Metrizamide: a review with emphasis on drug interactions.

The pharmacology, side effects, and possible drug interactions of metrizamide, a water-solulbe contrast medium for myelography, are reviewed. Metrizamide concentration in the brain reaches maximal levels two to six hour after lumbar injection, depending on dose and patient positioning, and is largely (55-96%) excreted from the body after 24 hours. Its lower neurotoxicity, compared with other water-soluble contrast agents, can be attributed in part to its undissociated, non-ionic nature. Common side effects, which include headache, nausea, and vomiting, occur to the same degree as with other myelographic contrast media. Reported data suggest that convulsions, which have occurred in a very small percentage of patients, are related to the amount of contrast medium reaching the brain which, in turn, is largely a factor of dose and examination technique. Although the risk of seizures is small, it is recommended that drugs that lower the seizure threshold (phenothiazine derivatives, butyrophenones, tricyclic antidepressants, and MAO-inhibitors) should be avoided 48 hours before metrizamide administration (if possible), should not be used to control nausea, and should not be resumed for 24 to 48 hours after the myelographic procedure. The value of premedication (e.g., with diazepam) to prevent seizures has not been established and is not recommended.