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A.     Background

Patients being treated for cancer have a higher incidence of P. carinii infection. This risk can effectively be reduced by administering trimethoprim/sulfamethoxazole (TMP/SMX).

The low dosage suggested below does not appear to enhance bone marrow suppression from moderately aggressive programs of chemotherapy However, this may not be true with more intensive cytotoxic regimens. When prolonged marrow suppression occurs in patients receiving TMP/SMX, consider withholding this agent rather than decreasing the dosage of chemotherapy and using pentamidine or dapsone.

The incidence of Pneumocystis infection varies from institution to institution and possibly from tumor to tumor and protocol to protocol, so the indications for prophylaxis may vary. However, in the interest of achieving uniformity of care, the use of TMP/SMX to prevent Pneumocystis pneumonia is recommended for all patients on chemotherapy.

B.     Dosage

TMP 5 mg/kg/day (150 mg/m2/day) and SMX 25 mg/kg/day (750 mg/m2/day) are given in two divided doses 3 days a week.

TMP/SMX therapy should start with the initiation of chemotherapy and continue for 8 to 12 weeks after chemotherapy is stopped.

C.     Preparations

Tablet: TMP 80 mg/SMX 400 mg Double-strength tablet: TMP 160 mg/SMX 800 mg

Suspension: TMP 40 mg/SMX 200 mg/5 ml.

D.     Intolerance of or allergy to TMP/SMX

For patients who are repeatedly unable to tolerate full doses of chemotherapy because of allergy or myelosuppression, omit TMP/SMX prophylaxis. Consider inhalation or intravenous pentamidine or dapsone where the possibility of Pneumocystis infection is high.

The prophylactic regimen for dapsone is 2 mg/kg/day as a single dose. (It comes in 25 and 100 mg tablets.)

The prophylactic regimen for IV pentamidine is 4 mg/kg (diluted in 50-250 ml of dextrose 5% in water) infused over 60 minutes IV q4wk.

The prophylactic regimen for inhalation pentamidine is 8 mg/kg for children < 5 years old and 300 mg for children > 5 years old. It is administered q4wk via the Respirgard II nebulizer.