Maprotiline is a tetracyclic antidepressant with similar pharmacological properties to tricyclic antidepressants (TCAs). Similar to TCAs, maprotiline inhibits neuronal norepinephrine reuptake, possesses some anticholinergic activity, and does not affect monoamine oxidase activity. It differs from TCAs in that it does not appear to block serotonin reuptake. Maprotiline may be used to treat depressive affective disorders, including dysthymic disorder (depressive neurosis) and major depressive disorder. Maprotiline is effective at reducing symptoms of anxiety associated with depression.
Indication
For treatment of depression, including the depressed phase of bipolar depression, psychotic depression, and involutional melancholia, and may also be helpful in treating certain patients suffering severe depressive neurosis.
Pharmacology
Maprotiline is a tetracyclic antidepressant. Although its main therapeutic use is in the treatment of depression, it has also been shown to exert a sedative effect on the anxiety component that often accompanies depression. In one sleep study, it was shown that maprotiline increases the duration of the REM sleep phase in depressed patients, compared to imipramine which reduced the REM sleep phase. Maprotiline is a strong inhibitor of noradrenaline reuptake in the brain and peripheral tissues, however it is worthy to note that it is a weak inhibitor of serotonergic uptake. In addition, it displays strong antihistaminic action (which may explain its sedative effects) as well as weak anticholinergic action. Maprotiline also has lower alpha adrenergic blocking activity than amitriptyline.
Toxicity
LD50=~900 mg/kg (Orally in rats); LD50=90 mg/kg (Orally in women); Signs of overdose include motor unrest, muscular twitching and rigidity, tremor, ataxia, convulsions, hyperpyrexia, vertigo, mydriasis, vomiting, cyanosis, hypotension, shock, tachycardia, cardiac arrhythmias, impaired cardiac conduction, respiratory depression, and disturbances of consciousness up to deep coma.
Affected Organisms
Humans and other mammals
Biotransformation
Hepatic. Maprotiline is metabolized by N-demethylation, deamination, aliphatic and aromatic hydroxylations and by formation of aromatic methoxy derivatives. It is slowly metabolized primarily to desmethylmaprotiline, a pharmacologically active metabolite. Desmethylmaprotiline may undergo further metabolism to maprotiline-N-oxide.
Absorption
Slowly, but completely absorbed from the GI tract following oral administration.
Half Life
Average ~ 51 hours (range: 27-58 hours)
Protein Binding
88%
Elimination
Approximately 60% of a single orally administered dose is excreted in urine as conjugated metabolites within 21 days; 30% is eliminated in feces.
Distribution
Maprotiline and its metabolites may be detected in the lungs, liver, brain, and kidneys; lower concentrations may be found in the adrenal glands, heart and muscle. Maprotiline is readily distributed into breast milk to similar concentrations as those in maternal blood.
