Antagonism of triazolam self-administration in rhesus monkeys responding under a progressive-ratio schedule: In vivo apparent pA2 analysis.

BACKGROUND: Conventional benzodiazepines bind non-selectively to GABAA receptors containing α1, α2, α3, and α5 subunits (α1GABAA, α2GABAA, α3GABAA, and α5GABAA receptors, respectively), and the role of these different GABAA receptor subtypes in the reinforcing effects of benzodiazepines has not been characterized fully. We used a pharmacological antagonist approach with available subtype-selective ligands to evaluate the role of GABAA receptor subtypes in the reinforcing effects of the non-selective conventional benzodiazepine, triazolam. METHODS: Rhesus monkeys (n=4) were trained under a progressive-ratio schedule of intravenous midazolam delivery and dose-response functions were determined for triazolam, in the absence and presence of flumazenil (non-selective antagonist), ßCCT and 3-PBC (α1GABAA-preferring antagonists), and XLi-093 (α5GABAA-selective antagonist). RESULTS: Flumazenil, ßCCT and 3-PBC shifted the dose-response functions for triazolam to the right in a surmountable fashion, whereas XLi-093 was ineffective. Schild analyses revealed rank orders of potencies of flumazenil=ßCCT>3-PBC. Comparison of potencies between self-administration and previous binding studies with human cloned GABAA receptor subtypes suggested that the potencies for ßCCT and 3-PBC were most consistent with binding at α2GABAA and α3GABAA receptors, but not α1GABAA or α5GABAA receptor subtypes. CONCLUSIONS: Our findings were not entirely consistent with blockade of α1GABAA receptors and are consistent with the possibility of α2GABAA and/or α3GABAA subtype involvement in antagonism of the reinforcing effects of triazolam. The α5GABAA receptor subtype likely does not play a substantial role in self-administration under these conditions.

Flumazenil reversal of sublingual triazolam: a randomized controlled clinical trial.

BACKGROUND: Incremental sublingual (SL) dosing of triazolam has emerged as a popular sedation technique. Nevertheless, few studies have evaluated the technique's safety or efficacy. Given its popularity, an easily administered rescue strategy is needed. METHODS: The authors conducted a randomized controlled clinical trial to investigate how intraoral submucosal flumazenil (0.2 milligram) attenuates central nervous system depression produced by incremental SL dosing of triazolam (three doses of 0.25 mg across 90 minutes) in 14 adults. The authors assessed outcomes by using the Observer's Assessment of Alertness/Sedation (OAA/S) scale, bispectral index (BIS) and physiological monitoring. RESULTS: The OAA/S and BIS scores increased after the flumazenil injection at the 30-minute observation point, but they were not sustained. Six hours after the initial dose of triazolam had been administered (four hours after the flumazenil or placebo challenge), all patients could be discharged from the dental clinic. CONCLUSIONS: Deep sedation from incremental SL dosing of triazolam is incompletely reversed by a single intraoral injection of flumazenil. The reversal did not persist. The authors discharged the patients from the dental clinic at 360 minutes. CLINICAL IMPLICATIONS: A single intraoral injection of flumazenil (0.2 mg) cannot immediately reverse oversedation with triazolam. A higher dose might be effective. Reversal for the purpose of discharging the patient early is neither appropriate nor safe.

Inhibitory action of 5-HT1A agonist MKC-242 on triazolam-induced phase advances in hamster circadian activity rhythms.

Mammalian circadian rhythms can be entrained by photic and non-photic stimuli. Although we know that non-photic entrainment interferes with photic entrainment signals, there is no information about whether photic entrainment interferes with non-photic entraining signals. We examined whether triazolam (TRZ), a non-photic form of entrainment, could be attenuated by pre-treatment with (S)-5-[3-[(1,4-benzodioxan-2-ylmethyl)amino]propoxy]-1,3-benzodioxole hydrochloride (MKC-242), a photic enhancing drug. We found that TRZ-induced phase advances in hamster behavioral circadian rhythms and the increase of locomotor activity were both significantly attenuated by MKC-242. Thus, in hamsters, the photic enhancing drug MKC-242 seemed to hinder benzodiazepine-induced non-photic entrainment.

In vitro metabolism of midazolam, triazolam, nifedipine, and testosterone by human liver microsomes and recombinant cytochromes p450: role of cyp3a4 and cyp3a5.

Midazolam, triazolam (TRZ), testosterone, and nifedipine have all been widely used as probes for in vitro metabolism of CYP3A. We used these four substrates to assess the contributions of CYP3A4 and CYP3A5 to in vitro biotransformation in human liver microsomes (HLMs) and in recombinant enzymes. Recombinant CYP3A4 and CYP3A5 (rCYP3A4 and rCYP3A5) both produced 1-OH and 4-OH metabolites from midazolam and triazolam, 6 beta-hydroxytestosterone from testosterone, and oxidized nifedipine from nifedipine. Overall, the metabolic activity of CYP3A5 was less than that of CYP3A4. Ketoconazole potently inhibited midazolam, triazolam, testosterone, and nifedipine metabolite formation in HLMs and in rCYP3A4. The inhibitory potency of ketoconazole in rCYP3A5 was about 5- to 19-fold less than rCYP3A4 for all four substrates. In testosterone interaction studies, testosterone inhibited 1-OH-TRZ formation, but significantly activated 4-OH-TRZ formation in HLMs and rCYP3A4 but not in rCYP3A5. Oxidized nifedipine formation was inhibited by testosterone in rCYP3A4. However, in rCYP3A5, testosterone slightly activated oxidized nifedipine formation at lower concentrations, followed by inhibition. Thus, CYP3A4 and CYP3A5 both contribute to midazolam, triazolam, testosterone, and nifedipine biotransformation in HLMs, with CYP3A5 being metabolically less active than CYP3A4 in general. Because the inhibitory potency of ketoconazole in rCYP3A5 is substantially less than in rCYP3A4 and HLMs, CYP3A5 is probably less important than CYP3A4 in drug-drug interactions involving ketoconazole and CYP3A substrates.

Prediction of in vivo interaction between triazolam and erythromycin based on in vitro studies using human liver microsomes and recombinant human CYP3A4.

PURPOSE: To quantitatively predict the in vivo interaction between triazolam and erythromycin, which involves mechanism-based inhibition of CYP3A4, from in vitro studies using human liver microsomes (HLM) and recombinant human CYP3A4 (REC). METHODS: HLM or REC was preincubated with erythromycin in the presence of NADPH and then triazolam was added. alpha- and 4-hydroxy (OH) triazolam were quantified after a 3 min incubation and the kinetic parameters for enzyme inactivation (k(inact) and K('app)) were obtained. Drug-drug interaction in vivo was predicted based on a physiologically-based pharmacokinetic (PBPK) model, using triazolam and erythromycin pharmacokinetic parameters obtained from the literature and kinetic parameters for the enzyme inactivation obtained in the in vitro studies. RESULTS: Whichever enzyme was used, triazolam metabolism was not inhibited without preincubation, even if the erythromycin concentration was increased. The degree of inhibition depended on preincubation time and erythromycin concentration. The values obtained for k(inact) and K('app) were 0.062 min(-1) and 15.9 microM (alpha-OH, HLM), 0.055 min(-1) and 17.4 microM (4-OH, HLM), 0.173 min(-1) and 19.1 microM (alpha-OH, REC), and 0.097 min(-1) and 18.9 microM (4-OH, REC). Based on the kinetic parameters obtained using HLM and REC, the AUCpo of triazolam was predicted to increase 2.0- and 2.6-fold, respectively, following oral administration of erythromycin (333 mg t.i.d. for 3 days), which agreed well with the reported data. CONCLUSIONS: In vivo interaction between triazolam and erythromycin was successfully predicted from in vitro data based on a PBPK model involving a mechanism-based inhibition of CYP3A4.

Synergistic inhibition by benzodiazepine and barbiturate drugs of the clock control of ovulation in hamsters.

A surge of pituitary luteinizing hormone (LH) into the bloodstream occurs in hamsters every 4 days between 1:30 p.m. and 3 p.m. in response to a signal from a biological clock. This surge initiates behavioral estrus approximately 2 h later and ovulation approximately 12 h later. Phenobarbital at a dose > or = 100 mg/kg consistently blocks LH release. Barbiturate and benzodiazepine drugs have separate binding sites in the GABAA receptor/chloride channel complex. Binding of either drug increases GABA-mediated chloride conductance, which suppresses the postsynaptic neuron. Barbiturate binding also increases benzodiazepine binding. This suggested that these drugs might synergize to inhibit LH release. A combination of triazolam and phenobarbital at doses of 10 mg/kg injected s.c. at 1:30 p.m. inhibited ovulation and extended the 4-day vaginal cycle in all treated hamsters. Either drug dose injected alone at 1:30 p.m., or the combination at 3 p.m., was completely ineffective. Bicuculline prevented inhibition by the combination at 1:30 p.m. The clock signal for LH release may act by antagonizing GABA transmission, which may be chronically inhibiting LH release. The combination delimited a 75-min period (1:30-2:45 p.m.) within which the clock signal for LH release occurred in all individuals (ET50 = 2:08 p.m.). This period appears to arise from individuals with different but constant clock settings rather than from a 75-min variation in the clock setting of the individual.

Tolerance, cross-tolerance and dependence measured by operant responding in rats treated with triazolam via osmotic pumps.

Previous research has found that drugs with affinity for omega (benzodiazepine) sites differ in their abilities to produce tolerance and dependence. The present study therefore investigated the effects of ligands of omega (BZ) sites in rats that had been rendered tolerant to a benzodiazepine. Two experiments were carried out in separate groups of rats. Behavioral changes induced by chronic infusion of triazolam (3 mg/kg/day, SC, for 14 days) via osmotic pumps were studied in animals trained on a fixed ratio 10 schedule of food presentation. Control animals were implanted with pumps containing the vehicle. Test drugs were administered IP using cumulative dosing. In one experiment triazolam decreased response rates on days 1, 2 and 3 after implantation of the pumps and tolerance developed to this depressant effect. In the other experiment, vehicle and triazolam treated rats differed in their responding during chronic infusion but differences were not statistically significant on any particular day. Flumazenil (3.0-30 mg/kg) greatly decreased rates of responding on day 11 in triazolam treated rats. This effect may represent a precipitated withdrawal syndrome. However, no withdrawal effects on operant performance were observed upon pump removal. Chronic infusion of triazolam did not affect the sensitivity of rats to alpidem on day 11 (10-100 mg/kg) whereas it abolished the stimulant effect of bretazenil (0.1-1.0 mg/kg). Chronic triazolam treatment produced tolerance to the depressant effects of triazolam (1.0-3.0 mg/kg), lorazepam (0.3-3.0 mg/kg) and zopiclone (10 mg/kg) but no tolerance to those of CL 218,872 (3.0-30 mg/kg) and zolpidem (0.3-3.0 mg/kg) when tested 3-14 days after pump removal.(ABSTRACT TRUNCATED AT 250 WORDS)

Nifedipine blocks effects of triazolam injected into the dorsal raphe nucleus on sleep.

In previous studies, the author has reported both in vitro and in vivo sleep studies in which there were complex interactions between benzodiazepine hypnotics and the dihydropyridine calcium channel blocker nifedipine. The author has also reported that microinjections of triazolam into the dorsal raphe nucleus of the rat result in enhancement of wakefulness. In the present study, nifedipine and triazolam were coadministered into this site. As previously was observed, triazolam produced a dose-dependent increase in sleep latency and a decrease in total sleep, primarily by reducing non-rapid-eye-movement sleep. Nifedipine had no effect on sleep when given by itself but prevented the alterations in sleep by triazolam. These various sleep effects were not associated with alterations in core temperature. These data are consistent with the view that aspect of the sleep-altering activity of triazolam involves interaction with voltage-dependent calcium channel activity.

Monoamine depletion blocks triazolam-induced phase advances of the circadian clock in hamsters.

Injections with the short-acting benzodiazepine, triazolam (Tz), 6 h before activity onset (CT6) produce large phase advances of the circadian pacemaker in hamsters. An increase in locomotor activity and/or the state of arousal is considered essential for the effects of Tz, suggesting the potential involvement of central monoaminergic systems in this process. The present study examines the effect of reserpine-induced monoamine depletion on the phase-shifting effects of Tz in hamsters. Wheel running activity of 16 male golden hamsters (14 weeks old) was continuously monitored in constant darkness. After a stable free-running circadian rhythm was established half of the animals received reserpine (2.5 mg/kg, s.c.) and the other half vehicle treatment. Ten days later all animals were given Tz injections (10 mg/kg i.p.) at CT6 and the circadian activity rhythm was monitored for 2 more weeks. An additional 10 animals were used to determine the effect of reserpine on the central monamine levels using high pressure liquid chromatography. A circadian rhythm of locomotor activity with reduced amplitude and longer free-running period persisted after reserpine treatment, despite the significant monoamine depletion. Triazolam injections at CT6 induced large phase-advances (93.1 +/- 14.9) in the control group that were markedly attenuated in 7 out of the 8 reserpine-treated animals (3.12 +/- 17.7 min, P < 0.01). Our results suggest that monoaminergic systems are essential for the phase-shifting effect of Tz upon the circadian system in hamsters.

Cognitive impairments induced by triazolam in healthy volunteers: antagonism by a partial inverse agonist of benzodiazepine receptor.

Pharmacological studies revealed that SR 25776 possesses marked stimulant activity characteristic of a partial inverse agonist of benzodiazepine receptor. The effects of SR 25776 500 mg alone and in combination with triazolam 0.25 mg on psychomotor performance and memory were assessed in 8 healthy consenting male volunteers in a double-blind placebo controlled trial. Treatment effects were monitored before and two and half hours following oral medication. The present study suggest that at the studied dose SR 25776 may incompletely antagonize the sedative and amnesic effects of a benzodiazepine agonist without producing marked effects of its own.

Caffeine moderately antagonizes the effects of triazolam and zopiclone on the psychomotor performance of healthy subjects.

To determine whether caffeine antagonizes the decremental effects of triazolam and zopiclone on human performance, oral single doses of 0.250 mg triazolam, 7.5 mg zopiclone, or respective placebos, with and without 300 mg caffeine, were given to parallel groups of student volunteers in two double-blind studies. Objective tests and subjective visual analogue ratings were done at baseline and 30 min. and 90 min. after the intake. In Study I, triazolam produced drowsiness at 30 min. but did not differ from the placebo in other tests. Caffeine induced alerting effects in various tests and differed from triazolam in some (digit substitution, drowsiness, calmness, mental slowness) but not all variables measured. Caffeine and triazolam were interpreted as being antagonists. In Study II, zopiclone impaired digit substitution and flicker fusion, produced exophoria and lowered systolic blood pressure. Caffeine differed from zopiclone in several test functions, but it also differed from caffeine + zopiclone whereas zopiclone differed from caffeine + zopiclone only in two tests (Maddox wing, systolic blood pressure). Thus, zopiclone counteracted the effects of caffeine more easily than caffeine counteracted the decremental effects of zopiclone. We conclude that triazolam may not differ importantly from diazepam as regards their antagonism towards caffeine, whereas further research on the antagonism between zopiclone and caffeine needs to be done.

Study of the potential reversal of triazolam memory and cognitive deficits by RU 41 656 in healthy subjects.

The potential antagonism of a single oral dose of RU 41 656 (10 mg) on the memory and attention disturbances induced by oral administration of triazolam (0.25 mg) have been investigated in a 3-period, placebo controlled, double blind, cross-over study involving 12 healthy young volunteers. The effects of the compounds were evaluated by objective tests (Buschke selective reminding test, CFF, simple reaction time, tapping, arithmetical calculation) and subjective measurements (visual analogue scale, side effects questionnaire). Measurements were taken before treatment and 2, 4 and 7 h after RU 41 656 intake. Triazolam caused anterograde amnesia as already described with other benzodiazepine with few sedative effects at this dosage. Under the experimental conditions of the trial, RU 41 656 failed to counteract the memory deficits induced by triazolam.

A benzodiazepine antagonist, Ro 15-1788, can block the phase-shifting effects of triazolam on the mammalian circadian clock.

A single injection of the short acting benzodiazepine, triazolam, can induce permanent phase advances as well as phase delays in the onset of the circadian rhythm of wheel running behavior in hamsters free-running under constant environmental conditions. If the phase shifting effects of triazolam on the circadian system are mediated through the benzodiazepine-GABA receptor complex, then it should be possible to block these effects with RO 15-1788, a selective benzodiazepine antagonist, which acts at the benzodiazepine-GABA receptor level. To test this hypothesis, hamsters free running in constant light received an intraperitoneal injection of various doses of Ro 15-1788 15 min before a single i.p. injection of 0.5 mg of triazolam. This dose of triazolam is known to induce maximal phase shifts in the circadian rhythm of wheel running behavior in hamster. Treatment with Ro 15-1788 totally blocked both the phase advancing and phase delaying effects of triazolam, while the administration of Ro 15-1788 alone did not phase shift the activity rhythm. These results support the hypothesis that the phase shifting effects of triazolam are mediated through the benzodiazepine-GABA receptor complex. The absence of any phase shifting effects of Ro 15-1788 when delivered alone suggests that Ro 15-1788 has no partial agonist properties in this experimental paradigm.

Reversal by caffeine of triazolam-induced impairment of waking function.

Twelve, healthy normal men aged 21-25 years received each of four treatments (triazolam placebo plus caffeine placebo, triazolam 0.50 mg plus caffeine placebo, triazolam 0.50 mg plus caffeine 4 mg/kg, triazolam 0.50 mg plus caffeine 8 mg/kg), double blind, in a Latin-Square design. Triazolam or placebo was administered at 0830 and caffeine or placebo at 1000 and 1245. On two memory tasks, administered at 1015 with an immediate recall and a delayed recall at 1230 following a 90 min nap (1030-1200), both immediate and delayed recall was impaired by triazolam. Neither caffeine dose reversed the impairments. Sleep latency and sleep efficiency were improved by triazolam and not reversed by caffeine. On a performance battery presented at 1300 most measures of performance were impaired by triazolam; in general the caffeine dose of 4 mg/kg partially reversed the effect while the dose of 8 mg/kg completely restored performance.