Trimethoprim and Sulfamethoxazole

Trimethoprim and Sulfamethoxazole

Drug monograph · NCLEX study reference
Trade names	Bactrim
Therapeutic class	Antibacterial
Pharmacologic class	Sulfonamide combination (folate synthesis inhibitor)
Onset / peak / duration	Rapid; twice daily.
Half-life / level	Moderate; no routine level.
Routes	PO (oral), IV
High-alert (ISMP)	No
Black box warning	None
Antidote / reversal	Supportive care; leucovorin for marrow toxicity in some cases.
Pregnancy / lactation	Avoid near term and while breastfeeding a young infant.

Nursing pharmacology study reference (NCLEX-style monograph). Numeric values are standard teaching ranges for study and must be verified against current manufacturer labeling before clinical use. This is educational content, not prescribing guidance.

Trimethoprim and Sulfamethoxazole (brand name Bactrim) — Antibacterial; Sulfonamide combination (folate synthesis inhibitor).

Identification

• Therapeutic class: Antibacterial.
• Pharmacologic class: Sulfonamide combination (folate synthesis inhibitor).

Pharmacology

• Mechanism of action: Sequentially blocks folic acid synthesis (bactericidal in combination).
• Onset / peak / duration: Rapid; twice daily.
• Half-life / therapeutic level: Moderate; no routine level.

Clinical use

• Indications: Urinary infections, MRSA skin infections, Pneumocystis pneumonia (treatment and prophylaxis), some respiratory and GI infections.
• Usual dose, route, frequency: PO twice daily; IV and suspension available; higher doses for Pneumocystis.
• Maximum dose / adjustments: Reduce in renal impairment; encourage fluids.

Safety

• Contraindications: Sulfonamide hypersensitivity, megaloblastic anemia from folate deficiency, late pregnancy, infants under 2 months, severe hepatic or renal disease.
• Black box warning: None.
• Interactions: Warfarin (raises INR), ACE inhibitors and ARBs and potassium-sparing diuretics (hyperkalemia), methotrexate, sulfonylureas (hypoglycemia), phenytoin.
• Pregnancy / lactation: Avoid near term and while breastfeeding a young infant.
• High-alert: No.

Adverse effects

• Common side effects: Nausea, rash, photosensitivity.
• Serious effects to report: Stevens-Johnson syndrome, blood dyscrasias, hyperkalemia, acute kidney injury, hypoglycemia.
• Antidote / reversal: Supportive care; leucovorin for marrow toxicity in some cases.

Nursing process

• Assessment before administration: Sulfa allergy, renal function, potassium, CBC, hydration.
• Interventions during therapy: Encourage fluids; monitor potassium and warfarin effect; watch for rash.
• Monitor: Renal function, potassium, CBC, INR if on warfarin, infection resolution.
• Evaluation / expected outcome: Resolution of infection.

Patient teaching

• Patient teaching: Drink plenty of fluids; use sun protection; report any rash immediately.
• Notify provider if: Rash, sore throat or fever, decreased urination, easy bruising.
• Administration tips: With a full glass of water; maintain hydration.