Home Drug Guide Sulfamethoxazole; Trimethoprim

Drug Guide

Generic Name

Sulfamethoxazole; Trimethoprim

Brand Names Septra, Septra Ds, Bactrim, Bactrim Ds, Bactrim Pediatric, Septra Grape, Sulfamethoxazole And Trimethoprim, Sulfamethoxazole And Trimethoprim Double Strength, Sulfatrim Pediatric, Sulfatrim, Sulfamethoprim, Sulfamethoxazole And Trimethoprim Single Strength, Sulfamethoprim-ds, Cotrim, Cotrim D.s., Sulmeprim, Sulmeprim Pediatric, Sulfatrim-ss, Sulfatrim-ds, Uroplus Ss, Uroplus Ds, Trimeth/sulfa

Classification

Therapeutic: Antibacterial/Antimicrobial

Pharmacological: Folate synthesis inhibitor (sulfonamide and trimethoprim)

FDA Approved Indications

Urinary tract infections
Otitis media
Bronchitis
Pneumocystis jirovecii pneumonia (PCP) prevention and treatment
Traveler's diarrhea

Mechanism of Action

Sulfamethoxazole inhibits dihydropteroate synthase, interfering with bacterial folic acid synthesis. Trimethoprim inhibits dihydrofolate reductase, blocking folic acid conversion. Together, they act synergistically to inhibit bacterial DNA synthesis.

Dosage and Administration

Adult: Typically 160 mg sulfamethoxazole / 80 mg trimethoprim every 12 hours; dosage varies by infection.

Pediatric: Based on weight; usual dose is 6-12 mg/kg/day of trimethoprim, divided into doses every 12 hours.

Geriatric: Adjust dose considering renal function; increased risk of side effects.

Renal Impairment: Dose adjustment needed; caution in patients with renal impairment.

Hepatic Impairment: Use with caution; no specific adjustment data.

Pharmacokinetics

Absorption: Well absorbed orally.

Distribution: Widely distributed, including in CSF.

Metabolism: Primarily hepatic metabolism.

Excretion: Renal excretion of unchanged drug and metabolites.

Half Life: About 10 hours for trimethoprim, 10 hours for sulfamethoxazole.

Contraindications

Hypersensitivity to sulfonamides or trimethoprim
Recent use of drugs causing hyperkalemia
Severe hepatic or renal impairment

Precautions

G6PD deficiency (risk of hemolytic anemia)
Pregnancy (particularly 1st and 3rd trimesters)
Lactation

Adverse Reactions - Common

Nausea, vomiting, rash, pruritus (Common)
Hyperkalemia (Less common)

Adverse Reactions - Serious

Stevens-Johnson syndrome, toxic epidermal necrolysis (Rare)
Hematologic reactions (e.g., neutropenia, anemia, thrombocytopenia) (Rare)
Hepatotoxicity (Rare)
Hypersensitivity reactions including anaphylaxis (Rare)

Drug-Drug Interactions

Warfarin (increased bleeding risk)
Methotrexate (increased toxicity)
Phenytoin (altered levels)

Drug-Food Interactions

N/A

Drug-Herb Interactions

N/A

Nursing Implications

Assessment: Monitor for allergies, blood counts, renal function, hepatic function.

Diagnoses:

Risk for allergic reaction
Impaired skin integrity
Imbalanced nutrition: less than body requirements

Implementation: Administer with plenty of water to prevent crystalluria; monitor CBC and renal function during therapy.

Evaluation: Assess infection resolution, monitor for adverse effects, ensure compliance.

Patient/Family Teaching

Complete full course of therapy.
Report any rash, fever, mouth sores.
Use adequate hydration.
Be aware of signs of allergic reaction or side effects.

Special Considerations

Black Box Warnings:

Hypersensitivity reactions, including Stevens-Johnson syndrome and toxic epidermal necrolysis, can be severe.
Bone marrow suppression may occur.
Use with caution in patients with G6PD deficiency.

Genetic Factors: G6PD deficiency increases risk of hemolytic anemia.

Lab Test Interference: Can cause false elevation of serum creatinine without affecting GFR.

Overdose Management

Signs/Symptoms: Nausea, vomiting, dizziness, seizures, hematologic abnormalities.

Treatment: Supportive care; dialysis in severe cases.

Storage and Handling

Storage: Store at room temperature away from moisture and light.

Stability: Stable under recommended conditions.