Indications
Sulphamethoxazole is an antibiotic that is almost always given together with Trimethoprim (this combination is called co-trimoxazole). It is used for urinary tract infections, some chest and ear infections, some bacterial diarrhoea, and to treat and prevent Pneumocystis pneumonia in people with weak immunity, such as people living with HIV.
How It Works
Sulphamethoxazole is a sulfonamide. It blocks bacteria from making folic acid, which they need to grow. Trimethoprim blocks a later step in the same process, so the two together work better than either alone.
Dosage and Administration
- Adults: usually 800 mg sulphamethoxazole with 160 mg Trimethoprim (one double-strength tablet or two standard tablets) every 12 hours. The length of the course depends on the infection, often 3 to 14 days.
- Pneumocystis treatment or prevention, and children: as prescribed.
- Injection: given by a doctor or nurse in hospital.
Take with food and drink plenty of water.
Interactions
It can increase the effect of Warfarin (bleeding risk), Phenytoin, and diabetes tablets such as Glibenclamide (low blood sugar). With Methotrexate or Pyrimethamine it can cause serious blood problems. With ACE inhibitors such as Enalapril, Spironolactone or potassium supplements it can raise blood potassium. It may also raise levels of Digoxin and affect Ciclosporin.
Contraindications
- Allergy to sulfonamides (sulfa medicines) or to Trimethoprim.
- Severe liver disease, or severe kidney disease where blood levels cannot be checked.
- Anaemia caused by lack of folic acid.
- Babies under 6 weeks of age.
- Porphyria.
Side Effects
Common: nausea, vomiting, loss of appetite, rash and itching.
Get urgent medical help if you have a rash with blisters, peeling skin or mouth sores, especially with fever; yellowing of the skin or eyes; unusual bruising or bleeding; sore throat, fever or mouth ulcers that do not go away; severe or bloody diarrhoea; or swelling of the face or difficulty breathing.
Pregnancy and Lactation
It is usually avoided in the first three months of pregnancy, because it works against folic acid, and near delivery, because it can cause jaundice in the newborn. A doctor may still use it when the benefit is greater than the risk. In breastfeeding, avoid it if the baby is premature, jaundiced, ill or has G6PD deficiency; otherwise ask the doctor.
Precautions and Warnings
Older people are more likely to have serious side effects. People with G6PD deficiency may have breakdown of red blood cells. Tell the doctor about kidney or liver disease, asthma or severe allergies. Drink plenty of fluids, avoid strong sunlight, and expect blood tests on long courses. People living with HIV are more prone to side effects.
Overdose
Symptoms include nausea, vomiting, dizziness, headache and confusion. Get urgent medical help. Long-term high doses can affect blood cell production.
Therapeutic Class
Sulfonamide antibiotic (used with Trimethoprim as a folate antagonist combination).
Storage
Store below 30°C in a dry place, away from light and out of the reach of children.
Prepared by the Oshud Alo team from standard drug references. For information only; always follow your doctor's advice.