Clinical importance of the interaction of diazepam and cimetidine

The effect of cimetidine on serum concentrations of piroxicam

To evaluate the effect of cimetidine on serum concentrations of piroxicam, we administered a single 20-mg oral dose of piroxicam to 10 healthy male volunteers on 2 occasions. The first was given on day 1 of the study and the second on day 15, 7 days after starting cimetidine 300 mg orally 4 times a day. Nineteen blood samples were drawn for 7 days after each piroxicam dose to characterize its pharmacokinetics. Piroxicam was analyzed by high-performance liquid chromatography. The mean piroxicam elimination rate constants (Kel), elimination half-lives, and area under the serum concentration-time curves (AUC) were as follows (mean +/- standard deviation): (formula; see text) Data were analyzed with a Wilcoxon matched-pairs, signed-ranks, two-tailed statistical test. Although the increase in AUC was statistically significant, it was of low amplitude (mean 15%) and is probably not clinically significant. The results of this study suggest that cimetidine does not significantly alter the elimination kinetics of a single dose of piroxicam in young healthy males. Additional investigation is needed to confirm these findings in other patient populations.

Adverse reactions and interactions with H2-receptor antagonists

Histamine H2-receptor antagonists have been used in the treatment of gastrointestinal diseases for more than a decade and during this period have become one of the most commonly prescribed groups of drugs in the world. The deserved popularity of the H2-receptor antagonists reflects, in part, their therapeutic efficacy, which has revolutionised the treatment of peptic ulcer disease. An equally, or more, important reason for the widespread use of H2-receptor antagonists is their remarkably low toxicity. We have attempted, in this review, to present a detailed account of the minor and more serious adverse reactions, while emphasising the low incidence of the former and the rarity of the latter. The toxicology of the H2-receptor antagonists is discussed under two main headings: adverse effects; and drug interactions. The latter category is potentially the more significant, since the frequent use of therapy with multiple drugs may give rise to drug interactions, some of which are serious and may even be lethal. These drug interactions occur especially in the gastrointestinal tract, the liver and the kidneys. Thus, the absorption of other drugs may be altered because the H2-receptor antagonists inhibit gastric secretion--an effect illustrated by ketoconazole, the absorption of which is reduced when given in combination with cimetidine. Very important drug interactions are caused by inhibition of the hepatic microsomal enzyme cytochrome P450 by some of the H2-receptor antagonists. This effect appears to be related to the chemical structure of the individual H2-receptor antagonists and is not attributable to histamine H2-receptor blockade. For example, cimetidine is a powerful inhibitor of cytochrome P450, while the interaction of ranitidine with this system is weaker. Consequently, cimetidine reduces the metabolism of many drugs which are normally degraded by phase I reactions, leading to potentially toxic plasma concentrations of therapeutic agents such as some oral anticoagulants, beta-blockers, anticonvulsants, benzodiazepines and xanthines. Some of the H2-receptor antagonists are actively secreted by the renal tubules and may thus compete with other drugs for cationic tubular transport mechanisms, resulting in reduced urinary excretion and hence potentially toxic plasma concentrations. This type of drug interaction has been reported after administration of both cimetidine and ranitidine with procainamide or quinidine.(ABSTRACT TRUNCATED AT 400 WORDS)

Interaction of diazepam with famotidine and cimetidine, two H2-receptor antagonists

Famotidine is currently under investigation as an H2-receptor antagonist. Eleven healthy male volunteers received a single 10 mg intravenous dose of diazepam on three occasions: once during coadministration of famotidine 40 mg bid, once during coadministration of cimetidine 300 mg qid, and once without other drug treatment (control). Multiple blood samples were drawn during the seven days after each diazepam dose. Diazepam and desmethyldiazepam plasma concentrations were measured by electron capture gas chromatography. There were no significant differences among the three treatment conditions in diazepam central compartment volume or total volume of distribution. During the cimetidine as compared with the control treatment, diazepam elimination half-life was significantly increased (72 vs 55 hr, P less than .05), total area under the curve (AUC) increased (11.8 vs 9.8 hr-micrograms/mL, P less than .05), and total clearance reduced (0.20 vs 0.28 mL/min/kg, P less than .05). Seven-day AUC for desmethyldiazepam also increased (4.6 vs 3.8 hr-micrograms/mL, P less than .05). However, there were no significant differences between famotidine and control treatment conditions in diazepam elimination half-life (53 vs 55 hr), total AUC (9.5 vs 9.8 hr-micrograms/mL), or total clearance (0.28 vs 0.28 mL/min/kg) or in seven-day AUC for desmethyldiazepam (3.9 vs 3.8 hr-micrograms/mL). Thus, therapeutic doses of cimetidine significantly impair the clearance of diazepam and desmethyldiazepam. Therapeutic doses of famotidine do not impair diazepam and desmethyldiazepam kinetics, suggesting that there is no significant kinetic interaction when diazepam and famotidine are administered concurrently in clinical practice.

Importance of the interaction of midazolam and cimetidine

Six healthy volunteers were given in an open study 15 mg of midazolam orally, and a couple of weeks later the same treatment preceded by 400 mg of cimetidine orally. We followed midazolam serum concentrations and the following pharmacodynamic parameters for five hours: subjective sedation, Maddox wing readings, critical flicker fusion frequency and peak velocity of saccadic eye movements. A statistically significant change was found in Cmax and total AUC between the two sessions. The pharmacodynamic responses differed also clearly from each other suggesting a significant change in midazolam effect even after a single oral dose of cimetidine.

Kinetic and dynamic interaction of brotizolam and ethanol

Thirteen healthy male volunteers ingested a single 0.25 mg dose of the thienodiazepine hypnotic, brotizolam, on two occasions: once with a typical social cocktail (containing 60 ml of vodka), and in a second trial with an 'ethanol-placebo' cocktail. Brotizolam kinetics were determined from multiple plasma concentrations measured during the 24 h after dosage. Coadministration of brotizolam with ethanol, as opposed to the placebo cocktail, slightly imparied brotizolam clearance (1.85 vs 2.19 ml min-1 kg-1 P less than 0.005), increased peak plasma concentrations (5.3 vs 4.3 ng ml-1, P less than 0.05), and prolonged elimination half-life (5.2 vs 4.4 h, P less than 0.05). There was evidence of impairment of performance, although not statistically significant, for the first 4-6 h after brotizolam dosage in the reaction time test, the digit-symbol substitution test, and a tracking task. None of these was enhanced by ethanol. In both trials, brotizolam produced significant increases in self-rated perceptions of sedation, fatigue, feeling 'spaced-out', and thinking slowed down. These effects were more intense during the brotizolam-ethanol as compared to brotizolam-placebo. In both trials, recovery was essentially complete by 6-8 h after dosage. Coadministration of brotizolam with ethanol produces a small but significant impairment of brotizolam clearance. Brotizolam produced self-rated perceptions of sedation and fatigue during 4-6 h after dosage, but objective impairment of psychomotor performance was minimal. Subjective perceptions of sedation were enhanced by ethanol coadministration, but the effects on psychomotor performance were not.

Interaction of oxaprozin with acetaminophen, cimetidine, and ranitidine

Twelve healthy male volunteers participated in a single-dose four-way crossover study to evaluate potential drug interactions with oxaprozin, a nonsteroidal antiinflammatory agent of the propionic class. The four modes of administration were: a. oxaprozin, 1200 mg alone; b. oxaprozin during concurrent acetaminophen, 500 mg 4 times daily; c. oxaprozin with cimetidine, 300 mg 4 times daily; d. oxaprozin with ranitidine, 150 mg every 12 hours. Acetaminophen, cimetidine, or ranitidine were begun 24 hours prior to oxaprozin dosage and continued for the 10-day duration of each trial. No significant differences existed among the four treatment conditions in peak plasma oxaprozin concentration (86 micrograms/ml), volume of distribution (0.23 l/kg), time of peak concentration (3.7 h after dosage), or elimination half-life (54 h). Oxaprozin oral clearance was significantly lower (by 20%) during both the cimetidine and ranitidine trials versus control (0.047 vs 0.047 vs 0.059 ml/min/kg), but clearance during acetaminophen was not significantly different from control. Thus acetaminophen, cimetidine or ranitidine has only a small influence on the pharmacokinetics of a single oral dose of oxaprozin. The reduction in oxaprozin clearance due to cimetidine or ranitidine is statistically significant but small in magnitude.

The action of cisapride on gastric emptying and the pharmacodynamics and pharmacokinetics of oral diazepam

The effects of the benzamide cisapride (C) (8 mg) i.v. have been compared to placebo (P) in a double blind randomised study. The effects on gastric emptying, the absorption and effects of oral diazepam, and BP and pulse were observed. Cisapride increased the rate of gastric emptying of 500 ml liquid containing diazepam 10 mg (t 1/2 C: 7.4 min, P: 14.9 min). The initial rate of absorption of diazepam contained in the drink was increased by C (AUC 0-1 h C: 328 micrograms h l-1, P: 253 micrograms h l-1, but there was no change in overall bioavailability. This change in diazepam kinetics was associated with a significantly greater impairment in reaction time in the first 45 min after drinking but not in self rated sedation. Cisapride produced a significant tachycardia (e.g. after 10 min C: 82 beats/min, P: 69 beats/min) which probably reflects a peripheral vasodilator action. Cisapride may therefore alter the pharmacokinetics and dynamics of concurrently administered drugs.

Pharmacokinetics and metabolism of omeprazole in man

Four studies of the pharmacokinetics and metabolism of omeprazole are briefly discussed. Two of these were carried out in young healthy subjects and indicated that about 54% of an oral dose is available to the systemic circulation. The distribution of omeprazole after an intravenous dose was consistent with localization of a major fraction of the drug in the extracellular water, with about 25% restricted to the blood. Omeprazole was rapidly cleared and possessed the characteristics of a high clearance drug; insignificant amounts of 14C-omeprazole were excreted by the kidneys, though metabolites were excreted very rapidly. Six different metabolites were reported, the major one being hydroxy-omeprazole. Increasing the intravenous dose of omeprazole from 10 mg to 40 mg had no significant effect on the pharmacokinetic parameters determined. A study in patients with impaired renal function showed that this had little effect on the kinetics of omeprazole, though excretion of metabolites was significantly affected. A study of elderly healthy subjects suggested that the disposition characteristics of omeprazole are affected to some extent by age; further studies are needed to elucidate the clinical implications. Omeprazole has been reported to prolong the half-life of diazepam which may be due to inhibition of the demethylation of diazepam. The interaction of omeprazole with the kinetics of aminopyrine and antipyrine was much less pronounced.

Psychotropic drugs in the elderly. Selection of the appropriate agent

Caution is required when prescribing psychotropic drugs to elderly patients, because of altered pharmacokinetics. Benzodiazepines with a relatively short half-life, such as temazepam (Restoril), alprazolam (Xanax), and lorazepam (Ativan), are better hypnotics for the elderly than those with a long half-life. Lorazepam and clorazepate dipotassium (Tranxene) are appropriate anxiolytics for elderly patients. Antipsychotics have anticholinergic and extrapyramidal symptoms in varying degrees. Thiothixene (Navane) and haloperidol (Haldol) in low doses are the drugs of choice despite their extrapyramidal symptoms. Trazodone (Desyrel) is a good antidepressant for the elderly because of its minimal anticholinergic effects, although it is quite sedating. Desipramine (Norpramin) is the least sedating and has the fewest anticholinergic effects of the tricyclic antidepressants and therefore may be better tolerated. Monoamine oxidase inhibitors and lithium should be used with great caution.

Famotidine, a new H2-receptor antagonist, does not affect hepatic elimination of diazepam or tubular secretion of procainamide

In 8 healthy male volunteers the pharmacodynamic responses to a single dose of diazepam and a single dose of procainamide were assessed before and after pre-treatment with the H2-receptor antagonist famotidine in a randomized crossover study. The pharmacokinetics of diazepam and procainamide were also studied, and the binding of famotidine to human liver microsomes was also measured. Cimetidine induced binding changes with a spectral dissociation constant (Ks) of 0.87 mM, whereas famotidine produced no measurable spectral alteration in concentrations up to 4 mM. The elimination half-life (t1/2: 45.6 h) and total plasma clearance (CL: 0.28 ml/min/kg) of diazepam were not significantly altered by famotidine (t1/2 = 39.0 +/- 11.4 h; CL = 0.31 +/- 0.08 ml/min/kg). Similarly, there was no enhancement of the sedative effect of diazepam by famotidine. The pharmacodynamics and pharmacokinetics of procainamide and N-acetylprocainamide (NAPA), too, were not significantly changed by famotidine: procainamide t1/2 2.9 vs 3.0 h under famotidine and renal clearance (CLR) 436 vs 443 ml/min; and NAPA CLR 195 vs 212 ml/min under famotidine. The data suggest that famotidine, in contrast to cimetidine, does not affect the pharmacokinetics of diazepam (hepatic elimination) or procainamide (tubular secretion). This new H2-receptor antagonist appears to be devoid of an interaction potential for either type of drug elimination.