Task-dependent development of cross-tolerance to psychomotor effects of lorazepam in man

Amnesic effects and subjective ratings during repeated dosing of flunitrazepam to healthy volunteers

Flunitrazepam (1 mg) or placebo was administered once daily over a treatment period of 8 days to healthy, male volunteers to study the time course of the effects on memory functions and on subjective ratings of alertness and tension. The plasma level of flunitrazepam increased by approximately 40% (P < 0.05) during the treatment period. The mean pre-dose level of flunitrazepam on day 4 and day 8 was approximately 0.005 microM, and no residual effects on memory functions were observed. Intake of flunitrazepam decreased the number of freely recalled words by about 85% (P < 0.05) and significantly affected the subjects' rating of attention when tested during the first few hours after drug intake on day 1 of treatment. However, no significant effect on the subjects' rating of relaxation was observed. When tested similarly after 8 days treatment, flunitrazepam significantly affected the subjects' rating of relaxation (P < 0.01). Furthermore, no tolerance developed for the effect of flunitrazepam on free recall (P > 0.3) and the subjects' rating of attention (P > 0.7), and these effects had nearly equal time courses during the treatment period. This may indicate that the amnesic effect of benzodiazepines is at least partially mediated through the effects on attention or general arousal. Two of the subjects in the active drug group reported adverse reactions or incidents of discomfort during the 1st week following the treatment period, whereas none in the placebo group reported such reactions.

Chronic benzodiazepine administration. XII. Anticonvulsant cross-tolerance but distinct neurochemical effects of alprazolam and lorazepam

Tolerance to the sedative and anticonvulsant effects of benzodiazepines has been reported, but cross-tolerance among benzodiazepines is poorly characterized. To evaluate cross-tolerance between lorazepam and alprazolam in a reliable anticonvulsant pharmacodynamic model, we treated mice with either drug for 14 days, and with the two drugs sequentially for 7 days each. Pentylenetetrazole-induced seizure thresholds were similar in mice treated for 14 days with lorazepam or alprazolam, 2 mg/kg/day. For both compounds, a discontinuation effect characterized by reduced seizure threshold occurred at 4 days after discontinuation. Substitution of alprazolam for lorazepam after 1 week, and vice versa, did not interrupt tolerance. [3H]flumazenil binding in vivo was downregulated in cortex after 14 days of either drug. However, binding was also reduced in hippocampus for lorazepam but not for alprazolam. Substitution of alprazolam for lorazepam resulted in downregulation in cortex only, similar to lorazepam alone. Conversely, substitution of lorazepam for alprazolam led to binding changes similar to lorazepam alone. These data demonstrate cross-tolerance to the convulsant effects of pentylenetetrazole between lorazepam and alprazolam. However, effects of the two compounds on benzodiazepine receptor binding in hippocampus remain distinct.

Comparative study of the abuse liability of alprazolam, lorazepam, diazepam, methaqualone, and placebo

Subjective effects of two benzodiazepines--alprazolam and lorazepam--were compared with two drugs of known abuse potential--diazepam and methaqualone--and placebo. This double-blind, crossover trial tested 30 casual recreational sedative users in a seminaturalistic setting. Methaqualone was more euphoriant and less sedative than the benzodiazepines. Diazepam and lorazepam were more euphoriant than placebo; alprazolam's euphoriant effect did not differ from these treatments. On other measures of abuse liability the benzodiazepines rated similarly, diazepam rating highest.

The natural history of tolerance to the benzodiazepines

Dependence on benzodiazepines following continued use is by now a well-documented clinical phenomenon. Benzodiazepines differ in their dependence potential. The present studies were aimed at examining the possibility that differential rates of tolerance development might account for differences in dependence risk. Four studies are reported. The first three studies concerned normal subjects. The development of tolerance over a fifteen day period was demonstrated for three different benzodiazepines (ketazolam, lorazepam and triazolam) using two paradigms. Tolerance in terms of a reduction in effectiveness of a repeated given dose was most notable for the benzodiazepine with a medium elimination half-life (lorazepam) for physiological, behavioural and subjective measures. In the case of the drug with the longest elimination half-life (ketazolam) reduction in effectiveness could only be assumed to be occurring if account was taken of the steady increase in plasma concentrations of active metabolites. For this drug it seemed that the physiological measures were those most likely to demonstrate the development of tolerance. Although triazolam showed few significant drug effects on this paradigm (testing being 12 hours after ingestion of this short half-life benzodiazepine), tolerance was seen to develop on some subjective measures. Using an alternative method of testing tolerance, assessing responses to a diazepam challenge dose, a high degree of tolerance on two-thirds of the measures was observed in subjects when pretreated with the benzodiazepine with the most marked accumulation of active metabolites (ketazolam). The other two drugs also led to tolerance development on a range of measures; this was more marked for lorazepam than triazolam. Blunting of the growth hormone response to diazepam was the most sensitive and reliable method of detecting tolerance to the benzodiazepines. Symptoms on discontinuation of the two weeks' intake of the benzodiazepines were marked for all the drugs but unrelated to either the tolerance induced or the elimination half-life of the particular drug. A further clinical study revealed that tolerance persisted in a group of long-term benzodiazepine users for between four months and two years following complete abstinence from the drug. These patients appeared to be less affected by diazepam in terms of its commonly observed subjective effects, regardless of their original medication. These ex-long-term users of benzodiazepines were, however, more likely to manifest two specific types of effects--immediate 'symptom' reduction and exacerbation of 'withdrawal symptoms' over the subsequent week.(ABSTRACT TRUNCATED AT 400 WORDS)

Influence of dosing regimen on alprazolam and metabolite serum concentrations and tolerance to sedative and psychomotor effects

The relationships between alprazolam and metabolite concentrations and CNS effects were determined in a double-blind placebo controlled four-way crossover trial in 16 normal male volunteers. Active drug treatments consisted of 4-day regimens of 4 mg alprazolam PO daily as 2 mg bid., 1 mg qid, and 0.25 mg each hour. On days 1 and 4, the kinetics, sedative and psychomotor effects were evaluated. Plasma concentrations of the 4- and alpha-hydroxy metabolites of alprazolam were less than 10% of unchanged alprazolam levels on both days. Accumulation of these metabolites and alprazolam was dependent on alprazolam half-life (11.6 h). Acute and chronic tolerance to the sedative and psychomotor effects was observed with all active drug treatments. All alprazolam treatments resulted in significantly greater sedation than placebo on days 1 and 4. However, on day 4, sedation was 16-36% less than observed on day 1, despite plasma concentrations 1.4-2.76 times the day 1 concentrations. Sedation from alprazolam was reduced in each successive study phase, suggesting a tolerance which was sustained during the 10-day washout between phases. By day 4, psychomotor performance was not different from placebo, indicating more complete development of tolerance than occurred for the sedative effect. Sedation and psychomotor impairment on day 1 were greatest with 2 mg alprazolam bid. During the initiation of therapy, the patient will likely experience less sedation and psychomotor impairment with smaller, more frequent doses. Since tolerance develops to these effects, the advantage of more frequent dosing regimen dissipates by the 4th day.

Benzodiazepine cross-tolerance in mice extends to sodium valproate

Slow intravenous infusion of pentylenetetrazol was used to measure the convulsive threshold in mice. The anticonvulsant effects of clobazam, clonazepam, diazepam, lorazepam, sodium phenobarbitone and sodium valproate were assessed in naive animals and compared with the effects of the same compounds in animals which had been pretreated (twice daily for 3 days) with one of the benzodiazepines or sodium valproate. Cross-tolerance was observed between all the benzodiazepines but not between benzodiazepines and sodium phenobarbitone. Animals pretreated with the benzodiazepines were cross-tolerant to valproate, but the converse was not true; nor did sodium valproate induce tolerance to itself.

Benzodiazepines, but not antidepressants or neuroleptics, induce dose-dependent development of tolerance to lorazepam in psychiatric patients

Psychomotor effects of oral lorazepam 3 mg were studied in psychiatric patients stratified into four groups: 1) a group of six patients with no previous use of psychotrophic drugs (NoD), 2) a group of 12 patients treated with antidepressants and/or neuroleptics (PsyD), 3) a group of 10 patients treated with low doses of benzodiazepines (BZs) (lowBZ), and 4) a group of nine patients treated with high doses of BZs (high BZ). Similar objective psychomotor tests and subjective assessments were administered under single-blind conditions to all treatment groups at baseline, after intake of placebo, and after intake of 3 mg lorazepam. Both lorazepam (CGC) and total BZs (bioassay) in serum were assayed. The results demonstrate that treatment with BZs induce dose-dependent development of tolerance to psychomotor effects of lorazepam. Antidepressants and neuroleptics failed to induce cross-tolerance to lorazepam. The rise in serum lorazepam concentrations after lorazepam intake was similar (about 28 micrograms/l) in all treatment groups, suggesting a functional, not dispositional, tolerance. However, the initial learning effect in psychomotor performance was poorer among BZ users than among others.