Haemolytic effect of trimethoprim:Sulphamethoxazole in G-6-PD deficiency

Observations are reported on the survival of 51Cr-labelled glucose-6-phosphate dehydrogenase (G-6-PD) deficient cells transfused into normal recipients before and after the administration to the recipient of trimethoprim and sulphamethoxazole, alone or in combination, in varying doses. Trimethoprim did not reduce the of the transfused deficient red cells. In 4 of 6 instances sulphamethoxazole did so but only in the somewhat high dose of 90 mg./kg./day, the being unaffected by smaller doses. However it cannot be concluded from the foregoing that the haemolysis of G-6-PD deficient red cells, provoked by sulphamethoxazole is dose dependent, for severe intravascular haemolysis has been encountered in 2 G-6-PD deficient patients with trivial infections within 48 hours of starting to take 30 mg./kg./day of sulphamethoxazole. It is concluded that the drug should be administered to those of ethnic groups in which this deficiency is common only when the deficiency has been excluded.