Influence of alcohol on the pharmacokinetics of diazepam controlled-release formulation in healthy volunteers

Alcohol-medication interactions: A systematic review and meta-analysis of placebo-controlled trials

Alcohol and other xenobiotics may limit the therapeutic effects of medications. We aimed at investigating alcohol-medication interactions (AMI) after the exclusion of confounding effects related to other xenobiotics. We performed a systematic review and meta-analysis of controlled studies comparing the effects induced by alcohol versus placebo on pharmacodynamic and/or pharmacokinetic parameters of approved medications. Certainty in the evidence of AMI was assessed when at least 3 independent studies and at least 200 participants were available. We included 107 articles (3097 participants): for diazepam, cannabis, opioids, and methylphenidate, we found significant AMI and enough data to assign the certainty of evidence. Alcohol consumption significantly increases the peak plasma concentration of diazepam (low certainty; almost 290 participants), cannabis (high certainty; almost 650 participants), opioids (low certainty; 560 participants), and methylphenidate (moderate certainty; 290 participants). For most medications, we found some AMI but not enough data to assign them the certainty grades; for some medications, we found no differences between alcohol and placebo in any outcomes evaluated. Our results add further evidence for interactions between alcohol and certain medications after the exclusion of confounding effects related to other xenobiotics. Physicians should advise patients who use these specific medications to avoid alcohol consumption. Further studies with appropriate control groups, enough female participants to investigate sex differences, and elderly population are needed to expand our knowledge in this field. Short phrases suitable for indexing terms.

Multi-centre general practitioner comparative study of controlled-release ('Valrelease') and conventional ('Valium') forms of diazepam in patients suffering from anxiety

A multi-centre, double-blind, parallel group study was carried out in 114 patients with an anxiety disorder to compare the effectiveness of diazepam given as 5 mg 3-times daily or as a once-daily 10 mg dose of a controlled-release formulation designed to provide smooth drug concentrations over about 24 hours, without the heavy sedation caused by a high initial peak. Patients were allocated at random to receive one or other dosage regimen for 1 week and treatment could be continued for a further week if necessary. Clinical assessments of response to treatment showed that whilst both formulations were equally effective in providing symptomatic improvement, a much higher proportion of patients on controlled-release diazepam were ready to terminate treatment after 1 week, having attained the desired relief of symptoms. Moreover, as indicated by patient diary records, significantly fewer patients on the controlled-release formulation complained of drowsiness in the morning and evening.

Reinterpretation of the pharmacokinetic mechanism of oral benzodiazepine ethanol interaction

Previously published studies investigating the oral benzodiazepine ethanol interaction have utilized a single dose of ethanol, a single dose of oral benzodiazepine, and measured plasma benzodiazepine concentration over varying time periods. Most studies reported an increase or no change in benzodiazepine plasma concentrations following ethanol administration, which the investigators usually ascribed to an ethanol-induced increase in the benzodiazepine absorption rate constant. However, ethanol decreases the hepatic clearance of benzodiazepines that are biotransformed via the P450 enzyme system and this effect was not taken into account in evaluation of the results of these studies. Computer simulations have been used to investigate possible mechanisms of the oral benzodiazepine-ethanol interaction. The effects of a constant or transient decrease in clearance and an increase in absorption rate constant upon maximum concentration, time of maximum concentration, and area under the benzodiazepine plasma concentration curve (AUC) have been examined. A transient 75% decrease in benzodiazepine clearance resulted in a 13.6% increase in AUC (0-36 hr), a 3.4% increase in Cmax and a 5.7% increase in tmax. These changes are qualitatively consistent with, but quantitatively shy, of those observed in most studies. Consequently, an effect of ethanol upon benzodiazepine absorption must still be considered.

Effects of ethanol on drug and metabolite pharmacokinetics

Pharmacokinetic interactions of ethanol with other drugs, including its effects upon drug metabolite disposition, are reviewed in terms of clearance concepts. This approach is particularly useful in understanding the mechanisms of ethanol-drug interactions, i.e. in separating the effects of ethanol upon drug clearance, volume of distribution and plasma protein binding. The application of clearance concepts provides the basis for understanding the qualitative differences in ethanol interactions with low and high hepatic extraction ratio drugs. The effects of short and long term ethanol consumption upon different types of drug metabolism (oxidative, acetylation and glucuronidation) have been considered. Long term ethanol consumption may increase the clearance of a drug by induction of oxidative metabolism whereas short term consumption may decrease the clearance of such a drug. Clearance by N-acetylation appears to be increased in the presence of ethanol, and clearance by conjugation to glucuronic acid is decreased for some drugs by single-dose consumption of ethanol.

Pharmacokinetics of diazepam from a controlled release capsule in healthy elderly volunteers

A single dose open labelled two-way randomized crossover study was used to assess the pharmacokinetics of diazepam from a controlled release capsule relative to standard release tablets in elderly volunteers. Eighteen volunteers received a single 15 mg controlled release capsule or a 5 mg tablet t.i.d. on one day. Diazepam plasma concentrations were determined at specific times over a 96-h interval by an electron capture-gas chromatographic method. Mean plateau plasma concentrations endured from 2 to 24 h avoiding the peak to trough fluctuations associated with conventional t.i.d. dosing. Similar areas under the plasma concentration-time curve (AUC) values indicated equal extent of absorption between formulations and regimens. Comparing parameters in this same elderly population to a young adult population, previously administered the controlled release capsule, shows lower maximum concentrations and a longer plateau duration in the elderly volunteers. Although there is a twofold increase in the mean diazepam half-life in the elderly when compared to young adults, the estimated apparent volume of distribution increased proportionately with half-life to maintain a constant clearance. Thus, the total body clearance of diazepam appears to be age independent. The age-dependent pharmacokinetics observed in this study are consistent with previously reported data involving diazepam. Overall, the controlled release capsule administered once daily mimics a t.i.d. regimen in elderly volunteers.

Absolute bioavailability and effect of food and antacid on diazepam absorption from a slow-release preparation

A series of healthy volunteers received a single 7.5-mg intravenous dose of diazepam on one occasion and a single 15-mg oral dose of slow-release diazepam (DZ-SR) on another occasion. Diazepam concentrations were measured by gas chromatography in multiple plasma samples drawn during seven days after each dose. Absorption of diazepam from DZ-SR was slow, with mean +/- S.E. peak concentrations attained at 3.8 +/- 0.5 hours after dosage. Absolute bioavailability of DZ-SR averaged 0.98 +/- 0.06. In two other studies, diazepam absorption from DZ-SR was evaluated when coadministered with a standard breakfast or with an antacid preparation (Maalox). Neither food nor antacid altered the rate of diazepam absorption and did not impair the completeness of absorption. Higher peak total plasma diazepam concentrations occurred in the postprandial as opposed to the fasting state, but this was an artifact of reduced protein binding (increased free fraction) due to fasting. Thus, diazepam absorption from DZ-SR is slow and essentially complete.