Fatal maprotiline intoxication

Inhibition of cardiac HERG potassium channels by antidepressant maprotiline

Many drugs block delayed rectifier K+ channels and prolong the cardiac action potential duration. Here we investigate the molecular mechanisms of voltage-dependent block of human ether-a-go-go-related gene (HERG) K+ channels expressed in cells HEK-293 and Xenopus oocytes by maprotiline. The IC50 determined at 0 mV on HERG expressed HEK-293 cell and oocytes was 5.2 and 23.7 microM, respectively. Block of HERG expressed in oocytes by maprotiline was enhanced by progressive membrane depolarization and accompanied by a negative shift in the voltage dependence of channel activation. The potency of maprotiline was reduced 7-fold by point mutation of a key aromatic residue (F656T) and 3-fold for Y652A, both located in the S6 domain. The mutation Y652A inverted the voltage dependence of HERG channel block by maprotiline. Together, these results suggest that voltage-dependent block of HERG results from gating dependent changes in the accessibility of Y652, a critical component of the drug binding site.

Tricyclic antidepressants, QT interval prolongation, and torsade de pointes

The authors postulate mechanisms linking tricyclic antidepressants, QT interval prolongation, torsade de pointes, and sudden cardiac death. Case reports identify amitriptyline and maprotiline as the tricyclic antidepressants most likely to provoke torsade de pointes. Risk factors of family history of congenital long QT syndrome, age, female sex, metabolic and cardiovascular disease, metabolic inhibitors, hypokalemia, drug overdose, and co-prescription of drugs associated with QT interval prolongation were found in cases of torsade de pointes associated with tricyclic antidepressants. Clinicians should be cautious when prescribing tricyclic antidepressants with other drugs, such as thioridazine, that are capable of prolonging the QT interval.

Fatal blood and tissue concentrations of more than 200 drugs

Fatal drug concentrations in body fluids and tissue samples are presented for more than 200 drugs and chemicals of toxicologic interest. Additionally, a reference list is added with more than 600 original papers concerning intoxications with a lethal outcome. The data can be helpful for the interpretation and plausibility control in own cases of intoxication. However, they should be used with caution, because use of drug data without sufficient knowledge about the patient or victim, the circumstances of the case, and about toxicokinetics and toxicodynamics might give a wrong interpretation in a special case.

Review of the results from clinical studies on the efficacy, safety and tolerability of mirtazapine for the treatment of patients with major depression

Mirtazapine is a presynaptic alpha-2 antagonist that has dual action by increasing noradrenergic and serotonergic neurotransmission. The enhancement of serotonergic neurotransmission is specifically mediated via 5-HT1 receptors because mirtazapine is a postsynaptic serotonergic 5-HT2 and 5-HT3 antagonist. In addition, mirtazapine has only a weak affinity for 5-HT1 receptors and has very weak muscarinic anticholinergic and histamine (H1) antagonist properties. As a consequence of its unique pharmacodynamic properties, mirtazapine is an effective, safe and well-tolerated addition to the antidepressant armamentarium. Mirtazapine is well absorbed from the gastrointestinal tract following oral administration, and it is extensively metabolized in the liver to four metabolites via demethylation and hydroxylation, followed by glucuronide conjugation. The unconjugated desmethyl metabolite is pharmacologically less active than the parent compound. Mirtazapine lacks auto-induction of hepatic isoenzymes. Although mirtazapine is a substrate of P450 isoenzymes 1A2, 2D6 and 3A4, in vitro studies show that it is not a potent inhibitor or inducer of any of these enzymes. Mirtazapine has been evaluated in a worldwide clinical development program involving approximately 4500 patients. Controlled clinical trials involving almost 2800 mirtazapine-treated patients have demonstrated the compound to be effective for the treatment of moderate-to-serve major depression. Mirtazapine was consistently superior to placebo, and equivalent in efficacy to the tricyclic antidepressants amitriptyline, doxepin and clomipramine, but with an improved tolerability profile. Mirtazapine has shown a rapid onset of action in patients with predominantly severe depressive illness in a comparative study against fluoxetine. Mirtazapine has a unique tolerability profile, since the specific postsynaptic 5-HT2 and 5-HT3 receptor blockade of mirtazapine provides early antidepressant effects without causing unwanted serotonin-related side-effects. Transient somnolence, hyperphagia and weight gain are the most commonly reported adverse events, which may be attributed to the antihistaminic (H1) activity of mirtazapine at low doses. Somnolence, the most commonly reported side-effect, appears to be less frequent at higher dosages. Mirtazapine also demonstrates important anxiolytic and sleep-improving effects, which may be related to its pharmacodynamic properties. In addition, mirtazapine does not appear to be associated with sexual dysfunction. Mirtazapine has shown no significant cardiovascular adverse effects at multiples of 7 to 22 times the maximum recommended dose. Mirtazapine is a unique addition to the antidepressant armamentarium as first-line therapy in patients with major depression and symptoms of anxiety/agitation or anxiety/somatization or complaints of insomnia and as a useful alternative in depressed patients who do not adequately respond to or are intolerant of tricyclic antidepressants or serotonin-specific reuptake inhibitors.

Relative toxicity of cyclic antidepressants

To compare the relative central nervous system and cardiac toxicity of amoxapine, maprotiline, and trazodone with the older tricyclic antidepressants, a three-year (1981 through 1983) retrospective review was performed on 1,313 cases involving cyclic antidepressant exposures reported to the Maryland Poison Center. Seizures were more common in the amoxapine (24.5%) and maprotiline (12.2%) groups, compared with either the tricyclic antidepressants (3.0%) or trazodone (0%) (P less than .01). A higher incidence of seizures also was observed in desipramine ingestors (17.9%) compared with other tricyclic antidepressants. No significant differences in the incidence of central nervous system depression or cardiotoxicity was found between the groups. These findings support reports of an increased incidence of seizures in overdoses of amoxapine and maprotiline, but do not substantiate claims of less cardiotoxicity.

[Heart conduction disorders in acute maprotiline poisoning]

A case is reported of self-poisoning with maprotiline followed by prolonged disorders of intraventricular conduction. The cardiotoxicity of tetracyclic antidepressants was well established, but few cases were reported. Maprotiline pharmacokinetics explained the duration of the cardiovascular side-effects. The severity of maprotiline overdoses should not be underestimated.

Second generation antidepressants: a comparative review

The authors review four "second generation" antidepressants (maprotiline, amoxapine, trazodone, and nomifensine) in terms of action on biogenic amines and receptors, antidepressive efficacy, and adverse effects. Doxepin is used as a comparative agent and is similar to the prototypical tricyclic agents in all the above categories. Maprotiline is a selective noradrenergic agent, but shares a similar adverse effect profile with doxepin and may be associated with a high frequency of seizures in overdose. Amoxapine is a mixed action antidepressant with significant neuroleptic activity in vivo. Its adverse effect profile is highlighted by symptoms related to its neuroleptic activity, and seizures and acute renal failure in overdose. Trazodone is a selective serotonergic agent with low anticholinergic activity, and minimal morbidity/mortality in overdose. Reports of priapism, leading to impotence in some men, however, is of concern. Nomifensine is a potent noradrenergic and dopaminergic agent with low anticholinergic activity, and minimum cardiotoxicity and low morbidity/mortality in overdose. Its most important adverse effects include overstimulation and infrequent, usually reversible, immunologic hypersensitivity reactions. Trazodone and nomifensine have favorable profiles for use in the elderly. Trazodone may be more favorable in the anxious/agitated patient due to its sedative effects, whereas nomifensine may be more beneficial in the retarded, apathetic patient.