All infants born to HIV-positive women should be given prophylactic co-trimoxazole from 6 weeks until one year or until HIV infection in the child has been excluded by PCR testing. Prophylaxis should be continued beyond one year in any child with clinical signs of HIV infection. Prophylactic co-trimoxazole syrup is usually given daily for 5 days a week (Monday to Friday). The dose depends on the child’s weight:
| Weight | Daily dose |
| < 5 kg | 2.5 ml paediatric suspension |
| 5–9 kg | 5 ml paediatric suspension |
| 10–14 kg | 7.5 ml paediatric suspension |
| 15–22 kg | 10 ml (or 1 regular strength tablet) |
| > 22 kg | 15 ml (or 1.5 regular strength tablets) |
Co-trimoxazole can also be given 3 times a week (e.g. Monday, Wednesday and Friday)
Prophylactic co-trimoxazole decreases the risk of pneumonia caused by Pneumocystis. It also reduces the risk of other bacterial infections and diarrhoea due to some opportunistic infections.
Side effects to co-trimoxazole are uncommon in children. However, co-trimoxazole must be stopped immediately and the child referred if a maculopapular rash (red and easily palpable) develops as this may be the first sign of severe allergy to the drug.
Prophylactic co-trimoxazole reduces the risk of pneumocystis pneumonia.