Cigarette smoking and plasma nortriptyline levels

The effect of smoking on the plasma concentration of tricyclic antidepressants: a systematic review

Smoking is highly prevalent in the psychiatric population, and hospital admittance usually results in partial or complete smoking cessation. Tobacco use is known to affect the metabolism of certain psychoactive drugs, but whether smoking influences the plasma concentration of tricyclic antidepressants (TCAs) remains unclear. This article investigates the possible effect of smoking on the plasma concentration of TCAs. A systematic review of the literature available on PubMed and EMBASE as of October 2020 was carried out using PRISMA guidelines. Studies reporting plasma concentrations of any TCA in both a smoking and a non-smoking group were included and compared. Ten eligible studies were identified and included. In the eight studies investigating the effect of smoking on amitriptyline and/or nortriptyline, five studies found no significant effect. Two studies investigating the effect of smoking on imipramine found a significant effect, and one study investigating the effect of smoking on doxepin found no significant effect. The majority of studies included in this review were influenced by small study populations and other methodical issues. The effect of smoking on the plasma concentration of TCAs is still not entirely clear. There is a possibility that smoking affects the distribution of TCA metabolites, but this is probably not of clinical importance.

Benzodiazepines: some aspects of their clinical pharmacology

Benzodiazepine derivatives are the most commonly prescribed anti-anxiety agents in clinical practice. Six benzodiazepine anxiolytics are now available in the United States. Additional drugs are used in other parts of the world, and many others are in various stages of clinical testing. All these benzodiazepine derivatives have similar neuropharmacological properties--they reduce anxiety, produce sedation and sleep, have anticonvulsant effects, and can produce muscle relaxation. Faced with this bewildering array of drugs from the same class which are very similar in intrinsic effects upon the brain, the clinician may well ask how best to make a rational choice among the available derivatives. Despite neuropharmacological similarities, there are differences among benzodiazepines in patterns of absorption, distribution, and elimination by the human body. These pharmacokinetic differences may in turn lead to apparent differences in clinical action. This review summarizes pertinent pharmacokinetic characteristics of benzodiazepine anti-anxiety agents.

Therapeutic drug monitoring of nortriptyline in smoking cessation: a multistudy analysis

Multiple, controlled clinical trials support the efficacy of nortriptyline as a smoking cessation agent. Although therapeutic plasma nortriptyline concentrations (PNCs) are known for the treatment of depression, little is known about PNCs in smoking cessation treatment. PNCs from three randomized, placebo-controlled smoking cessation trials (N=244) were analyzed both separately and pooled. PNCs normalized for dose and weight were associated with cigarettes per day and race, but not with sex or age. Greater smoking was associated with decreased normalized PNCs. In addition, both Asian and black populations had significantly higher normalized PNCs than the white populations. Weak and inconsistent associations between PNCs and self-reported side effects were observed. PNCs were linearly related to end of treatment and long-term biochemically verified smoking abstinence. Maximum therapeutic effects were observed over a range of plasma concentrations somewhat lower than those found effective for the treatment of depression.

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.

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.

Recent developments in the study of the effects of cigarette smoking on clinical pharmacokinetics and clinical pharmacodynamics

With the ever-increasing population of cigarette smokers, the potential for cigarette smoke to affect drug therapy both pharmacokinetically and pharmacodynamically is significant. The overriding pharmacokinetic effect is increased drug metabolism through the induction of liver enzymes. The constituents of tobacco smoke, primarily nicotine, have their own pharmacological effects which may potentiate or antagonise the desired pharmacological effect of a particular drug, thereby affecting its efficacy. Furthermore, end-organ responsiveness may also be altered by tobacco. These latter 2 aspects constitute altered clinical pharmacodynamics. Approximately 30 drugs have been evaluated in terms of cigarette smoking. Induction of liver enzymes has been shown to increase the metabolism of imipramine, meprobamate, oestrogens, pentazocine, phenylbutazone, theophylline and warfarin. Nicotine has been shown to inhibit diuresis, alter ulcer healing, impair subcutaneous absorption, affect protein binding and stimulate catecholamine release; these effects have been evaluated in terms of therapy with frusemide (furosemide), histamine H2-antagonists, insulin, lignocaine (lidocaine) and beta-blockers, respectively. The interactions have not been correlated with clinical significance in all cases. Diminished end-organ responsiveness may account for reduced drowsiness in smokers receiving chlorpromazine and benzodiazepines, compared with non-smokers. Smoking has been associated with diminished pain tolerance, requiring increased dosages of morphine, pethidine (meperidine) and propoxyphene. Enzyme-inducers such as carbamazepine, phenytoin and phenobarbitone appear to be minimally affected by cigarette smoke, perhaps because hepatic enzymes are already maximally stimulated. Codeine, corticosteroids and nortriptyline do not appear to be affected by cigarette smoke. The bioavailability of glutethimide is higher in smokers, but this has not been associated with greater efficacy. The effect of smoking on paracetamol (acetaminophen) has been variable, depending on the extent of smoking, and does not appear to be of clinical significance.

No effect of smoking on sulfamethazine acetylation

Seven healthy subjects who smoked at least one pack of cigarettes/d were acetylator-phenotyped with sulfamethazine (SMZ) while they were actively smoking, and again at least one month after they had completely stopped. There were no significant differences of the acetylation profiles in the smoking vs. nonsmoking state, as measured by %ASMZ in serum six hours post-SMZ dosing or by %ASMZ in urine five to six hours post-SMZ dosing. We conclude that smoking does not influence SMZ acetylation and probably does not affect drug acetylation in general.

Tobacco smoking and drugs: a clinically important interaction?

Tobacco smoking may interact with the metabolism of a number of drugs. This has been demonstrated clearly in pharmacokinetic studies in animals and man. HOwever, tobacco smoking as a variant has been studied with relatively few clinically essential drugs and these studies do not always demonstrate a consistent effect of smoking. This review therefore not only records what data have emerged from pharmacokinetic or other studies, but it also attempts to determine whether such interactions have clinical significance. The main finding of this review is that, in the majority of examples, there is little evidence that there is a recognizable hazard from the interaction per se. The exceptions to this general conclusion are limited to four drugs: insulin, propoxyphene, propranolol, and theophylline preparations. With these drugs, there is some evidence of clinical importance of an interaction with tobacco smoking.

Tricyclic plasma levels in depressed outpatients treated with amitriptyline

Seventy-four patients were treated with 150 mg/day amitriptyline (AT) to determine possible correlations between clinical improvement, demographic variables, and AT and nortriptyline (NT) plasma levels. Plasma level determinations after 2 and 6 weeks of treatment revealed that moderately significant correlations existed between AT plasma levels and clinical improvement, dosage intake, age, weight, sex, and coffee intake. Some of these findings were more pronounced after 2, and some after 6 weeks of treatment.

A double-blind study of zimelidine, a serotonin uptake inhibitor, and desipramine, a noradrenaline uptake inhibitor, in endogenous depression. I. Clinical findings

A comparative evaluation of zimelidine, a potent and selective serotonin (5-HT) uptake inhibitor, and desipramine, a potent noradrenaline (NA) uptake inhibitor, was carried out in a 4-week randomized, double-blind study in 65 hospitalized patients with endogenous depression. For evaluation of the clinical effect, Hamilton Rating Scale for depression (HRS) and a 14-item scale chosen from the Comprehensive Psychopathological Rating Scale (CPRS) were used. The concentration of drug in plasma was determined on the same days as the clinical ratings. There were no significant difference in the overall therapeutic effect between the two drugs. However, zimelidine had significantly better effect on anxiety. Although both agents were well tolerated, the zimelidine-treated patients reported significantly less severe anticholinergic side effects. Body weight did not change significantly in either treatment group. In the total material ther were no significant correlation between plasma concentrations of zimelidine, norzimelidine and desipramine and the amelioration score of either HRS and CPRS.

Monitoring and interpretation of antidepressant plasma concentrations

A brief review of the factors influencing plasma tricyclic concentrations and the relationship between clinical response and plasma concentration is presented. It is concluded that routine monitoring of tricyclics is unwarranted. In some specific instances monitoring tricyclic antidepressant plasma concentrations may be indicated: in cases of therapeutic failure a low level may indicate poor compliance or rapid metabolism and the need to increase the dose; for the management of side effects, especially when cardiac abnormalities exist prior to therapy; in cases of polypharmacy when drug interactions can occur; the management of overdoses and in patients with physical illnesses especially renal and hepatic disease. The elderly also constitute a group of patients in whom drug monitoring may be advisable. This group of patients tends to develop higher plasma levels than younger patients on equivalent doses. Some guidelines for the interpretation of laboratory results are presented and discussed.

The relationships between clinical response, psychophysiological variables and plasma levels of amitriptyline and diazepam in neurotic outpatients

In a 4 week study of the response of neurotic outpatients to treatment with amitriptyline, diazepam, amitriptyline and diazepam, or placebo clinical and psychophysiological variables and plasma levels of the drug were assessed. Clinical improvements were substantial in all treatment groups but clear relationships between clinical change, psychophysiological change and plasma levels of the drugs were not established. There was no relationship between plasma levels of the drugs and cigarette smoking. It is concluded that neither plasma levels of amitriptyline and diazepam nor change in skin conductance responsivity offer a useful guide to clinical response to drug treatment.

Inhibition of platelet uptake of serotonin in plasma from patients treated with clomipramine and amitriptyline

The inhibition of serotonin uptake by platelets has been measured in blood from 20 patients on amitriptyline (50--225 mg daily), 14 patients on clomipramine (25--200 mg daily), and in an untreated group of 21 depressed patients. A complete kinetic analysis was carried out in each patient. Using the increase in the kinetic parameter Km as a measure of uptake inhibition, there was high correlation between the daily dose and inhibition within each drug group, clomipramine being about 10 times more potent than amitriptyline. The inhibition did not vary with age, sex, duration of treatment (up to 3 years), or concomitant use of moderate doses of benzodiazepines, neuroleptics or lithium. In the amitriptyline group the inhibition was significantly smaller in smokers than in non-smokers. The kinetic parameter Vmax was essentially unchanged in the amitriptyline group, and was markedly reduced in the clomipramine group, but without any correlation with dose. The mixed competitive-noncompetitive effect of clomipramine confirms previous in vitro findings.

Influence of cigarette smoking on drug metabolism in man

The pervasiveness of tobacco use in our society and the frequency of altered disposition of many common therapeutic and recreational drugs in smokers makes it apparent that the smoking habit should be considered as one of the primary sources of drug interactions in man. Each scientific report dealing with drug disposition should list the smoking status of the subjects studied as smoking should be included as a basic characteristic of each subject along with age, race, body weight, and presence and type of disease. Most of the experimental work in human and animal systems indicates that the dominant effect of smoking is enhanced disposition caused by induction of hepatic microsomal enzymes. The primary causal agents are probably the polynuclear aromatic hydrocarbons which are potent and persistent in tissues. There are numerous examples of both an increased metabolism rate and absence of an effect of smoking on drug disposition in man. This selectivity is consistent with the known inductive effects of P-448 stimulators in animal systems. Studies with theophylline have demonstrated that both tobacco and marijuana markedly alter its clearance in man. However, smoking is only one of numerous factors which can perturb hepatic biotransformation as patient surveillance studies show that age and cardiac and liver disease may be of greater importance in actual patients undergoing therapy.