Lack of influence of cigarette smoking on triazolam pharmacokinetics

Conversion factors for assessment of driving impairment after exposure to multiple benzodiazepines/z-hypnotics or opioids

AIMS

Norway has introduced legal concentration limits in blood for 28 non-alcohol drugs in driving under the influence cases. As of 2016 this legislation also regulates the assessment of combined effects of multiple benzodiazepines and opioids. We herein describe the employed methodology for the equivalence tables for concentrations of benzodiazepines/z-hypnotics and opioids implemented in the Norwegian Road Traffic Act.

METHODS

Legislative limits corresponding to impairment at blood alcohol concentrations (BAC) of 0.02%, 0.05% and 0.12% were established for 15 different benzodiazepines and opioids. This was based on a concept of a linear relationship between blood drug concentration and impairment in drug naïve users. Concentration ratios between these drugs were used to establish conversion factors and calculate net impairment using diazepam and morphine equivalents.

RESULTS

Conversion factors were established for 14 benzodiazepines/z-hypnotics (alprazolam, bromazepam, clobazam, clonazepam, etizolam, flunitrazepam, lorazepam, nitrazepam, nordiazepam, oxazepam, phenazepam, temazepam, zolpidem and zopiclone) and two opioids (methadone and oxycodone).

CONCLUSIONS

Conversion factors to calculate diazepam and morphine equivalents for benzodiazepines/z-hypnotics and selected opioids, respectively, have been operative in the Norwegian Road Traffic Act as of February 2016. Calculated equivalents can be applied by the courts to meter out sanctions.

Human variability in CYP3A4 metabolism and CYP3A4-related uncertainty factors for risk assessment

CYP3A4 constitutes the major liver cytochrome P450 isoenzyme and is responsible for the oxidation of more than 50% of all known drugs. Human variability in kinetics for this pathway has been quantified using a database of 15 compounds metabolised extensively (>60%) by this CYP isoform in order to develop CYP3A4-related uncertainty factors for the risk assessment of environmental contaminants handled via this route. Data were analysed from published pharmacokinetic studies (after oral and intravenous dosing) in healthy adults and other subgroups using parameters relating primarily to chronic exposure [metabolic and total clearances, area under the plasma concentration-time curve (AUC)] and acute exposure (Cmax). Interindividual variability in kinetics was greater for the oral route (46%, 12 compounds) than for the intravenous route (32%, 14 compounds). The physiological and molecular basis for the difference between these two routes of exposure is discussed. In relation to the uncertainty factors used for risk assessment, the default kinetic factor of 3.16 would be adequate for adults, whereas a CYP3A4-related factor of 12 would be required to cover up to 99% of neonates, which have lower CYP3A4 activity.

Biologic and molecular mechanisms for sex differences in pharmacokinetics, pharmacodynamics, and pharmacogenetics: Part I

There are pharmacological differences between women and men that have important clinical consequences. For several drugs, there is a higher incidence in women of drug-induced QT prolongation and a potentially fatal arrhythmia, torsades de pointes. This may be a reflection of the longer baseline QT interval in women. A difference in cardiovascular disease between women and men is that women have a higher mortality rate after myocardial infarction (MI). Women also have a higher rate of hemorrhagic stroke after receiving thrombolytic therapy for an MI. Differences in effectiveness of analgesics have been demonstrated, with kappa opioids providing pain relief for women but not men. Drugs may have different pharmacokinetics in women and men because of differences in phase I and phase II enzymes that metabolize drugs. Conflicting results about biological sex differences have been reported for the major drug metabolizing enzyme, cytochrome P450 3A4 (3A4) and may be related to a role for P-glycoprotein, a cell membrane transporter, reported as two times higher in male livers than those of females. It has been reported that boys need a higher dose of 6-mercaptopurine, which is metabolized by thiopurine methyltransferase (TPMT). TPMT is reported to be 14% higher in male human liver biopsies than those from females. Verapamil, a drug for angina and hypertension, has different clearance and side effects in men and women. Ethnic/racial variations have also been demonstrated with the drug metabolizing enzymes, CYP2C9, 2C19, and 2D6.

Biologic and molecular mechanisms for sex differences in pharmacokinetics, pharmacodynamics, and pharmacogenetics: Part II

There are specific pharmacology issues related to women's unique physiology, including the hormonal changes that occur throughout their life span. Studies have shown alterations in drug metabolism in relation to phase of menstrual cycle, during pregnancy, or after menopause. In the brain, hormones can alter the response to drugs through various mechanisms. Estrogen and other compounds can bind to the estrogen receptor and modulate a wide range of activities within the cell. In addition, animal studies have demonstrated sexual dimorphism in the brain in terms of both the type of response to estrogen and the response as related to timing of administration. Many normal physiological changes that occur during pregnancy can affect pharmacokinetics and pharmacodynamics. These changes during pregnancy are dramatic rises in levels of estrogen and progesterone, increases in maternal blood volume, altered protein binding resulting from a drop in albumin levels, and a rise in levels of other plasma proteins. The field of chronobiology offers a way to study these changes in biological functions. Chronopharmacology is the study of how biological rhythms, particularly 24-hour, menstrual cycle, and annual rhythms, impact the pharmacokinetics and pharmacodynamics of drugs as a function of their timing. Chronopharmacokinetics is the study of the absorption, distribution, metabolism, and elimination of medicines according to the time of day, menstrual cycle, or year. In addition to applying chronobiology to the study of drugs used in women, new technologies were addressed from computer modeling, pharmacogenetics (genetics of the response to drugs), and in vivo drug metabolism studies.

Smoking in patients receiving psychotropic medications: a pharmacokinetic perspective

Many psychiatric patients smoke, and are believed to be heavier smokers than those without psychiatric disorders. Cigarette smoking is one of the environmental factors that contributes to interindividual variations in response to an administered drug. Polycyclic aromatic hydrocarbons (PAHs) present in cigarette smoke induce hepatic aryl hydrocarbon hydroxylases, thereby increasing metabolic clearance of drugs that are substrates for these enzymes. PAHs have been shown to induce 3 hepatic cytochrome P450 (CYP) isozymes, primarily CYP1A1, 1A2 and 2E1. Drug therapy can also be affected pharmacodynamically by nicotine. The most common effect of smoking on drug disposition in humans is an increase in biotransformation rate, consistent with induction of drug-metabolising enzymes. Induction of hepatic enzymes has been shown to increase the metabolism and to decrease the plasma concentrations of imipramine, clomipramine, fluvoxamine and trazodone. The effect of smoking on the plasma concentrations of amitriptyline and nortriptyline is variable. Amfebutamone (bupropion) does not appear to be affected by cigarette smoking. Smoking is associated with increased clearance of tiotixene, fluphenazine, haloperidol and olanzapine. Plasma concentrations of chlorpromazine and clozapine are reduced by cigarette smoking. Clinically, reduced drowsiness in smokers receiving chlorpromazine, and benzodiazepines, compared with nonsmokers has been reported. Increased clearance of the benzodiazepines alprazolam, lorazepam, oxazepam, diazepam and demethyl-diazepam is found in cigarette smokers, whereas chlordiazepoxide does not appear to be affected by smoking. Carbamazepine appears to be minimally affected by cigarette smoke, perhaps because hepatic enzymes are already stimulated by its own autoinductive properties. Cigarette smoking can affect the pharmacokinetic and pharmacodynamic properties of many psychotropic drugs. Clinicians should consider smoking as an important factor in the disposition of these drugs.

Interindividual variability in inhibition and induction of cytochrome P450 enzymes

Drug interactions have always been a major concern in medicine for clinicians and patients. Inhibition and induction of cytochrome P450 (CYP) enzymes are probably the most common causes for documented drug interactions. Today, many pharmaceutical companies are predicting potential interactions of new drug candidates. Can in vivo drug interactions be predicted accurately from in vitro metabolic studies? Should the prediction be qualitative or quantitative? Although some scientists believe that quantitative prediction of drug interactions is possible, others are less optimistic and believe that quantitative prediction would be very difficult. There are many factors that contribute to our inability to quantitatively predict drug interactions. One of the major complicating factors is the large interindividual variability in response to enzyme inhibition and induction. This review examines the sources that are responsible for the interindividual variability in inhibition and induction of cytochrome P450 enzymes.

Clinically significant pharmacokinetic drug interactions with benzodiazepines

The reports of interactions between benzodiazepines (BZPs) and other drugs (e.g., antidepressants, selective serotonin reuptake inhibitors, antiulcer drugs, antiepileptic drugs, macrolide antibiotics) during their combined use are reviewed. In general, metabolism of BZPs is delayed when combined with a number of other drugs but some reports have suggested otherwise. In recent years, the cytochrome P450 (P450 or CYP) isoenzyme that catalyses the metabolism of BZPs has also been identified. BZPs are mainly catalysed by CYP3A4. When published reports are studied, it appears necessary to be exceptionally careful about interactions mainly between BZPs and selective serotonin reuptake inhibitors, cimetidine, antiepileptic drugs, macrolide antibiotics and antimycotics. More information is necessary to identify individuals at greatest risk of drug interactions and adverse events.

Drug interactions with tobacco smoking. An update

Cigarette smoking remains highly prevalent in most countries. It can affect drug therapy by both pharmacokinetic and pharmacodynamic mechanisms. Enzymes induced by tobacco smoking may also increase the risk of cancer by enhancing the metabolic activation of carcinogens. Polycyclic aromatic hydrocarbons in tobacco smoke are believed to be responsible for the induction of cytochrome P450 (CYP) 1A1, CYP1A2 and possibly CYP2E1, CYP1A1 is primarily an extrahepatic enzyme found in lung and placenta. There are genetic polymorphisms in the inducibility of CYP1A1, with some evidence that high inducibility is more common in patients with lung cancer. CYP1A2 is a hepatic enzyme responsible for the metabolism of a number of drugs and activation of some procarcinogens. Caffeine demethylation, using blood clearance or urine metabolite data, has been used as an in vivo marker of CYP1A2 activity, clearly demonstrating an effect of cigarette smoking, CYP2E1 metabolises a number of drugs as well as activating some carcinogens. Our laboratory has found in an intraindividual study that cigarette smoking significantly enhances CYP2E1 activity as measured by the clearance of chlorzoxazone. In animal studies, nicotine induces the activity of several enzymes, including CYP2E1, CYP2A1/2A2 and CYP2B1/2B2, in the brain, but whether this effect is clinically significant is unknown. Similarly, although inhibitory effects of the smoke constituents carbon monoxide and cadmium on CYP enzymes have been observed in vitro and in animal studies, the relevance of this inhibition to humans has not yet been established. The mechanism involved in most interactions between cigarette smoking and drugs involves the induction of metabolism. Drugs for which induced metabolism because of cigarette smoking may have clinical consequence include theophylline, caffeine, tacrine, imipramine, haloperidol, pentazocine, propranolol, flecainide and estradiol. Cigarette smoking results in faster clearance of heparin, possibly related to smoking-related activation of thrombosis with enhanced heparin binding to antithrombin III. Cutaneous vasoconstriction by nicotine may slow the rate of insulin absorption after subcutaneous administration. Pharmacodynamic interactions have also been described. Cigarette smoking is associated with a lesser magnitude of blood pressure and heart rate lowering during treatment with beta-blockers, less sedation from benzodiazepines and less analgesia from some opioids, most likely reflecting the effects of the stimulant actions of nicotine. The impact of cigarette smoking needs to be considered in planning and assessing responses to drug therapy. Cigarette smoking should be specifically studied in clinical trials of new drugs.

Clinical pharmacokinetic considerations in the elderly. An update

There are a number of areas in which advances have been made over the last few years in the area of pharmacokinetics in the elderly. There is increasing understanding of the diversity of cytochrome P450s (CYP) and the variability of the age-related decline in CYP activity. This has helped to explain some of the interindividual variability in drug metabolism with age. The importance of ethnic differences has emerged, but specific work is needed in this area in the elderly. Differences in the handling of chiral compounds has been reported but as yet no clinically important findings that may lead to a change in clinical practice have emerged. The emerging importance of extrahepatic drug metabolism, especially in the intestine, has added a new complexity to our understanding of pharmacokinetics. The issue of frailty is also discussed in this article. Whether it will be of value at the bedside has yet to emerge. Nonetheless, as a concept, recent data has supported its potential use to define those more at risk of clinically meaningful pharmacokinetic alterations. Other advances have included the appreciation that selectivity in induction and inhibition in the elderly are due to the existence of multiple CYP forms. Similarly, the role of these various enzymes in disease is also improving our clinical understanding, as exemplified in Parkinson's disease.

Single-dose pharmacokinetics and pharmacodynamics of oral triazolam in relation to cytochrome P4502C19 (CYP2C19) activity

Previous studies have suggested that triazolam is at least partly metabolized by cytochrome P4503A4 (CYP3A4). However, no study has examined the relationship between the metabolism of triazolam and CYP2C19, which is involved in the metabolism of diazepam. Therefore, the single-dose pharmacokinetics and pharmacodynamics of oral triazolam were studied in relation to the CYP2C19 status assessed by the S-mephenytoin 4-hydroxylation capacity in 12 healthy male volunteers, consisting of seven extensive metabolizers (EMs) and five poor metabolizers (PMs) of S-mephenytoin 4-hydroxylation. Each subject was administered a single oral dose of 0.5 mg of triazolam, and blood was sampled up to 12 hours after the dosing. Psychomotor function was assessed by the Digit-Symbol Substitution test, Visual Analogue Scale, and Udvalg for Kliniske Undersøgelser (UKU) scale. Plasma triazolam concentrations were measured by high-performance liquid chromatography. There were no significant differences in plasma concentrations from 20 minutes to 6 hours after the dosing nor in pharmacokinetic parameters of triazolam between the EM and PM groups. No significant difference was found in psychomotor function between the EM and PM groups. These results suggest that CYP2C19 is not involved in the metabolism of triazolam and that CYP2C19 status is not a pharmacodynamic determinant of this triazolobenzodiazepine.

Metabolism of quinine in man: identification of a major metabolite, and effects of smoking and rifampicin pretreatment

Our previous studies have shown that cigarette smoking and rifampicin pretreatment enhance the elimination of quinine, metabolism assumed, by analogy with quinidine, to be carried out by CYP3A (P450IIIA). This finding is unexpected since it has been shown that smoking induces the CYP1A rather than the CYP3A enzyme family, suggesting that the metabolism of quinine may be catalysed by CYP1A. Therefore, we conducted this study to identify possible quinine metabolites in human urine and to determine which metabolic pathway is induced by cigarette smoking and rifampicin pretreatment. A specific HPLC procedure was employed to identify metabolites of quinine in urine samples collected from healthy volunteers after an oral dose of 600 mg quinine sulphate. The results showed that there were at least seven possible metabolites of quinine detected in human urine. Three of these were identified as 2'-oxoquininone, quinine glucuronide and 3-hydroxyquinine. The 3-hydroxyquinine appeared to be a major metabolite of quinine in urine samples from every subject who took an oral dose of quinine. Although cigarette smoking and rifampicin pretreatment were shown to cause a marked increase in the elimination of quinine there were no significant changes in the formation of 3-hydroxyquinine as measured in the urine samples. This suggests that the effects of smoking and rifampicin are more complicated than we expected and require further investigation.

The lack of effect of smoking on the pharmacokinetics and pharmacodynamics of adinazolam and N-demethyladinazolam

The pharmacokinetics and pharmacodynamics of adinazolam and N-demethyladinazolam (NDMAD) were evaluated in twelve healthy non-smokers (NS) and twelve smokers (S, > or = 20 cigarettes/day) following a single 60 mg dose of adinazolam mesylate sustained-release tablets in an open-label, parallel-group design. Venous blood samples were collected for up to 36 h following drug administration and assayed for adinazolam and NDMAD by HPLC. Urine samples were also collected and assayed for NDMAD by HPLC. Psychomotor performance was measured using the Neurobehavioral Evaluation System. No significant differences were observed in adinazolam oral clearance (51.8 +/- 25.8 versus 48.2 +/- 14.01 h-1) or peak adinazolam plasma concentrations (Cmax) (93.3 +/- 31.8 versus 90.4 +/- 18.0 ng ml-1) between groups. NDMAD AUC (2541 +/- 457 versus 2798 +/- 447 ng h ml-1) and Cmax (173 +/- 30.3 versus 175 +/- 26.9 ng ml-1) did not differ significantly between groups. NDMAD renal clearance was significantly lower in smokers than non-smokers (8.7 +/- 0.7 versus 10.7 +/- 2.71 h-1; p < 0.05), but the clinical significance of this observation is unclear. Marginally significant differences were seen between groups in the symbol-digit substitution and digit span (forward) tasks. The results suggest that smoking has little effect on adinazolam and NDMAD pharmacokinetics or psychomotor effects but that smoking may slightly decrease renal clearance of NDMAD.

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.

Simultaneous modeling of the pharmacokinetic and pharmacodynamic properties of benzodiazepines. II. Triazolam

This study compares the time course of triazolam effects on psychomotor and cognitive skills with triazolam plasma concentrations in a combined pharmacokinetic-pharmacodynamic (sigmoid-Emax) model. Ten male subjects received a single oral dose (1 mg) of triazolam or placebo. The CNS impairment effects were measured by using computerized tracking, body sway, and digit symbol substitution tests, and triazolam plasma concentration was measured by gas chromatography. The drug-induced effect changes lagged behind the plasma drug level changes. The magnitude of the time lag was quantified by the half-time of equilibration between concentrations in the hypothetical effect compartment and the plasma triazolam levels (t 1/2 keo). Essentially the same t 1/2 keo (approximately 6 min) was found for subcritical tracking, body sway, and digit symbol substitution tests. When using the predicted drug concentrations at the effect site, the hysteresis of the plasma concentration-effect disappears, suggesting that the hysteresis is not caused by drug induced tolerance. Moreover, the model allows for estimation of the effect site concentration that causes one-half of the maximal predicted effect (EC50, approximately 5 ng/ml) which is a measure of an individual's sensitivity to triazolam. On the basis of the EC50 values of the effect measures, body sway was slightly less sensitive to triazolam than subcritical tracking and digit symbol substitution tests.

Pharmacokinetics of the newer benzodiazepines

The assay methods used to determine the concentrations of the newer benzodiazepines include electron-capture gas-liquid chromatography, high performance liquid chromatography with ultraviolet detection, gas chromatography-mass spectrometry, radioassay and radioreceptor assay. The method used frequently is the highly sensitive and specific electron-capture gas-liquid chromatography. Other methods are associated with limitations. The triazolo- and imidazolebenzodiazepines differ structurally from the 'classical' benzodiazepines such as diazepam, and offer distinct differences in pharmacological activity and in time-course of effect. Alprazolam and triazolam, both 1,4-triazolobenzodiazepines, have high affinities for the benzodiazepine receptor as do midazolam and loprazolam, which are 1,4-imidazolebenzodiazepines. Absorption is characteristically rapid, with peak alprazolam and triazolam concentrations occurring within 1 hour after oral administration. Sublingual administration results in peak alprazolam and triazolam concentrations that are higher and occur earlier than with the oral route. The volume of distribution of alprazolam and triazolam is approximately 1L. Alprazolam is 70% bound to plasma proteins and the extent of binding is independent of concentration. Similarly, triazolam is approximately 85% bound to plasma proteins, variability in binding being explained by variations in alpha 1-acid glycoprotein concentration. The 1,4-triazolo ring prevents the oxidative metabolism of the classical benzodiazepines which results in formation of active metabolites with long elimination half-lives. Alprazolam is extensively metabolised: 29 metabolites have been identified in the urine, and its major metabolite, alpha-hydroxyalprazolam, has pharmacological activity. alpha-Hydroxyalprazolam and 4-hydroxyalprazolam are detectable in plasma in amounts which account for less than 10% of the administered dose. Mean alprazolam elimination half-life in healthy adult subjects ranges from 9.5 to 12 hours; liver disease prolongs alprazolam elimination, but renal insufficiency does not. Triazolam also undergoes oxidation and subsequent glucuronidation. alpha-Hydroxytriazolam is the major metabolite, in addition to which 4-hydroxyalprazolam and alpha-4-hydroxytriazolam have been identified in plasma and urine. The elimination half-life of triazolam ranges between 1.8 and 5.9 hours, while that of the conjugated metabolites is short, approximately 3.8 hours. Accumulation of triazolam or its metabolites after multiple doses does not occur. Liver disease prolongs triazolam elimination from the body, but renal disease does not.(ABSTRACT TRUNCATED AT 400 WORDS)

Effect of gradual withdrawal on the rebound sleep disorder after discontinuation of triazolam

Sixty volunteers with insomnia participated in a randomized, double-blind, controlled clinical trial. After an initial six nights of placebo, 30 subjects (the abrupt-withdrawal group) received 0.5 mg of triazolam nightly for 7 to 10 nights, after which they received placebo. The other 30 subjects (the tapered-dosage group) received the same initial placebo treatment, then triazolam at 0.5 mg for seven nights, at 0.25 mg for two nights, and at 0.125 mg for two nights, and then placebo. As compared with the initial placebo period, the triazolam period significantly reduced the interval before the onset of sleep (sleep latency), and it prolonged sleep duration, reduced the number of awakenings, and improved the self-rated soundness of sleep in all cohorts. In the abrupt-withdrawal group, plasma levels of triazolam were undetectable the morning after the first night of placebo substitution, and subjects reported prolongation of sleep latency (57 minutes longer than base line), reduction in sleep duration (1.4 hours less than base line), and increased awakenings (1.2 per night above base line). The symptoms of rebound sleep disorder lasted one or possibly two nights, and there was a reversion toward base line on subsequent placebo nights. In the tapered-dosage group, however, plasma triazolam levels fell gradually to zero, and rebound symptoms were decreased or eliminated. Thus, rebound sleep disorder following abrupt discontinuation of triazolam can be attenuated by a regimen of tapering.