TRIMETHOPRIM

What it is

TRIMETHOPRIM VIATRIS is a tablet containing 300 mg of trimethoprim as the active ingredient. Trimethoprim is a synthetic antibacterial that blocks the formation of tetrahydrofolic acid from dihydrofolic acid by binding to and reversibly inhibiting the enzyme dihydrofolate reductase. Its affinity for the bacterial dihydrofolate reductase enzyme is much stronger than for the corresponding mammalian enzyme, so trimethoprim selectively interferes with bacterial biosynthesis of nucleic acids and proteins.

Approved indications

— Treatment of acute urinary tract infections caused by sensitive organisms.

Dosing overview

Adults and children over 12 years should take one tablet daily for 7 days. Children over 6 years should take half a tablet daily for 7 days. The dose may be taken before bedtime to ensure maximal urinary concentration, and may be taken with some food to minimise the possibility of gastrointestinal disturbance. The use of trimethoprim in patients with creatinine clearance of less than 15 mL/minute is not recommended; if the creatinine clearance is between 15 and 30 mL/minute, a reduced dose should be considered.

Key safety warnings

Close monitoring of serum electrolytes is advised in patients at risk of hyperkalaemia. Elevations in serum potassium have been observed in some patients treated with trimethoprim. Patients at risk for the development of hyperkalaemia include older patients, those with renal insufficiency, poorly controlled diabetes mellitus, or those using concomitant potassium-sparing diuretics, potassium supplements, potassium-containing salt substitutes, renin angiotensin system inhibitors or those taking other medicines that are known to increase serum potassium. Care should be exercised in treating suspected folate deficient patients and folate supplementation should be considered. Regular monthly blood counts are advisable when trimethoprim is given for long periods since there exists a possibility of symptomatic changes in haematological laboratory indices due to lack of available folate. Trimethoprim should be discontinued if a skin rash appears. Rarely, erythema multiforme, Stevens-Johnson syndrome and toxic epidermal necrolysis occur. At the recommended dose of 300 mg daily, the incidence of rash is 7.9%, with rashes being maculopapular, morbilliform, pruritic and generally mild to moderate, appearing 7 to 14 days after the initiation of therapy. Trimethoprim has been associated with acute attacks of porphyria and is considered unsafe in porphyria patients.

Contraindications

Trimethoprim should not be given to patients with a history of trimethoprim hypersensitivity, or hypersensitivity to any other constituents of this medicine. Patients with severely impaired renal function (creatinine clearance less than 10 mL/min) should not be prescribed trimethoprim unless the plasma concentration of trimethoprim is monitored repeatedly during treatment. Severe hepatic insufficiency is a contraindication. Trimethoprim should not be given to patients with severe haematological disorders or documented megaloblastic anaemia due to folate deficiency. Trimethoprim should not be administered to premature infants or children under 4 months of age. Trimethoprim should not be administered to pregnant women and during the nursing period.

PBS listing

No source document contains PBS listing information for TRIMETHOPRIM VIATRIS.

Regulatory history

TRIMETHOPRIM tablets 300 mg were first listed on the Australian Register of Therapeutic Goods on 15 March 2007. TRIMETHOPRIM VIATRIS trimethoprim 300 mg tablet blister pack was registered on the ARTG with entry AUST R 338350 on 7 September 2020.