Class: Sulfonamide Antibiotic
Dosage Forms. Tablet: (SMZ/TMP) 400 mg/80 mg (single strength), 800 mg/160 mg (double strength); Suspension: (SMZ/TMP) 200 mg/40 mg/5 mL
Common FDA Label Indication, Dosing, and Titration.
1. Acute infective exacerbation of COPD: 800 mg SMZ and 160 mg TMP po bid × 21 d
2. HIV infection—Pneumocystis pneumonia: 1600 mg SMZ and 320 mg TMP po bid × 21 d
3. HIV infection—Pneumocystis pneumonia, prophylaxis: Adults, 800 mg SMZ and 160 mg TMP po daily; Children 1 mo of age and older, 750 mg/m2/d SMZ and 150 mg/m2/d TMP in 2 divided doses po 3 times a wk on consecutive days
4. Traveler’s diarrhea: 800 mg SMZ and 160 mg TMP po bid × 5 d
5. Urinary tract infection: Adult: 800 mg SMZ and 160 mg TMP po bid × 10-14 d; Children 2 mo of age and older, 8 mg/kg TMP component/d po bid × 10 d
Off-Label Uses.
1. Sinusitis: 800 mg SMZ and 160 mg TMP po bid × 10-14 d
MOA. SMZ competitively inhibits the synthesis of dihydropteric acid (an inactive folic acid precursor) in microorganisms. TMP inhibits the enzymatic reduction of dihydrofolic acid to tetrahydrofolic acid. The combination is active against many bacteria and Pneumocystis carinii. TMP/SMZ has in vitro activity against methicillin-resistant Staphylococcus aureus (MRSA), but clinical success has been variable and unpredictable.
Drug Characteristics: Trimethoprim/Sulfamethoxazole
Medication Safety Issues: Trimethoprim/Sulfamethoxazole
Drug Interactions: Trimethoprim/Sulfamethoxazole
Adverse Reactions: Trimethoprim/Sulfamethoxazole
Efficacy Monitoring Parameters. Resolution of signs of infection within 2-3 d. Decreased episodes of pneumocystis pneumonia.
Toxicity Monitoring Parameters. Monitor potassium in those with concurrent ACI inhibitors. Monitor FPG with concurrent sulfonylureas. CBC monthly if using for PCP prophylaxis. Seek medical attention for severe diarrhea, dark urine, yellowing of skin or eye, unusual bruising or bleeding, blistering skin rash, or shortness of breath.
Key Patient Counseling Points. Complete full course of therapy. For the suspension, shake well and store at room temperature. Symptoms should improve within 2-3 d; if they worsen, seek follow-up with healthcare practitioner. May cause photosensitivity, use sunscreen.
Clinical Pearls. Avoid use in patients with G6PD deficiency (increased risk of hemolytic anemia). Preferred agent for pneumocystis pneumonia prevention in HIV-infected patients when CD4 count is <200.