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Trimethoprim

Trimethoprim is a generic medication for the drug :

Trimethoprim medication comes in several different strengths; click on the strength you need to view prices from pharmacies competing to earn your business.

Trimethoprim 100 mg	Trimethoprim 200 mg	Trimethoprim/sulfamethoxazole 800mg/160mg

Trimethoprim 100 mg

Trimethoprim 200 mg

Trimethoprim/sulfamethoxazole 800mg/160mg

Technical Information

Drug Interactions

Trimethoprim

Drug-Drug Interactions

Interacting Drug	Effect	Clinical Comment
Angiotensin Converting Enzyme Inhibitors	↑ potassium levels	Monitor serum potassium and renal function, especially if other co-existing factors for hyperkalemia are present such as diabetes mellitus, pre-existing renal dysfunction and age-related decline in glomerular filtration rate.
Cyclosporine	↓ serum concentration of cyclosporine. Risk of nephrotoxicity may ↑ with combination.	If administered concomitantly, monitor renal function and cyclosporine levels. Adjust cyclosporine dose during trimethoprim treatment and upon discontinuation.
Dapsone	Serum levels of both drugs may ↑ due to interference with clearance. May lead to ↑ toxicity from either agent.	Monitor for signs and symptoms of toxicity (e.g., methemoglobinemia, leukopenia, rash, fever, vomiting). Combination of trimethoprim and dapsone may result in megaloblastic anemia in patients with underlying vitamin B₁₂ deficiency, especially in AIDS patients.
Lamivudine	May ↑ plasma lamivudine levels through inhibiting renal secretion.	Not clinically significant. Consider adjusting lamivudine dose in renal impairment.
Methotrexate	May ↑ the risk of methotrexate-induced hematologic toxicity (e.g., bone marrow suppression, megaloblastic anemia, pancytopenia).	If concomitant treatment is necessary, monitor patients (e.g., elderly) closely for signs of hematologic toxicity. Monitor CBC with differential.
Phenytoin	Inhibition of hepatic metabolism of phenytoin. May ↑ serum phenytoin concentrations.	Monitor for ↑ pharmacologic and adverse effects of phenytoin. Monitor phenytoin levels during trimethoprim treatment and after discontinuation.
Procainamide	Reduces renal clearance through ↓ net tubular cationic secretion. May ↑ plasma concentrations of procainamide and its active metabolite, N-acetylprocainamide (NAPA).	Monitor procainamide and NAPA levels and adjust dose accordingly upon addition and discontinuation of trimethoprim.
Repaglinide	May ↑ repaglinide plasma concentration by inhibiting its CYP2C8 metabolism.	Monitor blood glucose levels during trimethoprim treatment and after discontinuation. Adjust repaglinide dose if necessary.
Rosiglitazone	May ↑ rosiglitazone plasma concentration by inhibiting its CYP2C8 metabolism.	Monitor blood glucose levels during trimethoprim treatment and after discontinuation. Adjust rosiglitazone dose if necessary.
Theophylline	May ↑ the risk of developing hyponatremia.	Monitor for symptoms of hyponatremia, e.g., fatigue, weakness, nausea, vomiting, dizziness.
Zidovudine	May ↑ plasma concentration of zidovudine by ↓ renal clearance	Monitor for increased pharmacologic and adverse effects (gastrointestinal disturbances, headache, fatigue) of zidovudine. Consider adjusting zidovudine dose in renal impairment.

Drug-Food Interactions

May be taken with food or milk to minimize gastrointestinal upset.

Trimethoprim does not interfere with the radioimmunoassay method for determining serum methotrexate levels; however, trimethoprim interferes with methotrexate assays that use a competitive binding protein technique with bacterial dihydrofolate reductase as the binding protein.

Falsely elevated creatinine values (overestimation of 10%) may result from trimethoprim therapy using creatinine assays using the Jaffe alkaline picrate reactions.

Serum alkaline phosphatase levels may be elevated by trimethoprim.

Serum potassium levels may be elevated by trimethoprim.

Overview

Folic acid may be administered during therapy with trimethoprim without interfering with its antibacterial effect.

Dosage and Administration

Dialysis

Trimethoprim is dialyzable. A maintenance dose is recommended after dialysis.

Trimethoprim

Dose in Adult Patients

Indication	Usual Dose	Duration of Therapy	Clinical Comment
Bacteriuria, asymptomatic	100 mg po q12h or 200 mg po q24h	3 days	Avoid in first trimester of pregnancy due to concerns of limiting availability of folic acid to the fetus thereby increasing the risk of neural tube defects. Follow-up culture after completion of therapy and monthly culture is recommended in pregnancy. Screening for asymptomatic bacteriuria is recommended in patients undergoing pre-operative genitourinary procedures and in pregnancy.
Cystitis, recurrent (< 1 month)	100 mg po BID or 200 mg po daily	10–14 days
Cystitis, recurrent (≥ 3 episodes/ year)	Prophylaxis: 100 mg po QHS or post-coital	≥ 3 UTIs/year: 12 months	With suppressive therapy, bacterial growth is suppressed. Active infection is not eliminated. If < 3 UTIs/year: consider short course self-treatment.
Urinary tract infection, acute uncomplicated	100 mg po q12h or 200 mg po q24h	7–10 days	First-line agent. May be used as an alternative in patients with a sulfa allergy. Monotherapy as effective as sulfamethoxazole-trimethoprim with comparatively fewer side effects. Avoid in first trimester of pregnancy. Recommended if prevalence of resistant E. coli is < 20%. Consider resistance in patients who have failed empiric therapy or who have had recent TMP therapy.
Urinary tract infection, acute uncomplicated	100–200 mg po BID	3 days	First-line agent. Monotherapy as effective as sulfamethoxazole-trimethoprim with fewer side effects. Avoid in first trimester of pregnancy. Recommended if prevalence of resistant E. coli is < 20%. Consider resistance in patients who have failed empiric therapy or who have had recent TMP therapy.
Urinary tract infections, prophylaxis	100 mg po once daily	< 3 UTIs/year: 6 months ≥ 3 UTIs/year: 12 months	With suppressive therapy, bacterial growth is suppressed. Active infection is not eliminated.
Pneumonia, P. jirovecii	15–20 mg/kg po daily divided q6–8h	21 days	Alternative agent for mild to moderate disease. Administered in conjunction with dapsone 100 mg po daily × 21 days.
Prostatitis, acute	200 mg po q12h	4–12 weeks	For mild to moderate acute prostatitis. Only prescribed once culture and sensitivity results are available. Used in situations where prevalence of resistant E. coli is < 20%. Used in sulfa-allergic patients.
Prostatitis, chronic	200 mg po BID	4–6 weeks	Second-line agent.
Pyelonephritis, uncomplicated, non-obstruction, mild	100 mg po BID or 200 mg po daily	10–14 days

Trimethoprim

Dose in Adult Patients with Renal Impairment

Creatinine Clearance	Interval Adjustment
> 30 mL/min	q12h
10–30 mL/min	q18h
< 10 mL/min	q24h

Trimethoprim

Dose in Pediatric Patients

Indication	Usual Dose	Duration of Therapy	Clinical Comment
Urethritis, nongonococcal	< 9 y: 4 mg/kg daily po divided q12h	10 days	Second- line agent.
Urinary tract infection, uncomplicated	< 12 y: 4 mg/kg daily po divided q12h, max 200 mg/day	10 days	Second- line agent.
Urinary tract infection, prophylaxis	2 mg/kg daily po divided BID or given as a single dose
Vesicoureteral Reflux	¼ to ⅓ of the dose necessary to treat an acute infection given once daily	Continue until the child remains free of infection	Continue prophylaxis with trimethoprim until resolution of reflux or until the risk of reflux is considered low by the physician. Perform a urine culture and sensitivity test if there are signs and symptoms of a urinary tract infection.

Recommended Dose and Dosage Adjustment

Adverse Reactions

Hepatic/Biliary/Pancreatic

elevated serum transaminases, cholestatic jaundice.

Gastrointestinal

glossitis.

Hematologic

leukopenia, megaloblastic anemia, neutropenia, thrombocytopenia.

Immune

anaphylaxis, vasculitis.

Allergic/Dermatologic

erythema multiforme, exfoliative dermatitis, Stevens-Johnson syndrome, toxic epidermal necrolysis, erythematous skin eruptions, fixed drug eruption.

Adverse Drug Reactions Overview

Although trimethoprim is generally well tolerated, deaths have rarely been associated with hypersensitivity reactions, fulminant hepatocellular necrosis, agranulocytosis, aplastic anemia or other blood dyscrasias.

Less Common Adverse Drug Reactions (< 1%)

Endocrine and Metabolism

hyperkalemia (dose dependent), hyponatremia, arthritis.

Central Nervous System

aseptic meningitis, encephalitis.

Ophthalmologic

uveitis.

Trimethoprim

More Common Adverse Drug Reactions (≥1%)

Body System	Effect	Clinical Comment
Dermatologic	Pruritus, rash	Frequency of maculopapular rash increases with higher doses of trimethoprim.
Gastrointestinal	Nausea, vomiting	Incidence and severity may be dose-related.
Renal	↑ creatinine	May ↑ creatinine without affecting glomerular filtration rate due to inhibition of tubular secretion of creatinine.

Supplied

See Summary Product Information.

Indications and Clinical Use

Pediatrics

Trimethoprim is used as a second-line agent in the treatment of acute urinary tract infection in children. It may be used as prophylaxis in children with vesicoureteral reflux. Trimethoprim is recommended as a second-line agent in children > 9 years for the treatment of nongonococcal urethritis.

Overdosage

For management of a suspected drug overdose, CPhA recommends that you contact your regional Poison Control Centre. See the eCPS Directories section for a list of Poison Control Centres.

Warnings and Precautions

Geriatrics

Elderly patients may have an increased risk of severe adverse reactions to trimethoprim, especially in those with impaired renal function or in those receiving drugs with the potential to interact with trimethoprim.

Special Populations

Pregnant Women

Category C. Trimethoprim crosses the placenta. The drug levels are similar in maternal and fetal serum and in amniotic fluid. Trimethoprim use during the first trimester may limit the availability of folic acid to the fetus and therefore be associated with structural defects in the newborn. (See Indications and Clinical Use.) The risk of neural tube defects is increased by treatment with trimethoprim. An increased risk of cardiovascular defects was found in newborns when trimethoprim was taken in the second or third month of pregnancy.

Nursing Women

Because trimethoprim is excreted into breast milk in low concentrations, the levels may be negligible to the infant. According to the American Academy of Pediatrics, the combination of sulfamethoxazole and trimethoprim is compatible with breastfeeding.

Monitoring and Laboratory Tests

Monitor renal function (serum creatinine, urea) and perform urinalysis in patients with renal impairment. Monitor complete blood count in those at higher risk of folate deficiency or during long-term therapy. Monitor serum potassium in patients at risk of hyperkalemia.

Action and Clinical Pharmacology

Mechanism of Action

Trimethoprim reversibly inhibits dihydrofolate reductase in susceptible bacteria preventing the conversion of dihydrofolic acid to tetrahydrofolic acid. Tetrahydrofolic acid is a precursor required for de novo synthesis of purines. By blocking the enzyme, trimethoprim inhibits bacterial DNA replication and transcription.

Trimethoprim is 50 000 to 100 000 times more active against bacterial dihydrofolate reductase than human dihydrofolate reductase. For this reason, human purine synthesis is not significantly affected.

Trimethoprim

Summary of the Pharmacokinetic Properties of Trimethoprim After Oral Administration

Oral bioavailability	80-90%
Serum half-life	Normal renal function: 9–13 h End-stage renal disease: 20–49 h
Peak serum concentration following single-dose oral administration (within 1–4 hours after administration)	100 mg	1 µg/L
	200 mg	2 µg/L
Range of urine concentration following single-dose oral administration of 100 mg	30–60 µg/mL
Plasma protein binding (%)	30–70
Volume of distribution (L/kg)	1.0–2.2
Total clearance	0.12 L/hour/kg
Primary route of elimination	60-80% renally excreted unchanged

Contraindications

Patients who are hypersensitive to trimethoprim or to any ingredient in the formulation or component of the container.

Patients with documented megaloblastic anemia due to folate deficiency.

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