Acetylator status and response to phenelzine in depressed patients

N-acetyltransferase: the practical consequences of polymorphic activity in man

Over the years, numerous studies have supported the premise that individuals possessing the "slow acetylator" phenotype are more at risk from developing drug side-effects. Most prominent amongst these reports are those concerned with hepatotoxicity and peripheral neuropathy following treatment with isoniazid, lupus-like symptoms during procainamide therapy and experiencing hypersensitivity reactions to the various sulphonamide derivatives. Similarly, "slow acetylators" undergoing heavy exposure to arylamines and related carcinogens are more likely to develop bladder cancer. Contrariwise, there appears a slight risk of "rapid acetylators" developing pancreatic tumours.Other therapeutic agents for which polymorphic N-acetylation plays a minor role in their metabolism have been investigated but any impact of this metabolic difference on clinical efficacy or associated toxicity is still under question. In the search for clues as to the underlying aetiology, patient groups with many disease states have been examined for association with differences in N-acetylation and the majority have provided data that could be interpreted as equivocal. Studies have given contradictory, often opposing, results, calculated risk factors that are (perhaps) just significant but certainly not high, and patients within the cohorts who are always exceptions. Undoubtedly, other as yet unappreciated factors are at play.

Phenelzine in urine: assay and relation to acetylator status

Phenelzine cannot be extracted as such from biological fluids. Formation of the acetonide derivative prior to extraction allows phenelzine to be extracted and assayed by gas chromatography at levels down to 0.5 microg/ml. At this sensitivity the drug can be detected in urine but not in plasma, after therapeutic doses. Persons typed as slow acetylators of sulphadimidine excreted approximately twice as much unmetabolized phenelzine in urine compared to fast acetylators.

Acetylator phenotype and the clinical pharmacology of slow-release procainamide

Slow-release procainamide given 8-hourly is shown to produce plasma levels generally accepted as giving effective prophylaxis against ventricular dysrhythmias occurring after recent myocardial infarction. Patients can be classified into 'slow' and 'fast' acetylators of procainamide. Knowledge of acetylator status is helpful in determining the dose of procainamide necessary to attain effective steady-state plasma levels while avoiding toxic ones. Acetylator status cannot be assessed accurately using sulphadimidine when the patients are also taking procainamide.

Pharmacogenetic response to antidepressants in a multicase family with affective disorder

Eight members from two generations of a family met the DSM-III-R criteria for major depression. Four individuals had severe prolonged depressive disorders that did not respond to standard therapeutic doses of tricyclic and new generation antidepressants, but subsequently responded to the monoamine oxidase inhibitor, tranylcypromine. The literature on pharmacogenetics of the antidepressants is sparse. The pattern of selective response to tranylcypromine in this family supports the view that there is a familial tendency to respond to specific antidepressants or antidepressant groups. A history of response to a specific antidepressant in a relative may be helpful when selecting an antidepressant. Families demonstrating preferential response to specific psychotropics may be suitable pedigrees in which to perform linkage analysis using candidate genes related to the site of action of that psychotropic drug.

Tissue levels and some pharmacological properties of an acetylated metabolite of phenelzine in the rat

The metabolic generation of N2-acetylphenelzine by rats treated with phenelzine, and the activity of this metabolite as an inhibitor of monoamine oxidase enzymes in vivo were confirmed. The isomeric amide N1-acetylphenelzine was not a metabolic product of phenelzine and also did not inhibit monoamine oxidase enzymes. Levels of N2-acetylphenelzine in rat blood, after treatment with a dose (0.1 mmol.kg-1) of N2-acetylphenelzine sufficient to inhibit monoamine oxidase enzymes but not to increase brain levels of dopamine or noradrenaline, were higher than those generated metabolically from a higher dose (0.38 mmol.kg-1) of phenelzine which did increase brain levels of these biogenic amines. Metabolically derived N2-acetylphenelzine, therefore, probably does not contribute in any significant way to monoamine oxidase inhibition by phenelzine.

Current issues in monoamine oxidase inhibitor treatment

Interest in the monoamine oxidase (MAO) inhibitors has been revived over the past fifteen years since the publication of studies and reviews which argue their relative safety and efficacy in certain patient subgroups. The authors conclude that there is a continuing role for the MAO inhibitors in treating atypical depressive illness and panic disorders. Careful selection of patients to be commenced on MAO inhibitor treatment is advised. When prescribed alone or in combination with lithium there is evidence to support a usefulness for MAO inhibitors in depression resistant to the tricyclic antidepressants. Their efficacy in the depressed phase of bipolar affective disorder or in combination with the tricyclic antidepressants remains unproven. The risk of anaesthesia while a patient is receiving MAO inhibitor treatment may be less than heretofore believed. There is realistic hope of finding among the short-acting selective MAO inhibitors an effective antidepressant which is also free from tyramine related effects. With the increasing difficulties of evaluating new drugs on account of ethical and governmental constraints, it may however be some time before the preliminary hopeful findings can be substantiated in larger groups of patients.

Monoamine oxidase inhibitors in anxiety disorders

Monoamine oxidase inhibitors (MAOI's) have been shown to be significantly superior to placebo in the treatment of some anxiety disorders, particularly agoraphobia and mixed anxiety--depressive states. There is no convincing evidence that MAOI's are effective treatment in pure anxiety states, whether or not panic is present as a major symptom, although they are effective in so-called endogenous anxiety. Many past published studies of MAOI's have yielded poor results because the drugs have been prescribed for insufficient time (less than four weeks) or at too low dosage. There are no important therapeutic differences between the MAOI's apart from the faster speed of response with the nonhydrazine compound, tranylcypromine. Treatment often has to be long-term, and some degree of pharmacological dependence may develop. A few clinical studies have compared the efficacy of MAOI's and tricyclic antidepressants in anxious disorders. There is growing evidence that MAOI's are somewhat more effective than tricyclic antidepressants in the treatment of anxiety disorders and when phobic anxiety is an important component of a depressive disorder.

Ethnicity and psychopharmacology

In clinical studies and cross-national surveys, cultural or ethnic factors have been found to be significant determinants in patients' responses to psychotropic medication. Dosage requirements and the potential for toxic reactions might differ amongst racial and ethnic groups. In this paper, the authors review the relevant literature and examine pharmacodynamic, pharmacokinetic and cultural-psychological factors, all of which could be responsible for such ethnic variations.

The present status of monoamine oxidase inhibitors

The present status of monoamine oxidase inhibitors in the treatment of depression is reviewed. With adequate doses they are effective antidepressants, but dosages have in the past been too low. Provided proper dietary precautions are taken, the incidence of fatality from dietary interactions is very small and should not deter doctors from using these drugs, especially in those depressed patients who do not respond to tricyclic-type antidepressants. The present status of combining monoamine oxidase inhibitors with tricyclics is discussed, as are the newer specific inhibitors particularly clorgyline and deprenyl.

Survey of the human acetylator polymorphism in spontaneous disorders

There is ample evidence that the human acetylator phenotypes are associated with drug induced phenomena. It is principally the slow acetylators who exhibit toxic adverse effects because of their relative inability to detoxify the original drug compounds. In rare instances, however, it is the rapid acetylators who are at a disadvantage. In the matter of association of spontaneous disease with either acetylator phenotype, there are two groups of disorders to consider. First, disorders in which carcinogenic amines are known to be an aetiological factor. This is because these amines are substrates for the polymorphic N-acetyltransferase activity and hence there is a possible rational basis for searching for an association. Secondly, other disorders where searches for associations are based more on hunches. In the first group there is a definite statistical association between cancer of the bladder and the slow acetylator phenotype. In prevalence studies the slow phenotype is 39% more associated with bladder cancer than is the rapid phenotype. On the basis of the evidence now available it is not possible to say whether this association is because slow acetylators develop the disease more frequently or whether they survive longer. In the second group the relevant studies show (1) a greatly increased prevalence of slow acetylators in Gilbert's disease; (2) a confirmed association between the rapid acetylator phenotype and diabetes; (3) a possible association between the rapid acetylator phenotype and breast cancer; (4) a possible association between the slow acetylator phenotype and leprosy in Chinese patients; (5) an earlier age of onset of thyrotoxicosis (Graves' disease) in slow acetylators than in rapid acetylators; (6) no evidence of an association between either phenotype and spontaneous systemic lupus erythematosus.

Determination of phenelzine in human plasma with gas chromatography-mass spectrometry using an isotope labeled internal standard

A quantitative gas chromatographic-mass spectrometric assay was developed for the determination of phenelzine in human plasma. Phenelzine, in aqueous solution or in plasma reacts at room temperature with pentafluorobenzaldehyde to form quantitatively a hydrazone derivative. The derivative has good gas chromatographic characteristics. The assay utilizes selected ion monitoring in a gas chromatographic effluent, the molecular ion generated by electron impact ionization of phenelzine derivative. Phenelzine-d, was synthesized and used as an internal standard. The assay can measure 2 ng/ml of the drug with about 10% precision. The method was used for the determination of steady state levels of phenelzine in the plasma of patients taking a therapeutic dose of the drug.

Monoamine oxidase inhibitors: prescription and patient management

The historical roots of the current avoidance of MAOIs are reviewed. A practical approach to the careful prescription of MAOIs is outlined. Medical contraindications, side effects and their management and drug and food interactions with MAOIs are discussed. With careful patient selection, adequate caution by the physican, and appropriate preparation of the patient, MAOIs are often uniquely effective (as in endogenous anxiety) and have an acceptably low potential for serious toxicity.

Acetylation of phenelzine

Microsome-free preparations of rodent and human liver were shown to contain N-acetyl transferase from experiments using procainamide as substrate. These preparations then acetylated phenelzine from the quantitative transfer of radiolabeled acetate. This in vitro demonstration of phenelzine acetylation in rodent and human liver was corroborated by the finding of a negative correlation between excretion of phenelzine in urine and sulphadimidine acetylation in 27 patients.

Perspectives and practical applications in psychopharmacogenetics

1. Individual response to drugs is to a great extent influenced by hereditary factors. 2. The interaction between genetic and environmental factors affecting drug metabolism in man is of crucial importance to the understanding of therapeutic response in psychopharmacology. This proposition is illustrated for various psychotropic drugs such as the monoamineoxydase inhibitors (MAOI), tricyclic drugs and lithium salts as well as for enzymes involved in the synthesis and degradation of biogenic amines. 3. New perspectives in pharmacogenetics and their relevance to psychopharmacology are discussed.

Drug response and psychiatric nosology

The possibility that pharmacological response might help to refine psychiatric nosology has been the subject of recurrent speculation, but few clear-cut results have been obtained. Only bipolar depressives and several other minor patient subgroups manifest consistent drug responses in association with characteristic psychobiological features. The presence of multiple intervening variables, such as individual differences in drug metabolism, drug-taking behaviour and biological sensitivity to drugs, may mitigate against the reliable identification of clinically distinguishable drug-responding subgroups. Futhermore, the majority of available psychoactive drugs have either multiple or broad spectrum effects inconsistent with hypotheses utilizing the mechanism or site of drug action to argue for a diagnosis-specific biological disorder at such sites. Nonetheless, the successful use of drug-response models in other areas of medicine suggests a rationale for continued exploration in this area, and a number of recent advances make this approach potentially more productive. Pharmacological developments have rendered it possible to assess the biological availability of drugs in potential responders, thus eliminating some of the confounding intervening variables. Further consideration should also be given to the use of drugs with more specific neurochemical effects, even when they themselves are not necessarily therapeutic. The comparison of drug responder and non-responder group has also been made more meaningful by the availability of more reliable methods of assessing clinical phenomena, more sophisticated diagnostic models and the introduction of other biological measures. Combining several of these approaches may allow the use of one to validate the other.

Indications for the use of tranylcypromine and trifluoperazine (Parstelin)

Thirty-two patients were treated with the combination of tranylcypromine and trifluoperazine (Parstelin). The patients fell into 3 clinical groups, namely, endogenous depression (7 patients), neurotic depressive reaction (10 patients) and phobic anxiety with some depressive features (15 patients). Satisfactory response was found in 10 out of the 15 patients with phobic symptoms. The response in the other 2 groups was not significant. Side effects were troublesome in the neurotic depressive reaction group. In the phobic group the symptoms of the patients who responded were inclined to recur when the treatment was discontinued. It is considered that it is a useful preparation in the treatment of some phobic patients, but one must expect that the patients are likely to have to remain on the drug for long periods of time.

The influence of acetylator phenotype on the outcome of treatment with phenelzine, in a clinical trial

1 It has been suggested that the rate of metabolism of phenelzine is dependent on the acetylator phenotype of the recipient and, therefore, that acetylator phenotype may be an indicator of clinical importanc e.

2 Acetylator phenotype was determined in a group of patients suffering from depressive, anxiety or phobic neurosis. These patients were blindly allocated to treatment with phenelzine or placebo, in addition to diazepam.

3 Ratings of clinical state were made at weekly intervals. A principle component analysis of the improvement scores on all the clinical rating scales was used to provide a slight measure of improvement for each patient. Increases in severity of undesirable symptoms or spontaneous complaints were taken to indicate side effects.

4 Assessments of whole blood MAO and 5-HT, and urinary 5-HIAA and VMA were made before treatment and at weekly intervals during the course of treatment.

5 Data from improvement scores indicate that there is a treatment effect only in the first 2 weeks and there is no significant difference between fast and slow acetylators.

6 For the dropouts, the ratio of slow to fast acetylators is not significantly different from that in the total group.

7 MAO is inhibited by phenelzine and the degree of inhibition is independent of acetylator phenotype.

8 Changes of whole blood 5-HT concentration during the course of treatment are complex and suggest that there is an interaction between treatment and acetylator phenotype. The results suggest that fast acetylation is associated with an increased metabolism of 5-HT.

9 It is concluded that acetylator phenotype should not be regarded as a prognostic indication of clinical importance and that the rate of acetylation is not directly related to the appearance or disappearance of monoamine oxidase inhibition by phenelzine.

The placebo dilemma

Placebos have been used since about 1950 in evaluation and interpretation of drug efficacy, especially of new drugs, and in comparison with existing compounds to establish their clinical therapeutic value. There are a number of problems connected with use of an "inert nothing" the informed consent, which is required in a human experiment, the doctor's consciousness of deceitful behaviour, the potential risk for the patient and the doctor, the high effect rate of placebos (+/- 35%), unexpected side-effects, dependency of patients on placebos, discovery by the patient of the placebo treatment, factors independent of the medication, such as the doctor's bias, the nurses influence, the significance of colour, the inconsistency of placebo-reactor or non-reactor types and the genetic state of the patient, as well as the problems associated with a double blind test, which can hardly be used when a patient has previously received a medicine, such as morphine, with its euphoric effect, and the colour change produced in urine by drugs like rifampicin or riboflavin. Only a well-trained and experienced clinical observer should employ a placebo in establishing the therapeutic value of drugs whilst avoiding undesirable pitfalls.

Some of the problems and difficulties associated with clinical studies of antidepressant agents

1 The fact that the classification of psychopharmacological agents depends on clinical studies is emphasized.

2 The difficulties in defining homogeneous groups of depressed patients are emphasized.

3 Some contradictions in the literature are considered.

4 Caution in interpreting the literature on antidepressant agents is recommended.

The relationship between acetylator status and inhibition of monoamine oxidase, excretion of free drug and antidepressant response in depressed patients on phenelzine

This study was designed to examine the hypothesis that phenelzine is metabolized by polymorphic acetylation and that its effects are dependent on acetylator status. 30 depressed inpatients were given a 3-week course of phenelzine 30 mg t.i.d. The antidepressant effect, the degree of inhibition of monoamine oxidase and the amount of free phenelzine excreted in the urine were all significantly greater in slow acetylators than in fast. These findings strongly support the hypothesis.