Effect of age and sex on disposition of desmethyldiazepam formed from its precursor clorazepate

An explorative approach to understanding individual differences in driving performance and neurocognition in long-term benzodiazepine users

OBJECTIVE

Previous research reported cognitive and psychomotor impairments in long-term users of benzodiazepine receptor agonists (BZRAs). This article explores the role of acute intoxication and clinical complaints.

METHODS

Neurocognitive and on-road driving performance of 19 long-term (≥6 months) regular (≥twice weekly) BZRA users with estimated plasma concentrations, based on self-reported use, exceeding the therapeutic threshold (C_BZRA +), and 31 long-term regular BZRA users below (C_BZRA -), was compared to that of 76 controls.

RESULTS

BZRA users performed worse on tasks of response speed, processing speed, and sustained attention. Age, but not C_BZRA or self-reported clinical complaints, was a significant covariate. Road-tracking performance was explained by C_BZRA only. The C_BZRA  + group exhibited increased mean standard deviation of lateral position comparable to that at blood-alcohol concentrations of 0.5 g/L.

CONCLUSIONS

Functional impairments in long-term BZRA users are not attributable to self-reported clinical complaints or estimated BZRA concentrations, except for road-tracking, which was impaired in CBZRA + users. Limitations to address are the lack of assessment of objective clinical complaints, acute task related stress, and actual BZRA plasma concentrations. In conclusion, the results confirm previous findings that demonstrate inferior performance across several psychomotor and neurocognitive domains in long-term BZRA users.

Slow Accumulation and Elimination of Diazepam and Its Active Metabolite With Extended Treatment in the Elderly

Age-related changes in disposition of diazepam and its principal active metabolite, desmethyldiazepam (DMDZ), during and after extended dosage with diazepam were studied in healthy volunteers. Eight elderly subjects (ages 61-78 years) and 7 young subjects (21-33 years) received 2.5 mg of diazepam twice daily for 15 days. Predose (trough) concentrations of diazepam and DMDZ were measured during the 15 days of dosing, and in the postdosage washout period. Kinetic properties were determined by nonlinear regression using a sequential drug-to-metabolite pharmacokinetic model. Steady-state plasma concentrations of diazepam and DMDZ were 30% to 35% higher in elderly subjects compared to young volunteers, and steady-state clearances correspondingly lower, though differences did not reach significance. Large and significant differences were found between young and elderly groups in mean half-life of diazepam (31 vs 86 hours; P < .005) and DMDZ (40 vs 80 hours; P < .02). Half-life values from the multiple-dose study were closely correlated with values from previous single-dose studies of diazepam (R² = 0.85) and DMDZ (R² = 0.94) in the same subjects. With extended dosing of diazepam in the elderly, slow accumulation and delayed washout of diazepam and DMDZ is probable. After discontinuation, withdrawal or rebound effects are reduced in likelihood, but delayed recovery from sedative effects is possible due to slow elimination of active compounds. Safe treatment of elderly patients with diazepam is supported by understanding of age-related changes in pharmacologic and pharmacokinetic properties.

Metabolic profile of oxazepam and related benzodiazepines: clinical and forensic aspects

Anxiolytic drugs, namely benzodiazepines, are the most commonly used psychoactive substances since anxiety disorders are prevalent mental disorders particularly in the Western world. Oxazepam is a short-acting benzodiazepine and one of the most frequently prescribed anxiolytic drugs. It is also the active metabolite of a wide range of other benzodiazepines, such as diazepam, ketazolam, temazepam, chlordiazepoxide, demoxazepam, halazepam, medazepam, prazepam, pinazepam, and chlorazepate. Therefore, relevant clinical and forensic outocomes may arise, namely those related to interference in driving performance. It is clinically available as a racemic formulation, with S-enantiomer being more active than R-enantiomer. In humans, it is mainly polimorphically metabolized by glucuronide conjugation at the 3-carbon hydroxyl group, yielding stable diastereomeric glucuronides (R- and S-oxazepam glucuronide). Relevant metabolic and stereoselective interspecies differences have been reported. In this work, the pharmacokinetics of oxazepam with particular focus on metabolic pathways is fully reviewed. Moreover, the metabolic profile of other prescribed benzodiazepines that produce oxazepam as a metabolite is also discussed. It is aimed that knowing the metabolism of oxazepam and related benzodiazepines may lead to the development of new analytical strategies for its early detection and help in further toxicological and clinical interpretations.

Sex-dependent modulation of treatment response

The response to a psychotropic medication reflects characteristics of both the medication and the substrate, ie, the individual receiving the medication. Sex is an individual characteristic that influences all elements of the pharmacokinetic process - absorption, distribution, metabolism, and elimination. The effects of sex on these components of the pharmacokinetic process often counterbalance one another to yield minimal or varying sexual differences in blood levels achieved. However, sex also appears to influence pharmacodynamics, the tissue response to a given level of medication. Consideration by the practitioner of sex as a possible contributing factor to treatment nonresponse will enhance the efficacy and precision of clinical interventions.

In vitro drug allergy detection system incorporating human liver microsomes in chlorazepate-induced skin rash: drug-specific proliferation associated with interleukin-5 secretion

BACKGROUND

Chlorazepate is a benzodiazepine often used for pre-operative anxiolysis. The central metabolite responsible for the pharmacological and probably for the adverse effects of most benzodiazepines, including chlorazepate, is N-desmethyldiazepam. We report a woman who developed a generalized exanthem 1 day after receiving chlorazepate and four other drugs related to anaesthesia for surgery of the larynx. Patch tests pointed to chlorazepate as the culprit drug for the skin rash.

OBJECTIVES

The purpose of this study was to detect drug allergy to chlorazepate or a metabolite in vitro by means of the lymphocyte transformation test (LTT), and to determine the concentrations of the T-helper (Th) 2-type cytokine interleukin (IL)-5 and the Th1-type cytokine interferon (IFN) -gamma in the culture supernatants.

METHODS

We performed an LTT with peripheral blood mononuclear cells from the patient and a control, employing human liver microsomes containing cytochrome P450 enzymes as a metabolizing system, in parallel cultures. IL-5 and IFN-gamma concentrations in the culture supernatants were assessed by enzyme-linked immunosorbent assay.

RESULTS

In the LTT, no T-cell reactivity was observed to the parent compound chlorazepate, whereas coincubation of the drug with human liver microsomes yielded proliferative T-cell reactivity, which was associated with secretion of IL-5 but not of IFN-gamma.

CONCLUSIONS

We conclude that addition of a metabolizing system may be advantageous for in vitro detection of T-cell reactivity to drug metabolites in the LTT.

Age-related changes in protein binding of drugs: implications for therapy

The plasma protein binding of drugs, particularly those that are highly bound, may have significant clinical implications. Although protein binding is a major determinant of drug action, it is only one of a myriad of factors that influence drug disposition. The extent of protein binding is a function of drug and protein concentrations, the affinity constant for the drug-protein interaction and the number of protein binding sites per class of binding site. Age-related changes in protein binding are usually not clinically important in drug therapy. Albumin levels are generally decreased in the elderly, whereas alpha1-acid glycoprotein levels are not altered by age per se. Alterations in plasma protein binding that occur in the elderly are generally not attributed to age, but rather to physiological and pathophysiological changes or disease states that may occur more frequently in the elderly and most often account for altered protein binding. Age-related physiological changes, such as decreased renal function, decreased hepatic function and decreased cardiac output, generally produce more clinically significant alterations in drug disposition than that seen with alterations in drug plasma protein binding. An understanding of the inter-relationships between drug concentrations, protein binding, the physiology of aging, disease, pharmacokinetics and pharmacodynamics is necessary for effective therapeutic monitoring. Monitoring of unbound drug concentrations simplifies these relationships and provides the fundamental information needed for dosage regimen development and adjustment. Drug therapy in the elderly should be individualised taking into account all of these factors.

Preoperative anxiolysis with minimal sedation in elderly patients: bromazepam or clorazepate-dipotassium?

BACKGROUND

In elderly patients undergoing ophthalmic surgery the loss of co-operation due to over-sedation, induced by drugs given preoperatively, may jeopardise the success of microsurgery performed under regional anaesthesia. The aim of this study was to compare the psychotropic effects of bromazepam and clorazepate-dipotassium, two benzodiazepines with predominantly anxiolytic and only weak sedative action.

METHODS

A randomised, placebo-controlled, double-blind study was designed to include 60 patients, ASA physical status II-III, older than 60 years scheduled for ophthalmic surgery under regional anaesthesia. The patients were randomised to receive either bromazepam (3 mg) or clorazepate-dipotassium (20 mg) or placebo. The study drugs were given at 10 p.m. the night before surgery and 90 min before surgery. Using the State-Trait Anxiety Inventory (STAI), the patient's anxiety was assessed at the end of the preoperative visit, on the next morning before the study drug was given and on arrival at the operating theatre.

RESULTS

Bromazepam induced a marked anxiolytic effect as documented by a significant reduction in the STAI State values after both applications (P<0.01). Clorazepate did not differ from placebo at any evaluation time with regard to the STAI and haemodynamic values. Sedative effects and oxygen saturation (SpO2) were comparable in all groups.

CONCLUSION

Bromazepam is superior to clorazepate in its anxiolytic action and suitable as preoperative medication in the elderly patient because of lack of overt sedative effects.

Pharmacokinetics of nordiazepam in physical dependence and precipitated abstinence in dogs

Previous studies suggested that the extensive accumulation of benzodiazepines is an important factor in the induction of physical dependence. The mechanistic basis for accumulation of nordiazepam (ND) and its metabolite, oxazepam (OX), have been examined in crossover studies in drug-naive and in ND-dependent dogs that exhibited a flumazenil-precipitated abstinence syndrome. ND and parent OX have similar pharmacokinetic profiles. Steady-state plasma levels of ND and OX cannot be predicted from single-dose pharmacokinetics. Reduced plasma clearance of ND and altered plasma protein binding were observed in dogs physically dependent upon ND. The benzodiazepine antagonist, flumazenil, significantly reduces steady-state plasma levels of total and free ND.

Clinical pharmacokinetics of anxiolytics and hypnotics in the elderly. Therapeutic considerations (Part II)

Part I of this article, which appeared in the previous issue of the Journal, discussed the scope of and scientific basis for special pharmacokinetic studies of anxiolytic and hypnotic drugs in the elderly, and examined the methodology and results of such studies and the prediction of pharmacokinetic changes. In Part II the authors continue their review, focusing on age-related pharmacodynamic changes in the effects of these drugs, the attempts to correlate pharmacokinetic with pharmacodynamic findings, and the clinical applications of these data.

Benzodiazepine poisoning. Clinical and pharmacological considerations and treatment

Benzodiazepines are among the most frequently prescribed drugs worldwide. This popularity is based not only on their efficacy but also on their remarkable safety. Pure benzodiazepine overdoses usually induce a mild to moderate central nervous system depression; deep coma requiring assisted ventilation is rare, and should prompt a search for other toxic substances. The severity of the CNS depression is influenced by the dose, the age of the patient and his or her clinical status prior to the ingestion, and the coingestion of other CNS depressants. In severe overdoses, benzodiazepines can occasionally induce cardiovascular and pulmonary toxicity, but deaths resulting from pure benzodiazepine overdoses are rare. Quantitative determinations of benzodiazepines are not useful in the clinical management of intoxicated patients since there is no correlation between serum concentrations and pharmacological and toxicological effects. Benzodiazepine overdoses occurring during pregnancy rarely induce serious morbidity in mothers or fetuses, although large doses administered near delivery can induce respiratory depression in neonates. The teratogenic potential of benzodiazepines remains controversial, but is probably small if it exists at all. There is clear evidence that the prolonged use of even therapeutic doses of benzodiazepines will lead to dependence. The risk of developing significant withdrawal symptoms is related to dosage and duration of treatment. Prevention of gastrointestinal absorption should be initiated in all intentional benzodiazepine overdoses. Forced diuresis and dialysis techniques are not indicated since they will not significantly accelerate the elimination of these agents. Intravenous administration of flumazenil, a pure benzodiazepine antagonist, effectively reverses benzodiazepine-induced CNS depression.

Hepatic drug metabolism and aging

Although there is considerable variation in the effect of age on drug biotransformation, the metabolism of many drugs is impaired in the elderly. Age-related physiological changes, such as a reduction in liver mass, hepatic metabolising enzyme activity, liver blood flow and alterations in plasma drug binding may account for the decreased elimination of some metabolised drugs in the elderly. It is difficult, however, to separate an effect of aging from a background of marked variation in the rate of metabolism due to factors such as individual metabolic phenotype, environmental influences, concomitant disease states and drug intake. The prevailing data suggest that initial doses of metabolised drugs should be reduced in older patients and then modified according to the clinical response. In most studies the elderly appear as responsive as young individuals to the effects of compounds which induce or inhibit the activity of cytochrome P450 isozymes. Concurrent use of other agents, which induce or inhibit drug metabolism, mandates dose adjustment as in younger patients. Many questions remain unanswered. For instance, limitations of in vitro studies prevent any firm conclusion about changes in hepatic drug metabolising enzyme activity in the elderly. With aging, some pathways of drug metabolism may be selectively affected, but this has not been adequately scrutinised. The possibility that metabolism of stereoisomers may be altered in the elderly has not been adequately tested. The effect of aging on the distribution of polymorphic drug metabolism phenotypes is still not established, despite potential implications for disease susceptibility and survival advantage.

Pharmacokinetics of buspirone in elderly subjects

Twenty-four men and 24 women ages 20-77 years received a single 15 mg oral dose of buspirone followed by 4 days of 15 mg tid administration. Plasma concentrations of buspirone and 1-pyrimidinylpiperazine following both single and multiple dosing were determined by RIA and GCMS, respectively. There were no significant differences between the young and elderly of either gender with regard to buspirone AUC, Cmax, Tmax and half-life values. The 1-PP AUC values were higher for young of either gender compared to the corresponding group of elderly subjects and the 1-PP Cmax values were higher for women than men. These differences are unlikely to be of clinical significance. The buspirone and 1-PP AUC values for a dosing interval during multiple dosing are not significantly different than the respective single dose AUC values. Buspirone treatment was well-tolerated by all subjects even though the 45 mg/day dose was 3 times the recommended starting dose in clinical practice. Overall, the lack of marked or consistent differences in buspirone or 1-PP pharmacokinetics in elderly subjects compared to younger subjects of the same gender suggest there is no need to alter the initial dose of buspirone based solely on patient age.

Effects of age, gender and oral contraceptives on intramuscular midazolam pharmacokinetics

The effects of age, gender and low-dose (50 mcg or less) oral contraceptive steroids (OCS) on the pharmacokinetics of midazolam were evaluated following a single 7.5 mg intramuscular dose to five groups (8/group) of healthy volunteers consisting of young males, young females, elderly males, elderly females, and young female users of oral contraceptives. Blood samples were collected at specified times over a 24-hour period, and plasma concentrations of midazolam and its 1-hydroxymethyl metabolite were determined by a GC-EC assay. Midazolam was rapidly absorbed following intramuscular administration to the different groups. Comparison of young men vs elderly men, young women vs elderly women, young men vs young women, elderly men vs elderly women, and young women OCS-users vs young women non-OCS users indicated no substantial differences in the pharmacokinetic profile of midazolam between groups except for the comparison between the young and elderly men groups. The rate of elimination of midazolam was significantly slower in the elderly males compared to the young men. The pharmacokinetic profile of 1-hydroxymethyl midazolam paralleled that of the parent compound. This is to be expected since this metabolite exhibits formation rate-limited kinetics. Except for one subject who reported hives and itching, considered to be remotely related to test drug, no other adverse experiences or laboratory abnormalities were reported.

Desmethyldiazepam pharmacokinetics: studies following intravenous and oral desmethyldiazepam, oral clorazepate, and intravenous diazepam

After single 10-mg intravenous (IV) doses of desmethyldiazepam (DMDZ) to 12 healthy human volunteers, (mean age, 62 years) blood samples were obtained over the next 14 or more days. Mean kinetic variables were volume of distribution (Vd), 90 liters; elimination half-life (t1/2), 93 hours; and clearance, 12.3 mL/min. Vd was significantly correlated with body weight (r = .73, P less than .01) and with percent ideal body weight (r = .91, P less than .001). Eleven of the same subjects also received 5- to 15-mg doses of IV diazepam (DZ). Mean kinetic variables were Vd, 180 liters; t1/2, 83 hours; and clearance, 28 mL/min. Clearances of DZ and DMDZ were significantly correlated (r = .73, P less than .02). Based on area analysis, the extent of conversion of DZ to systemic DMDZ averaged 53%. After oral administration of DMDZ in tablet form (10 mg), or of clorazepate dipotassium in capsule form (15 mg), systemic availability of DMDZ from each of the oral dosage forms was not significantly different from 100%.

Changes in some hepatic enzyme activities related to phase II drug metabolism in male and female rats as a function of age

Changes in activity of some hepatic enzymes related to UDP-glucuronic acid conjugation (UDP-glucose dehydrogenase and UDP-glucuronyl transferase) and glutathione-related enzymes (glutathione reductase and glutathione peroxidase) were investigated in male and female Wistar rats as a function of age. UDP-glucose dehydrogenase activity showed a decrease in the ageing period in both sexes (26.4% and 37.7% in males and females respectively), and no sex differences were found in all the ages studied. The UDP-glucuronyl transferase (using p-nitrophenol as substrate) showed an age-dependent decrease in its activity for males, but an increase for female rats. A sex difference (male values were higher than female values) was observed only in young rats (1 and 3 months old). Glutathione peroxidase activity increased with age in both sexes (the activity found in male and female old rats was about 162% and 149% respectively to those found in adulthood), and a marked difference was observed between sexes in young and old rats (57.8% and 45.4% higher in females in young and old rats respectively). In contrast, the glutathione reductase activity showed a decrease in the ageing (39% in male and 35.5% in female) and the highest levels during lifetime was found in males.

Elimination of and heart rate response to atropine in the elderly are independent of sex

Sex-related changes in the pharmacokinetics and pharmacodynamics (heart rate) of atropine were studied in female (n = 9) and male (n = 9) elderly patients after a single 0.02 mg/kg i.v. injection of the drug at the beginning of a combination anaesthesia. No significant differences were found between the sexes, which indicates that there are no sex-related alterations in the response to this anticholinergic agent.

Benzodiazepine hypnotics in the elderly

A review is presented of the changes that occur in the pharmacodynamics of benzodiazepines during normal ageing and as a result of disease. Controlled studies in which subjects of different ages have received single doses of diazepam, temazepam, nitrazepam and flunitrazepam have consistently shown an increase in the response to benzodiazepines in the elderly which is not explained by the effects of disease or by altered plasma concentrations. In general, healthy elderly subjects have a 2-3 fold greater response compared with the young. This change appears to be due to a change in the post-receptor mechanism of action. Cerebral diazepam concentrations are similar in young and elderly rats, though older animals also show an increased response and no consistent changes have been demonstrated in brain receptor binding. However, benzodiazepine-induced increases in GABA binding and GABA-induced increases in post-synaptic inhibition have been reported to be greater in aged animals. Regular daily dosing with most benzodiazepines leads to drug accumulation which is proportional to the elimination half-life. Regular dosing with diazepam, chlordiazepoxide, nitrazepam and flurazepam has also been found to produce more sedation in the elderly, particularly long stay patients who have a high incidence of dementia, and those with a low albumen or chronic renal failure. A controlled trial of 1 week's dosing with 5 mg of nitrazepam or 20 mg of temazepam in elderly in-patients showed that these doses produced significant impairment of psychomotor performance the morning after the last dose. Only about 50% of the patients were affected and many of these were frail patients with mild dementia on rehabilitation or long stay wards. The doses prescribed for these types of patients should not exceed 2.5 mg of nitrazepam or 10 mg temazepam.

Influence of propranolol coadministration or cigarette smoking on the kinetics of desmethyldiazepam following intravenous clorazepate

The influence of propranolol coadministration or of cigarette smoking on the kinetics of desmethyldiazepam following a single 20-mg intravenous dose of clorazepate dipotassium was evaluated in healthy volunteers. In Study One, intravenous clorazepate was given once in the control condition, and again during coadministration of propranolol, 80 mg twice daily. Compliance with the prescribed propranolol regimen was verified by measurement of serum propranolol concentrations (mean, 37 ng/ml). In control vs propranolol treatment conditions, there was no significant difference in desmethyldiazepam volume of distribution (1.27 vs 1.23 liters/kg) or in free fraction in serum (1.83 vs 1.80% unbound). There was a small although statistically significant prolongation of desmethyldiazepam half-life (55 vs 61 h, P less than 0.05) and reduction in clearance (0.281 vs 0.247 ml/min/kg, P less than 0.02) attributable to propranolol. In Study Two, desmethyldiazepam kinetics were compared in eight cigarette smokers (mean, 19 cigarettes/day) and in 11 nonsmoking controls matched for age, sex, and body weight. There was no significant difference between controls and cigarette smokers in desmethyldiazepam volume of distribution (1.29 vs 1.34 liters/kg), elimination half-life (55 vs 59 h), clearance (0.284 vs 0.276 ml/min/kg), or free fraction in serum (1.96 vs 1.92% unbound). Thus, propranolol slightly although significantly impairs the clearance of desmethyldiazepam and prolongs its half-life. Cigarette smoking has no apparent influence on desmethyldiazepam kinetics.

Pharmacogeriatrics

The elderly comprise one of the fastest growing populations in the United States. By the year 2020, an estimated 45 million will be classified as elderly. Aging is a highly variable process as declines occur in physiologic functions. Alterations in cardiovascular, renal and hepatic function have the greatest effect on drug therapy. All pharmacokinetic and pharmacodynamic variables may be altered by age. Adverse drug reactions, drug interactions and poor compliance are frequent and may further complicate drug therapy. A review of those processes that commonly influence pharmacologic response and patient compliance to drug therapy is appropriate.

Single dose pharmacokinetics and pharmacodynamics of oral loprazolam in the elderly

The pharmacokinetics of the benzodiazepine hypnotic, loprazolam (1.0 mg orally), and the pharmacodynamic response to single oral doses (0.5 mg and 1.0 mg) have been compared in young and elderly healthy volunteers. No difference between the groups in peak plasma concentration (Cmax) or in the time to peak (tmax) was found, but the elimination half-life t1/2,z and area under the plasma concentration-time curve (AUC) were significantly greater in the elderly group. The immediate effects of loprazolam on all three performance tests used (postural sway, critical flicker fusion threshold (CFFT) and choice reaction time (CRT] and on subjective sedation tended to be more pronounced in the elderly subjects, though intersubject variability in response was high in both groups. The corresponding plasma concentrations did not differ significantly between the two groups. The higher (1.0 mg) dosage was associated with significant residual (11 h) impairment of standing steadiness in the elderly subjects. No other hangover effects were observed. The results are compatible with previous evidence of increased 'sensitivity' to benzodiazepines in the elderly and suggest that a lower (0.5 mg) starting dose of loprazolam would be appropriate for older recipients. Further investigation would be necessary to establish whether clinically relevant accumulation of loprazolam occurs in the elderly following repeated dosage.

Responsiveness to oral diazepam in the elderly: relationship to total and free plasma concentrations

The immediate and residual response to single doses of oral diazepam 10 mg was measured in 11 young and 12 elderly healthy volunteers using postural sway, digit symbol substitution scores and subjective ratings. The effect on postural sway was markedly accentuated in the older volunteers, but the difference between groups in the effect on the other measures used did not achieve significance. The corresponding plasma total diazepam concentrations were lower in the older subjects beyond 0.5 h post dose and the concentrations of plasma desmethyldiazepam did not differ between the groups. Diazepam plasma protein binding was significantly reduced in the elderly subjects, but the plasma free (unbound) diazepam concentrations did not exceed those in the young group. There was poor correlation between the responses measured and the concentrations of either total diazepam, desmethyldiazepam or free diazepam. The results suggest the occurrence of a non-uniform effect of age on different aspects of benzodiazepine response, and that where an accentuated effect occurs the mechanisms are substantially pharmacodynamic.

Effect of clorazepate in spasticity and rigidity: a quantitative study of reflexes and plasma concentrations

The effect on increased myotatic reflexes of desmethyldiazepam, formed from its precursor clorazepate, was assessed in a double-blind cross-over study of 27 days duration. Eight patients with spasticity or rigidity were given placebo or active substance; first in loading doses for 2 days, then 5 mg every 12 h for a total of 10 days. A wash-out period of 7 days was interposed between the 2 10-day periods. Desmethyldiazepam had a normalizing effect on the increased phasic ankle reflexes seen in spasticity, but not on the increased tonic reflex seen in rigidity. The mean concentration of desmethyldiazepam in the steady state was 1227 nmol/l (range 600-1990 nmol/l). The plasma concentration of desmethyldiazepam tended to correlate with the percent decrease in phasic reflex activity (P = 0.08, 2-tailed). A slight drowsiness in 2 patients was the only side-effect seen. In conclusion, desmethyldiazepam given as clorazepate seems to be a suitable medicament in the treatment of spasticity.

Comparative single-dose kinetics of oxazolam, prazepam, and clorazepate: three precursors of desmethyldiazepam

Twelve healthy volunteers received a single 40-mg oral dose of the benzodiazepine derivative oxazolam, which serves primarily as a precursor of the active substance desmethyldiazepam (DMDZ). Concentrations of DMDZ were measured in multiple serum samples drawn for up to two weeks after the dose. Peak serum DMDZ concentrations averaged 115 ng/ml, measured at 8.6 hours after dosage. Mean DMDZ elimination half-life averaged 61 hours. Three of the subjects also received 40 mg each of prazepam and clorazepate, two other DMDZ precursors, on separate occasions. Although DMDZ elimination half-life was similar, total area under the curve (AUC) for DMDZ was larger for clorazepate, known to be completely transformed into DMDZ, than for oxazolam or prazepam the extent of whose conversion to DMDZ has not been previously established. After correcting for the different molar equivalent of DMDZ available from each preparation, the DMDZ ratio averaged 0.22 for oxazolam vs. clorazepate and 0.51 for prazepam vs. clorazepate. Thus, both oxazolam and prazepam lead to slow appearance of DMDZ in the systemic circulation. Furthermore the extent of DMDZ formation from oxazolam and prazepam is either incomplete or the drugs are incompletely absorbed. Equivalent doses of oxazolam, prazepam, and clorazepate should not be interchanged in clinical practice.

Clinical importance of the interaction of diazepam and cimetidine

Cimetidine is known to impair the hepatic microsomal oxidation of diazepam, reducing its clearance and prolonging its half-life. We studied the clinical importance of this effect in 10 patients, who were receiving long-term treatment with diazepam for anxiety, tension, or difficulty in sleeping, in an eight-week double-blind controlled study during which the diazepam dosage remained constant. The study was in four two-week phases: base-line or adaptation, coadministration of cimetidine (300 mg) or matching placebo four times daily, crossover to the opposite treatment (placebo or cimetidine), and recovery treatment with diazepam alone. During the cimetidine phase, plasma concentrations of diazepam plus desmethyldiazepam rose an average of 57 per cent (P less than 0.005), then fell when cimetidine was withdrawn. However, there were no significant changes in scores on the digit-symbol-substitution test, a tracking task, or a reaction-time test. Clinical self-ratings indicated no increases in sedation, fatigue, or drowsiness. Patients experienced shortening of sleep latency (P less than 0.05) and an increase in self-rated depth or soundness of sleep (P less than 0.001) during the cimetidine period, but there were no changes in sleep duration or in the number of nocturnal awakenings. Although coadministration of cimetidine to diazepam-treated patients causes a large increase in plasma diazepam and desmethyldiazepam concentrations, the increase is of minimal clinical importance.

Long-acting and short-acting benzodiazepines in the elderly: kinetic differences and clinical relevance

A review of available information about the pharmacokinetics of pro-nor-diazepam-like compounds in the elderly shows substantial impairment of the metabolism compared to oxazepam-like benzodiazepines, which are metabolized with virtually no change in this age group. Results of clinical trials point in the same direction, although small numbers of patients, different criteria for measuring clinical benefit and adverse reactions and different dosages for various periods of time make the comparison difficult. Qualified clinical guidelines are mainly to reduce dosage and use oxazepam-like compounds in the elderly, but routine clinical practice does not seem to apply these recommendations. Further research is therefore needed, mainly in the area of clinical practice, to describe the 'real' situation of benzodiazepine prescription for in-patients and out-patients in terms of risk-benefit ratio of drug treatment and to monitor the changes occurring when a more rational approach is introduced as regards the need for treatment, dose and duration of treatment.

Disposition of clotiazepam: influence of age, sex, oral contraceptives, cimetidine, isoniazid and ethanol

Factors influencing the disposition of clotiazepam in man were evaluated in a series of pharmacokinetic studies in healthy volunteers given a single 5 mg dose. Old age caused an increased volume of distribution of clotiazepam in women, and its clearance tended to be reduced in elderly men. Use of oral contraceptives, cimetidine, isoniazid or a single dose of ethanol had no significant effect on the kinetics of clotiazepam. Although clotiazepam is biotransformed by microsomal oxidation, its clearance appears to be relatively uninfluenced by factors known to alter the clearance of other oxidized benzodiazepines.

Antipyretic analgesic drugs as models for studies of drug disposition in old age

Alterations in drug metabolizing capacity associated with the aging process can be elucidated using analgesic-antipyretic agents as model compounds. Antipyrine serves to profile drug oxidizing capacity. Drug oxidation is significantly impaired in old age, but age-related changes are far greater in men than in women. Acetaminophen analogously serves to profile conjugating capacity, which is minimally influenced by age both in men and in women. Changes in the capacity to biotransform these model compounds are reasonably well predictive of parallel changes in the same person's ability to metabolize other drugs transformed by the same pathway.

[Benzodiazepines: significance of kinetics for therapy]

The onset and duration of action of benzodiazepines after single oral doses depend largely on absorption rate and the rate and extent of distribution. The rate and extent of accumulation during multiple dosage depend on elimination half-life and clearance. A framework is proposed for classification of benzodiazepines according to elimination half-life. Long acting benzodiazepines have half-life values usually exceeding 24 h. Drugs in this category have long-acting pharmacologically active metabolites, often desmethyldiazepam, accumulate extensively during multiple dosage, and may have impaired clearance in the elderly and those with liver disease. Intermediate and short-acting benzodiazepines have half-life values from 5-24 h and active metabolites are uncommon. Accumulation during multiple dosage is less extensive than with the long-acting group and diminishes as the half-life becomes shorter. Age and liver disease have a small influence on metabolic clearance. The half-life of ultrashort-acting benzodiazepines is less than 5 h. These drugs are essentially nonaccumulating. Pharmacokinetic classification may assist in understanding differences among benzodiazepines, but does not explain all of their clinical actions.

Reduced clearance of triazolam in old age: relation to antipyrine oxidizing capacity

Thirty-three healthy male and female volunteers aged 21 to 87 years received a single 0.5 mg oral dose of triazolam. Plasma triazolam concentrations were measured in multiple samples drawn during 24 h after the dose. Mean triazolam elimination half-life was not significantly different between young and elderly men (3.0 vs 4.6 h), nor between young and elderly women (2.7 vs 3.2 h). However, apparent oral clearance of triazolam was significantly reduced in elderly as compared to young groups of both sexes, leading to higher peak plasma concentrations and increased total area under the curve. Values of half-life and clearance of antipyrine, a low-extraction hepatically oxidized compound, were poorly correlated with those of triazolam (r = 0.34 and 0.44, respectively), suggesting different mechanisms controlling age-related changes in clearance of these two hepatically oxidized drugs.

Close correlation of acetaminophen clearance with that of conjugated benzodiazepines but not oxidized benzodiazepines

The clearance of the antipyretic-analgesic drug acetaminophen, biotransformed in humans by glucuronide and sulfate conjugation, was evaluated in 32 healthy young and elderly volunteers. Subjects received a single 650-mg dose of acetaminophen, and multiple plasma concentrations measured over the next 12 h. Random subgroups of subjects also participated in studies of the oxidized benzodiazepines diazepam, desmethyldiazepam and alprazolam, and of the conjugated benzodiazepines lorazepam, oxazepam and temazepam. Acetaminophen clearance was not related to that of the oxidized benzodiazepines, but was highly correlated with clearance of lorazepam (r = 0.70, n = 11, p less than 0.02), oxazepam (r = 0.76, n = 14, p less than 0.005) and temazepam (r = 0.63, n = 16, p less than 0.01). Thus acetaminophen may serve as a probe or marker compound to evaluate drug conjugating capacity in humans.

Halazepam as a precursor of desmethyldiazepam: quantitation by electron-capture gas-liquid chromatography

Halazepam and its major metabolite desmethyldiazepam (DMDZ) can be reliably quantitated in human plasma following single doses of halazepam. After addition of appropriate internal standards, halazepam and DMDZ are extracted directly into an organic solvent at physiological pH. The organic extract is separated, evaporated to dryness, reconstituted, and directly chromatographed using a 50:50 methyl:phenyl silicone column (SP-2250) and an electron-capture detector. After a single 40 mg oral dose of halazepam, the parent compound appears in plasma only transiently and at low levels. DMDZ appears in higher concentrations and is slowly eliminated. During multiple-dose therapy with halazepam, DMDZ will be the major active substance in blood.

Reduced single-dose clearance of clobazam in elderly men predicts increased multiple-dose accumulation

The rate and extent of accumulation of clobazam and its major metabolite, desmethylclobazam, during multiple dosage with clobazam were evaluated in 4 similarly sized groups of young male, young female, elderly male, and elderly female volunteers. Subjects received single 10mg doses of clobazam daily for 22 consecutive days. Plasma levels were measured during and after the period of dosage. Compared with the young male subjects, elderly males had slower rates of clobazam accumulation and washout, higher steady-state plasma levels, and lower steady-state clearance. Accumulation of desmethylclobazam also was slower and more extensive in the elderly male group. Among females, however, age-related kinetic differences did not approach significance. Among all subjects, pharmacokinetic variables for clobazam determined in a previous single-dose study were highly consistent with the multiple-dose pharmacokinetic profile. Single-dose vs post-multiple dosage half-life, single-dose vs steady-state clearance, observed vs predicted accumulation ratios, and observed vs predicted steady-state plasma concentrations were all highly correlated, with regression line slopes close to unity. Thus, reduced single-dose clearance of clobazam in elderly men leads to slower and more extensive accumulation during multiple dosage. The single-dose pharmacokinetic profile of clobazam is highly predictive of drug behaviour during repeated dosage, suggesting that clobazam kinetics are dose- and concentration-independent within the range studied, and that self-induction or inhibition of clearance is not evident during 3 weeks of dosage.

Cimetidine impairs clearance of antipyrine and desmethyldiazepam in the elderly

Sixteen young (21-40 years) and nine elderly (65-78 years) volunteers received single intravenous doses of antipyrine on two occasions: once in the control state, and again while receiving therapeutic doses of cimetidine (300 mg every six hours). In the control state, antipyrine half-life was longer in elderly than in young subjects (16.4 vs 11.0 hours), and metabolic clearance lower (0.48 vs 0.72 ml/min/kg). However, coadministration of cimetidine prolonged antipyrine half-life to a similar extent in elderly and in young groups (150 and 153 per cent of control) and reduced metabolic clearance to a similar extent in both (79 vs 69 per cent of control) groups. Three young and six elderly volunteers received a single 15 mg oral dose of clorazepate, a precursor of desmethyldiazepam, with and without cimetidine. As in the case of antipyrine, cimetidine prolonged desmethyldiazepam half-life similarly in young and elderly groups (175 vs 164 per cent of control) and similarly reduced metabolic clearance (51 vs 65 per cent of control). The elderly population may already have an impaired capacity to oxidize drugs. This capacity is further impaired by coadministration of cimetidine.

Desmethyldiazepam kinetics after intravenous, intramuscular, and oral administration of clorazepate dipotassium

The pharmacokinetics and bioavailability of desmethyldiazepam (DMDZ), formed from its precursor clorazepate (CZP) dipotassium, were assessed in a series of 17 healthy volunteers aged 21--66 years. After a single 20-mg intravenous dose of CZP, mean kinetic variables for DMDZ were: volume of distribution, 1.24 l/kg; elimination half-life, 65 h; total clearance, 0.24 ml/min/kg. Among males, DMDZ half-life tended to be prolonged and clearance reduced with age, but this was not true for females. After oral administration of 20 mg CZP, appearance of DMDZ in the circulation was rapid; the mean peak plasma level was 356 ng/ml, reached an average of 0.9 h after dosage. Based on comparison with IV dosage, systemic availability of DMDZ was complete (100% absorption). Ten of the subjects also received a single 20-mg intramuscular dose of CZP. Mean peak DMDZ levels were 290 ng/ml, reaching an average of 2.7 h after dosage. Systemic availability of DMDZ was complete. Elimination half-life of DMDZ for a given individual was highly replicable from trial to trial regardless of the route of CZP administration.

Clobazam kinetics in the elderly

1 The effects of age and sex on the disposition of clobazam (CBZ), a 1.5-benzodiazepine derivative, were evaluated in a series of 29 healthy volunteers aged 18 to 72 years, who ingested single 20 mg oral doses. CBZ kinetics were determined from multiple plasma concentrations measured during 7 days after the dose. 2 CBZ was rapidly absorbed, with peak levels reached an average of 1.5 h after dosing (range 0.5--2.5 h). Mean absorption half-life was 19.7 min. Absorption kinetics were not influenced by age of sex. 3 Elimination half-life ranged from 11 to 77 h, and was significantly longer in elderly v young males (48 v 17 h, P less than 0.01). In women, half-life also increased with age, but differences between young and elderly women were less striking (31 v 49 h, P less than 0.05). 4 Volume of distribution (Vd) was influenced by age and sex. Vd became larger with age regardless of sex, and within each age group was larger in women than in men. Total clearance was unrelated to age in women, but declined significantly with age in men (P less than 0.01). 5 The mean free fraction for CBZ in plasma was 11.5% (range 8.6--15.0%), and tended to increase with age, partly due to a significant age-related decline in plasma albumin concentration (r = -0.68, P less than 0.001). Correction of Vd and clearance for individual differences in binding did not alter their relation to age and sex. 6 As in the case of other benzodiazepines biotransformed by oxidative pathways, the capacity for N-demethylation of CBZ declines with age in men, but age has a minimal effect on CBZ clearance in women.