Symptoms: The maximum tolerated dose in humans is unknown. Nausea, vomiting, dizziness and confusion are likely symptoms of overdosage. ln cases of known, suspected or accidental overdosage, therapy should be stopped. If vomiting has not occurred, induction of vomiting may be desirable. Gastric lavage may be useful though absorption from the gastrointestinal tract is normally very rapid and complete in approximately 2 hours. This may not be the case in gross overdosage.
Treatment: Acidification of the urine will increase the elimination of trimethoprim. Including diuresis plus alkalinisation of the urine will enhance the elimination of sulphamethoxazole. Alkalinations will reduce the rate of elimination of trimethoprim. Calcium folinate (5 - 10 mg/day) will reverse any folate deficiency effect of trimethoprim on the bone marrow should this occur.
General supportive measures are recommended. Both trimethoprim and active sulphamethoxazole are dialyzable by renal dialysis.
The patients should be monitored with blood counts and appropriate blood chemistry including electrolytes.
Hypersensitivity reactions may require treatment with steroids. Calcium folinate 3 to 6 mg intramuscularly for 5 to 7 days may be given to counteract the effects of trimethoprim and haemopoieses.