trimethoprim/sulfamethoxazole (Rx)

Brand and Other Names:Bactrim, Bactrim DS, more...Septra, Septra DS, Cotrim, cotrimoxazole, Sulfatrim
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Dosing & Uses


Dosage Forms & Strengths


injected solution

  • (16mg/80mg)/mL

oral suspension

  • (40mg/200mg)/5mL


  • 80mg/400mg
  • 160mg/800mg

Dosing Guidelines for Infections

1-2 DS tablets PO q12-24hr

8-20 mg TMP/kg/day IV q6-12hr  

Chronic Bronchitis

Acute exacerbations of chronic bronchitis due to susceptible strains of Streptococcus pneumoniae or Haemophilus influenzae

DS tablet: 1 PO q12h for 10-14 days

Meningitis, Bacterial

10-20 mg TMP/kg/day IV divided q6-12hr  

Pneumocystis (Carinii) Jiroveci Pneumonia

Documented Pneumocystis jiroveci pneumonia (PCP); also, prophylaxis against PCP in individuals who are immunosuppressed


  • Tablet: 80-160 mg TMP PO qDay or 160 mg TMP 3 times/week on consecutive or alternate days


  • 15-20 mg TMP/kg/day PO/IV divided q6-8hr  


20 mg TMP/kg/day IV divided q6hr  


Enteritis caused by susceptible strains of Shigella flexneri and S sonnei

DS tablet: 1 tab PO q12hr for 5 days

Alternatively, 8-10 mg TMP/kg/day IV divided q6-12hr for up to 5 days  

Traveler's Diarrhea

Traveler's diarrhea due to susceptible strains of enterotoxigenic Escherichia coli

DS tablet: 1 tab PO q12hr for 5 days

Urinary Tract Infections

UTIs caused by susceptible strains of Escherichia coli, Klebsiella species, Enterobacter species, Morganella morganii, Proteus mirabilis, and Proteus vulgaris

Pyelonephritis: 1 DS tab or 2 regular-strength tabs PO q12hr x 14 days

Prostatitis: 1 DS tab or 2 regular-strength tabs PO q12hr x 14 days or 2-3 months if chronic infection

A 3 to 5 day course may be used for acute, uncomplicated cystitis

Prophylaxis (off-label): Various regimens exist; may use regular-strength tablet once/twice per week

Acne Vulgaris (Off-label)

1 DS tab or 1 regular-strength tab PO qDay or q12hr for up to 18 weeks

Community Acquired Pneumonia (Off-label)

1 DS tab PO q12hr for 10-14 days

Dosage Modifications

Renal impairment

  • CrCl >30 mL/min: Dose adjustment not necessary
  • CrCl 15-30 mL/min: Decrease dose by 50%
  • CrCl <15 mL/min: Do not use

Renal impairment, off-label

  • Administer doses PO/IV
  • Dosing (Dose based on Total Body Weight(TBW) and trimethoprim component; use TBW in obese patients)
  • Pneumocystis jjirovecii pneumonia (PJP) prophylaxis
    • CrCl < 30mL/min: 160 mg (1DS) q24hr or 80 mg (1 SS) q24hr or 160 mg (1DS) 3x week
    • Hemodialysis (HD): 80 mg (1 SS) q24 hr or 160 mg (1DS) 3 x week; on hemodialysis days, administer dose post-HD
    • Continuous renal replacement therapy (CRRT): 160 mg (1 DS) q24hr or 80 mg (1SS) q24hr or 160 mg (1DS) 3x week
  • Pneumocystis jjirovecii pneumonia (PJP) treatment
    • CrCl < 30mL/min: 5 mg/kg q12hr
    • HD: 10 mg/kg post-HD
    • CRRT: 5 mg/kg q12hr
    • Total daily dose: 15-20 mg/kg/day for Pneumocystis treatment
  • Skin and soft tissue infection
    • CrCl < 30mL/min: 80-160 mg (1-2 SS) q12hr
    • HD: 80 mg (1SS) q24hr; on hemodialysis days, administer dose post-HD
    • CRRT: 80-160 mg (1-2SS) q12hr
  • Stenotrophomonas treatment
    • CrCl<30mL/min: 4 mg/kg q12hr
    • HD: 8 mg/kg post-HD
    • CRRT: 4 mg/kg q12hr
    • Total daily dose: 12-15 mg/kg/day for Stenotrophomonas treatment
  • Urinary tract infection
    • CrCl < 30mL/min: 80 mg (1SS) q12hr
    • HD: 80 mg (1SS) q12hr; on hemodialysis days, administer dose post-HD
    • CRRT: 160 mg (1DS) q12hr
  • Other Infections
    • CrCl < 30mL/min: 3 mg/kg q12hr
    • HD: 6 mg/kg post-HD
    • CRRT: 3 mg/kg q12hr
    • Total daily dose: 8-12 mg/kg/day

Dosing Considerations

Susceptible organisms

  • Acinetobacter baumannii, Actinobacillus actinomycetemcomitans, Aeromonas hydrophila, Alcaligenes xylosoxidans, Bartonella henselae, Bordetella pertussis, Brucella spp, Burkholderia pseudomallei, Burkholderia cepacia, Chryseobacterium meningosepticum, Enterobacter aerogenes, Enterobacter cloacae, Escherichia coli, Haemophilus aphrophilus, Haemophilus influenzae, Hafnia alvei, Kingella spp, Klebsiella pneumoniae, Klebsiella granulomatis, Legionella spp, Listeria monocytogenes, Moraxella catarrhalis, Morganella morganii, MRSA, MSSA, Nocardia asteroides, Plesiomonas shigelloides, Pneumocystis jiroveci (PCP), Proteus mirabilis, Proteus vulgaris, Providencia rettgeri, Providencia stuartii, Salmonella typhi, Serratia spp, Shigella spp, Staphylococcus saprophyticus, Stenotrophomonas maltophilia, Streptococcus pneumoniae, Tropheryma whippelii, Vibrio cholerae, Yersinia enterocolitica, Yersinia pseudotuberculosis, various Mycobacteria

Dosage Forms & Strengths


injected solution

  • (16mg/80mg)/mL

oral solution

  • (40mg/200mg)/5mL


  • 80mg/400mg
  • 160mg/800mg

Mild to Moderate Infections

<2 months: Contraindicated

>2 months

  • 8 mg TMP/kg/day PO divided q12hr  

Serious Infections

<2 months: Contraindicated

>2 months

  • 15-20 mg TMP/kg qDay PO divided q6hr  
  • 8-12 mg TMP/kg/day IV divided q6-12hr

Acute Otitis Media

Acute otitis media in pediatric patients due to susceptible strains of Streptococcus pneumoniae or Haemophilus influenzae

<2 months: Contraindicated

>2 months: 6-10 mg TMP/kg/day PO divided q12hr for 10 days  

Pneumocystis (Carinii) Jiroveci Pneumonia

<2 months: Contraindicated

>2 months

  • Treatment: 15-20 mg TMP/kg/day PO/IV divided q6-8hr for 21 days  
  • Prophylaxis: 150 mg TMP/m²/day PO divided q12 hr for 3 days/week on consecutive or alternate days  


<2 months: Contraindicated

>2 months

  • 8 mg TMP/kg/day PO divided q12hr for 5 days  
  • 8-10 mg TMP/kg/day IV divided q6-12hr for 5 days

Urinary Tract Infection

<2 months: Contraindicated

>2 months

  • 8 mg TMP/kg/day PO divided q12hr for 7-14 days if serious infection  
  • 8-10 mg TMP/kg/day IV divided q6-12hr for 14 days if serious infection
  • Prophylaxis: 2 mg TMP/kg/dose PO qDay or 5 mg TMP/kg/dose twice weekly

Skin/soft Tissue Infection Due to Community Acquired MRSA (Off-label)

8-12 mg TMP/kg/day PO divided q12hr for 5-10 days; add beta-lactam antibiotic to regimen if beta-hemolytic Streptococcus spp also suspected  



Interaction Checker

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            Adverse Effects

            Frequency Not Defined






            Peripheral neuritis

            Erythema multiforme




            Immune hypersensitivity reaction

            Stevens-Johnson syndrome

            Toxic epidermal necrolysis


            Aplastic anemia


            Disorder of hematopoietic structure

            Fulminant hepatic necrosis

            Postmarketing Reports

            Thrombotic thrombocytopenia purpura

            Idiopathic thrombocytopenic purpura

            QT prolongation resulting in ventricular tachycardia and torsade de pointes

            Embryo-fetal toxicity

            Hypersensitivity and other fatal reactions


            Clostridium difficile-associated diarrhea

            Sulfite sensitivity

            Risk associated with concurrent use of leucovorin for

            Pneumocystis jirovecii


            Infusion reactions


            Electrolyte abnormalities


            Propylene glycol Toxicity

            Metabolic acidosis

            Drug reaction with eosinophilia and systemic symptoms (DRESS)

            Acute generalized exanthematous pustulosis (AGEP)

            Acute febrile neutrophilic dermatosis (AFND)

            Circulatory shock

            Acute and delayed lung injury

            Interstitial lung disease

            Acute respiratory failure

            Renal failure, interstitial nephritis, BUN and serum creatinine elevation, renal insufficiency, oliguria and anuria, crystalluria, and nephrotoxicity in association with cyclosporine




            Known hypersensitivity

            Age <2 months

            CrCl <15 mL/min when renal function status cannot be monitored

            Documented megaloblastic or folate deficiency anemia

            Significan hepatic impairment

            Contraindicated in pregnant patients at term and in nursing mothers, because sulfonamides, which pass the placenta and are excreted in the milk, may cause kernicterus

            History of drug-induced immune thrombocytopenia with use of trimethoprim and/or sulfonamides

            Concomitant administration with dofetilide


            Not for use in areas with resistance rates >10%

            Severe and symptomatic hyponatremia can occur in patients receiving sulfamethoxazole/ trimethoprim, particularly for treatment of P. jirovecii pneumonia; evaluation for hyponatremia and appropriate correction is necessary in symptomatic patients to prevent life-threatening complications

            If patient treated for Pneumocystis jirovecii develops skin rash, fever, leukopenia, or any other sign of adverse reaction, therapy or re-challenge should be re-evaluated

            Circulatory shock with fever, severe hypotension, and confusion requiring intravenous fluid resuscitation and vasopressors has occurred within minutes to hours of re-challenge with trimethoprim-sulfamethoxazole in patients with history of recent (days to weeks) exposure to sulfamethoxazole-trimethoprim

            Fatalities associated with the administration of sulfonamides, although rare, have occurred due to severe reactions, including severe cutaneous adverse reactions (SCARs), including Stevens-Johnson Syndrome, toxic epidermal necrolysis, drug reaction with eosinophilia and systemic symptoms (DRESS), acute generalized exanthematous pustulosis (AGEP) and acute febrile neutrophilic dermatosis (AFND), fulminant hepatic necrosis, agranulocytosis, aplastic anemia and other blood dyscrasias; clinical signs, such as rash, sore throat, fever, arthralgia, pallor, purpura or jaundice may be early indications of serious reactions; discontinue therapy at first appearance of skin rash or any sign of serious adverse reaction

            Acute and delayed lung injury; anaphylaxis and circulatory shock have occurred with administration of sulfamethoxazole and trimethoprim products

            Cough, shortness of breath and pulmonary infiltrates potentially representing hypersensitivity reactions of the respiratory tract reported in association with sulfamethoxazole and trimethoprim treatment

            Severe pulmonary adverse reactions occurring within days to week of initiation of treatment and resulting in prolonged respiratory failure requiring mechanical ventilation or extracorporeal membrane oxygenation (ECMO), lung transplantation or death also reported in patients and otherwise healthy individuals treated with sulfamethoxazole and trimethoprim products

            Caution when used in elderly individuals; risk of bone marrow suppression

            PCP prophylaxis with AIDS: Rash, fever, leukopenia, and elevated transaminase values reported; hyperkalemia and hyponatremia also appear to be increased

            Severe cases (including fatalities) of immune-mediated thrombocytopenia reported; monitor patients for hematologic toxicity; resolves within a week upon discontinuation of therapy

            Sulfonamides should not be used to treat group A beta-hemolytic streptococcal infections; they will not eradicate streptococcus or prevent rheumatic fever

            Clostridium difficile-associated diarrhea reported

            Coadministration with leucovorin for the treatment of HIV-positive patients with PCP resulted in treatment failure and excess mortality in a randomized, placebo-controlled trial; avoid coadministration

            Development of drug-resistant bacteria may occur when prescribed in absence of strongly suspected bacterial infection or prophylactic indication

            Prolonged use may result in fungal or bacterial superinfection

            Caution with impaired renal or hepatic function, patients with possible folate deficiency (eg, the elderly, chronic alcoholics, patients receiving anticonvulsant therapy, patients with malabsorption syndrome, and patients in malnutrition states), and patients with severe allergies or bronchial asthma

            Hematological changes indicative of folic acid deficiency may occur in elderly patients or in patients with preexisting folic acid deficiency or kidney failure; effects are reversible by folinic acid therapy

            Hemolysis may occur if administered to patients with G6PD deficiency

            Hypoglycemia (rare) reported in nondiabetic patients; patients with renal dysfunction, liver disease, or malnutrition or those receiving high doses at particular risk

            Trimethoprim may impair phenylalanine metabolism but may have no significance in phenylketonuric patients on appropriate dietary restriction

            Caution with porphyria or thyroid dysfunction; sulfonamides can precipitate porphyria crisis and hypothyroidism; avoid use in patients with porphyria or thyroid dysfunction

            Complete blood counts should be done frequently in patients receiving therapy; discontinue therapy if a significant reduction in count of any formed blood element is noted’ perform urinalyses with careful microscopic examination and renal function tests during therapy, particularly for those patients with impaired renal function

            When administered at high doses as for the treatment of P. jirovecii pneumonia, monitor for total daily intake of propylene glycol from all sources and for acid-base disturbances; discontinue therapy if propylene glycol toxicity suspected

            Treatment failure and excess mortality were observed when trimethoprim-sulfamethoxazole was used concomitantly with leucovorin for treatment of HIV positive patients with Pneumocystis jirovecii pneumonia; co-administration of trimethoprim-sulfamethoxazole and leucovorin during treatment of Pneumocystis jirovecii pneumonia should be avoided

            During treatment, adequate fluid intake and urinary output should be ensured to prevent crystalluria; patients who are “slow acetylators” may be more prone to idiosyncratic reactions to sulfonamides


            • High dosage of trimethoprim, as used in patients with P. jirovecii pneumonia, induces a progressive but reversible increase of serum potassium concentrations in a substantial number of patients
            • Treatment with recommended doses may cause hyperkalemia when trimethoprim is administered to patients with underlying disorders of potassium metabolism, with renal insufficiency, or if drugs known to induce hyperkalemia are given concomitantly; close monitoring of serum potassium recommended

            Risk in treatment of Pneumocystis jirovecy pneumonia

            • AIDS patients may not tolerate or respond to sulfamethoxazole/ trimethoprim in same manner as non-AIDS patients
            • Incidence of adverse reactions, particularly rash, fever, leukopenia and elevated aminotransferase (transaminase) values, with therapy in AIDS patients who are being treated for P. jirovecii pneumonia reported to be increased compared with incidence normally associated with use of drug in non-AIDS patients
            • If a patient develops skin rash, fever, leukopenia or any sign of adverse reaction, reevaluate benefit-risk of continuing therapy or re-challenge with drug

            Pregnancy & Lactation


            Therapy may cause fetal harm if administered to pregnant woman; some epidemiologic studies suggest that exposure to drug during pregnancy may be associated with increased risk of congenital malformations, particularly neural tube defects, cardiovascular abnormalities, urinary tract defects, oral clefts, and club foot

            Urinary tract infection in pregnancy is associated with adverse perinatal outcomes such as preterm birth, low birth weight, and pre-eclampsia, and increased mortality to pregnant woman

            P. jirovecii pneumonia in pregnancy is associated with preterm birth and increased morbidity and mortality for the pregnant woman

            Use during pregnancy only if potential benefit justifies potential risk to fetus


            Levels of drug in breast milk are approximately 2 to 5% of recommended daily dose for pediatric patients over two months of age; there is no information regarding effect of therapy on breastfed infant or effect on milk production; because of potential risk of bilirubin displacement and kernicterus on breastfed child, advise women to avoid breastfeeding during therapy

            Pregnancy Categories

            A: Generally acceptable. Controlled studies in pregnant women show no evidence of fetal risk.

            B: May be acceptable. Either animal studies show no risk but human studies not available or animal studies showed minor risks and human studies done and showed no risk.

            C: Use with caution if benefits outweigh risks. Animal studies show risk and human studies not available or neither animal nor human studies done.

            D: Use in LIFE-THREATENING emergencies when no safer drug available. Positive evidence of human fetal risk.

            X: Do not use in pregnancy. Risks involved outweigh potential benefits. Safer alternatives exist.

            NA: Information not available.



            Mechanism of Action

            Blocks 2 consecutive steps in the biosynthesis of nucleic acids and proteins essential to many bacteria

            Trimethoprim: Inhibits dihydrofolate reductase, thereby blocking production of tetrahydrofolic acid from dihydrofolic acid

            Sulfamethoxazole: Inhibits bacterial synthesis of dihydrofolic acid by competing with para-aminobenzoic acid


            Time to peak: 1-4 hours


            Protein bound: TMP (44%); SMX (70%)



            Enzymes inhibited: Hepatic CYP2C9


            Half-life: TMP (8-10 hr); SMX (10 hr)

            Excretion: Urine (as unchanged drug)



            IV Incompatibilities

            Additive: Fluconazole, linezolid, verapamil

            Y-site: Cisatracurium (incompatible at 2 mg/mL cisatra; may be compatible at much lower concs), fluconazole, foscarnet (may be compatible at very low TMP/SMX concs), midazolam, vinorelbine

            IV Preparation

            Do not use NS as diluent

            Injection vehicle contains benzyl alcohol and sodium metabisulfite

            Stability of parenteral admixture at room temperature (25°C)

            • 5 mL/125 mL D5W: 6 hr
            • 5 mL/100 mL D5W: 4 hr
            • 5 mL/75 mL D5W: 2 hr

            IV Administration

            Infuse over 60-90 min; give q6hr, 8hr, or 12hr

            Must be diluted well

            May be given less diluted in a central line

            Not for IM

            Maintain adequate fluid intake to prevent crystalluria


            Do not refrigerate injection

            Less soluble in more alkaline pH

            Protect from light





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            Tier Description
            1 This drug is available at the lowest co-pay. Most commonly, these are generic drugs.
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