Why is this drug prescribed?

Bactrim infusion, tablets, forte tablets and suspensions all contain the active ingredients sulfamethoxazole and trimethoprim, which together are known as co-trimoxazole. Co-trimoxazole is also available without a brand name, ie as the generic drug. Sulfamethoxazole and trimethoprim are both antibiotics that are used to treat infections caused by bacteria. Sulfamethoxazole is a type of antibiotic called a sulphonamide. Trimethoprim is related to the sulphonamides. These two antibiotics work in synergy together against certain types of bacteria. In order to grow and multiply in numbers, bacterial cells need to produce genetic material. To produce DNA they require folic acid. However, bacterial cells can't take up folic acid supplied in the diet like human cells can. Instead, they synthesise it themselves. Sulfamethoxazole and trimethoprim act on two different stages in the synthesis of bacterial folate, preventing the bacteria from producing folate. Without folate, the bacteria cannot produce DNA and so are unable to increase in numbers. Co-trimoxazole therefore stops the spread of infection. The remaining bacteria are killed by the immune system or eventually die. To make sure the bacteria causing an infection are susceptible to co-trimoxazole, your doctor may take a tissue sample, for example a swab from the infected area, or a urine or blood sample. Co-trimoxazole is used to treat a small number of serious infections, but serious side effects limit its use. Less serious infections such as urinary tract infections and otitis media are only treated with co-trimoxazole when there is good evidence from microscopy and culture that the bacteria are sensitive to co-trimoxazole, and there is good reason to prefer the combination to a single antibiotic.

Treatments

* Prevention and treatment of pneumonia caused by the bacterium pneumocystis carinii. This infection is most common in people with decreased immune system function, for example due to HIV or AIDS. * Prevention and treatment of toxoplasmosis * Treatment of a lung infection called nocardiosis * Infection of the bladder or tubes that pass urine * Flare-ups of chronic bronchitis * Middle ear infections

What side effects can this drug cause?

* Headache * Rash * Diarrhoea * Nausea and vomiting * Overgrowth of the yeast Candida, which may cause infection such as thrush * Increased amount of potassium in the blood * Disturbances in the normal numbers of blood cells in the blood * Decreased amount of sodium in the blood * Low blood sugar level * Loss of appetite * Inflammation of the lining of the mouth * Dizziness * Depression * Hallucinations * Cough * Shortness of breath * Pain in the muscles * Seizures * Liver or kidney disorders * Severe blistering skin reactions, eg Stevens-Johnson Syndrome, toxic epidermal necrolysis