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Bactrim DS Side Effects

Generic Name: sulfamethoxazole / trimethoprim

Note: This page contains information about the side effects of sulfamethoxazole / trimethoprim. Some of the dosage forms included on this document may not apply to the brand name Bactrim DS.

For the Consumer

Applies to sulfamethoxazole / trimethoprim: oral suspension, oral tablet

Other dosage forms:

In addition to its needed effects, some unwanted effects may be caused by sulfamethoxazole / trimethoprim. In the event that any of these side effects do occur, they may require medical attention.

Major Side Effects

You should check with your doctor immediately if any of these side effects occur when taking sulfamethoxazole / trimethoprim:

  • Abdominal or stomach pain
  • black, tarry stools
  • blistering, peeling, or loosening of the skin
  • changes in skin color
  • chest pain
  • chills
  • cough or hoarseness
  • dark urine
  • diarrhea
  • dizziness
  • fever with or without chills
  • general feeling of tiredness or weakness
  • headache
  • itching
  • joint or muscle pain
  • light-colored stools
  • loss of appetite
  • lower back or side pain
  • nausea
  • pain, tenderness, or swelling of the foot or leg
  • painful or difficult urination
  • pale skin
  • rash
  • red skin lesions, often with a purple center
  • red, irritated eyes
  • shortness of breath
  • sore throat
  • sores, ulcers, or white spots in the mouth or on the lips
  • swollen or painful glands
  • tightness in the chest
  • unpleasant breath odor
  • unusual bleeding or bruising
  • vomiting of blood
  • wheezing
  • yellow eyes or skin
Incidence not known:
  • Abdominal or stomach tenderness
  • back, leg, or stomach pains
  • bleeding gums
  • blindness or vision changes
  • blisters, hives, or itching
  • bloating
  • blood in the urine or stools
  • bluish-colored lips, fingernails, or palms
  • burning, crawling, itching, numbness, painful, prickling, "pins and needles", or tingling feelings
  • burning of the face or mouth
  • chest pain
  • cloudy urine
  • confusion
  • constipation
  • continuing ringing or buzzing or other unexplained noise in the ears
  • convulsions
  • cracks in the skin
  • decreased frequency or amount of urine
  • diarrhea, watery and severe, which may also be bloody
  • difficulty with breathing
  • difficulty with swallowing
  • fainting spells
  • general body swelling
  • general feeling of discomfort or illness
  • hair loss
  • hearing loss
  • hives
  • increased thirst
  • indigestion
  • irregular heartbeat
  • large, flat, blue, or purplish patches in the skin
  • large, hive-like swelling on the face, eyelids, lips, tongue, throat, hands, legs, feet, or sex organs
  • loss of heat from the body
  • muscle or joint pain
  • nosebleeds
  • not able to pass urine
  • numbness or tingling in the hands, feet, or lips
  • pain or burning while urinating
  • pinpoint red spots on the skin
  • puffiness or swelling of the eyelids or around the eyes, face, lips, or tongue
  • raised red swellings on the skin, the buttocks, legs, or ankles
  • redness of the white part of the eyes
  • redness, swelling, or soreness of the tongue
  • sores, ulcers, or white spots on the lips or in the mouth
  • soreness of the muscles
  • stiff neck or back
  • swelling of the face, hands, legs, and feet
  • unsteadiness, trembling, or other problems with muscle control or coordination
  • unusual weight loss
  • weakness in the hands or feet
  • weakness or heaviness of the legs
  • weight gain

Minor Side Effects

Some of the side effects that can occur with sulfamethoxazole / trimethoprim may not need medical attention. As your body adjusts to the medicine during treatment these side effects may go away. Your health care professional may also be able to tell you about ways to reduce or prevent some of these side effects. If any of the following side effects continue, are bothersome or if you have any questions about them, check with your health care professional:

More common:
  • Passing of gas
Incidence not known:
  • Discouragement
  • feeling of constant movement of self or surroundings
  • feeling sad or empty
  • increased sensitivity of the skin to sunlight
  • irritability
  • lack of feeling or emotion
  • loss of interest or pleasure
  • nervousness
  • redness or other discoloration of the skin
  • seeing, hearing, or feeling things that are not there
  • sensation of spinning
  • severe sunburn
  • trouble concentrating
  • trouble sleeping
  • uncaring
  • weight loss

For Healthcare Professionals

Applies to sulfamethoxazole / trimethoprim: intravenous solution, oral suspension, oral tablet


Rare (less than 0.1%): Thrombophlebitis
Postmarketing reports: QT prolongation resulting in ventricular tachycardia and torsade de pointes[Ref]


Dermatologic side effects were usually due to hypersensitivity to the sulfamethoxazole component.

A few cases of acute febrile neutrophilic dermatosis (Sweet's syndrome), characterized by abrupt onset of painful erythematous plaques or nodules and a fever greater than 38 degrees Celsius, have been reported.[Ref]

Rare (less than 0.1%): Acute febrile neutrophilic dermatosis (Sweet's syndrome), acute patchy exanthematous pustulosis (at least 1 case)
Frequency not reported: Mild erythroderma, severe exfoliative dermatitis, Stevens-Johnson syndrome, toxic epidermal necrolysis, erythema multiforme, exfoliative dermatitis, generalized skin eruptions, photosensitivity, phototoxicity, pruritus, urticaria, rash[Ref]


Frequency not reported: Nausea, vomiting/emesis, diarrhea, stomatitis, glossitis, abdominal pain, anorexia, pseudomembranous colitis, Clostridium difficile associated diarrhea, pancreatitis[Ref]


Because trimethoprim inhibits a step in folate synthesis, patients that are likely to have preexisting folate deficiencies (e.g., alcoholics, malnourished patients, patients on phenytoin or antifolate metabolites, and those with chronic hemolysis) are at risk of developing megaloblastic anemia during sulfamethoxazole-trimethoprim therapy. Folate replenishment reverses this effect.

Methemoglobinemia occurred twice in an HIV-infected patient who inadvertently received sulfamethoxazole-trimethoprim a second time after the first course was discontinued due to development of methemoglobinemia.[Ref]

Frequency not reported: Agranulocytosis, aplastic anemia, thrombocytopenia, leukopenia, neutropenia, hemolytic anemia, megaloblastic anemia, hypoprothrombinemia, methemoglobinemia, eosinophilia
Postmarketing reports: Thrombotic thrombocytopenic purpura, idiopathic thrombocytopenic purpura[Ref]


Cholestatic hepatitis associated with sulfamethoxazole-trimethoprim therapy may present with other signs of hypersensitivity, such as rash, fever, and eosinophilia. Biopsy findings in patients with sulfamethoxazole-trimethoprim-associated cholestatic hepatitis have included hepatic necrosis, hepatocyte degeneration, hepatic granuloma, centrilobular congestion, and inflammatory infiltrates.

A 34-year-old female developed pancreatitis and hepatitis after inadvertently receiving sulfamethoxazole-trimethoprim for treatment of a urinary tract infection several years after experiencing a previous episode of sulfamethoxazole-trimethoprim-associated hepatitis.[Ref]

Frequency not reported: Hepatitis (including cholestatic jaundice, hepatic necrosis), elevated serum transaminase, elevated bilirubin, elevated liver function tests, fulminant hepatic failure, hepatic and/or cholestatic lesions, hepatitis with simultaneous pancreatitis, hepatorenal failure, cholestatic liver disease with ductopenia[Ref]


Frequency not reported: Anaphylaxis, allergic myocarditis, angioedema, Henoch-Schonlein purpura, serum sickness-like syndrome, generalized allergic reactions, fixed drug eruption, hypersensitivity reactions (including cholestatic jaundice, interstitial nephritis, liver failure, renal failure, pancytopenia, hypotension, pulmonary edema, elevated serum transaminases)[Ref]

A case of fixed drug eruption due to polysensitivity (sulfamethoxazole-trimethoprim and tenoxicam) and reactivation of previous (10 years earlier) sulfamethoxazole-trimethoprim-associated fixed drug eruption lesions has been reported.

Hypersensitivity reactions may be more likely in patients with HIV infection, with opportunistic infections, or patients who are slow acetylators.

Hypotension, pulmonary edema, and elevated serum transaminases have been reported following sulfamethoxazole-trimethoprim administration to HIV-infected patients.

Hypersensitivity reactions in some cases have included cholestatic jaundice, interstitial nephritis, liver failure, renal failure, and pancytopenia.

A 48-year-old male developed liver failure, renal failure requiring hemodialysis, and pancytopenia requiring blood transfusions after 10 days of treatment with sulfamethoxazole-trimethoprim for pyelonephritis. This was believed to be a hypersensitivity reaction. He was a slow acetylator phenotype and had concurrently taken acetaminophen and diclofenac; the acetaminophen may have contributed to the reaction by inhibiting NAT2.[Ref]


Rare (less than 0.1%): Local reaction, pain, slight irritation[Ref]

Local reaction, pain, and slight irritation on intravenous administration have been reported infrequently.[Ref]


Rare (less than 0.1%): Hypoglycemia
Frequency not reported: Hyperkalemia, metabolic acidosis, hyponatremia, hypouricemia[Ref]

Hyperkalemia may occur as a result of the blocking of sodium channels by trimethoprim, which causes a reduction of potassium excretion in the distal tubule.

High doses of intravenous sulfamethoxazole-trimethoprim appear to be associated with a greater incidence of metabolic acidosis.

Sulfonamides may induce hypoglycemia. However, the establishment of a causal relationship has been difficult in most cases of suspected sulfa-induced hypoglycemia because many of the affected patients had AIDS, may have had another viral infection, or were on other medications.

Hypouricemia has been associated with high-dose therapy.[Ref]


Isolated cases of rhabdomyolysis have been reported, primarily in patients with AIDS.[Ref]

Rare (less than 0.1%): Rhabdomyolysis
Frequency not reported: Arthralgia, myalgia, periarteritis nodosa, systemic lupus erythematosus[Ref]

Nervous system

Exacerbation of posthypoxic action myoclonus occurred in a patient with non-Hodgkin's lymphoma who was receiving high-dose intravenous sulfamethoxazole-trimethoprim (115 mg/kg/day) for suspected Pneumocystis pneumonia.

HIV-infected patients receiving high-dose intravenous sulfamethoxazole-trimethoprim appear to have a greater incidence of tremors. The tremors generally appear several days after initiating therapy and resolve several days after discontinuation or dose reduction.

An 82-year-old male developed higher-level gait disorder on day 37 of treatment, 2 days after his dosage was doubled to sulfamethoxazole 320 mg-trimethoprim 1600 mg orally twice a day. During this time, the patient also had nocturnal delirium. Sulfamethoxazole-trimethoprim was discontinued on day 48 and the patient's gait returned to normal and his nocturnal delirium resolved by day 51.[Ref]

Rare (less than 0.1%): Higher-level gait disorder (at least 1 case)
Frequency not reported: Aseptic meningitis, convulsions, peripheral neuritis, ataxia, vertigo, tinnitus, headache, dizziness, tremors, lightheadedness, coma, seizures, multifocal myoclonus, bilateral asterixis, exacerbation of posthypoxic action myoclonus[Ref]


Frequency not reported: Conjunctival and scleral injection[Ref]


Frequency not reported: Hallucinations, depression, apathy, nervousness, insomnia, irritability, confusion, disorientation, catatonia, nocturnal delirium, exacerbation of panic attacks, acute psychoses[Ref]


Frequency not reported: Renal failure, interstitial nephritis, elevated BUN and serum creatinine, toxic nephrosis with oliguria and anuria, tubular necrosis, crystalluria, aggravation of renal disease, azotemia, hyperkalemic renal tubular acidosis, overestimations of normal creatinine values[Ref]

Trimethoprim inhibits renal tubular creatinine secretion, which can result in a significant decrease in creatinine clearance. These changes appear to be completely reversible upon discontinuation of therapy. Sulfamethoxazole may cause sulfa crystalluria, especially during low urine output states.

Interstitial nephritis and tubular necrosis may be due to hypersensitivity.

The propylene glycol vehicle in intravenous sulfamethoxazole-trimethoprim and lorazepam has also been implicated in the development of acute tubular necrosis in a patient.

Hyperkalemia has occurred with both standard and high-dose therapy. Reported cases have resolved upon discontinuation of the drug, although a few have required treatment with sodium polystyrene sulfonate. Up to 20% of patients with AIDS who are given sulfamethoxazole-trimethoprim for Pneumocystis pneumonia develop mild hyperkalemia.

Sulfamethoxazole-trimethoprim may interfere with creatinine determinations by the Jaffe alkaline picrate assay, resulting in overestimations of normal values.[Ref]


Hypersensitivity reactions of the respiratory tract associated with sulfonamides have included cough, shortness of breath, and pulmonary infiltrates.[Ref]

Frequency not reported: Cough, shortness of breath, pulmonary infiltrates[Ref]


1. Cerner Multum, Inc. "Australian Product Information." O 0

2. Cerner Multum, Inc. "UK Summary of Product Characteristics." O 0

3. "Product Information. Sulfamethoxazole-Trimethoprim (sulfamethoxazole-trimethoprim)." SICOR Pharmaceuticals Inc, Irvine, CA.

Not all side effects for Bactrim DS may be reported. You should always consult a doctor or healthcare professional for medical advice. Side effects can be reported to the FDA here.

Disclaimer: Every effort has been made to ensure that the information provided is accurate, up-to-date and complete, but no guarantee is made to that effect. In addition, the drug information contained herein may be time sensitive and should not be utilized as a reference resource beyond the date hereof. This material does not endorse drugs, diagnose patients, or recommend therapy. This information is a reference resource designed as supplement to, and not a substitute for, the expertise, skill , knowledge, and judgement of healthcare practitioners in patient care. The absence of a warning for a given drug or combination thereof in no way should be construed to indicate safety, effectiveness, or appropriateness for any given patient. does not assume any responsibility for any aspect of healthcare administered with the aid of materials provided. The information contained herein is not intended to cover all possible uses, directions, precautions, warnings, drug interactions, allergic reactions, or adverse effects. If you have questions about the substances you are taking, check with your doctor, nurse, or pharmacist.