Br J Clin Pharmacol 1996; 41: 319–323 Fluconazole, but not terbinafine, enhances the effects of triazolam by inhibiting its metabolism ANU VARHE, KLAUS T. OLKKOLA & PERTTI J NEUVONEN Department of Clinical Pharmacology, University of Helsinki and University Central Hospital, Helsinki, Finland 1 The interaction between triazolam and two antifungal agents, fluconazole and terbinafine, was investigated in a double-blind, randomized crossover study of three phases. 2 Twelve healthy young volunteers received 100 mg fluconazole, 250 mg terbinafine or placebo orally once a day for 4 days. On day 4 they took a single 0.25 mg dose of triazolam. Plasma samples were collected and pharmacodynamic effects were measured up to 17 h after the intake of triazolam. 3 Fluconazole increased the area under the triazolam concentration time-curve more than twofold (P<0.001) and prolonged the elimination half-life of triazolam nearly twofold (P<0.001). The peak concentration of triazolam was also increased significantly (P<0.05) by fluconazole. 4 During the fluconazole phase pharmacodynamic effects of triazolam (e.g. digit symbol substitution test, body sway and drowsiness) were enhanced signifi- cantly (P<0.05) when compared with the placebo phase. 5 Terbinafine did not change significantly the pharmacokinetics or pharmacodyn- amics of triazolam. 6 Care should be taken when triazolam is prescribed to patients using fluconazole. Although the interaction is not as strong as that of triazolam with ketoconazole or itraconazole, it is clinically significant. Triazolam and probably other drugs metabolized by CYP3A4 can be used in normal doses with terbinafine. Keywords triazolam fluconazole terbinafine interaction pharmacokinetics pharmacodynamics Introduction fluconazole has been less susceptible than other azoles to interact with drugs metabolized by cytochrome P450 Triazolam, a widely used benzodiazepine hypnotic, has enzymes (e.g. terfenadine) [5–7]. Recent studies have an elimination half-life of 2 to 4 h and an oral shown, however, that fluconazole may also interact with bioavailability of approximately 60% [1]. Triazolam is some drugs which are metabolized by CYP3A4 [8–10]. metabolized in the liver and in the gut wall by Both fluconazole and terbinafine inhibit fungal growth cytochrome P450 3A4 [2]. Therefore inhibitors and by suppression of ergosterol biosynthesis. The mode of inducers of this isoenzyme may lead to drug interactions fluconazole action is the inhibition of the cytochrome with triazolam. Ketoconazole and itraconazole increase P-450 enzyme lanosterol 14-a-demethylase [11]. Ter- the AUC of oral triazolam more than 20-fold [3]. The binafine, an allylamine antimycotic, inhibits a non- elimination half-life of triazolam is also prolonged by cytochrome P-450 enzyme, squalene epoxidase [12]. these antimycotics. Terbinafine is only weakly bound to CYP450, and it The in vitro interaction potential of fluconazole with inhibits only slightly the metabolism of tolbutamide, many substrates of CYP3A4 is considerably less than ethinyloestradiol, cyclosporin and ethoxycoumarin [13]. that of ketoconazole or itraconazole [4]. Also in vivo, Because triazolam is often used by patients on antimy- Correspondence: Dr. Anu Varhe, Department of Clinical Pharmacology, University of Helsinki, Paasikivenkatu 4, FIN-00250 Helsinki, Finland © 1996 Blackwell Science Ltd 319 320 Anu Varhe et al. cotic therapy, we have studied the effects of fluconazole concentration-time curve was identified visually for each and terbinafine on the pharmacokinetics and pharmaco- subject. The elimination rate constant (l ) was deter- z dynamics of triazolam in healthy volunteers. mined by regression analysis of the log-linear part of the curve. The elimination half-life (t ) was calculated 1/2,z from t ln2/l . The areas under the triazolam 1/2,z= z concentration-time curves (AUC(0,17 h)) were calculated Methods using the linear trapezoidal rule, with extrapolation to infinity (AUC) [18]. Study design Twelve healthy volunteers (10 females and two males) Pharmacodynamic measurements aged 19–31 years and weighing 48–80 kg gave written informed concent to participate in this study. The study Pharmacodynamic effects of triazolam were assessed at protocol and the consent form were approved by the the time of blood sampling by use of a battery of tests: Ethics Committee of the Department of Clinical the digit symbol substitution test, DSST, the critical Pharmacology, University of Helsinki and Finnish flicker fusion test, the Maddox wing test, subjective National Agency for Medicines. A randomized, double- drowsiness ( VAS) and body sway with eyes open and blind, cross-over study design in three phases was used. eyes closed, as described earlier [3]. For each pharmaco- The phases were separated by an interval of 4 weeks. dynamic variable, the areas under the response-time The subjects were given orally either 100 mg fluconazole curves were determined by the trapezoidal rule from 0 (Diflucan, Pfizer, Amboise, France), 250 mg terbinafine to 7 h (AUC(0,7 h)). (Lamisil, Sandoz, Basle, Switzerland), or placebo orally at 14.00 h daily for 4 days. On day 4, the subjects ingested a single 0.25 mg oral dose of triazolam (Halcion, Statistics Upjohn, Kalamazoo, MI, USA) with 150 ml water at 15.00 h. The volunteers fasted for 3 h before adminis- The results are expressed as mean values±s.e.mean, and tration of triazolam and had a standard meal 4 h 95% confidence intervals on major differences between afterward. Tobacco, as well as ingestion of alcohol, tea, the phases were calculated. ANOVA with repeated coffee and cola was forbidden during the test days. measures was used; a posteriori testing was done by the Eight of the 10 female subjects used oral contraceptive Tukey’s test. The t values were compared with max steroids. Other concomitant drugs were not used. Friedman’s two-way ANOVA and the Wilcoxon signed- rank test. Pearson’s product-moment correlation coefficient was used to investigate possible relationship Blood sampling and determination of drugs in plasma between the ratio of the AUC(0,17 h) of triazolam during the fluconazole phase to the AUC(0,17 h) during On day 4, blood was sampled into EDTA-tubes before the placebo phase versus the C of fluconazole. max administration of triazolam and 0.5, 1, 1.5, 2, 3, 4, 5, 6, Differences were regarded as statistically significant if P 7 and 17 h afterward. Plasma was separated within 30 values were <0.05. Systat for Windows, a statistical min and stored at −20° C until triazolam and anti- program, was used for the analyses of the data. mycotic concentrations were analysed. Plasma triazolam concentrations were determined by gas chromatography with use of a modified method of DeKroon et al. [14, 15]. The sensitivity of the method was 0.1 ng ml−1. Results The coefficient of day-to-day variation was 11.6% (at 0.34 ng ml−1, n=11). Plasma samples for antimycotic Pharmacokinetics determinations were taken 1, 1.5, 3, 5, 8 and 18 h after their fourth (=last) dose (i.e. before and 0.5, 2, 4, 7 and Fluconazole increased the mean AUC more than 17 h after the administration of triazolam). Terbinafine twofold, from a control value of 12.2±1.4 ng ml−1 h and fluconazole concentrations were determined by to 30.0±2.6 ng ml−1 h(P<0.001) (Table, Figure 1). h.p.l.c. with u.v.-detection [16, 17]. The sensitivity of The t of triazolam was prolonged nearly twofold 1/2,z the method for terbinafine was 10 ng ml 1 and the (P 0.001), and the C of triazolam was also increased − < max coefficient of day-to-day variation was 3.5% (at by fluconazole (P<0.05). Despite considerable interindi- 248 ng ml−1, n=6). The sensitivity of the fluconazole vidual differences in the extent of interaction, fluconazole method was 100 ng ml−1 and the coefficient of day-to- increased the AUC(0,17 h) in each subject. The ratio of day variation 1.3% (at 3.9 mg l−1,n=7). the AUC(0,17 h) of triazolam during the fluconazole phase to the AUC(0,17 h) during the placebo phase ranged from 1.3 to 4.3. Pharmacokinetics of triazolam Terbinafine did not change any of the pharmacokinetic variables of triazolam to a statistically significant degree Peak-concentrations (C ) and concentration peak (Figure 1, Table 1). In nine of the 12 subjects the max times (t ) were derived directly from the original AUC(0,17 h) of triazolam was smaller during the max values. The terminal log-linear phase of the plasma terbinafine phase than during the placebo phase. The © 1996 Blackwell Science Ltd British Journal of Clinical Pharmacology 41, 319–323 Fluconazole, but not terbinafine, interacts with triazolam 321 Table The pharmacokinetic variables of triazolam 0.25 mg (mean±s.e.mean or median and range) following pretreatment with oral fluconazole 100 mg, terbinafine 250 mg or placebo for 4 days in 12 healthy volunteers. In parentheses are the 95% confidence intervals for the differences from the placebo phase. Variable Placebo (Control) Fluconazole phase T erbinafine phase C (ng ml 1) 2.0 0.2 2.5 0.2† (0.1, 1.1) 1.7 0.2( 0.7, 0.2) max − ± ± ± − (% of control) (100) (125) (85) t (h) 1.8 (0.5, 2.0)* 2.0 (1.0, 4.0)* 1.5 (0.5, 3.0)* max AUC(0,17 h) (ng ml−1 h) 11.5±1.3 24.1±1.8‡ (9.0, 16.2) 9.8±1.3 (−4.0, 0.4) (% of control) (100) (210) (85) AUC (ng ml−1 h) 12.2±1.4 30.0±2.6‡ (13.1, 22.8) 9.9±1.2 (−4.7, 0.1) (% of control) (100) (246) (81) t (h) 3.7 0.3 6.8 0.6‡ (1.7, 4.4) 3.2 0.3 ( 0.8, 0.2) 1/2,z ± ± ± − − (% of control) (100) (184) (86) * Median (range).