ALPRIM

What it is

ALPRIM is a tablet containing 300 mg of trimethoprim as the active ingredient. Trimethoprim is a synthetic antibacterial. It blocks the formation of tetrahydrofolic acid from dihydrofolic acid by binding to and reversibly inhibiting the enzyme dihydrofolate reductase, with much stronger affinity for the bacterial enzyme than the mammalian enzyme, thus selectively interfering 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 receive one tablet daily for 7 days. Children over 6 years receive half a tablet daily for 7 days. For the treatment of acute urinary tract infection due to susceptible organisms it is not necessary to use trimethoprim for longer than 7 days. To ensure maximal urinary concentration, it may be advantageous to take the dose before bedtime. The use of trimethoprim in patients with creatinine clearance of less than 15 mL/minute is not recommended, and if the creatinine clearance is between 15 and 30 mL/minute, a reduced dose should be considered.

Key safety warnings

Elevations in serum potassium have been observed in some patients treated with trimethoprim, particularly in 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 other medicines known to increase serum potassium. Close monitoring of serum electrolytes is advised in patients at risk of hyperkalaemia. 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. 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

The 300 mg tablet is listed on the PBS with 3 items; the restriction type is streamlined; the ex-manufacturer price is A$5.07.

Regulatory history

ALPRIM trimethoprim 300 mg tablet was first listed on the Australian Register of Therapeutic Goods on 6 April 1998. The most recent approval date is 7 September 2020.