Seizures associated with high-dose intravenous morphine containing sodium bisulfite preservative

OBJECTIVE: To report a case of seizures occurring during administration of high-dose intravenous morphine containing sodium bisulfite as a preservative. CASE SUMMARY: A 56-year-old woman hospitalized with multiple myeloma developed myoclonic and tonic-clonic seizures following administration of intravenous morphine with sodium bisulfite preservative at doses exceeding 400 mg/h. These seizures resolved when the morphine was discontinued, anticonvulsants were administered, and the drug therapy was changed to intravenous fentanyl without preservative. DISCUSSION: The factors potentially associated with this adverse reaction are discussed and the literature concerning the adverse central nervous system effects of opiates and sulfites is reviewed. CONCLUSIONS: High doses of intravenous morphine with sulfite preservative may be associated with seizure development. If patients require high doses of intravenous morphine, a preservative-free formulation should be used to avoid possible additive or synergistic toxicities.