Phenothiazines Metrizamide

HindmarshT, Grepe Aand WidenL. Metrizamide phenothiazine interaction. Report of a case with seizures following myelography. ActaRa[Pg.1255]

The role of chlorpromazine in facilitating metrizamide-induced convulsions has been confirmed in animal studies (539) phenothiazines should be withdrawn at least 48 hours before intrathecal use of metrizamide. 

Additive effects are likely after concomitant use of nortriptyline with CNS depressants, including alcohol, analgesics, barbiturates, narcotics, tranquilizers, and anesthetics (oversedation) atropine and other anticholinergic drugs, including phenothiazines, antihistamines, meperidine, and antiparkinsonian agents (oversedation, paralytic ileus, visual changes, and severe constipation) and metrizamide (increased risk of convulsions). 

Two isolated case reports describe epileptiform reactions in two patients when metrizamide was used for lumbar myelography in the presence of chlorpromazine or dixyrazine. No such cases appear to have been reported for intrathecal iohexol nevertheless, the manufacturer of iohexol advises the avoidance of phenothiazines and other drugs that lower seizure threshold when iohexol is used intrathecally. 

Intrathecal metrizamide or iohexol alone are rarely associated with seizures. Theoretically, this risk might be increased in patients taking other drugs that lower the seizure threshold, such as the phenothiazines. 

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