Trimethoprim/Sulfamethoxazole: Price, Dosage & Where to Buy

Trimethoprim/sulfamethoxazole is an antibacterial medicine used for bacterial infections, with uncomplicated urinary tract infections being the main use described here. It requires a prescription in the United Kingdom, and generic availability dates from 1985-06-06. The treatment and safety details below relate to trimethoprim alone, so they should not be interpreted as dosing guidance for the combination product.

Trimethoprim and sulfamethoxazole are antibacterial medicines that interfere with the way bacteria make and use folate. Bacteria need folate to produce essential building blocks for their genetic material and to multiply. The medicines act at different stages of this process, limiting bacterial growth.

This explains why bacterial susceptibility matters: treatment depends on the bacteria being sensitive to the medicine. This antibacterial action is distinct from simply relieving the discomfort associated with an infection.

The trimethoprim label describes treatment of initial episodes of uncomplicated urinary tract infections caused by bacteria susceptible to trimethoprim. These include Escherichia coli, Proteus mirabilis, Klebsiella pneumoniae, Enterobacter species and certain Staphylococcus species, including Staphylococcus saprophyticus. Antibacterial treatment should be used only for infections proven or strongly suspected to involve susceptible bacteria.

Cultures and susceptibility tests help establish whether the bacteria are sensitive to treatment, although treatment may begin before results are available. These indications are stated for trimethoprim alone rather than specifically for trimethoprim/sulfamethoxazole.

The label lists oral trimethoprim/sulfamethoxazole tablets with strengths of 160 mg; 800 mg. The label lists trimethoprim-only tablets of 100 mg. The label lists the usual adult oral trimethoprim dosage as 100 mg every 12 hours or 200 mg every 24 hours, each for 10 days.

The label lists 50 mg of trimethoprim every 12 hours for patients with a creatinine clearance of 15 to 30 mL/min. The label lists use of trimethoprim as not recommended when creatinine clearance is less than 15 mL/min. These regimens concern trimethoprim alone, not the combination tablets; they must not be treated as interchangeable combination-product dosing information.

The trimethoprim tablet label specifies storage at 20° to 25°C in a tight, light-resistant container with a child-resistant closure. Keep the medicine in its labelled container and out of the reach of children.

A missed antibiotic dose can interrupt the intended treatment schedule. General pharmacy advice is to resume the prescribed schedule rather than double a dose to compensate. If the timing is unclear, a pharmacist can advise using the dispensing label and the exact product prescribed, particularly because trimethoprim alone and the combination are different products.

Trimethoprim may interfere with folic acid metabolism. The label states that it should be used during pregnancy only when the potential benefit justifies the potential risk to the fetus. Animal studies reported developmental harm, and there are no large, well-controlled studies in pregnant women.

Discuss pregnancy with the prescriber. The label does not specify human breastfeeding guidance; discuss this with a doctor or pharmacist.