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Role of GABAA/benzodiazepine receptors containing alpha 1 and alpha 5 subunits in the discriminative stimulus effects of triazolam in squirrel monkeys.

RATIONALE: Conventional benzodiazepines (BZs), clinically used for treatment of anxiety and insomnia, bind to GABA(A) receptors containing alpha(1), alpha(2), alpha(3), or alpha(5) subunits. The role of these different GABA(A) receptor subtypes in mediating the subjective effects of BZs remains largely unknown. OBJECTIVE: The purpose of the present study was to evaluate the role of GABA(A) receptors containing the alpha(1) or alpha(5) subunits in the discriminative stimulus (DS) effects of the conventional BZ agonist triazolam. METHODS: Squirrel monkeys were trained to discriminate triazolam (0.03 mg/kg, i.v.) from vehicle under a fixed-ratio 10 schedule of food reinforcement. RESULTS: The GABA(A)/alpha(1)-preferring agonists zolpidem and zaleplon engendered responses predominantly on the triazolam lever (73-80% drug-lever responding), and the GABA(A)/alpha(1) partial agonist CL 218,872 engendered an average maximum of less than 50% triazolam-lever responding. The GABA(A)/alpha(1)-preferring antagonists beta-carboline-3-carboxylate-t-butyl ester (betaCCT) and 3-(propyloxy)-beta-carboline (3-PBC) blocked the DS effects of triazolam and zolpidem in a surmountable manner. Schild analyses for betaCCT and 3-PBC in combination with triazolam and zolpidem suggest that the interactions between these compounds were competitive in nature and mediated by a common population of receptors, presumably GABA(A)/alpha(1) receptors. In contrast, the GABA(A)/alpha(5)-preferring agonist QH-ii-66 did not engender triazolam-lever responding regardless of dose and did not alter the DS effects of triazolam when administered in combination. CONCLUSIONS: The results are consistent with GABA(A)/alpha(1) receptor involvement in mediating the DS effects of triazolam. In contrast, binding to GABA(A)/alpha(5) receptors may not play a critical role in mediating triazolam's DS effects.

Animals↗

Acute behavioral effects and abuse potential of trazodone, zolpidem and triazolam in humans.

The present study examined the acute behavioral effects and abuse potential of three drugs commonly used to treat sleep disorders, trazodone, zolpidem and triazolam, and placebo in ten male volunteers with histories of alcohol and drug abuse. Trazodone (100, 200 and 300 mg), a triazolopyridine antidepressant, was included because antidepressants are being used more frequently to treat sleep disorders, but it is unclear whether they have a distinct behavioral pharmacologic profile relative to benzodiazepine hypnotics. Zolpidem (15, 30 and 45 mg), an imidazopyridine hypnotic, was tested because it is the most commonly prescribed hypnotic and purportedly has a unique benzodiazepine-receptor binding profile. Triazolam (0.25, 0.5 and 0.75 mg), a triazolobenzodiazepine hypnotic, was included as the standard component because previous laboratory studies have demonstrated that it has at least some abuse potential. Trazodone, zolpidem and triazolam generally produced comparable dose-related increases in scores on the PCAG scale of the ARCI, which suggests the doses tested were equivalent on some behavioral dimension. The effects of trazodone on subject-rated items thought to measure abuse potential (e.g., subject ratings of Willing to Take Again) were less than those observed with triazolam. Zolpidem and triazolam produced comparable effects on these measures. The highest dose of zolpidem, but not triazolam, increased ratings of Like Drug, Happy, Good Effects, Friendly, Elated, Carefree and Bad Effects. Triazolam and zolpidem produced dose-dependent impairment on all of the performance tasks. Trazodone impaired performance on some, but not all, of these tasks. Consistent with the pharmacokinetics of these compounds, the time-action functions of trazodone, zolpidem and triazolam were similar on these measures. These data suggest that trazodone has less abuse potential than triazolam, and may be a viable alternative to benzodiazepine hypnotics in individuals with histories of alcohol or drug abuse. By contrast, despite its unique neuropharmacological profile, the acute behavioral effects and abuse potential of zolpidem are comparable to those of triazolam.

Adult↗

A study of the in vitro interaction between ethanol, and triazolam and its two metabolites using human liver microsomes.

AIM: Triazolam is widely used as an ultrashort-acting anxiolytic drug and hypnosedatives and its effect appears at very low doses. Ethanol is used as a social drug worldwide. Sometimes, toxic interactions occur following combined administration of these two drugs. In this study, we have investigated the interaction between alcohol and triazolam in vitro. METHODS: The interaction effects between alcohol and triazolam were examined by a mixed-function oxidation reaction using a human liver microsomal preparation. Triazolam and its two metabolites (alpha-hydroxytriazolam: alpha-OH triazolam, 4-hydroxytriazolam: 4-OH triazolam) were measured by HPLC/UV. RESULTS: The production of alpha-OH triazolam and 4-OH triazolam was shown to be weakly inhibited by 13-29% (p < 0.05) and 8-14%,respectively, by ethanol (20-80 mM). CONCLUSIONS: These results using a human liver microsomal preparation show that the formation of both metabolites of triazolam is weakly inhibited by ethanol. Toxic levels may be reached by simultaneous administration of ethanol and triazolam.

Anti-Anxiety Agents↗

Diltiazem enhances the effects of triazolam by inhibiting its metabolism.

BACKGROUND: Triazolam is metabolized by CYP3A4. Diltiazem is an inhibitor of this isozyme and interacts with midazolam, another substrate of this enzyme. Therefore the possible interaction between triazolam and diltiazem is worth investigation. METHODS: A balanced, randomized, double-blind crossover study design was used, with an interval of 2 weeks between phases. Ten healthy volunteers were given 60 mg diltiazem orally or placebo three times a day for 2 days. On the second day they received a single 0.25 mg oral dose of triazolam, after which plasma samples were collected and effects of triazolam measured for up to 17 hours. RESULTS: Diltiazem increased the mean area under the triazolam concentration-time curve threefold (p < 0.001) and the elimination half-life (p < 0.001) and the peak plasma concentration of triazolam twofold (p < 0.005). The increased concentrations of triazolam during the diltiazem phase were associated with increased and prolonged pharmacodynamic effects. CONCLUSIONS: Diltiazem has a clinically significant interaction with oral triazolam. The data is highly suggestive that diltiazem inhibits the metabolism of triazolam during the first-pass and elimination phases. Prescription of triazolam should be avoided if a patient is using diltiazem or other potent inhibitors of CYP3A.

Administration, Oral↗

Triazolam is ineffective in patients taking rifampin.

BACKGROUND: Triazolam is metabolized predominantly by cytochrome P450 3A4 (CYP3A4). Rifampin (rifampicin) is a potent inducer of CYP3A4 and it is known to markedly reduce plasma concentrations and effects of drugs such as midazolam. The possible interaction between rifampin and triazolam was examined in this study. METHODS: The pharmacokinetics and pharmacodynamics of triazolam were investigated in a randomized, double-blind crossover study with two phases. Ten young healthy volunteers took either 600 mg rifampin once daily or placebo for 5 days. On the sixth day, 0.5 mg triazolam was administered orally. Timed blood samples were collected and the effects of triazolam were measured with five psychomotor tests for 10 hours. RESULTS: The area under the plasma triazolam concentration-time curve in the rifampin phase was only 5.1% of that in the placebo phase (0.74 +/- 0.14 versus 14.8 +/- 1.0 ng.hr/ml [mean +/- SEM; p < 0.001]). Rifampin pretreatment decreased the maximum plasma concentration of triazolam to 12.4% of the control value (i.e., from 2.9 +/- 0.2 to 0.36 +/- 0.06 ng/ml [p < 0.001]) and the elimination half-life from 2.8 +/- 0.1 to 1.3 +/- 0.1 hours (p < 0.001). All psychomotor tests showed markedly reduced effects (p < 0.01) of triazolam after rifampin pretreatment. CONCLUSIONS: Triazolam is ineffective during rifampin treatment. This is most likely due to increased metabolism of triazolam after induction of CYP3A4 in the gut wall and liver by rifampin. It is advisable to use hypnotic agents that are not metabolized by CYP3A4 during treatment with rifampin or other potent inducers of CYP3A4.

Adult↗

A follow-up study of the acute behavioral effects of benzodiazepine-receptor ligands in humans: comparison of quazepam and triazolam.

Quazepam, a trifluoroethylbenzodiazepine hypnotic, and triazolam, a triazolobenzodiazepine hypnotic, differ in terms of their benzodiazepine-receptor binding profile. Previous studies have suggested that quazepam produces less performance impairment than triazolam. Whether these effects are due to differences between quazepam and triazolam in terms of their benzodiazepine-receptor binding profile or to the testing of insufficient doses is unknown. The present study compared the acute behavioral effects of triazolam (0.1875, 0.3750, and 0.5625 mg), quazepam (30, 60, and 90 mg), and placebo in 12 healthy humans using a within-subjects, placebo-controlled, crossover design. Quazepam and triazolam produced comparable dose-dependent performance impairment and increased ratings of drug effect and drowsy. Quazepam, but not triazolam, increased ratings of dizzy/light-headed, performance impaired, and sleepy. Triazolam, but not quazepam, increased ratings of high. Thus, across a sufficient range of doses, the performance-impairing effects of quazepam were similar to those of triazolam. By contrast, quazepam and triazolam produced somewhat different constellations of participant-rated drug effects. These differential drug effects may be attributable to differences between quazepam and triazolam in terms of their benzodiazepine-receptor binding profile.

Adult↗

Oral triazolam is potentially hazardous to patients receiving systemic antimycotics ketoconazole or itraconazole.

BACKGROUND: Triazolam is metabolized by CYP3A4 isozyme. Ketoconazole and itraconazole may seriously interact with some of the substrates of CYP3A4 (e.g., terfenadine); hence their possible interaction with triazolam in humans is important to uncover. METHODS: In this double-blind, randomized, three-phase crossover study, the interaction between ketoconazole, itraconazole, and triazolam was investigated. Nine healthy young volunteers received either 400 mg ketoconazole, 200 mg itraconazole, or matched placebo (control phase) orally once a day for 4 days. On day 4, each ingested a single 0.25 mg dose of triazolam. Plasma concentrations of triazolam and antimycotics were determined, and pharmacodynamic effects were measured up to 17 hours. RESULTS: On average, ketoconazole and itraconazole increased the area under the triazolam concentration-time curve [AUC(0-infinity)] 22-fold and 27-fold (p < 0.001), the peak concentrations threefold (p < 0.001), and the elimination half-life sixfold and sevenfold (p < 0.001), respectively. In seven of the nine subjects, even the maximum concentration of triazolam in plasma was lower without the antimycotics than were the 17-hour concentrations during the ketoconazole and itraconazole phases. All pharmacodynamic effects (e.g., the Digit Symbol Substitution Test) revealed a significant difference between the antimycotic and placebo phases. CONCLUSIONS: Both ketoconazole and itraconazole seriously affect the pharmacokinetics of triazolam and increase the intensity and duration of its effects. Inhibition of CYP3A4 during the absorption and elimination phases of triazolam seems to explain the interaction observed. Because of the potentially hazardous consequences of this interaction, triazolam should be avoided if patients are using ketoconazole or itraconazole.

Administration, Oral↗

Sensitivity to triazolam in the elderly.

BACKGROUND: Elderly persons frequently appear to be sensitive to the effects of many drugs that depress the central nervous system. We studied the effect of age on the pharmacokinetics and pharmacodynamics of the benzodiazepine hypnotic agent triazolam, now the most frequently prescribed hypnotic drug in the United States. METHODS: Twenty-six healthy young subjects (mean age, 30 years) and 21 healthy elderly subjects (mean age, 69 years) participated in a four-way crossover study. After a single-blind adaptation trial with placebo, each subject received, in random order and in double-blind fashion, single doses of placebo, 0.125 mg of triazolam, and 0.25 mg of triazolam. For 24 hours after the administration of each of the three study medications, plasma triazolam levels were determined and psychomotor performance, memory, and degree of sedation were assessed. RESULTS: Plasma triazolam concentrations increased in proportion to the dose, but the elderly subjects had higher plasma concentrations due to reduced clearance of the drug. The degree of sedation as rated by an observer and the reduction in the subjects' performance on the digit-symbol substitution test were both greater in the elderly than in the young subjects after they were given the same doses. The relation of the plasma triazolam concentration to the degree of impairment was similar for the two groups. As part of the study, information was presented 1 1/2 hours after the administration of the drugs; the subjects' ability to recall the information 24 hours later was impaired by both doses of triazolam, and the percent decrease was similar in the young and elderly groups. CONCLUSIONS: Triazolam caused a greater degree of sedation and greater impairment of psychomotor performance in healthy elderly persons than in young persons who received the same dose. These effects resulted from reduced clearance and higher plasma concentrations of triazolam rather than from an increased intrinsic sensitivity to the drug. On the basis of these results, the dosage of triazolam for elderly persons should be reduced on average by 50 percent.

Adult↗

Comparison of the effects of intravenously administered midazolam, triazolam and their hydroxy metabolites.

The aim of the study was to compare the pharmacological activity and clinical effect after i.v. administration of midazolam, triazolam and their hydroxy metabolites, and, secondly, to compare the clinical effects of midazolam and triazolam in doses yielding the same duration of action (15 mg and 0.25 mg, respectively). In a randomized, cross-over procedure, six healthy volunteers received one of the following in the morning at approximately weekly intervals: 15 mg midazolam; 9 mg alpha-hydroxy midazolam; 1 mg triazolam; 1 mg alpha-hydroxy triazolam; 1 mg 4-hydroxy triazolam. Tests of drug effect (investigator's assessment, psychometric testing, and self-rating by subjects) were carried out at different times in the 24-h period following administration. Triazolam 0.25 mg was also studied in four of these six subjects to supplement the findings in the cross-over study. Triazolam 1 mg was shown to have the strongest, most long-lasting effect. Midazolam 15 mg had almost the same intensity of effect but this was shorter lasting, i.e. 5 h as against 10 h for 1 mg triazolam. The alpha-hydroxy metabolites had a duration of action about half that of the parent compounds and a less potent effect, and 4-hydroxy triazolam was virtually devoid of effect. The lower 0.25-mg dose of triazolam had about the same duration of action as 15 mg midazolam but did not achieve the same degree of maximum effect as measured by psychometric tests and self-assessment by subjects. The findings of this study indicate that midazolam would be suitable for use in situations in which a brief but intense hypnotic sedative effect is desired.

Adult↗

Effects of acute and chronic triazolam treatments on brain GABA levels in albino rats.

The present study investigated the effects of acute and chronic intraperitoneal administration of Triazolam on g-aminobutyric acid (GABA) levels in different brain areas of albino rats. Three experiments were conducted. In the first, five groups of rats were acutely treated with different doses of Triazolam (0.25 mg/kg-4.0 mg/kg). In the second experiment, rats were treated chronically with a single daily dose of Triazolam (started with 0.25 mg/kg and increased by time to 1.0 mg/kg) for 5 weeks, simulating clinical use. In the third, rats were treated chronically with three daily doses of Triazolam (started with 0.25 mg/kg and increased by time to 0.5 mg/kg) for 20 days, representing a form of drug abuse. Brain levels of GABA and plasma levels of Triazolam were measured using high performance liquid chromatography (HPLC). The acute Triazolam administration produced an increase in GABA levels in all brain areas studied. The chronic administration of single daily dose of Triazolam produced normal GABA levels in all brain areas except brain stem where the levels were significantly decreased; this indicates the development of tolerance to Triazolam action on increasing GABA content. The chronic administration of three daily doses of Triazolam produced a decrease in GABA levels in all brain regions studied. In conclusion, chronic single daily dose treatment (representing normal use) produces tolerance to Triazolam effects on brain GABA levels, while chronic three daily doses administration (akin to drug abuse) causes a fall in GABA levels.

Animals↗

A comparison of the acute behavioral effects of triazolam and temazepam in normal volunteers.

Two experiments were conducted to assess the acute behavioral effects of triazolam and temazepam in healthy, non-drug abusing men in double-blind, placebo-controlled, crossover trials, where all subjects received all possible doses. These drugs were compared to examine allegations that triazolam produces greater behavioral impairment than temazepam. Drug effects were assessed during 4-h sessions using measures of recall, learning, psychomotor performance, and subject ratings assessing drug effects and abuse potential. In experiment 1, triazolam (0.25 and 0.5 mg/70 kg) produced greater behavioral impairment than temazepam (15 and 30 mg/70 kg). However, triazolam also produced greater increases than temazepam in subject ratings of drug strength, drunkenness and sleepiness, suggesting the dose ranges compared may not have been clinically equivalent. Experiment 2 was conducted to assess whether a higher dose of temazepam than tested in experiment 1 would produce levels of behavioral impairment comparable to those observed with triazolam in experiment 1. In experiment 2, the temazepam dose was increased to 60 mg/70 kg while the triazolam dose was 0.5 mg/70 kg which was the highest dose tested in experiment 1. These doses produced comparable increases in subject ratings of drug strength, drunkenness and sleepiness, but temazepam produced significantly more behavioral disruption than triazolam. These findings do not support the position that triazolam produces greater behavioral impairment than temazepam, and may even suggest that across a wide range of doses triazolam is less disruptive than temazepam.

Adult↗

Interaction between grapefruit juice and hypnotic drugs: comparison of triazolam and quazepam.

OBJECTIVE: Grapefruit juice (GFJ) inhibits cytochrome P450 (CYP) 3A4 in the gut wall and increases blood concentrations of CYP3A4 substrates by the enhancement of oral bioavailability. The effects of GFJ on two benzodiazepine hypnotics, triazolam (metabolized by CYP3A4) and quazepam (metabolized by CYP3A4 and CYP2C9), were determined in this study. METHODS: The study consisted of four separate trials in which nine healthy subjects were administered 0.25 mg triazolam or 15 mg quazepam, with or without GFJ. Each trial was performed using an open, randomized, cross-over design with an interval of more than 2 weeks between trials. Blood samples were obtained during the 24-h period immediately following the administration of each dose. Pharmacodynamic effects were determined by the digit symbol substitution test (DSST) and utilizing a visual analog scale. RESULTS: GFJ increased the plasma concentrations of both triazolam and quazepam and of the active metabolite of quazepam, 2-oxoquazepam. The area under the curve (AUC)(0-24) of triazolam significantly increased by 96% (p<0.05). The AUC(0-24) of quazepam (+38%) and 2-oxoquazepam (+28%) also increased; however, these increases were not significantly different from those of triazolam. GFJ deteriorated the performance of the subjects in the DSST after the triazolam dose (-11 digits at 2 h after the dose, p<0.05), but not after the quazepam dose. Triazolam and quazepam produced similar sedative-like effects, none of which were enhanced by GFJ. CONCLUSION: These results suggest that the effects of GFJ on the pharmacodynamics of triazolam are greater than those on quazepam. These GFJ-related different effects are partly explained by the fact that triazolam is presystemically metabolized by CYP3A4, while quazepam is presystemically metabolized by CYP3A4 and CYP2C9.

Adult↗

Brain glycine levels in triazolam-treated albino rats.

The present study investigates the effects of acute and chronic administration of triazolam in albino rats on glycine levels in different brain areas. Three experiments were conducted. In the first, five groups of rats were acutely treated with different doses of triazolam (0.25 mg/kg-4.0 mg/kg i.p.). In the second experiment, rats were treated chronically by a single daily dose of triazolam (started by 0.25 mg/kg and increased by time to 1.0 mg/kg) for 5 weeks, simulating clinical use. In the third, rats were treated chronically three daily doses of triazolam (started by 0.25 mg/kg and increased by time to 0.5 mg/kg) for 20 days, simulating a form of drug abuse. Brain levels of glycine and plasma levels of triazolam were measured using HPLC technique. The acute triazolam administration produced an increase in glycine levels in almost all brain areas studied. The chronic administration of single daily dose of triazolam produced normal glycine levels in most of the brain areas; this indicates the development of tolerance to glycine content increasing action of triazolam. The chronic administration of three daily doses of triazolam produced a decrease in glycine levels in almost all brain regions studied, which might be a prerequisite for oncoming withdrawal syndrome.

Animals↗

Plasma concentrations of triazolam are increased by concomitant ingestion of grapefruit juice.

BACKGROUND: Grapefruit juice increases the bioavailability of several drugs known to be metabolized by CYP3A enzymes. Ketoconazole and itraconazole can increase the area under the concentration-time curve [AUC(0-infinity)] of triazolam, a substrate of CYP3A, by more than twenty times. METHODS: In this randomized crossover study the effect of grapefruit juice on the pharmacokinetics and pharmacodynamics of triazolam was investigated. Ten healthy young subjects received a single 0.25 mg dose of triazolam with either 250 ml grapefruit juice or water. Plasma concentrations and effects of triazolam were measured up to 17 hours. RESULTS: Grapefruit juice increased the AUC(0-infinity) of triazolam in each subject and the peak concentration in nine of the 10 subjects. The mean AUC(0-infinity) of triazolam was increased 1.5-fold (p < 0.001) and the peak concentration was increased 1.3-fold (p < 0.05) by grapefruit juice. Grapefruit juice postponed the peak time of triazolam from 1.6 hours to 2.5 hours (p < 0.05). Grapefruit juice increased the effects of triazolam slightly; drowsiness was significantly (p < 0.05) enhanced. CONCLUSIONS: Grapefruit juice can increase the plasma concentrations and effects of oral triazolam.

Administration, Oral↗

Secobarbital in humans discriminating triazolam under two-response and novel-response procedures.

Humans were trained to discriminate the benzodiazepine triazolam (0.32 mg/70 kg) from placebo under a two-response (drug vs. placebo) drug discrimination procedure. Dose-effect curves for several drugs were then determined in a crossover design using the two-response procedure and a 'novel-response procedure' that provided a novel-appropriate response for drugs unlike triazolam or placebo. Three subjects were tested with triazolam (0.1-0.32 mg/70 kg), the barbiturate secobarbital (56-177 mg/70 kg), and caffeine (320 and 560 mg/70 kg). Triazolam dose dependently increased triazolam-appropriate responding under both procedures and generally did not occasion novel-appropriate responding under the novel-response procedure. Secobarbital substituted for triazolam in the two-response procedure and dose-dependently increased novel-appropriate responding as well as occasioned some triazolam-appropriate responding in the novel-response procedure. Caffeine generally occasioned placebo-appropriate responding under the two-response procedure and a mix of novel- and placebo-appropriate responding under the novel-response procedure. Triazolam and secobarbital produced qualitatively similar self-reported drug effects. These results suggest that the novel-response procedure for human drug discrimination may enhance the pharmacological selectivity of triazolam- and placebo-appropriate responding.

Adult↗

Effects of alprazolam, caffeine, and zolpidem in humans trained to discriminate triazolam from placebo.

This study compared the discriminative stimulus effects of zolpidem, a nonbenzodiazepine hypnotic, to benzodiazepines. Eight participants learned to discriminate triazolam (0.35 mg/70 kg) from placebo. The discriminative stimulus effects, self-reported subjective effects, and performance effects of triazolam (0.05-0.35 mg/70 kg), alprazolam (0.25-1.75 mg/70 kg), zolpidem (2.5-35 mg/70 kg) and caffeine (75-525 mg/70 kg) were assessed under two-response and novel-response drug discrimination procedures. Under the two-response procedure, triazolam, alprazolam and zolpidem fully substituted for triazolam and caffeine did not. Under the novel-response procedure, triazolam and alprazolam substituted for triazolam and zolpidem partially substituted for triazolam. Zolpidem, but not triazolam or alprazolam, also produced some novel responding. Caffeine produced both placebo-appropriate and novel responding. The self-reported effects of triazolam, alprazolam and zolpidem were similar. Overall, zolpidem produced similar, but not identical, effects as the benzodiazepines.

Adolescent↗

Comparison of sublingually and orally administered triazolam for premedication before oral surgery.

OBJECTIVES: This study evaluated sublingual administration of triazolam for preoperative sedation in dental outpatients. STUDY DESIGN: A double-blind, placebo-controlled study compared 0.25 mg sublingual triazolam, 0.25 mg oral triazolam, and placebo administered 1 hour before oral surgery. RESULTS: Sublingual triazolam resulted in significantly less anxiety and pain at 15 minutes intraoperatively than both oral triazolam and placebo (p < 0.05). Patients' global evaluation of the efficacy of sedation ranked sublingual triazolam as significantly more efficacious than placebo (p < 0.05) with oral triazolam intermediate between the two. No difference was demonstrated in the rate of recovery or incidence of side effects between the two drug groups. Plasma triazolam levels were higher after sublingual administration during and after the surgical procedure. CONCLUSIONS: These results indicate that sublingual triazolam results in greater anxiolytic activity and less pain perception than oral administration as a result of greater plasma drug levels and may be useful as an alternative for nonparenteral outpatient sedation.

Administration, Oral↗

Mibefradil but not isradipine substantially elevates the plasma concentrations of the CYP3A4 substrate triazolam.

BACKGROUND: The calcium channel blockers mibefradil and isradipine inhibit CYP3A4 in vitro. However, their in vivo inhibitory effects on CYP3A4 are not known in detail, although mibefradil was recently withdrawn from the market because of serious drug interactions. METHODS: The effects of mibefradil and isradipine on the pharmacokinetics and pharmacodynamics of oral triazolam, a model substrate of CYP3A4, were studied in a randomized, double-blind crossover study with three phases. Nine healthy subjects took 50 mg mibefradil, 5 mg isradipine, or placebo orally once a day for 3 days. On day 3, each subject received a single 0.25 mg oral dose of triazolam. Thereafter, blood samples were collected up to 18 hours, and pharmacodynamic effects of triazolam were measured up to 8 hours. RESULTS: Mibefradil increased the total area under the plasma triazolam concentration-time curve [AUC(0 - infinity)] 9-fold compared with placebo (P < .001). The peak plasma concentration of triazolam was increased 1.8-fold (3.4+/-0.1 ng/mL versus 1.8+/-0.2 ng/mL [mean +/- SEM]; P < .001), and the elimination half-life (t 1/2) was increased 4.9-fold (18.5+/-1.9 hours versus 4.0+/-0.5 hours; P < .001) by mibefradil. In addition, mibefradil was associated with increased pharmacodynamic effects of triazolam. In contrast to mibefradil, isradipine reduced the AUC(0 - infinity) and t 1/2 of triazolam by about 20% (P < .05) and had no significant effects on the pharmacodynamics of triazolam. CONCLUSION: Mibefradil but not isradipine markedly increases the plasma concentrations of triazolam and thereby enhances and prolongs its pharmacodynamic effects, consistent with potent inhibition of CYP3A4.

Administration, Oral↗