Hesperian Health Guides

Antibiotics Fight Infection

Good Food Makes Good Health: Medicines

Cotrimoxazole, Trimethoprim/ sulfamethoxazole, TMP-SMX

Cotrimoxazole, a combination of 2 antibiotics, is inexpensive and fights a wide range of infections. It is an important medicine for people with HIV and can prevent the many infections that come as a result of infection with HIV. See HIV and AIDS (in development).


Avoid giving cotrimoxazole to babies less than 6 weeks old and to women in the last 3 months of pregnancy. Allergy to this medicine is common. Signs of allergic reaction are fever, difficulty breathing, or rash. Stop using it if a rash develops or if you think there may be an allergy.

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Cotrimoxazole comes in different strengths of each of the 2 medicines it contains. So it may say 200/40 (meaning 200 mg sulphamethoxazole and 40 mg trimethoprim) or 400/80 or 800/160. A dose is sometimes described only in terms of the amount of trimethoprim (the second number).
6 weeks to 5 months: give sulfamethoxazole 100 mg + trimethoprim 20 mg, 2 times a day for 5 days.
6 months to 5 years: give sulfamethoxazole 200 mg + trimethoprim 40 mg, 2 times a day for 5 days.
6 to 12 years: give sulfamethoxazole 400 mg + trimethoprim 80 mg, 2 times a day for 5 days.
Over 12 years: give sulfamethoxazole 800 mg + trimethoprim 160 mg, 2 times a day for 5 days.


Amoxicillin is a broad-spectrum penicillin, which means it kills many kinds of bacteria. It is usually interchangeable with ampicillin. When you see a recommendation for amoxicillin in this book, you will often be able to use ampicillin in its place, in the correct dose. Both are very safe and are especially useful for babies and small children.

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Amoxicillin often causes nausea and diarrhea (but not as often as ampicillin does). Avoid giving it to those who already have diarrhea if you can give another antibiotic instead.

The other common side effect is rash. But raised, itchy bumps that come and go in a few hours are probably a sign of penicillin allergy. Stop giving the medicine right away and do not give the person a penicillin medicine again. Future allergic reactions may be more severe and even life-threatening. For some problems, erythromycin can be used instead. A flat rash that looks like measles, and usually appears a week after starting the medicine and takes days to go away, is not necessarily an allergy. But it is impossible to know for sure if the rash is from allergy or not, so it is usually better to stop taking the medicine.


Resistance to amoxicillin is growing more common. Depending on where you live, it may not work any more against staphylococcus, gonorrhea, shigella, or other infections.

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Amoxicillin works well when taken by mouth. To give tablets or capsules to a baby, crush the pills or empty the capsules and divide the powder to get the amount you need. Then mix it into a little breast milk. Feed the milk and medicine to the baby with a cup or spoon.

As with other antibiotics, always give these medicines for at least the shorter number of days shown here. If the person still has signs of infection, have her continue taking the same amount every day until all signs of infection have been gone for at least 24 hours. If the person has taken the medicine for the maximum number of days and is still sick, stop giving the antibiotic and get medical help. For people with HIV, give the medicine for the full number of days listed.

Likewise, the amount of antibiotic to take depends on the age or weight of the person and the severity of the infection. In general, give the smaller amount for a thinner person or a less severe infection, and the larger amount for a heavier person or a more severe infection.

Give 45 to 50 mg per kg each day, divided into 2 doses a day. If you cannot weigh the person,
dose by age:
Under 3 months: give 125 mg, 2 times a day for 7 to 10 days.
3 months to 3 years: give 250 mg, 2 times a day for 7 to 10 days.
4 to 7 years: give 375 mg, 2 times a day for 7 to 10 days.
8 to 12 years: give 500 mg, 2 times a day for 7 to 10 days.
Over 12 years: give 500 to 875 mg, 2 times a day for 7 to 10 days.

This page was updated:05 Jan 2024