Severe hyperkalemia during magnesium sulfate therapy in two pregnant drug abusers.

Severe hyperkalemia developed in two pregnant intravenous drug abusers during prolonged parenteral magnesium sulfate therapy in the absence of any obvious cause. The serum potassium concentration returned to normal after magnesium therapy was discontinued. Hypermagnesemia, acting through several possible mechanisms, was probably responsible for the reversible hyperkalemia observed.