Drug interactions between amitriptyline/perphenazine and Methylin

amitriptyline ↔ methylphenidate

Applies to:amitriptyline/perphenazine and Methylin (methylphenidate)

MONITOR: The coadministration with methylphenidate may increase the serum concentrations of tricyclic antidepressants (TCAs). Case reports involving primarily methylphenidate and imipramine have suggested favorable as well as unfavorable clinical effects from this combination. In vitro studies suggest that methylphenidate may inhibit the metabolism of imipramine and other TCAs, although the extent is probably subject to considerable interindividual variation.

MANAGEMENT: Pharmacologic response to TCAs should be monitored more closely whenever methylphenidate (racemic) or dexmethylphenidate (the more pharmacologically active d-enantiomer) is added to or withdrawn from therapy, and the TCA dosage adjusted as necessary.

perphenazine ↔ methylphenidate

Applies to:amitriptyline/perphenazine and Methylin (methylphenidate)

GENERALLY AVOID: Phenothiazines may antagonize the pharmacologic effects of amphetamine, amphetamine derivatives, and other centrally-acting sympathomimetic agents (i.e., CNS stimulants). Conversely, these agents may diminish the neuroleptic efficacy of phenothiazines. The exact mechanism of interaction is unknown but may involve opposing effects on dopaminergic activity. Several clinical studies have demonstrated the reduction or lack of effect of amphetamines on weight loss in obese psychiatric patients treated with chlorpromazine and other neuroleptic agents. In one of these studies, dextroamphetamine also had no effect on sleep patterns. As for the reverse interaction, it is uncertain whether CNS stimulants actually antagonize the neuroleptic effect of phenothiazines, since CNS stimulants alone have been reported to cause or aggravate preexisting psychotic symptoms. Finally, it is conceivable that, because of their sympathomimetic effects, CNS stimulants may also potentiate the arrhythmogenicity of phenothiazines. A case of fatal ventricular arrhythmia was reported in a patient treated chronically with thioridazine who ingested a single capsule containing phenylpropanolamine 50 mg and chlorpheniramine 4 mg. However, a causal relationship was not established.

MANAGEMENT: Amphetamine, amphetamine derivatives, and other CNS stimulants should generally not be used, particularly for weight reduction, in patients treated with phenothiazines.