Acute intermittent porphyria in two patients on anticonvulsant therapy and with normal erythrocyte porphobilinogen deaminase activity.

1. Acute intermittent porphyria (AIP) is sometimes termed a 'pharmacogenetic' disease. patients with genetic deficiency of the enzyme porphobilinogen deaminase are liable to develop acute attacks of porphyria if exposed to a variety of drugs. 2. Two patients are reported who had no evidence of deficiency of erythrocyte porphobilinogen deaminase yet developed typical attacks of AIP while on anticonvulsant therapy. 3. Normal activity of erythrocyte porphobilinogen deaminase does not completely exclude porphyria. 4. Acute porphyria should be suspected if clinical deterioration occurs during therapy with anticonvulsants, or other porphyrinogenic drugs, even in the absence of an underlying genetic defect in haem synthesis in peripheral blood cells.