Trimethoprim

Trimethoprim is an antibiotic used to treat bacterial infections. It works by stopping the growth of bacteria.

Trimethoprim treats only bacterial infections. It will not work for viral infections (e.g., common cold, flu). Unnecessary use or overuse of any antibiotic can lead to its decreased effectiveness.

Trimethoprim may also be used to treat some lung infections (Pneumocystis carinii pneumonia) and to prevent kidney infections in certain patients.

Trimethoprim is available under the following different brand names: Primsol, Proloprim, and TMP.

Dosage Forms and Strengths

Oral solution

• 50 mg/5mL

Tablets

• 100 mg

Dosage Considerations – Should be Given as Follows:

Susceptible Infections

• 100 mg orally every 12 hours

Renal Impairment

• CrCl 15-30 mL/min: 50 mg every 12 hours
• CrCl less than 15 mL/min: 100 mg every 24 hours or avoid use

Other Information

• See also combo with sulfamethoxazole (Cotrim/Bactrim/Septra/Sulfatrim)
• Available also as a combo with sulfadiazine (Coptin) in Canada

Other Indications and Uses

• Urinary tract infection (UTI) caused by E. coli, Enterobacter spp., K. pneumoniae, P. mirabilis, coagulase-negative Staphylococcus spp
• Pediatric: Children under 12 years old: safety and efficacy not established

Common side effects of trimethoprim include:

• Aseptic meningitis
• BUN and creatinine increased
• Changes in taste
• Cholestatic jaundice
• Diarrhea
• Erythema multiforme
• Exfoliative dermatitis
• Fever
• Headache
• High blood potassium (hyperkalemia)
• Hypersensitivity reactions
• Itching (common)
• Liver enzyme elevation
• Loss of appetite
• Low blood platelet count (thrombocytopenia)
• Low blood sodium (hyponatremia)
• Low white blood cell count (leukopenia, neutropenia)
• Maculopapular rash (3-7% at 200 mg/day; incidence higher with larger daily doses)
• Megaloblastic anemia
• Methemoglobinemia
• Nausea
• Phototoxic skin eruptions
• Severe allergic reaction (anaphylaxis)
• Skin sensitivity to sunlight
• Stevens-Johnson syndrome
• Stomach pain or upset
• Swollen tongue
• Toxic epidermal necrolysis
• Vomiting

This document does not contain all possible side effects and others may occur. Check with your physician for additional information about side effects.

If your doctor has directed you to use this medication, your doctor or pharmacist may already be aware of any possible drug interactions and may be monitoring you for them. Do not start, stop, or change the dosage of any medicine before checking with your doctor, health care provider or pharmacist first.

• Trimethoprim has no known severe interactions with other drugs.
• Trimethoprim has serious interactions with at least 21 different drugs.
• Trimethoprim has moderate interactions with at least 124 different drugs.
• Trimethoprim has mild interactions with at least 29 different drugs.

This information does not contain all possible interactions or adverse effects. Therefore, before using this product, tell your doctor or pharmacist of all the products you use. Keep a list of all your medications with you, and share this information with your doctor and pharmacist. Check with your health care professional or doctor for additional medical advice, or if you have health questions, concerns or for more information about this medicine.

Warnings

This medication contains trimethoprim. Do not take Primsol, Proloprim, or TMP if you are allergic to trimethoprim or any ingredients contained in this drug.

Keep out of reach of children. In case of overdose, get medical help or contact a Poison Control Center immediately.

Contraindications

• Hypersensitivity
• Megaloblastic anemia due to folate deficiency

Effects of Drug Abuse

• None

Short-Term Effects

• See "What Are Side Effects Associated with Using Trimethoprim?"

Long-Term Effects

• Large doses or long-term therapy may interfere with hematopoiesis; monitor for signs/symptoms of hematologic disorders
• Prolonged use may cause fungal or bacterial superinfection, including Clostridium difficile-associated diarrhea and pseudomembranous colitis; may occur greater than 2 months post-antibiotic treatment
• See "What Are Side Effects Associated with Using Trimethoprim?"

Cautions

• Decreases urinary potassium excretion; may cause hyperkalemia, particularly with high doses, renal insufficiency, or when combined with other drugs that cause hyperkalemia
• Large doses or long-term therapy may interfere with hematopoiesis; monitor for signs/symptoms of hematologic disorders
• Prolonged use may cause fungal or bacterial superinfection, including Clostridium difficile-associated diarrhea and pseudomembranous colitis; may occur greater than 2 months post-antibiotic treatment
• Hypersensitivity reactions reported
• Use caution in patients with renal or hepatic impairment
• Use caution in patients with potential for folate deficiency, including malnourished, chronic anticonvulsant therapy, or elderly; folates may be administered concomitantly without interfering with antibacterial action of trimethoprim
• Some dosage forms may contain benzyl alcohol and derivatives; avoid in neonates
• Not indicated for prophylactic or prolonged administration in otitis media at any age

Pregnancy and Lactation

• Use trimethoprim with caution during pregnancy if benefits outweigh risks
• Animal studies show risk and human studies are not available or neither animal nor human studies were done
• Trimethoprim enters breast milk. Consult your doctor before breastfeeding