Anaemia malarial

Drugs. Antiepilepsy drugs, particularly phenytoin, primidone and phenobarbital, occasionally cause a macrocytic anaemia that responds to folic acid. This may be due to enzyme induction by the antiepileptics increasing the need for folic acid to perform hydroxylation reactions (see Epilepsy) but other factors such as reduced absorption may be involved. Administration of folic acid causes a recurrence of seizures in some patients. Some anti-malarials, e.g. pyrimethamine, may interfere with conversion of folates to the active tetrahydrofolic acid, causing macrocytic anaemia. Methotrexate, another folate antagonist, may cause a megaloblastic anaemia especially when used long-term for leukaemia, rheumatoid arthritis or psoriasis. 

The selection pressure exerted by malaria is strong enough to maintain sickle-cell anaemia and the thalassaemias at a high frequency in populations across Africa and Asia. These conditions are not isolated curiosities, but part of a spectrum of adaptations that enable people to survive in areas where malaria is endemic. Among the most important of these adaptations is malarial tolerance. Tolerance develops after infections in early childhood and lasts a lifetime. It is not the result of a heightened ability to kill parasites (as in vaccination) but the triumph of realpolitik —... 

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