SIDE EFFECTS
The most common adverse effects are gastrointestinal disturbances (nausea, vomiting, anorexia) and allergic skin reactions (such as rash and urticaria). FATALITIES ASSOCIATED WITH THE ADMINISTRATION OF SULFONAMIDES, ALTHOUGH RARE, HAVE OCCURRED DUE TO SEVERE REACTIONS, INCLUDING STEVENS-JOHNSON SYNDROME, TOXIC EPIDERMAL NECROLYSIS, FULMINANT HEPATIC NECROSIS, AGRANULOCYTOSIS, APLASTIC ANEMIA AND OTHER BLOOD DYSCRASIAS (SEE WARNINGS SECTION). Local reaction, pain and slight irritation on IV administration are infrequent. Thrombophlebitis has rarely been observed. Hematologic: Agranulocytosis, aplastic anemia, thrombocytopenia, leukopenia, neutropenia, hemolytic anemia, megaloblastic anemia, hypoprothrombinemia, methemoglobinemia, eosinophilia. 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, conjunctival and scleral injection, photosensitivity, pruritus, urticaria and rash. In addition, periarteritis nodosa and systemic lupus erythematosus have been reported. Gastrointestinal: Hepatitis (including cholestatic jaundice and hepatic necrosis), elevation of serum transaminase and bilirubin, pseudomembraneous enterocolitis, pancreatitis, stomatitis, glossitis, nausea, emesis, abdominal pain, diarrhea, anorexia. Genitourinary: Renal failure, interstitial nephritis, BUN and serum creatinine elevation, toxic nephrosis with oliguria and anuria, and crystalluria. 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 rarely in patients receiving sulfonamides. Musculoskeletal: Arthralgia and myalgia. Respiratory: Pulmonary infiltrates. Miscellaneous: Weakness, fatigue, insomnia.
DRUG INTERACTIONS
In elderly patients concurrently
receiving certain diuretics, primarily thiazides, an increased incidence of
thrombocytopenia with purpura has been reported.
It has been reported that Bactrim may prolong the prothrombin time in patients
who are receiving the anticoagulant warfarin. This interaction should be kept
in mind when Bactrim is given to patients already on anticoagulant therapy,
and the coagulation time should be reassessed.
Bactrim may inhibit the hepatic metabolism of phenytoin. Bactrim, given at
a common clinical dosage, increased the phenytoin half-life by 39% and decreased
the phenytoin metabolic clearance rate by 27%. When administering these drugs
concurrently, one should be alert for possible excessive phenytoin effect.
Sulfonamides can also displace methotrexate from plasma protein binding sites,
thus increasing free methotrexate concentrations.
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