Preclinical pharmacokinetics and metabolism of BMS-214778, a novel melatonin receptor agonist

BMS-214778 is a novel melatonin receptor agonist that may be a useful treatment for sleep disorders that result from disruption of circadian rhythms. Pharmacokinetic studies following intravenous and oral administration and 1 month oral steady-state studies were carried out in rats and monkeys. Rat brain was analyzed for BMS-214778 to determine the extent of its penetration from plasma. Equilibrium dialysis was employed to determine the extent of binding of [(14)C]-BMS-214778 to rat, monkey, and human sera proteins. In vitro metabolism studies with BMS-214778 in rat, monkey, and human liver homogenate preparations (S-9), with monkey and human liver slice preparations, and with pooled human liver microsomes were performed and the incubates analyzed for potential metabolites. Recombinant microsomes expressing specific human cytochrome P(450) (CYP) enzymes were employed to identify possible human metabolic pathways. BMS-214778 showed a high hepatic extraction and high degree of tissue distribution. BMS-214778 also displayed non-linear oral pharmacokinetics. Systemic exposures following oral doses in rats and monkeys increased more than proportionally to the increment in dose. Loss of systemic exposure to BMS-214778 upon chronic oral dosing was observed in male rats where exposure was one-half to two-thirds compared to a single dose, while modest decreases in exposure were observed upon chronic dosing in both sexes of monkey. This was suggestive of induction of BMS-214778 clearance and/or excretion mechanisms. BMS-214778 distributed from the plasma to brain in the rat (mean +/- SD brain:plasma ratio of 0.9 +/- 0.1, N = 3). [(14)C]-BMS-214778 was moderately bound to serum proteins (<91% bound) in all species examined. In vitro metabolism of BMS-214778 was mostly by hydroxylation and dehydrogenation, with CYP1A1, 1A2, 2D6, and 2C9 being the most likely isoforms to be involved in its metabolism in humans.

Pharmacology and pharmacokinetics of milnacipran

Milnacipran is a dual-action antidepressant drug with equivalent inhibitory action at noradrenaline and serotonin neuronal reuptake systems. This dual action has been demonstrated in vitro and in vivo in experimental animals, and ex vivo in man. Milnacipran has no relevant affinity for any neurotransmitter receptor studied, in particular postsynaptic adrenergic, muscarinic and histamine receptors, and is therefore expected to be devoid of the prominent side-effects of many earlier antidepressants. Studies in human volunteers have not demonstrated any impact of milnacipran on cognitive function, consistent with its lack of anticholinergic properties. These pharmacodynamic properties are well preserved in vivo in humans, because milnacipran is only metabolized to a limited extent, and therefore circulates in the body principally as the unchanged parent drug, which is the only pharmacologically active compound at clinical doses. The pharmacokinetic profile of milnacipran is characterized by rapid absorption, high bioavailability, low protein binding, and rapid elimination, both by hepatic glucuronidation and renal excretion. This gives milnacipran certain pharmacokinetic advantages, such as low inter-individual variation in plasma levels, low potential for drug interactions, and limited impact on hepatic cytochrome P450 systems. These pharmacokinetic properties differentiate milnacipran from most other antidepressant drugs and contribute to the good safety profile of milnacipran and allow it to be used simply and flexibly in clinical practice.

[Pharmacokinetics and drug interactions of antidepressive agents]

Tricyclic antidepressive agents(TCAs) are conventional antidepressant. Cytochrome P450(CYP) 2D6 is involved in the hydroxylation of TCAs, while N-demethylation of TCAs is mediated by other such as CYP2C19, 3A4 and 1A2. The elimination of TCAs is impaired by CYP2D6 inhibitors such as quinidine. Newer antidepressants, selective serotonin uptake inhibitors(SSRIs), are also metabolized in the liver. Fluvoxamine, an SSRI, is a potent inhibitors for CYP1A2 and CYP2C19, moderate for CYP3A4 and weak for CYP 2D6. Paroxetine, another SSRI, causes substantial inhibition of CYP2D6 activity. Milnacipran, a serotonin and noradrenaline reuptake inhibitor, is mainly excreted unchanged in urine and some part as its glucronide conjugate. In contrast to many SSRIs, milnacipran is devoid of metabolic inhibition.

Uptake and translocation of carpropamid in rice (Oryza sativa L)

Translocation of the antiblast compound, carpropamid, was investigated in rice using [14C]carpropamid. When applied to the seed, carpropamid was not only readily absorbed but was translocated to different parts of the seedlings emerging from treated seeds. A substantial portion of fungicide appeared to be exuded onto the leaf surface. In 21-day-old plants grown from [14C]carpropamid-treated seeds, 27.2% of the radioactivity isolated from leaves was present on the surface of lamina. This exuded fraction is probably responsible for its action as a fungal anti-penetrant compound. Following 30-min root dipping of 14-day-old seedlings, carpropamid was rapidly absorbed and translocated throughout the seedling. Its intra-laminar distribution was uniform as determined by autoradiography. Only a small fraction (< 2%) of fungicide applied to the foliage was translocated beyond the site of application within the treated leaf. Translocation was primarily apoplastic. Approximately 54% of the radioactivity recovered from leaves was in the form of carpropamid. At least seven radiolabelled metabolic products were observed by TLC. Only 8.3% of radioactivity applied through the seeds could be recovered from 21-day-old seedlings.

Tedisamil: master switch of nature?

Decreasing heart rate is potentially useful in ischaemic heart disease. Tedisamil is a bradycardic agent resulting from its ability to inhibit transient outward current (I(to)) in atria. Tedisamil inhibits I(to), potassium current (IK), K(ATP) and the protein kinase A-activated chloride channel in ventricles as well as vascular IK and Ca(2+)-activated IK (IK((Ca))). Tedisamil prolongs cardiac action potentials and the corrected QT (QTc) of the ECG and also increases cardiac refractoriness. Tedisamil is anti-arrhythmic in animal models of ventricular arrhythmias and atrial flutter. The bradycardic effect of tedisamil is associated with a reduction in myocardial oxygen demand. On isolated rat ventricle, tedisamil is a positive inotrope and on isolated rabbit atria, tedisamil reverses the negative inotropic effect of pinacidil. Tedisamil contracts the isolated rat portal vein and aorta, reduces cromakalim-induced relaxations of contracted rat aorta and increases blood pressure in animals and humans. Tedisamil is 96% bound to plasma proteins, has a plasma half-life of about 10 h and is cleared from the kidney unchanged. Clinical trials have shown that the electrophysiology of tedisamil is that of a class III anti-arrhythmic. In coronary artery disease, tedisamil has no effect on inotropism and increases the threshold for angina. Potassium channel blockade with tedisamil may have advantages over calcium channel blockers or K(ATP) channel openers as an anti-ischaemic mechanism in coronary artery disease. In exercise-induced myocardial ischaemia, beta-blockers are probably favourable to tedisamil, as they will limit the increase in heart rate, contractility and blood pressure caused by sympathetic stimulation, whereas tedisamil will not. In heart failure patients, tedisamil reduces heart rate, but increases blood pressure. The usefulness of tedisamil as a bradycardic agent is limited by the increase in blood pressure. A drug that is bradycardic without increasing blood pressure would be an improvement on tedisamil as the master switch of nature for ischaemic heart disease.

Pharmacokinetic considerations in the design of better and safer new antiepileptic drugs

Valproic acid (VPA) is one of the major antiepileptic drugs. However, its anticonvulsant potency is less than the other three major antiepileptic drugs. Furthermore, VPA causes two rare but severe side effects: teratogenicity and hepatotoxicity. We utilized pharmacokinetic considerations in designing various amide derivatives of VPA which are more potent as anticonvulsants than VPA and have the potential to be nonteratogenic and nonhepatotoxic. The following three groups of VPA derivatives were designed and evaluated: (1) Isomers of valpromide (VPD) in order to explore the structural requirements for metabolically stable VPD isomers. Two chiral amides, valnoctamide and propylisopropyl acetamide, have emerged from a stereospecific study as the optimal compounds; (2) Cyclic amide derivatives of VPD. N-Methyl 2,2,3, 3-tetramethylcyclopropane carboxamide (M-TMCD) was found to be the optimal compound in this series. M-TMCD is a stable achiral VPD analogue acid which is nonteratogenic. Since M-TMCD contains four methyl substituents it cannot form a metabolite with a terminal double bond, and thus has the potential to be a nonhepatotoxic compound; (3) Conjugation products of VPA and gamma-amino butyric acid (GABA) or glycine. N-valproyl glycinamide (VGD) emerged as the best compound out of this group and is currently undergoing phase II clinical trials. VGD is mainly metabolized to N-valproyl glycine by a nonoxidative hydrolytic metabolic pathway. It did not operate as chemical drug delivery systems of VPA and glycine or GABA, but acted rather as a drug on its own.

Biosynthesis of radiolabeled curacin A and its rapid and apparently irreversible binding to the colchicine site of tubulin

Curacin A is a potent competitive inhibitor of colchicine binding to tubulin, and it inhibits the growth of tumor cells. We prepared [(14)C]curacin A biosynthetically to investigate its interaction with tubulin. Binding was rapid, even at 0 degrees C, with a minimum k(f) of 4.4 x 10(3) M(-1) s(-1). We were unable to demonstrate any dissociation of the [(14)C]curacin A from tubulin. Consistent with these observations, the K(a) value was so high that an accurate determination by Scatchard analysis was not possible. The [(14)C]curacin A was released from tubulin following urea treatment, indicating that covalent bond formation does not occur. We concluded that curacin A binds more tightly to tubulin than does colchicine. Besides high-affinity binding to the colchicine site, we observed significant superstoichiometric amounts of the [(14)C]curacin A bound to tubulin, and Scatchard analysis confirmed the presence of two binding sites of relatively low affinity with a K(a) of 3.2 x 10(-5) M(-1).

Milnacipran. A review of its use in depression

Milnacipran is a cyclopropane derivative which acts by inhibiting noradrenaline (norepinephrine) and serotonin (5-hydroxytryptamine; 5-HT) reuptake at presynaptic sites; no postsynaptic receptor activity has been demonstrated. It is most commonly administered at a dosage of 50 mg twice daily for the treatment of major depressive disorder. Improvement usually occurs within 2 weeks of treatment initiation, but some patients do respond sooner. Most studies which evaluated milnacipran were of short (4 to 8 weeks) duration and results were not published in full with rigorous peer review. Nonetheless, the drug is significantly more effective than placebo for the treatment of in- or outpatients with moderate to severe major depressive disorder. Limited data suggest that it may prevent relapse and be effective for long term use, although this requires confirmation. Milnacipran 200 mg/day is generally not significantly different from amitriptyline 150 mg/day in terms of onset and efficacy. However, when doses are titrated (not a requirement for milnacipran), milnacipran 50 or 100 mg/day has a slower onset than the tricyclic antidepressant. At a dosage of 100 mg/day for 4 to 12 weeks, milnacipran generally has similar efficacy to imipramine and clomipramine 150 mg/day, although milnacipran 50 to 150 mg/day had a faster onset of activity than imipramine 50 to 150 mg/day in Japanese patients. In a 6-month trial, milnacipran was less effective than clomipramine. Milnacipran 50 or 100 mg twice daily was as effective as fluoxetine 20 mg once daily or fluvoxamine 100 mg twice daily in 4- to 12-week studies. At a dosage of 50 then 100 mg daily it was also as effective as mianserin 30 then 60 mg daily in a 4-week study. However, when administered once daily (in the evening), milnacipran 100 mg/day was not as effective as fluoxetine 20 mg/day after 6 weeks. The drug is generally well tolerated, producing no more adverse events (including anticholinergic events) than placebo, selective serotonin reuptake inhibitors or mianserin and fewer adverse events than tricyclic antidepressants in clinical trials. However, dysuria has been reported in 7% of male patients receiving milnacipran.

CONCLUSIONS

Data from predominantly short term trials suggest that milnacipran generally has similar efficacy to tricyclic antidepressants and SSRIs. Although further published data are required to confirm its efficacy, good tolerability profile and pharmacokinetic profile which suggests a low potential for drug interactions, milnacipran should be considered a promising agent for the treatment of patients with major depressive disorder.

Inhibition of prostaglandin-induced intestinal secretion by igmesine in healthy volunteers

BACKGROUND & AIMS

Igmesine, a final sigma ligand, has been shown to inhibit intestinal secretion and diarrhea in animal models. The purpose of this study was to measure the inhibitory effect of igmesine on basal and prostaglandin E2 (PGE2)-induced jejunal secretion in normal volunteers.

METHODS

Jejunal absorption of water and electrolytes was measured with a three-lumen open-segment perfusion method in 16 volunteers. A double-blind crossover study was performed involving intraluminal infusion of PGE2 after oral administration of placebo or igmesine at two doses.

RESULTS

PGE2 induced net secretion of water and electrolytes (P < 0.01 vs. basal conditions). The effect of PGE2 on water and electrolytes was not changed by 25 mg of igmesine but was suppressed by 200 mg of igmesine. This effect lasted at least 3 hours after a single oral dose. Igmesine at a dose of 200 mg also produced a significant decrease in basal rates of water and electrolyte absorption.

CONCLUSIONS

Igmesine, a final sigma ligand, inhibits PGE2-induced intestinal secretion in normal humans. Evaluating the drug in chronic diarrheas may be of interest.

Disposition of two tetramethylcyclopropane analogues of valpromide in the brain, liver, plasma and urine of rats

2,2,3,3-Tetramethylcyclopropane carboxamide (TMCD) and N-methyl TMCD (M-TMCD) are analogues of valpromide (VPD) or amide derivatives of valproic acid (VPA), one of the major antiepileptic drugs (AEDs). In rodent models both TMCD and M-TMCD are more potent as anticonvulsants than VPA. The present study investigates the pharmacokinetics (PK) of TMCD and M-TMCD in rats by monitoring the levels of these two amides in the brain, liver, plasma and urine of rats. The disposition of TMCD and M-TMCD was analyzed in a comparative manner with that of VPD and VPA, previously studied by us. The following similar PK parameters were obtained for TMCD and M-TMCD, respectively: clearance, 5 and 5.6 ml/min/kg; volume of distribution (Vss), 0.72 and 0.96 l/kg; half-life (t1/2), 1.1 and 1. 2 h; and mean residence time (MRT), 2.41 and 2.8 h. The ratio of AUCs of TMCD of liver to plasma and brain to plasma were 1.67 and 1. 13, respectively. The ratios of the AUCs of M-TMCD of liver to plasma and brain to plasma were 1.43 and 0.99, respectively. Thus, both compounds distribute evenly between plasma and brain, but their distribution into the liver is 50% larger than that in the plasma. Therefore, PK analysis of TMCD and M-TMCD brain levels gave major PK parameters similar to those obtained from the plasma data. The fraction metabolized of M-TMCD to TMCD was 32%. The brain was not found to be a metabolic site for the M-TMCD to TMCD biotransformation which occurred primarily in the liver as indicated by the high liver concentrations of TMCD as a metabolite of M-TMCD. Unlike VPD, TMCD and M-TMCD did not undergo amide-acid biotransformation to their corresponding inactive acid, 2,2,3, 3-tetramethylcyclopropane carboxylic acid (TMCA). Both M-TMCD and TMCD distribute better into the brain than VPA, a fact that may contribute to their better anticonvulsant activity.

Which bioequivalence study for a racemic drug? Application to milnacipran

Milnacipran, a new non tricyclic antidepressant drug, is a racemic mixture (F2207) composed of two enantiomers: F2695 and F2696, both demonstrated to be active. A randomized open label, single-dose latin square study was undertaken in 24 healthy volunteers to compare, based on racemate data, the relative bioavailability of two new formulations to that of a reference formulation. Later on, as suggested by actual regulatory trend, analysis was carried out on enantiomer data, although in a supportive way. Bioequivalence was assessed on calculation of 90% confidence intervals for log-transformed Cmax and AUC(0-infinity) and on Wilcoxon test for Tmax with a 5% level of significance. Based on racemate data, both test formulations were demonstrated to be equivalent to the reference capsule in terms of Cmax and AUC-(0-infinity). Differences in Tmax reached statistical significance, although their mean magnitude was small, and probably not relevant when related to antidepressant long-term therapy. When considering the test capsule - reference capsule comparison, the equivalence demonstrated for the racemate reflect that of each enantiomer. On the contrary, equivalence between the test tablet and the reference capsule demonstrated for the racemate, is not supported by both enantiomers as Cmax of F2696 fails to reach bioequivalence criteria, making more uncertain the conclusion of bioequivalence. From this experience, it seems than when equivalence is demonstrated close to the limits for the racemate, it is difficult, especially for a low variability drug such as milnacipran, to comply with equivalence criteria for both enantiomers.

Pharmacokinetics of milnacipran in renal impairment

The pharmacokinetics of a single 50 mg dose of milnacipran, a new non tricyclic antidepressant drug, were compared in 8 chronic renal failure subjects (Clc(reat) between 9 to 84.5 ml.min(-1)) and in 6 healthy volunteers. Concentrations of unchanged (F2207 racemate and F2695 and F2696, enantiomers) and glucuroconjugated drug (main metabolite) were measured using HPLC and GC-MS. As for drugs mainly eliminated via renal route, the pharmacokinetics of milnacipran were markedly affected by impaired renal function with the elimination half-life of severely impaired subject being approximately three times that of the control group. Milnacipran apparent total clearance and renal clearance were positively correlated with glomerular filtration rate, while non-renal clearance and apparent volume of distribution were unaffected by renal impairment. Plasma concentrations of the glucuroconjugate were gradually increased in plasma, while its total urine excretion remained unchanged. As for the racemate, pharmacokinetics of each enantiomer were modified by renal failure, although, as predictable from its higher renal clearance value, it was more marked for F2696 than for F2695. Considering that modifications were shown to be proportional to the degree of renal impairment and that milnacipran presents low variability, the necessary dose adjustment is therefore easy to predict.

Pharmacokinetics of milnacipran in liver impairment

The pharmacokinetics of single 50 mg oral and intravenous doses of milnacipran, a new non tricyclic antidepressant drug, were compared in 11 chronic liver impaired (LI) subjects and in 6 control subjects. Hepatic impairments, classified according to the PUGH scale were moderate (1 grade A), intermediate (6 grade B) and severe (4 grade C). Concentrations of unchanged drug and its conjugated form (its main metabolite) were measured in plasma and urines. In control subjects, milnacipran present high absolute bioavailability (mean value of 90%). Around 50% of the dose are excreted in urines as unchanged, while around 14% are excreted as glucuroconjugate. The remaining is composed of free and conjugated phase I inactive metabolites. Administration of milnacipran in LI subjects results in non significant changes in its pharmacokinetics, although its variability is increased. Unchanged drug exposure is not modified in LI subjects, while plasma levels of the conjugate are slightly decreased compared to the control group. This could either be due to a slight reduction in the conjugation process, or to a change in the distribution of the drug as urine excretion of both unchanged and conjugated forms are not modified compared to the control group. A few LI subjects present supra-bioavailability resulting in higher drug exposure after oral administration than after intravenous infusion. These modifications are not clinically relevant as drug exposure of the parent drug is not modified. As the unchanged drug is the only compound responsible for the activity of milnacipran, no dosage adjustment is needed in patients presenting liver impairment.

Investigation of the potential interaction between terfenadine and tedisamil in human liver microsomes

1. The potential drug-drug interaction of terfenadine and tedisamil has been investigated. Terfenadine is a widely used antihistamine drug with the potential for QTC prolongation. Tedisamil is a potassium channel blocking agent known to produce bradycardia and prolong the effective refractory period in man. 2. Tedisamil and terfenadine were incubated with human liver microsomes for 30 min at 37 degrees C. No significant inhibition of terfenadine biotransformation was seen with 0.1 or 10 microM tedisamil as the formation of the terfenadine alcohol and acid metabolites were unaffected. 3. Based on the in vitro results it is suggested that tedisamil will not interact pharmacokinetically with terfenadine as it does not impair metabolism of terfenadine.

Effects of tedisamil, atenolol and their combination on heart and rate-dependent QT interval in healthy volunteers

AIMS

Tedisamil is a new blocker of K+ currents in cardiac tissues, exerts bradycardic effects and has shown clinical efficacy in angina pectoris. Theoretically, when coadministered with a beta-adrenoceptor blocker the tedisamil combination could induce dangerous bradycardia and QT interval prolongation. Therefore, the aim of this study was to evaluate the effects of tedisamil and atenolol alone and in combination, on heart rate and QT interval duration at rest and during exercise tests.

METHODS

The effects of tedisamil (100 mg twice daily) and atenolol (50 mg twice daily) on heart rate and QT interval duration were analysed in a three-period crossover study in healthy male volunteers.

RESULTS

This study showed that tedisamil exerted a significant (P<0.05) bradycardic action at rest (-10 beats min(-1); 95% CI: -6 to -15 beats min(-1)) similar to atenolol (-14 beats min(-1); -11 to -17) and drug combination (-9 beats min(-1); -6 to -12). During exercise, at the highest comparable workload, heart rate did not decrease significantly with tedisamil but decreased significantly with atenolol (-42 beats min(-1); -37 to -47) and combination (-47 beats min(-1); -41 to 52). Atenolol did not modify QT interval duration. Tedisamil alone and in combination with atenolol increased QT interval duration by 12% (95% CI: 7 to 17%) and 12% (8 to 16) respectively at RR=1000 ms, but not at RR<700 ms (combination). Tedisamil alone and in combination induced a reverse rate-dependent QT interval prolongation.

CONCLUSIONS

These results indicate that the combination of tedisamil and atenolol is not associated with excessive bradycardia or excessive QT interval prolongation in healthy subjects.

Pharmacokinetics of milnacipran in comparison with other antidepressants

Despite the large number of antidepressants currently available, it is still necessary to develop new drugs that combine the efficacy of the older antidepressant with improved safety, tolerability and therapeutic profile that will allow them to be used in depressed patients who are elderly or with cardiac, renal or hepatic disease. This article reviews the pharmacokinetic characteristics of the tricyclic antidepressants, the selective serotonin reuptake inhibitors (SSRIs) and more recently introduced antidepressants such as venlafaxine and nefazodone. Milnacipran (Ixel), a novel drug, combines antidepressant efficacy with some unique pharmacokinetic features. A summary of its pharmacokinetic profile shows that milnacipran has a high bioavailability, low plasma protein binding and that it is largely eliminated in the urine as parent drug or as a glucuronide. These features suggest that the likelihood of interactions with other drugs given concurrently is lower than would occur with most second generation antidepressants and the tricyclic antidepressants. Furthermore, studies in patients with liver dysfunction, and in the elderly, suggest that dose adjustment is not necessary when milnacipran is administered to these patients. The decrease in milnacipran elimination is correlated to the degree of renal impairment, allowing adjustment of schedules. In comparison to earlier antidepressants, milnacipran combines efficacy and a relatively low side-effect profile with the added advantage of fewer interactions with drugs that may be given concurrently.

Pharmacokinetic analysis and antiepileptic activity of tetra-methylcyclopropane analogues of valpromide

PURPOSE

The described structure pharmacokinetic pharmacodynamic relationships (SPPR) study explored the utilization of tetramethylcyclopropane analogues of valpromide (VPD), or tetramethylcyclopropane carboxamide derivatives of valproic acid (VPA) as new antiepileptics.

METHODS

The study was carried out by investigating the pharmacokinetics in dogs and pharmacodynamics (anticonvulsant activity and neurotoxicity) of the following three cyclopropane analogues of VPD: 2,2,3,3-tetramethylcyclopropane carboxamide (TMCD), N-methyl TMCD (M-TMCD) and N-[(2,2,3,3-tetramethylcyclopropyl)carbonyl]-glycinamide (TMC-GLD).

RESULTS

The three investigated compounds showed a good anticonvulsant profile in mice and rats due to the fact that they were metabolically stable VPD analogues which were not biotransformed to their nonactive acid, 2,2,3,3-tetramethylcyclopropane carboxylic acid (TMCA). M-TMCD was metabolized to TMCD and TMC-GLD underwent partial biotransformation to its glycine analogue N-[(2,2,3,3-tetramethylcyclopropyl)carbonyl]-glycine (TMC-GLN). Unlike TMC-GLN, the above mentioned amides had low clearance and a relatively long half life.

CONCLUSIONS

In contrast to VPD which is biotransformed to VPA, the aforementioned cyclopropane derivatives were found to be stable to amide-acid biotransformation. TMCD and M-TMCD show that cyclic analogues of VPD, like its aliphatic isomers, must have either two substitutions at the beta position to the carbonyl, such as in the case of TMCD, or a substitution in the alpha and in the beta positions like in the VPD isomer, valnoctamide (VCD). This paper discusses the antiepileptic potential of tetramethylcyclopropane analogues of VPD which are in animal models more potent than VPA and may be non-teratogenic and non-hepatotoxic.

Effects of low concentrations of cyclopropane and halothane on peak velocity of saccadic eye movements

We have investigated the effect of 4.7 and 8.8% MAC of cyclopropane, and 5.3 and 9.3% MAC of halothane on the peak velocity of saccadic eye movements (PSV) in six healthy volunteers. Both concentrations of cyclopropane and halothane significantly depressed PSV (P less than 0.01) compared with air, in a dose-related fashion. Halothane depressed PSV significantly more than cyclopropane (P less than 0.05). PSV returned to baseline within 5 min after discontinuation of the agents. There was no significant difference between cyclopropane, halothane and air in subjective assessment of sedation.

UTIs and two new antibiotics in the elderly

Of the new antimicrobials available for the treatment of urinary tract infections (UTIs), aztreonam and imipenem/cilastatin represent two structurally unique, but distinct, classes of beta-lactam antibiotics. Aztreonam has a directed spectrum of activity covering gram-negative bacilli usually associated with UTIs. In comparative clinical trials of patients with complicated UTIs, aztreonam is well-tolerated and is as effective as conventional control regimens, including aminoglycosides. On the other hand, the antimicrobial spectrum of imipenem/cilastatin includes not only gram-negative bacilli but also gram-positive cocci and anaerobes. As such, this broad-spectrum antibiotic should be reserved for the treatment of mixed infections.

Imipenem: a new carbapenem antibiotic

Imipenem is a new carbapenem antibiotic that has an extremely broad spectrum of antibacterial activity. It has been used to treat a variety of serious infections and an increasing volume of literature documents its value in infections due to multiresistant bacteria. This article reviews the antibacterial activity, pharmacology, and clinical uses of imipenem.

Pharmacokinetics of imipenem-cilastatin in patients with renal insufficiency undergoing continuous ambulatory peritoneal dialysis

In six patients with end-stage renal disease, a single bolus of imipenem-cilastatin (500 mg each) was given either intravenously or intraperitoneally in a randomized crossover protocol such that each patient received the drug by both routes at a 2- to 3-week interval. Drug levels in plasma and the peritoneal dialysis fluid were analyzed at frequent intervals, and various pharmacokinetic variables were calculated for a one-compartment open model. Data obtained in the present study suggest that while no significant difference in peak plasma levels or volume of distribution were noted, the following variables were significantly different for imipenem as compared with cilastatin: elimination half-life, total plasma clearance, area under the concentration-time curve, and percent drug excretion in the peritoneal dialysis fluid. The elimination half-life of imipenem (3.28 h) or cilastatin (8.84 h) in our patients was in the same range as observed in patients with minimal renal function undergoing hemodialysis. The dose of imipenem-cilastatin should be reduced appropriately in patients with end-stage renal disease undergoing peritoneal dialysis.

Imipenem/cilastatin, an alternative treatment of pseudomonas infection in cystic fibrosis

Imipenem, a new N-formimidoyl thienamycin was given together with cilastatin to 20 patients with cystic fibrosis and pulmonary infection due to Pseudomonas aeruginosa. The antibiotic was given in short-term infusions for 9-14 days (mean 11.5) in a dose of 45-60 mg/kg body weight/day. Good clinical results were obtained in all patients with significant improvement of clinical score, pulse rate, vital capacity and FEV1.0 (P less than 0.001). Blood PO2 increased and WBC decreased significantly. A slight increase in the minimum inhibitory concentration was noted during treatment but all strains examined were fully susceptible at follow-up one month later. The peak serum concentration was significantly increased in patients receiving the high dose of imipenem, but the sputum concentration was low in all patients and there was no difference in clinical or bacteriological outcome. The plasma and urinary clearance increased with body weight and was inversely correlated to clinical score. Imipenem/cilastatin appears a good alternative for the treatment of pulmonary infections caused by P. aeruginosa in cystic fibrosis.

Biliary excretion of imipenem-cilastatin in hospitalized patients

Imipenem-cilastatin concentrations in bile were measured in 12 cholecystectomy patients (group 1) and 12 patients with common duct drainage (group 2). Six patients in each group received 0.5 g, and six received 1.0 g intravenously over 30 to 60 min. In group 1, bile was collected a mean of 85 min postinfusion. The mean concentrations of imipenem in bile were 1.3 microgram/ml after the 0.5-g dose and 3.5 micrograms/ml after the 1.0-g dose. The mean concentrations of cilastatin in bile were 9.0 micrograms/ml after the 0.5-g dose and 38.0 micrograms/ml after the 1.0-g dose. In patients with common duct drainage, bile was collected predose and 0 to 2, 2 to 3, 3 to 4, and 4 to 6 h postinfusion. Peak imipenem concentrations in bile were 4.4 micrograms/ml after the 0.5-g dose and 8.6 micrograms/ml after the 1.0-g dose. Peak cilastatin concentrations in bile were 4.6 micrograms/ml for the 0.5-g dose and 10.9 micrograms/ml for the 1.0-g dose. Peak imipenem concentrations in bile occurred a mean of 2.3 h after administration of the drug; cilastatin peak concentrations occurred at a mean of 2.4 h. Less than 0.3% of each drug was recovered in the bile. Our results suggest that imipenem enters bile by simple diffusion and in most patients attains concentrations sufficient to inhibit susceptible organisms. In contrast, cilastatin had a bimodal entry into bile. Some patients had very high concentrations in bile, whereas others had very low or undetectable concentrations, suggesting that cilastatin may be actively secreted into the bile.