Mephenytoin hydroxylation in the Cuna Amerindians of Panama.

1 Mephenytoin p(4′)‐hydroxylation, which is deficient in 3‐5% of Caucasians, was examined in 96 Cuna Amerindians of Panama. 2 Attempts were made to exclude poor compliance with urine collection and ingestion of the drug dose since the assignment of phenotype was based upon urinary recovery of the metabolite. These involved the measurement of the urinary recovery of sparteine, added to the ingested capsule, and of the renal excretion of creatinine. 3 Of the 90 Cunas deemed to be reasonably complaint, none of them appeared to be deficient in p(4′)‐ hydroxylation of mephenytoin.