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Two severe hemolytic crises, in a month’s period, were induced by primaquine in a glucose-6-phosphate dehydrogenase deficient Sardinian male. Young red blood cells tagged with Fe59 10 to 16 days earlier were destroyed in the second hemolytic episode. The implications of these experiments on the nature of drug-induced hemolysis in Caucasians are briefly discussed.

A technique to investigate drugs which could cause haemolysis in subjects deficient in glucosc-6-phosphate dehydrogenase (~-glucose-6-phosphate: NADP oxidoreductase; G6PD) has been developed. The method is based on the technique of '"CO, evolution during the incubation of normal erythrocytes in the presence of [~-~~C]glucose and their own serum, the latter containing the active metabolites of the drugs received by normal subjects. By this method agents causing a stimulation of the hexosetnonophosphate pathway of normal erythrocytes should be regarded as potentially haemolytic for G6PD-deficient subjects. Two sulphonamides, sulphormethoxine and sulphalene, of which until now no haemolytic effects have been reported, together with chloroquine, have been investigated. While chloroquine does not affect the hexoseinonophosphate shunt of normal erythrocytes, the two sulphoiiamides stimulate this pathway. The results are confirmed by the reduction of the half-life of s ' Cr-labelled G6PD-dcficient red cells (Mediterranean variant) , after administration of the two sulphoiiamides.Human erythrocyte G6PD-deficiency is the most prevalent hereditary red cell eiizyme defect. Subjects with this X-linked defect are susceptible to haemolytic anaemia after exposure to drugs such as primaquine and sulphoiiamides (Kirkinan, 1968). Until now, methods to evaluate the haemolytic effects in G6PD-deficient subjects have not been completely satisfactory. In the past years, drugs have been administered in controlled studies to G6PDdeficient subjects (Dern ct al, 1954) but obviously this approach is quite hazardous. The method of transfusion of G6PD-deficient erythrocytes labelled with ' Cr to normal volunteer subjects, followed by the administration of a test drug, seems less hazardous (Dern et d, 1954)~ but a disadvantage could be the transmission of viral hepatitis. Fraser & Vesell(1968) suggested an in vitro method based on the study of the mechanical fragility of erythrocytes in the presence of drug metabolites. More often, the discovery of a haemolytic effect of a new drug occurs fortuitously, during the administration of the drug to a subject with unrecognized G6PD deficiency. Recently Welt et al(1971) studied the effect of primaquine on the hexosemonophosphate pathway (HMP) of normal erythrocytes by the method of l 4 c O 2 evolution during incubation of the erythrocytes in the presence of [ 1-l "C] glucose and homologous serum.Using the method of Welt et al (1971), the effect of two potentially hacmolytic drugs on

The reduced activity of glucose-6-phosphate dehydrogenase (D-glucose-6-phosphate; NADP+ 1-oxidoreductase; G6PF) in Mediterranean erythrocytes explains the precarious equilibrium of the hexose monophosphate pathway (HMP) and the susceptibility of these cells to haemolytic agents. G6PD-deficient erythrocytes, in steady-state conditions, have a low NADPH/NADP+ ratio, thus allowing the HMP to operate at its maximal intracellular rate and to compensate the intrinsic erythrocyte enzyme deficiency. Studies started soon after accidental intake of fava beans by sensitive G6PD-deficient subjects demonstrate a decrease of both NADPH/NADP+ ratio and reduced glutathione. The metabolic effects induced by fava beans may be attributed to oxidative stress probably associated with an inhibitor effect of some unknown metabolite on the HMP. The availability of erythrocytes from subjects recovering from haemolysis with high reticulocyte counts and increased G6PD activity, provides new information on the rate of synthesis as well as on the in vivo decay of the mutant enzyme. Correlation of G6PD activity to reticulocyte count and extrapolation to an ideally homogenous population of reticulocytes reveal that the mutant enzyme is synthesized at a nearly normal rate. Furthermore, the present correlation allows an estimate of the in vivo half-life of Mediterranean G6PD. The rate of decline of about 8 d observed in this study well correlates to the intracellular metabolic aspects of G6PD Mediterranean erythrocytes.