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Related to Primsol: Proloprim, Trimpex


(trye-meth-oh-prim) ,


(trade name)


Therapeutic: anti infectives
Pharmacologic: folate antagonists
Pregnancy Category: C


Treatment of uncomplicated urinary tract infections.Treatment of uncomplicated otitis media in children.Prophylaxis of chronic recurrent urinary tract infections.Treatment of head lice.With dapsone in the management of mild to moderate Pneumocystis jirovecii pneumonia (PCP).


Interferes with bacterial folic acid synthesis.

Therapeutic effects

Bactericidal action against susceptible organisms.
Some gram-positive pathogens, including:
  • Streptococcus pneumoniae,
  • Group A beta-hemolytic streptococci,
  • Some staphylococci and Enterococcus.
Gram-negative spectrum includes the following Enterobacteriaceae:
  • Acinetobacter,
  • Citrobacter,
  • Enterobacter,
  • Escherichia coli,
  • Haemophilus influenzae,
  • Klebsiella pneumoniae,
  • Proteus mirabilis,
  • Salmonella,
  • Shigella.
Other strains of Proteus, some Providencia, some Serratia, and P. jirovecii are also susceptible.


Absorption: Well absorbed following oral administration.
Distribution: Widely distributed. Crosses the placenta and is distributed into breast milk in high concentrations.
Metabolism and Excretion: 80% excreted unchanged in the urine; 20% metabolized by the liver.
Half-life: 8–11 hr (↑ in renal impairment).

Time/action profile (blood levels)

POrapid1–4 hr12–24 hr


Contraindicated in: Hypersensitivity; Megaloblastic anemia secondary to folate deficiency.
Use Cautiously in: Renal impairment (dose ↓ required if CCr ≤30 mL/min); Debilitated patients; Severe hepatic impairment; Folate deficiency; Obstetric / Lactation / Pediatric: Pregnancy, lactation, or children <12 yr (safety as a single agent not established).

Adverse Reactions/Side Effects


  • altered taste (most frequent)
  • epigastric discomfort (most frequent)
  • glossitis (most frequent)
  • nausea (most frequent)
  • vomiting (most frequent)
  • drug-induced hepatitis


  • pruritus (most frequent)
  • rash (most frequent)


  • megaloblastic anemia
  • neutropenia
  • thrombocytopenia


  • fever


Drug-Drug interaction

↑ risk of folate deficiency when used with phenytoin or methotrexate.↑ risk of bone marrow depression when used with antineoplastics or radiation therapy.Rifampin may ↓ effectiveness by ↑ elimination.


Treatment of Urinary Tract Infections
Oral (Adults and Children ≥12 yr) 100 mg q 12 hr or 200 mg as a single daily dose.
Treatment of Otitis Media
Oral (Children >6 mos) 5 mg/kg q 12 hr.
Prophylaxis of Chronic Urinary Tract Infections
Oral (Adults) 100 mg/day as a single dose (unlabeled).
Pneumocystis jirovecii Pneumonia
Oral (Adults) 20 mg/kg/day with 100 mg dapsone daily for 21 days (unlabeled).

Renal Impairment

Oral (Adults) CCr 15–30 mL/min—50 mg q 12 hr (for urinary tract infections.

Availability (generic available)

Tablets: 100 mg, 200 mg
Oral solution (alcohol-and dye-free)bubblegum flavor: 50 mg/5 mL
In combination with: sulfamethoxazole. See Trimethoprim/Sulfamethoxazole monograph.

Nursing implications

Nursing assessment

  • Assess patient for urinary tract infection (fever, cloudy urine, frequency, urgency, pain and burning on urination) or other signs of infection at beginning of and throughout therapy.
  • Obtain specimens for culture and sensitivity prior to initiating therapy. First dose may be given before receiving results.
  • Monitor intake and output ratios. Fluid intake should be sufficient to maintain urine output of at least 1200–1500 mL daily.
  • Lab Test Considerations: May produce elevated serum bilirubin, creatinine, BUN, AST, and ALT.
    • Monitor CBC and urinalysis periodically throughout therapy. Therapy should be discontinued if blood dyscrasias occur.

Potential Nursing Diagnoses

Risk for infection (Indications,  Side Effects)


  • Oral: Administer on an empty stomach, at least 1 hr before or 2 hr after meals, with a full glass of water. May be administered with food if GI irritation occurs.

Patient/Family Teaching

  • Instruct patient to take medication and to finish medication completely as directed, even if feeling better. Take missed doses as soon as remembered, with subsequent doses spaced evenly apart. Advise patient that sharing of this medication may be dangerous.
  • Advise patient to notify health care professional if skin rash, sore throat, fever, mouth sores, or unusual bleeding or bruising occurs. Leucovorin (folinic acid) may be administered if folic acid deficiency occurs.
  • Instruct patient to notify health care professional if symptoms do not improve.
  • Emphasize the importance of routine follow-up exams to evaluate progress.

Evaluation/Desired Outcomes

  • Resolution of the signs and symptoms of infection. Therapy is usually required for 10–14 days for resolution of urinary tract infection.
  • Decreased incidence of urinary tract infections during prophylactic therapy.
Drug Guide, © 2015 Farlex and Partners


Pediatrics A formulation of Trimethoprim for managing acute otitis media in younger children. See Acute otitis media.
McGraw-Hill Concise Dictionary of Modern Medicine. © 2002 by The McGraw-Hill Companies, Inc.