Tizanidine (Tizanidine Hydrochloride) - Drug Interactions, Contraindications, Overdosage

DRUG INTERACTIONS

Drug Interactions:

In vitro studies of cytochrome P450 isoenzymes using human liver microsomes indicate that neither tizanidine nor the major metabolites are likely to affect the metabolism of other drugs metabolized by cytochrome P450 isoenzymes.

Acetaminophen:

Tizanidine delayed the T_max of acetaminophen by 16 minutes. Acetaminophen did not affect the pharmacokinetics of tizanidine.

Overdosage:

A search of a safety surveillance database revealed a total of eighteen cases of tizanidine overdose. Of the fourteen intentional overdoses, five have resulted in fatality, and in at least three of the cases, other CNS depressants were involved. One fatality was secondary to pneumonia and sepsis, which were sequelae of the ingestion. The majority of cases involve depressed consciousness (somnolence, stupor, or coma), depressed cardiovascular function (bradycardia, hypotension), and depressed respiratory function (respiratory depression or failure).

Should overdosage occur, basic steps to ensure the adequacy of an airway and the monitoring of cardiovascular and respiratory systems should be undertaken. In general, symptoms resolve within one to three days following discontinuation of tizanidine and administration of appropriate therapy. Due to the similar mechanism of action, symptoms and management of tizanidine overdose are similar to those following clonidine overdose. For the most recent information concerning the management of overdose, contact a poison control center.

CONTRAINDICATIONS:

Tizanidine hydrochloride tablets are contraindicated in patients with known hypersensitivity to tizanidine hydrochloride or its ingredients.