose). After perfusion of the glucosides, the corresponding aglycone forms and conjugated derivatives appeared in the lumen. The conjugated metabolites were similar to those recovered after intestinal perfusion of the aglycone forms. Regardless of the aglycone or glucoside perfused, only conjugated forms were present in the mesenteric vein blood draining the perfused segment showing the importance of intestinal conjugation. The hydrolysis of glucosides was a prerequisite step before their conjugation by intestinal enzymes and their transport towards the mucosal and serosal sides. In contrast to phloridzin, lactase phloridzin hydrolase activity did not seem to be an essential pathway for isoquercitrin hydrolysis. The 3-O-glucosylation of quercetin improved the net absorption of the aglycone (P < 0.05), whereas phloretin absorption decreased when present as 2'-O-glucoside (P < 0.05). Whatever the perfused compound, the efficiency of the absorption seemed to be linked to the intestinal conjugation process and to the luminal secretion of metabolites.

A scintigraphic study to investigate the potential for altered gut distribution of loperamide from a loperamide-simethicone formulation in man

A loperamide simethicone combination formulation has recently been demonstrated to have significant clinical advantages compared to loperamide alone in the relief of diarrhoea and related symptoms. The product visualisation technique of gamma scintigraphy has been used to investigate the interaction of the formulation with the heterogenous environment of the human gut in a group of 12 healthy volunteers. The results suggest that changes in the intestinal kinetics of loperamide from the combination product, e.g. jejunal coating, could be contributing to the improved efficacy.

Increased drug delivery to the brain by P-glycoprotein inhibition

BACKGROUND

Although the antidiarrheal loperamide is a potent opiate, it does not produce opioid central nervous system effects at usual doses in patients. On the basis of in vitro studies demonstrating that loperamide is a substrate for the adenosine triphosphate-dependent efflux membrane transporter P-glycoprotein, we postulated that inhibition of P-glycoprotein with quinidine would increase entry of loperamide into the central nervous system with resultant respiratory depression.

METHODS

To test this hypothesis, a 16-mg dose of loperamide was administered to eight healthy male volunteers in the presence of either 600 mg quinidine, a known inhibitor of P-glycoprotein, or placebo. Central nervous system effects were measured by evaluation of the respiratory response to carbon dioxide rebreathing as a measure of opiate-induced respiratory depression.

RESULTS

Loperamide produced no respiratory depression when administered alone, but respiratory depression occurred when loperamide (16 mg) was given with quinidine at a dose of 600 mg (P < .001). These changes were not explained by increased plasma loperamide concentrations.

CONCLUSION

This study therefore demonstrates first the potential for important drug interactions to occur by a new mechanism, namely, inhibition of P-glycoprotein, and second that the lack of respiratory depression produced by loperamide, which allows it to be safely used therapeutically, can be reversed by a drug causing P-glycoprotein inhibition, resulting in serious toxic and abuse potential.

Racecadotril

Racecadotril is an oral enkephalinase inhibitor used in the treatment of acute diarrhoea. It prevents the degradation of endogenous opioids (enkephalins), thereby reducing hypersecretion of water and electrolytes into the intestinal lumen. In a randomised double-blind study in 6 adult volunteers with castor oil-induced diarrhoea, racecadotril significantly reduced stool weight and stool number in comparison with placebo. Similar results have been obtained in treating castor oil-induced diarrhoea in rats. Racecadotril was significantly more effective than placebo in randomised double-blind studies in adults or children with diarrhoea (of infectious origin or in adults with HIV infection). In well controlled trials, racecadotril had efficacy similar to that of loperamide and was generally as effective as loperamide-oxide. Racecadotril had a similar tolerability profile to placebo, and was better tolerated than loperamide, in adults and children with diarrhoea. It caused significantly less constipation after resolution of diarrhoea than loperamide.

Antidiarrheal effects of zaldaride maleate after oral, intravenous and subcutaneous administration to rats

The antidiarrheal action of zaldaride maleate (ZAL) after oral, intravenous and subcutaneous administration was examined to determine whether ZAL acts systemically or locally in the intestine of rats. Oral administration of ZAL inhibited castor oil- and 16,16-dimethyl prostaglandin E2-induced diarrhea; however, intravenous or subcutaneous administration of ZAL was ineffective. When ZAL was orally administered, the area under the plasma concentration time curve of the compound was lower than that of ZAL following intravenous or subcutaneous administration at the maximum doses studied. The antidiarrheal effect of ZAL was not dependent on its plasma concentration level. These results suggest that ZAL acts locally in the intestinal tract in rats.

Pluronic P85 increases permeability of a broad spectrum of drugs in polarized BBMEC and Caco-2 cell monolayers

PURPOSE

Previous studies demonstrated that inhibition of P glycoprotein (P-gp) by Pluronic P85 (P85) block copolymer increases apical (AP) to basolateral (BL) transport of rhodamine 123 (R123) in the polarized monolayers of bovine brain microvessel endothelial cells (BBMEC) and Caco-2 cells. The present work examines the effects of P85 on the transport of fluorescein (Flu), doxorubicin (Dox), etoposide (Et), taxol (Tax), 3'-azido-3'-deoxythymidine (AZT), valproic acid (VPA) and loperamide (Lo) using BBMEC and Caco-2 monolayers as in vitro models of the blood brain barrier and intestinal epithelium respectively.

METHODS

Drug permeability studies were performed on the confluent BBMEC and Caco-2 cell monolayers mounted in Side-Bi-Side diffusion cells.

RESULTS

Exposure of the cells to P85 significantly enhanced AP to BL permeability coefficients of Flu, Tax, Dox and AZT in both cell models. Further, P85 enhanced AP to BL transport of Et, VPA and Lo in Caco-2 monolayers. No changes in the permeability coefficients of the paracellular marker mannitol were observed in the presence of the copolymer.

CONCLUSIONS

P85 increases AP to BL permeability in BBMEC and Caco-2 monolayers with respect to a broad panel of structurally diverse compounds, that were previously shown to be affected by P-gp and/ or multidrug resistance associated protein (MRP) efflux systems. Broad specificity of the block copolymer effects with respect to drugs and efflux systems appears to be a valuable property in view of developing pharmaceutical formulations to increase drug accumulation in selected organs and overcome both acquired and intrinsic drug resistance that limits the effectiveness of many chemotherapeutic agents.

In vitro adsorption of mebeverine hydrochloride onto kaolin and its relationship to pharmacological effects of the drug in vivo

The in vitro uptake of mebeverine hydrochloride from an initial drug concentration of 0.25-4.25 or 0.2-3.6 g% w/v onto kaolin 5.0 g% w/v at pH 1.8 or 7.5, respectively, at 37 degrees C was represented by a double- layered adsorption isotherm. The calculated data were in accordance with a Langmuir adsorption isotherm for an initial drug concentration up to 2.1 or 2.0 g% w/v when a monolayer was formed at pH 1.8 or 7.5, respectively. The adsorption process is pH dependent, and is affected by the electrolyte concentration and valency. The amount of the drug desorbed (mg% w/v) by washing with different elution media at 37 degrees C followed the sequence 0.1 M hydrochloric acid > 0.1 M magnesium chloride > 0.1 M sodium chloride > simulated intestinal fluid. The results obtained from this study indicate that two mechanisms, ion exchange and physical adsorption, were involved in the uptake of mebeverine hydrochloride by kaolin. The presence of different concentrations of kaolin with the tablets or capsules of the drug, adversely affected the release rate. The in vivo and in vitro studies on guinea pig ileum showed that the presence of kaolin in a mixture with mebeverine hydrochloride did not affect to any significant level the inhibiting effect of the musculotropic drug on carbachol-induced contractions in the isolated guinea pig ileum. In vivo studies showed similar results for barium chloride as well.

Increased systemic availability of loperamide after oral administration of loperamide and loperamide oxide with cotrimoxazole

1. The effects of concurrent administration of cotrimoxazole on the plasma concentration-time profiles of loperamide and its oxide were investigated in two separate studies in healthy male volunteers. Cotrimoxazole (960 mg, twice daily) was administered for 24 h before and 48 h after an oral dose of loperamide oxide (4 mg) or loperamide (4 mg). 2. Coadministration of cotrimoxazole with loperamide oxide did not alter the tmax, Cmax and AUC of loperamide oxide, whereas the Cmax (0.32 +/- 0.14 ng ml-1 without cotrimoxazole; 0.45 +/- 0.18 ng ml-1 with cotrimoxazole; P < 0.05) and AUC (8.13 +/- 1.91 ng ml-1 h without cotrimoxazole; 12.50 +/- 4.60 ng ml-1 h with cotrimoxazole; P < 0.005) of loperamide were significantly increased. 3. Coadministration of cotrimoxazole with loperamide significantly increased the Cmax (0.74 +/- 0.22 ng ml-1 without cotrimoxazole; 1.49 +/- 0.81 ng ml-1 with cotrimoxazole; P < 0.01) and AUC (13.40 +/- 3.80 ng ml-1 h without cotrimoxazole; 25.30 +/- 11.10 ng ml-1 h with cotrimoxazole; P < 0.005) of loperamide, whilst its tmax and t1/2,z were not significantly altered. 4. The increase in loperamide AUC, following coadministration of either loperamide oxide or loperamide with cotrimoxazole, may be due to reduced first pass metabolism of loperamide.

[Clinical pharmacokinetics of fluorazole]

The ftorazole pharmacokinetics was studied in 14 patients after the oral administration of 40 and 80 mg as a single dose. The ftorazole concentrations in the serum specimens sampled within 8 hours were determined by GLC with an electron-capture detector. A pronounced variability was inherent in the individual concentration-time profiles: the mean values of the serum peak concentrations (Cmax) following the 40 and 80 mg dosing were 30-119 and 55-195 ng/ml respectively. Nonetheless, a dose-proportional increasing of the areas under the concentration-time curve (AUC) was observed. The mean values (SD) of the AUC related to the dose, absorption lag-time, time for reaching Cmax, the Cmax/AUC ratio as an index of the absorption rate, the elimination half-life and mean residence time were 6.64 (2.98) (ng.h/ml), 0.31 (0.17) h, 1.17 (0.55) h, 0.26 (0.05) h-1, 2.40 (0.70) h and 3.06 (0.28) h respectively. The data obtained are indicative of the ftorazole pharmacokinetics linearity in humans.

Bioequivalence evaluation of two different oral formulations of loperamide (Diarex Lactab vs Imodium capsules)

Twenty-four healthy male volunteers were treated with two different oral formulations of loperamide according to a randomized two-way cross-over design. The test preparation was Diarex Lactab (Mepha), the reference preparation Imodium 2 mg capsules. Divided in two periods the volunteers received single 8 x 2 mg (= 16mg) doses of the test and reference formulation, respectively. Blood samples were taken immediately prior to each administration and at 14 points within 60 h after the dose. A wash-out period of 1 week was interpaused between successive drug doses. The plasma concentration of the pharmacologically active compound, loperamide, was determined by HPLC with electrochemical detection. The calibration function was linear in the range 0-10.0 ng/ml. A lower limit of quantification of 0.2 ng/ml was established. The pharmacokinetic parameters Cmax and tmax were obtained directly from plasma data. The elimination constant was estimated by log-linear regression of the measured concentrations in the terminal phase. AUC was calculated by the trapezoidal rule and extrapolated to infinity. The following mean values were obtained after intake of 16 mg loperamide as film coated tablets: AUC0 infinity 62.04 ngh/ml, Cmax 3.35 ng/ml, tmax 4.08 h, t1/2 19.66 h and after administration of the capsules: AUC0 infinity 66.56 ngh/ml, Cmax 3.98 ng/ml, tmax 4.38 h, t1/2 18.43 h. The pharmacokinetic parameters AUC0 infinity and Cmax were tested for bioequivalence parametrically (two one-sided t-tests) after logarithmic transformation of data. Differences of tmax were evaluated non-parametrically. The preparations were found to be bioequivalent and, therefore, interchangeable.

[Effect of C-terminal derivatives of sorbin on duodenal ion transports in rats]

OBJECTIVES AND METHODS

Synthetic derivatives of sorbin have been shown to inhibit VIP stimulated fluxes in the ileum in decreasing plasma-to-mucosa Na and Cl effluxes. The effect of this group of new peptides, without homology with any known peptides, was determined in rat duodenum where ion transport mechanisms differ. The improved technique of ligated loops in situ, was used, permitting the simultaneous measurement of net fluxes, influxes and effluxes for Na and Cl, in an integrated in vivo model. To determine the minimal active fragment of sorbin, synthetic C5, C7 and C20 peptides were tested and compared with known anti-secretor drugs such as loperamide, neuropeptide Y, somatostatine and metenkephalinamide.

RESULTS

C7-sorbin was the minimal peptide able to decrease duodenal VIP-stimulated fluxes of water, Na and bicarbonate. It intervenes in increasing Na influx and more slightly Cl influx, which have been decreased by VIP. It does not modify much Na and Cl effluxes stimulated by VIP. Sorbin effect is in contrast with those of known antidiarrheic agents like somatostatine, loperamide, NPY and metenkephalinamide which chiefly decrease Cl efflux.

CONCLUSIONS

Sorbin acts like an activator of absorption in the duodenum, in contrast to the other peptides or drugs and to its own anti-secretor effect in the ileum.

Pharmacokinetic, metabolic, and antidiarrheal properties of (D and L) heptapeptides of sorbin in rodent

The C-terminal heptapeptide-amide (C7-sorbin) is the minimal biologically active fragment of sorbin inducing an increase in intestinal hydroelectrolytic absorption. An analogue (D7-sorbin), characterized by the replacement of the ultimate C-terminal amino acid L-alanine-amide by D-alanine-amide, was synthetized. For pharmacokinetic studies, D7-sorbin and C7-sorbin were tritium labeled. After IV injection, clearances were 10.6 and 30.2 ml-1 for D7-sorbin and C7-sorbin, respectively, and MRT were 34 and 18 min. After SC administration, Cmax attained 0.41% and 0.12% of the dose/ml, respectively. The IP route showed a 45-min delay before Cmax and a 100% bioavailability for both peptides. D7-sorbin was principally excreted in urine, as shown by balance study, and in part in intact form, as controlled by mass spectrometry. D7-sorbin induced a significant decrease of the VIP-induced ileal secretion, previously observed with C7-sorbin. The change of L-Ala to D-Ala increased the stability of the synthetic C-terminal peptide of sorbin whereas its biological activity, bioavailability, and route of elimination were unchanged.

Do antidiarrhoeal opiates accumulate in the rat intestinal lumen?

The opiate antidiarrhoeal drugs loperamide (0.6 mg kg-1, i.p.) or difenoxin (0.77 mg kg-1, s.c.), were administered in an anaesthetic mixture (pentobarbitone 60 mg kg-1) to rats. A length of jejunum (approx. 30 cm) was cannulated, washed and then perfused with iso-osmotic saline for 20 min. The perfusion commenced 50 min after drug administration and continued for 20 min. The perfusates were collected for analysis of fluid transport rates and antidiarrhoeal drug content. These doses of the antidiarrhoeals caused marked inhibition of intestinal fluid secretion induced by intra-arterial infusion of vasoactive intestinal peptide. However, neither of the antidiarrhoeal drugs were detected in the intestinal perfusates (< 0.5 ng by HPLC). The results indicate that loperamide and difenoxin have a different pharmacokinetic profile compared with that previously found for morphine under the same conditions.

Metabolism and pharmacokinetics of nufenoxole in animals and humans: an example of stereospecific hydroxylation of an isoquinuclidine ring

1. Nufenoxole, a novel antidiarrhoeal agent, was well absorbed in rat, monkey and human after oral administration. Systemic availability of nufenoxole was 85% in monkey and 102% in man. 2. The elimination rate was much faster in rat (t1/2 of 1.8 h) and monkey (t1/2 of 4.9 h) compared with human (t1/2 of 35.8 h). 3. After oral and i.v. 14C-nufenoxole, concentrations of 14C in human erythrocytes and saliva were approx. 3- and 4-fold lower, respectively, than plasma concentrations. 4. Nufenoxole was metabolized to metabolites hydroxylated on the methyl substituent and isoquinuclidine ring in rat and monkey. The isoquinuclidine ring hydroxylation, a major pathway in human, was stereospecific. 5. Following oral doses of 14C-nufenoxole the urinary excretion of radioactivity (about 8%) was less than the faecal excretion (66.6%) in rat, while urinary excretion was the major route of drug elimination (about 60%) in man. In monkey, urinary and faecal excretion were equally important.

Single- and multiple-dose pharmacokinetics of nufenoxole in healthy human subjects

1. In 12 healthy subjects, after single doses of 20, 40 and 80 mg of nufenoxole, mean peak plasma drug concentrations of 400, 815 and 1463 ng/ml were reached at 2.2, 2.5 and 2.5 h respectively. 2. Nufenoxole was absorbed with an apparent half-life of less than one hour at all three doses. Nufenoxole concentrations declined biphasically after the peak, with an initial and terminal half-life of four to five hours and about 27 h respectively. These half-lives were independent of the administered dose. 3. AUC and Cmax increased with increasing dose, but AUC did not increase proportionately to dose, due to a lower value for 80 mg than expected, possibly reflecting reduced absorption. 4. Observed nufenoxole concentrations, in another 12 healthy subjects receiving single, daily 80 mg oral doses of nufenoxole for eight days, were in excellent agreement with those predicted from single-dose pharmacokinetics.