The mephenytoin (cytochrome P450 2C 19) and dextromethorphan (cytochrome P450 2D6) polymorphisms in Saudi Arabians and Filipinos.

Hitherto no estimate has been available of the genetic polymorphisms of S-mephenytoin hydroxylation in the Saudi Arabian or any other Middle Eastern population. A total of 102 healthy Saudi Arabian volunteer subjects were tested simultaneously with mephenytoin and dextromethorphan. Two poor metabolizers of S-mephenytoin and two poor metabolizers of dextromethorphan were found. Also 55 healthy Filipino volunteer subjects were tested and 13 found to be poor metabolizers of S-mephenytoin, whilst none were found to be poor metabolizers of dextromethorphan. The Saudi Arabian population thus appears to resemble Europeans in the frequency of poor metabolizers of S-mephenytoin, but resembles Orientals in the frequency of poor metabolizers of dextromethorphan. The Filipino sample as expected resembles other Oriental samples in the frequencies of poor metabolizers of both drugs.