Fixed drug eruption of the penis due to co-trimoxazole

Fixed eruption of the penis, due to co-trimoxazole, is described in two boys. The eruption was accompanied by severe swelling of the penis, urine retention, and pain during micturition. The migration inhibiting factor assay for co-trimoxazole was negative, but the mast cell degranulation test was strongly positive, suggesting reaginic hypersensitivity reaction.