Renal insensitivity to frusemide caused by chronic anticonvulsant therapy.

The diuretic response to 20-mg and 40-mg oral doses of frusemide was significantly smaller in a group of epileptic patients on chronic anticonvulsant therapy than in a group of normal staff members. Furthermore, the peak response was considerably delayed in the epileptic patients. The difference in the volume of diuresis was maintained after intravenous injection of 20 mg of frusemide. It is suggested that the sensitivity of the renal tubule to the diuretic action of frusemide is reduced by anticonvulsant therapy and that there may also be delayed absorption of the drug from the gastrointestinal tract.