Hematological side effects of co-trimoxazole.

Decrease of blood cells may be induced by either components of co-trimoxazole. Side effects of the trimethoprim component are much more frequent, particularly in risk groups. They are dose dependent, usually not severe, only rarely of clinical significance and easily treated or prevented by folate supplementation. In contrast, side effects of the sulfamethoxazole component seem to be extremely rare. They are similar to the hematological side effects of other sulfonamide drugs. They are idiosyncratic, nonpredictable and mostly mediated by the immune-system. They may be of life-threatening severity and no therapy is known except termination of exposure and supportive measures such as substitution of blood cells and antiinfectious therapy by non-related antibiotics.