Infectotrimet (Trimethoprim)

Trimethoprim is used to treat bacterial infections that rely on folate synthesis for growth.

• Uncomplicated urinary tract infection: eradicates the causative bacteria and relieves symptoms.
• Acute otitis media: reduces bacterial load in middle‑ear infections.
• Traveler’s diarrhea (shigellosis): shortens the duration of diarrheal illness caused by susceptible strains.
• Respiratory tract infections (selected cases): provides antibacterial coverage when indicated.

• Trimethoprim selectively inhibits bacterial dihydrofolate reductase, an enzyme required for the conversion of dihydrofolic acid to tetrahydrofolic acid. By blocking this step, the drug impairs bacterial synthesis of nucleic acids and proteins, leading to inhibition of bacterial growth and replication without affecting human cells that use a different enzyme isoform.

Trimethoprim may cause a range of adverse reactions, most of which are mild and reversible.

Common Side Effects

• Nausea: mild to moderate stomach upset.
• Vomiting: occasional episodes after dosing.
• Diarrhea: loose stools during treatment.
• Skin rash: erythematous or maculopapular eruptions.
• Elevated serum creatinine: transient rise in kidney function tests.
• Hyperkalemia: modest increase in blood potassium levels.

Serious or Rare Side Effects

• Severe allergic reaction (anaphylaxis): difficulty breathing, swelling, hives.
• Hematologic abnormalities: agranulocytosis, aplastic anemia, thrombocytopenia.
• Stevens‑Johnson syndrome: severe skin blistering and mucosal involvement.
• Hepatotoxicity: elevated liver enzymes or jaundice.
• Renal toxicity: acute interstitial nephritis.
• Photosensitivity: heightened skin reaction to sunlight.

Before initiating therapy, consider patient‑specific factors and monitor appropriately.

• Renal impairment: adjust dose or avoid if severe.
• Hepatic dysfunction: use with caution and monitor liver enzymes.
• Pregnancy and lactation: assess risk‑benefit; limited data available.
• Concomitant folic‑acid antagonists: avoid combined use due to additive effects.
• History of blood dyscrasias: monitor complete blood count regularly.
• Store at ambient temperature: keep below 25 °C, retain in original packaging, protect from moisture and direct sunlight.

Trimethoprim can interact with several medicines, altering efficacy or safety.

Major Interactions (Avoid)

• Warfarin: increased anticoagulant effect, risk of bleeding.
• Phenytoin: reduced phenytoin levels, possible loss of seizure control.
• Aminoglycosides: heightened risk of nephrotoxicity.

Moderate Interactions (Monitor Closely)

• Methotrexate: additive folate antagonism, monitor for toxicity.
• Loop diuretics (e.g., furosemide): may exacerbate hyperkalemia.
• ACE inhibitors or ARBs: potential for increased serum potassium.
• Oral contraceptives: possible reduction in contraceptive efficacy.