The present status of monoamine oxidase inhibitors

Selective inhibition of MAO-A, not MAO-B, results in antidepressant-like effects on DRL 72-s behavior

The effects of monoamine oxidase inhibitors (MAOIs) that selectively inhibit the MAO-A or MAO-B forms of MAO were studied in rats performing under a differential-reinforcement-of-low-rate 72-s (DRL 72-s) schedule of reinforcement. Clorgyline and CGP11'305A, irreversible and reversible MAO-A inhibitors, respectively, increased the reinforcement rate, decreased the response rate, and enhanced temporal discrimination. The irreversible MAO-B inhibitor (-)-deprenyl did not produce similar effects. Pargyline did not increase the reinforcement rate at low doses that selectively inhibit MAO-B, but did increase the reinforcement rate at doses that inhibit MAO-A by more than 90%. The present results are in accord with clinical data demonstrating that MAO-A inhibitors are effective therapeutic agents in treating depression while MAO-B inhibitors are of questionable antidepressant efficacy. The present findings provide further evidence that the DRL 72-s schedule may be useful both as a screen for identifying new antidepressants and for investigating the neurochemical effects of antidepressant drugs that are responsible for their therapeutic effects.

Basic and clinical aspects of the activity of the new monoamine oxidase inhibitors

The clinical relevance of the neurobiochemical and pharmacological properties of the new generation of monoamine oxidase inhibitors (MAOIs) is reviewed and discussed. The most distinctive characteristics of these drugs are the selectivity, competitive nature and reversibility of their MAO-inhibiting action. The most selective MAO-A inhibitors are moclobemide and brofaromine, with ratios between their MAO-A and MAO-B inhibiting potency (estimated in in vitro assays) of 1: greater than or equal to 1000 and 1:500, respectively, whereas the least selective drug is cimoxatone with a ratio of 1:66. If in vitro findings are considered, the most potent MAO-A inhibitor seems to be cimoxatone and the least potent toloxatone. After oral administration, however, cimoxatone, brofaromine and moclobemide appear to be about equally effective in inhibiting brain MAO-A. All these drugs are short acting and their MAO-inhibiting action is reversible within 24 h or, in the case of brofaromine, 48 h. Due to the selectivity and reversibility of the MAO-A inhibition, they were found to be less likely to induce large increases in the pressor responses to tyramine, both in animals and in man. In patients treated with 150 mg/day for 4 weeks, brofaromine, which appears to be the best-characterized drug in this respect, produced about a 4-fold increase in sensitivity to tyramine. Although the clinical antidepressant efficacy of these drugs remains to be confirmed in more extensive studies, based on their neurobiochemical and pharmacological properties, clear advantages in respect to their side-effect profiles are to be expected in comparison with the classical MAOIs.

Combined MAO-inhibitor and tri- (tetra) cyclic antidepressant treatment in therapy resistant depression

1. One aspect of using MAO-inhibitors - combining them with tricyclic antidepressants in the treatment of therapy resistant depression - has always been controversely discussed in regard to its unusual toxicity and efficacy. 2. To obtain detailled information about safety and efficacy of such a combined treatment, the charts of 94 inpatients treated with a tranylcypromine - tri- (tetra) cyclic antidepressant combination were reviewed. 3. Within a mean treatment period of 21.9 days, 68% of the patients demonstrated a very good or good improvement to combined treatment, the most effective combination being tranylcypromine + amitriptyline. 4. The incidence of side effects among the patients on the combined regimen was slightly, but not significantly lower as compared to the patients on single tri- (tetra) cyclic antidepressant treatment. 5. Our retrospective study supports the general safety and efficacy of combined MAOI-TCA treatment and suggests that combined treatment, if properly administered, leads to neither serious complications nor an inordinate number of side effects.

Psychiatric morbidity and platelet monoamine oxidase activity in cancer patients

Psychometric ratings for both anxiety and depression in 30 cancer patients were significantly elevated compared with values in 16 controls. The scores were especially high in the 14 patients who did not have breast cancer. This group also had significantly greater platelet monoamine oxidase activity than either the breast cancer patients or controls. Platelet monoamine oxidase activity values correlated significantly with both depression and anxiety scores in the whole cancer group.

A remarkable response of chronic severe obsessive-compulsive neurosis to phenelzine

The author describes a 22-year-old male who suffered from chronic severe Obsessive-Compulsive Neurosis (OCN) complicated by frequent depressive episodes. Administering the monoamine oxidase inhibitor phenelzine in high dosage led to complete alleviation of his depression in 10 weeks, and 3 weeks afterwards the OCN was markedly improved. The illness relapsed shortly after discontinuance of the drug.

MAO inhibitors in mental disease: their current status

Available MAOIs seem to be mainly indicated for the heterogeneous group of patients with depressive syndromes. Although groups of patients with all the recognized major subtypes of depression (including "endogenous depression") probably respond in varying degrees, MAOIs appear to be particularly indicated for out-patients with "neurotic depression" complicated by panic disorder or hysteroid dysphoria, which involves repeated episodes of depressed mood in response to feeling rejected. MAOIs can also be effective in several anxiety syndromes, in particular panic disorder. Other reports have claimed success in a variety of other syndromes including bulimia, anorexia nervosa, obsessive-compulsive neurosis, atypical facial pain and some other types of chronic pain, childhood attention deficit disorder and delusions of infestation by parasites. The nature of any underlying personality disorder is an important response variable and the assessment of personality should be encouraged in further studies. The development of new drugs raises the prospect of a range of MAOIs targeted at specific patient populations. Tranylcypromine also merits further investigation as clinical experience suggests that it can produce a dramatic response in some patients with phenelzine-resistant disorders. This may be due, at least in part, to its amphetamine-like effects.

Attempts to attenuate the 'cheese effect'. Combined drug therapy in depressive illness

Although earlier results, employing intravenous tyramine challenge, had indicated that a tricyclic antidepressant plus monoamine oxidase inhibitor drug combination might be free from the 'cheese effect', the experiments reported here, involving oral tyramine challenge during the combined therapy, showed that relaxation of a tyramine-free diet during such a drug regimen might be unsafe. Preliminary observations indicated that combined (-)-deprenyl plus nonselective monoamine oxidase inhibitor therapy might lead to an unacceptable degree of orthostatic hypotension without reduction in tyramine sensitivity.