Feprazone: absence of hemolytic effects in glucose-6-phosphate dehydrogenase-deficient subjects

G6PD Variants and Haemolytic Sensitivity to Primaquine and Other Drugs

Restrictions on the cultivation and ingestion of fava beans were first reported as early as the fifth century BC. Not until the late 19th century were clinical descriptions of fava-induced disease reported and soon after characterised as “favism” in the early 20th century. It is now well known that favism as well as drug-induced haemolysis is caused by a deficiency of the glucose-6-phosphate dehydrogenase (G6PD) enzyme, one of the most common enzyme deficiency in humans. Interest about the interaction between G6PD deficiency and therapeutics has increased recently because mass treatment with oxidative 8-aminoquinolines is necessary for malaria elimination. Historically, assessments of haemolytic risk have focused on the clinical outcomes (e.g., haemolysis) associated with either a simplified phenotypic G6PD characterisation (deficient or normal) or an ill-fitting classification of G6PD genetic variants. It is increasingly apparent that detailed knowledge of both aspects is required for a complete understanding of haemolytic risk. While more attention has been devoted recently to better phenotypic characterisation of G6PD activity (including the development of new point-of care tests), the classification of G6PD variants should be revised to be clinically useful in malaria eliminating countries and in populations with prevalent G6PD deficiency. The scope of this work is to summarize available literature on drug-induced haemolysis among individuals with different G6PD variants and to highlight knowledge gaps that could be filled with further clinical and laboratory research.

Induction of hemolytic anemia by nonsteroidal antiinflammatory drugs

The incidence of immune hemolytic anemia (IHA) is increasing. The proliferation of pharmaceuticals is a contributing factor to this increase. IHA is an uncommon, though significant, adverse effect of a wide variety of drugs. Several recent case reports have implicated the nonsteroidal antiinflammatory drugs (NSAIDs). Because of the extensive use of this class of drugs, a review of case reports, clinical studies, and in vitro research was conducted on NSAID-induced IHA. Mefenamic acid, ibuprofen, sulindac, naproxen, tolmetin, feprazone, and aspirin are reported to cause IHA, with mefenamic acid most frequently implicated. Mefenamic acid appears to cause hemolytic anemia by an autoimmune mechanism similar to methyldopa and aspirin by an immune complex mechanism. However, there is insufficient information concerning ibuprofen, sulindac, naproxen, tolmetin, and feprazone to assign specific mechanisms of immune hemolysis. In individuals with glucose-6-phosphate dehydrogenase (G-6-PD) deficiency, aspirin at usual therapeutic doses is not a predisposing factor to hemolysis unless other risk factors are present. Although individuals with G-6-PD deficiency are at increased risk of developing hemolytic anemia when exposed to oxidizing stresses, the use of NSAIDs does not appear to increase this risk significantly. Because NSAID-induced IHA occurs infrequently and the sensitivity of currently used tests to detect drug-dependent antibodies is limited, routine serologic testing in patients receiving NSAIDs is not justified. If hemolytic anemia occurs in a NSAID-treated patient and the history is consistent with a drug-induced etiology, the NSAID should be discontinued. With discontinuation of the offending agent, the prognosis is good. There is a rapid hematologic recovery, with a slow resolution of abnormal serologic findings.

Adverse effects of drugs on the blood

Amongst adverse drug reactions blood dyscrasias are not frequent, but they may have serious consequences. Compared with Sweden, data from The Netherlands are scarce. It is to be expected that regular reports about the incidence of drug-induced blood dyscrasias may play an important role in general prevention. Blood dyscrasias may be caused by a variety of drugs, from many pharmacotherapeutic groups with diverse chemical structures and with all application forms. Metabolism and distribution may influence the activity of drugs. Drug-induced anaemias, including aplastic anaemia, are briefly discussed. Toxic and immune mechanisms may occur. The same holds with regard to the leucopenias. Drug-induced thrombocytopenia is mainly immune-mediated (cytostatics being excluded as causative agents). In immune-mediated drug-induced blood dyscrasias often haptens must be formed. They can be formed in vivo in the liver or in the lymphocytes. In some cases they appear to be formed even in vitro. Tracing the causative agent of a dyscrasia, be it a drug or some other substance, requires a series of investigations, comprising usage of the drug, serology and cell culture. Provocation tests are seldom justified. Distinct preventive measures can be taken to minimize the risk of blood dyscrasias: avoidance of risky drugs, awareness of the patient about early clinical signs and haematological control.