Trimethoprim-sulfamethoxazole (TMP-SMX, Bactrim, Septra) can be used as prophylaxis for Pneumocystis carinii infection.


Oral formulations for TMP-SMX (in fixed dose ratio of 1 to 5):

(1) single strength tablet (80 mg TMP, 400 mg SMX)

(2) double strength tablet (DS, 160 mg TMP, 800 mg SMX)

(3) suspension (8 mg TMP per mL, 40 mg SMX per mL)


Prophylaxis in adults may include one of the following:

(1) 1 double strength tablet daily

(2) 1 single strength tablet daily

(3) 1 double strength tablet daily for 3 consecutive days per week


Prophylaxis in children:

(1) daily dose based on body surface area (BSA) 150 mg TMP per square meter BSA and 750 mg SMX per square meter BSA

(2) maximum daily dose is 320 mg TMP and 1600 mg SMX

(3) daily dose divided in 2 and given orally every 12 hours

(4) therapy is given on 3 consecutive days per week

Body Surface Area

Tablet every 12 hours

< 0.53 square meter

use liquid suspension

0.53 square meter

0.5 single strength

1.06 square meter

1.0 single strength

1.59 square meters

1.5 single strength

2.12 square meter

2.0 single strength or 1 double strength


Side effects are relatively common in patients receiving prophylaxis. Lower dose or 3 day per week regimens have a lower risk of complications.


TMP-SMX is contraindicated in infants < 2 months old.


If renal function is impaired, then the dose should be reduced.


Creatinine Clearance

Dosing Adjustment

> 30 mL per min


15 - 30 mL per min

reduce by 50%

< 15 mL per min

use alternative therapy


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