TRIMETHOPRIM

(trye-meth'oh-prim)

Primsol, Proloprim
Classifications: antiinfective, urinary tract;
Therapeutic: antiinfective, urinary tract
Pregnancy Category: C

Availability

100 mg, 200 mg tablets; 50 mg/5 mL liquid

Action

Antiinfective and folic acid antagonist with slow bactericidal action. Binding and interference with bacterial cell growth.

Therapeutic Effect

Effective against most common UTI pathogens. Most pathogens causing UTI are in normal vaginal and fecal flora.

Uses

Initial episodes of acute uncomplicated UTIs, acute otitis media in children.

Unlabeled Uses

Treatment and prophylaxis of chronic and recurrent UTI in both men and women; treatment in conjunction with dapsone of initial episodes of Pneumocystis carinii pneumonia; treatment of travelers' diarrhea.

Contraindications

Megaloblastic anemia secondary to folate deficiency; creatinine clearance <15 mL/min, impaired kidney or liver function; possible folate deficiency; pregnancy (category C), or in children with fragile X chromosome associated with mental retardation. Safety in infants <2 mo has not been established.

Cautious Use

Renal disease; mild or moderate renal impairment; lactation.

Route & Dosage

Urinary Tract Infection
Adult: PO 100 mg b.i.d. or 200 mg once/d
Child: PO 2–3 mg/kg q12h x 10 d

Acute Otitis Media
Child (>6 mo): PO 10 mg/kg divided q12h x 10 d

Travelers' Diarrhea
Adult: PO 200 mg b.i.d.

Administration

Oral

Give with 240 mL (8 oz) of fluid if not contraindicated.
Store at 15°–30° C (59°–86° F) in dry, light-protected place.

Adverse Effects (≥1%)

GI: Epigastric discomfort, nausea, vomiting, glossitis, abnormal taste sensation. Hematologic: Neutropenia, megaloblastic anemia, methemoglobinemia, leukopenia, thrombocytopenia (rare). Skin: Rash, pruritus, exfoliative dermatitis, photosensitivity. Body as a Whole: Fever. Metabolic: Increased serum transaminases (ALT, AST), bilirubin, creatinine, BUN.

Diagnostic Test Interference

Interferes with serum methotrexate assays that use a competitive binding protein technique with a bacterial dihydrofolate reductase as the binding protein. May cause falsely elevated creatinine values when Jaffe reaction is used.

Interactions

Drug: May inhibit phenytoin metabolism causing increased levels.

Pharmacokinetics

Absorption: Almost completely absorbed from GI tract. Peak: 1–4 h. Distribution: Widely distributed, including lung, saliva, middle ear fluid, bile, bone, CSF; crosses placenta; appears in breast milk. Metabolism: In liver. Elimination: 80% in urine unchanged. Half-Life: 8–11 h.

Nursing Implications

Assessment & Drug Effects

Lab tests: Obtain C&S tests before trimethoprim therapy is initiated; therapy may be started before results are received. Obtain periodic urine cultures, BUN, creatinine clearance, CBC, Hgb, and Hct. Follow-up cultures may be ordered at end of treatment to verify elimination of causative organism.
Reinforce necessity to adhere to established drug regimen. Recurrent infection after terminating prophylactic treatment of UTI may occur even after 6 mo of therapy.
Assess urinary pattern during treatment. Altered pattern (frequency, urgency, nocturia, retention, polyuria) may reflect emerging drug resistance, necessitating change of drug regimen. Periodically check for bladder distention.
Be alert for toxic effects on bone marrow, particularly in older adults, malnourished, alcoholic, pregnant, or debilitated patients. Recognize and report signs of infection or anemia.
Drug-induced rash, a common adverse effect, is usually maculopapular, pruritic, or morbilliform and appears 7–14 d after start of therapy with daily doses of 200 mg or less.
Watch for overdose symptoms: Nausea, vomiting, diarrhea, mental depression, confusion, facial swelling, elevated serum transaminases.

Patient & Family Education

Take all prescribed medication; uncomplicated UTIs usually respond to treatment.
Drink fluids liberally (2000–3000 mL/d, if not contraindicated) to help flush out urinary bacteria.
Take urinary analgesic for pain and discomfort with voiding before full drug effects are experienced. Report pain and hematuria to physician immediately.
Do not postpone voiding even though increases in fluid intake may cause more frequent urination.
Do not use douches or sprays during treatment periods; practice careful perineal hygiene to prevent reinfection.
Report to physician promptly any symptoms of a hematologic disorder (fever, sore throat, pallor, purpura, ecchymosis).
Consult physician if severe traveler's diarrhea does not respond to 3–5 d therapy (i.e., persistence of symptoms of severe nausea, abdominal pain, diarrhea with mucus or blood, and dehydration).

Common adverse effects in italic, life-threatening effects underlined; generic names in bold; classifications in SMALL CAPS; Canadian drug name; Prototype drug

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