Drug Guide
Sulfamethoxazole
Classification
Therapeutic: Antibacterial, Sulfonamide
Pharmacological: Sulfonamide Antibiotic
FDA Approved Indications
- Urinary tract infections (UTIs)
- Otitis media
- Bronchitis caused by susceptible bacteria
- Traveler's diarrhea (in combination with trimethoprim)
Mechanism of Action
Sulfamethoxazole inhibits bacterial dihydropteroate synthase, blocking folic acid synthesis which is essential for bacterial growth.
Dosage and Administration
Adult: Typically, 400 mg every 12 hours for UTIs; dosage varies based on infection severity and site.
Pediatric: Dose determined based on weight, usually 8-12 mg/kg/day divided into two doses.
Geriatric: Adjust based on renal function and indication; monitor closely for adverse effects.
Renal Impairment: Dose adjustment required; usually reduce frequency or dose depending on degree of impairment.
Hepatic Impairment: Use with caution; no specific dose adjustments, but monitor liver function.
Pharmacokinetics
Absorption: Well absorbed from the gastrointestinal tract.
Distribution: Widely distributed, including into body fluids and tissues.
Metabolism: Minimal hepatic metabolism, metabolites are excreted renally.
Excretion: Primarily excreted unchanged in the urine.
Half Life: approximately 10 hours.
Contraindications
- Hypersensitivity to sulfonamides or other sulfa drugs.
- Severe hepatic or renal impairment without proper dose adjustment.
Precautions
- Use with caution in patients with folate deficiency, elderly, or those on other medications affecting renal function.
- Pregnancy Category C; avoid near term due to risk of kernicterus in neonates.
- Lactation: Crosses into breast milk; risk of bilirubin displacement.
Adverse Reactions - Common
- Rash (Common)
- Nausea, vomiting (Common)
- Loss of appetite (Common)
Adverse Reactions - Serious
- Stevens-Johnson syndrome, toxic epidermal necrolysis (Rare)
- Hematologic reactions (e.g., agranulocytosis, aplastic anemia) (Rare)
- Crystalluria and renal damage (Rare)
Drug-Drug Interactions
- Methotrexate (increased toxicity)
- Warfarin (increased anticoagulant effect)
- Methicillin (competes for renal excretion)
Drug-Food Interactions
N/ADrug-Herb Interactions
N/ANursing Implications
Assessment: Monitor for signs of allergic reactions, hematologic changes, renal function, and liver function.
Diagnoses:
- Risk for allergic reaction
- Impaired renal function
Implementation: Administer with plenty of water to prevent crystalluria. Monitor blood counts.
Evaluation: Assess resolution of infection, monitor for adverse effects.
Patient/Family Teaching
- Complete full course of therapy.
- Report any signs of rash, fever, jaundice, or unusual bleeding.
- Drink plenty of fluids to reduce risk of crystalluria.
- Use sunscreen; photosensitivity may occur.
Special Considerations
Black Box Warnings:
- Hypersensitivity reactions, including Stevens-Johnson syndrome, and toxic epidermal necrolysis, which can be life-threatening.
Genetic Factors: G6PD deficiency may predispose to hemolytic anemia with sulfonamides.
Lab Test Interference: False increases in serum creatinine levels due to interference with measurement.
Overdose Management
Signs/Symptoms: Nausea, vomiting, dizziness, seizures, renal failure.
Treatment: Supportive care, hydration, and correction of electrolyte imbalances. Hemodialysis may be considered in severe cases.
Storage and Handling
Storage: Store at room temperature, protected from light.
Stability: Stable until expiration if kept properly.