Sulfamethoxazole and Trimethoprim (Page 3 of 7)

5.13 Hypoglycemia

Cases of hypoglycemia in non-diabetic patients treated with sulfamethoxazole and trimethoprim injection have been seen, usually occurring after a few days of therapy. Patients with renal dysfunction, liver disease, malnutrition or those receiving high doses of sulfamethoxazole and trimethoprim injection are particularly at risk.

5.14 Impaired Phenylalanine Metabolism

Trimethoprim, component of sulfamethoxazole and trimethoprim injection, has been noted to impair phenylalanine metabolism, but this is of no significance in phenylketonuric patients on appropriate dietary restriction.

5.15 Porphyria and Hypothyroidism

Like other drugs containing sulfonamides, sulfamethoxazole and trimethoprim injection can precipitate porphyria crisis and hypothyroidism. Avoid use of sulfamethoxazole and trimethoprim injection in patients with porphyria or thyroid dysfunction.

5.16 Potential Risk in the Treatment of Pneumocystis jirovecii Pneumonia in Patients with Acquired Immunodeficiency Syndrome (AIDS)

AIDS patients may not tolerate or respond to sulfamethoxazole and trimethoprim injection in the same manner as non-AIDS patients. The incidence of adverse reactions, particularly rash, fever, leukopenia, and elevated aminotransferase (transaminase) values, with sulfamethoxazole and trimethoprim injection therapy in AIDS patients who are being treated for P. jirovecii pneumonia has been reported to be greatly increased compared with the incidence normally associated with the use of sulfamethoxazole and trimethoprim injection in non-AIDS patients. If a patient develops skin rash or any sign of an adverse reaction, reevaluate therapy with sulfamethoxazole and trimethoprim injection [see Warnings and Precautions (5.2)].

Avoid coadministration of sulfamethoxazole and trimethoprim injection and leucovorin during treatment of Pneumocystis jirovecii pneumonia [see Warnings and Precautions (5.8)]

5.17 Electrolyte Abnormalities


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. Even 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 is warranted in these patients.


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


During treatment, ensure adequate fluid intake and urinary output to prevent crystalluria. Patients who are “slow acetylators” may be more prone to idiosyncratic reactions to sulfonamides.

5.18 Monitoring of Laboratory Tests

Complete blood counts and clinical chemistry testing should be done frequently in patients receiving sulfamethoxazole and trimethoprim injection. Discontinue sulfamethoxazole and trimethoprim injection if a significant electrolyte abnormality, renal insufficiency or reduction in the 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.

5.19 Development of Drug-Resistant Bacteria

Prescribing sulfamethoxazole and trimethoprim injection in the absence of a proven or strongly suspected bacterial infection or a prophylactic indication is unlikely to provide benefit to the patient and increases the risk of the development of drug-resistant bacteria.


The following serious adverse reactions are described elsewhere in the labeling:

  • Embryo-fetal Toxicity [see Warnings and Precautions (5.1)]
  • Hypersensitivity and Other Serious or Fatal Reactions [see Warnings and Precautions (5.2)]
  • Thrombocytopenia [see Warnings and Precautions (5.3)]
  • Clostridium difficile -Associated Diarrhea [see Warnings and Precautions (5.5)]
  • Sulfite Sensitivity [see Warnings and Precautions (5.6)]
  • Risk Associated with Concurrent Use of Leucovorin for Pneumocystis jirovecii Pneumonia [see Warnings and Precautions (5.8)]
  • Propylene Glycol Toxicity [see Warnings and Precautions (5.9)]
  • Infusion Reactions [see Warnings and Precautions (5.12)]
  • Hypoglycemia [see Warnings and Precautions (5.13)]
  • Electrolyte Abnormalities [see Warnings and Precautions (5.17)]

6.1 Clinical Trials Experience

The following adverse reactions associated with the use of sulfamethoxazole and trimethoprim injection or sulfamethoxazole and trimethoprim were identified in clinical trials, postmarketing or published reports. Because some of these reactions were reported voluntarily from a population of uncertain size, it is not always possible to reliably estimate their frequency or establish a causal relationship to drug exposure.

The most common adverse reactions are gastrointestinal disturbances (nausea, vomiting, and anorexia) and allergic skin reactions (such as rash and urticaria).

Fatalities and serious adverse reactions, including severe cutaneous adverse reactions (SCARs), including Stevens-Johnson syndrome, toxic epidermal necrolysis, drug reaction with eosinophilia and systemic symptoms (DRESS), acute febrile neutrophilic dermatosis (AFND), acute generalized erythematous pustulosis (AGEP); fulminant hepatic necrosis; agranulocytosis, aplastic anemia and other blood dyscrasias; acute and delayed lung injury; anaphylaxis and circulatory shock have occurred with the administration of sulfamethoxazole and trimethoprim products, including sulfamethoxazole and trimethoprim injection [see Warnings and Precautions (5.2)].

Local reaction, pain and slight irritation on intravenous (IV) administration are infrequent. Thrombophlebitis has been observed.

Table 3: Adverse Reactions Reported with Sulfamethoxazole and trimethoprim injection

Body System Adverse Reactions
Hematologic Agranulocytosis, aplastic anemia, thrombocytopenia, leukopenia, neutropenia, hemolytic anemia, megaloblastic anemia, hypoprothrombinemia, methemoglobinemia, eosinophilia, thrombotic thrombocytopenic purpura, idiopathic thrombocytopenic purpura.
Allergic Reactions Stevens-Johnson syndrome, toxic epidermal necrolysis, anaphylaxis, allergic myocarditis, erythema multiforme, exfoliative dermatitis, angioedema, drug fever, chills, Henoch-Schoenlein purpura, serum sickness-like syndrome, generalized allergic reactions, generalized skin eruptions, photosensitivity, conjunctival and scleral injection, pruritus, urticaria, rash, periarteritis nodosa, systemic lupus erythematosus, drug reaction with eosinophilia and systemic symptoms (DRESS), acute generalized erythematous pustulosis (AGEP), and acute febrile neutrophilic dermatosis (AFND) [see Warnings and Precautions (5.2)].
Gastrointestinal Hepatitis (including cholestatic jaundice and hepatic necrosis), elevation of serum transaminase and bilirubin, pseudomembranous enterocolitis, pancreatitis, stomatitis, glossitis, nausea, emesis, abdominal pain, diarrhea, anorexia.
Genitourinary Renal failure, interstitial nephritis, BUN and serum creatinine elevation, renal insufficiency, oliguria and anuria, crystalluria and nephrotoxicity in association with cyclosporine.
Metabolic and Nutritional Hyperkalemia, hyponatremia [see Warnings and Precautions (5.17)] , metabolic acidosis.
Neurologic Aseptic meningitis, convulsions, peripheral neuritis, ataxia, vertigo, tinnitus, headache.
Psychiatric Hallucinations, depression, apathy, nervousness.
Endocrine The sulfonamides bear certain chemical similarities to some goitrogens, diuretics (acetazolamide and the thiazides) and oral hypoglycemic agents. Cross-sensitivity may exist with these agents. Diuresis and hypoglycemia have occurred.
Musculoskeletal Arthralgia, myalgia, rhabdomyolysis.
Respiratory Cough, shortness of breath and pulmonary infiltrates, acute eosinophilic pneumonia, acute and delayed lung injury, interstitial lung disease, acute respiratory failure [see Warnings and Precautions (5.2)].
Cardiovascular System QT prolongation resulting in ventricular tachycardia and torsades de pointes, circulatory shock [see Warnings and Precautions (5.2)].
Miscellaneous Weakness, fatigue, insomnia.

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