BACTRIM FORTE 800/160/MG TAB 10/TAB

Indications

Approved Uses

Urinary tract infections (UTIs), acute otitis media, acute exacerbations of chronic bronchitis, traveler's diarrhea, Pneumocystis jirovecii pneumonia (PCP) treatment and prophylaxis, shigellosis, nocardiosis

Off-Label Uses

Community-acquired MRSA skin/soft tissue infection; Stenotrophomonas maltophilia infections; toxoplasmosis prophylaxis (alternative); nocardiosis; selected prophylaxis regimens in immunocompromised patients beyond PCP per specialist guidance.

Dosage & Administration

Dosing by Condition

Uncomplicated cystitis (adult female, when appropriate): 1 DS/forte tablet (800/160 mg) PO q12h for 3 days. Complicated UTI/pyelonephritis (when susceptible): typically 7-14 days depending on severity. Acute bacterial exacerbation of chronic bronchitis: 1 DS PO q12h for 10-14 days. Shigellosis: 1 DS PO q12h for 5 days. Traveler’s diarrhea (when indicated): 1 DS PO q12h for ~5 days. Pneumocystis jirovecii pneumonia treatment: 15-20 mg/kg/day (trimethoprim component) in 3-4 divided doses for 14-21 days. PCP prophylaxis: 1 DS daily OR 1 DS three times weekly (common alternative regimen).

Initial Dose

1 Forte tablet (800 mg/160 mg) orally every 12 hours for most common infections.

Maintenance Dose

1 Forte tablet (800mg/160mg) every 12 hours. For long-term prophylaxis of PJP, 1 Forte tablet daily.

Maximum Dose

Typical adult infections: 2 Forte tablets (800/160 mg each) orally every 12 hours (i.e., TMP 320 mg per dose; TMP 640 mg/day; SMX 1600 mg per dose; SMX 3200 mg/day). PCP treatment (indication-specific): TMP 15-20 mg/kg/day with SMX 75-100 mg/kg/day in divided doses.

Children's Dosage

For children 2 months and older, dosing is weight-based. For UTIs and otitis media, the typical dose is 8 mg/kg/day of trimethoprim and 40 mg/kg/day of sulfamethoxazole, divided into two doses every 12 hours.

Dose Adjustment Notes

Dose adjustment is required in renal impairment (reduce dose when CrCl 15-30 mL/min; avoid/use with extreme caution when CrCl <15 mL/min unless dialysis-specific dosing). Use caution in hepatic impairment and ensure adequate hydration; monitor potassium and renal function when risk factors exist.

How to Take

Swallow tablet with a full glass of water; may take with or without food (take with food/milk if GI upset). Maintain adequate hydration throughout therapy to reduce risk of crystalluria/renal adverse effects.

Side Effects

Common Side Effects

Nausea, vomiting, diarrhea, decreased appetite; skin rash/urticaria; headache; dizziness; photosensitivity.

Side Effect Frequency

Common (≥1%): nausea, vomiting, anorexia, rash/urticaria/pruritus; diarrhea and headache are also commonly reported. Serious but rare: Stevens-Johnson syndrome/toxic epidermal necrolysis, blood dyscrasias (e.g., agranulocytosis, thrombocytopenia, aplastic anemia), severe hepatic reactions; clinically important metabolic effects include hyperkalemia and hyponatremia (risk increased with renal impairment/high dose).

Safety & Warnings

Contraindications

Contraindications include: hypersensitivity to sulfonamides or trimethoprim; history of drug-induced immune thrombocytopenia with TMP and/or sulfonamides; documented megaloblastic anemia due to folate deficiency; infants <2 months; severe renal insufficiency when renal function cannot be monitored; significant hepatic impairment; concomitant dofetilide; and pregnancy (particularly near term) unless the potential benefit clearly outweighs fetal risk.

Warnings & Precautions

Key precautions: stop immediately at first sign of rash or hypersensitivity; monitor CBC with prolonged/high-dose therapy or in high-risk patients; monitor renal function and ensure adequate hydration to reduce crystalluria/AKI risk; monitor potassium (and sodium) especially in elderly, renal impairment, and with ACEi/ARB or K-sparing diuretics; caution in G6PD deficiency (hemolysis risk) and folate deficiency; counsel on C. difficile diarrhea risk.

Age Restriction

Not approved for infants under 2 months of age.

Driving Warning

Safe

Drug Interactions

Drug Interactions

Key clinically significant interactions: dofetilide (contraindicated); warfarin (↑INR/bleeding via CYP2C9 inhibition); methotrexate (↑toxicity/myelosuppression); phenytoin (↑levels/toxicity); ACE inhibitors/ARBs and potassium-sparing diuretics (↑hyperkalemia); digoxin (↑levels esp. elderly). Additional important interactions to consider: sulfonylureas (↑hypoglycemia), cyclosporine (nephrotoxicity), and other drugs that raise potassium or prolong QT when combined with electrolyte disturbances.

Interaction Severity

MAJOR/Contraindicated: dofetilide. MAJOR: warfarin (↑INR/bleeding), methotrexate (↑toxicity/myelosuppression). MODERATE: ACE inhibitors/ARBs and potassium-sparing diuretics (hyperkalemia), phenytoin (↑levels), cyclosporine (nephrotoxicity), sulfonylureas (hypoglycemia), digoxin (↑levels, esp. elderly).

Food Interaction

No clinically significant food restriction; may take with food to reduce gastrointestinal upset.

Special Populations

Pregnancy

Category D

Breastfeeding

Caution

Children

For children 2 months and older, dosing is weight-based. For UTIs and otitis media, the typical dose is 8 mg/kg/day of trimethoprim and 40 mg/kg/day of sulfamethoxazole, divided into two doses every 12 hours.

Elderly

Use with caution; increased risk of severe adverse reactions including bone marrow suppression, skin reactions, and hyperkalemia. Monitor renal function, CBC, and potassium levels. Dose reduction may be required based on renal function.

Kidney Impairment

CrCl >30 mL/min: no adjustment; CrCl 15-30 mL/min: reduce dose by 50% (or extend interval); CrCl <15 mL/min: not recommended/avoid unless close monitoring and specialist oversight; in hemodialysis, dose after dialysis (regimen individualized).

Liver Impairment

No specific dose adjustment is defined for mild-moderate hepatic impairment, but use with caution and monitor; significant/severe hepatic impairment is generally considered a contraindication/avoid due to risk of severe hepatic adverse reactions.

Storage & Patient Advice

Missed Dose

Take as soon as remembered; skip if near next dose. Do not take a double dose to make up for a forgotten dose.

Stopping the Medicine

Complete the full prescribed course; do not stop early unless a serious adverse reaction occurs; no taper is required when stopping at the end of therapy.

Overdose

Overdose may cause GI upset (nausea/vomiting), dizziness/headache, confusion, crystalluria/hematuria and renal impairment, and delayed bone marrow depression; management is urgent medical evaluation with supportive care, GI decontamination if appropriate, aggressive hydration and urine output, consider urine alkalinization for sulfonamide crystalluria, folinic acid (leucovorin) for TMP-related hematologic toxicity, and dialysis has limited-to-moderate effectiveness (TMP partially dialyzable).

Patient Counseling

Finish the full prescribed course. Take each dose with a full glass of water and maintain good fluid intake; may take with food if stomach upset occurs. Avoid excessive sun exposure/use sunscreen (photosensitivity). Seek urgent care for rash/blistering/peeling, severe diarrhea, jaundice, unusual bruising/bleeding, sore throat/fever, or signs of hyperkalemia (weakness/palpitations). Tell your clinician about all medicines-especially warfarin, methotrexate, ACEi/ARB, spironolactone, and dofetilide. Not for infants <2 months unless specifically directed.

Monitoring Requirements

Baseline and periodic renal function (SCr/CrCl) and electrolytes (especially potassium) when risk factors exist; CBC with differential for prolonged/high-dose therapy or immunocompromised patients; consider hepatic function tests if prolonged therapy or underlying liver disease; monitor INR closely if on warfarin; monitor digoxin level if co-administered in susceptible patients.

Pharmacology

Mechanism of Action

Sulfamethoxazole inhibits dihydropteroate synthase (competes with PABA) and trimethoprim inhibits dihydrofolate reductase, producing sequential blockade of bacterial folate synthesis with synergistic (often bactericidal) activity.

Onset of Action

Peak plasma concentrations occur about 1-4 hours after an oral dose; clinical improvement in susceptible infections is often seen within 24-48 hours.

Duration of Effect

Approximately 12 hours (supports twice-daily dosing for many indications).

Half-Life

Sulfamethoxazole: ~9-11 hours; Trimethoprim: ~8-10 hours (both prolonged in renal impairment).

Bioavailability

>90% for both components.

Metabolism

Sulfamethoxazole: hepatic metabolism mainly by N4-acetylation and glucuronidation (CYP2C9 contributes to oxidative pathways but is not the primary route); Trimethoprim: limited hepatic metabolism (minor fraction), with most eliminated renally.

Excretion

Primarily renal elimination via glomerular filtration and active tubular secretion; sulfamethoxazole is excreted in urine as unchanged drug and metabolites (≈20% unchanged), and trimethoprim is excreted largely in urine (≈50-60% unchanged).

Protein Binding

Sulfamethoxazole: approximately 70%; Trimethoprim: approximately 44%.

Product Information

Available Dosage Forms

Tablet; oral suspension; intravenous infusion solution (TMP-SMX injection).

Composition per Dose

Each tablet: Sulfamethoxazole 800mg + Trimethoprim 160mg

Generic Availability

Yes

OTC Alternatives

No OTC alternative

Spectrum

Broad-spectrum

Antibiotic Class

Sulfonamide antibacterial combination (sulfamethoxazole/trimethoprim)

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