Brief Answer:
Information

Detailed Answer:
Hello and welcome,

With any FDA approved antibiotic or other medication, in the final phase of trials, the medication is given to a group of people while a placebo is given to a similar group. The patients from both groups report any symptoms they are having while taking the medication (or placebo). Some of these symptoms are directly from the medication and others are coincidental. So the two groups are compared for statistical significance of the symptoms and percentages are given in the literature. Once the medication is released to the public, some companies have post-marketing percentages of side effects because the original groups were limited in size.

I am listing here, data for health professionals, on the frequency of reported side effects:

Cardiovascular
Rare (0.01% to 0.1%): Thrombophlebitis
Very rare (less than 0.01%): Polyarteritis nodosa, syncope
Postmarketing reports: QT prolongation resulting in ventricular tachycardia and torsade de pointes[Ref]

Dermatologic
Common (1% to 10%): Skin rash, urticaria
Very rare (less than 0.01%): Photosensitivity, exfoliative dermatitis, fixed drug eruption, erythema multiforme, erythema nodosum, Stevens-Johnson Syndrome (SJS), toxic epidermal necrolysis, bullous dermatitis, purpura, angioedema
Frequency not reported: Pruritus[Ref]

Gastrointestinal
Common (1% to 10%): Diarrhea, nausea, vomiting, anorexia
Very rare (less than 0.01%): Constipation, glossitis, stomatitis, pseudomembranous colitis, pancreatitis, abdominal pain
Frequency not reported: Sore mouth, moniliasis[Ref]

Hematologic
Very rare (less than 0.01%): Leucopenia, neutropenia, thrombocytopenia, pancytopenia, bone marrow depression, agranulocytosis, aplastic anemia, hemolytic anemia, eosinophilia, purpura, hemolysis
Frequency not reported: Megaloblastic anemia, methemoglobinemia, hypoprothrombinemia, granulocytopenia[Ref]

Hepatic
Rare (0.01% to 0.1%): Jaundice
Very rare (less than 0.01%): Hepatitis (including cholestatic jaundice and hepatic necrosis), disturbance in liver enzymes, elevated serum transaminases, elevated bilirubin[Ref]

Hypersensitivity
Very rare (less than 0.01%): Hypersensitivity, anaphylaxis, anaphylactoid reaction drug fever, chills, allergic vasculitis resembling Henoch-Schonlein purpura
Frequency not reported: Stevens-Johnson syndrome (SJS), toxic epidermal necrolysis (TEN), anaphylaxis, allergic myocarditis, erythema multiforme, exfoliative dermatitis, angioedema, serum sickness-like syndrome, generalized allergic reactions, generalized skin eruptions, conjunctival and scleral injection, photosensitivity, pruritus, urticaria, rash, periarteritis nodosa, systemic lupus erythematosus (SLE)[Ref]

Immunologic
Common (1% to 10%): Monilial overgrowth[Ref]

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

Metabolic
Very common (10% or more): Hyperkalemia (particularly in the elderly and in HIV patients)
Very rare (less than 0.01%): Hypoglycemia, hyponatremia, metabolic acidosis[Ref]

Musculoskeletal
Rare (less than 0.1%): Rhabdomyolysis (mainly in AIDS patients)
Frequency not reported: Arthralgia, myalgia[Ref]

Nervous system
Very common (10% or more): Headache
Very rare (less than 0.01%): Aseptic meningitis (rapidly reversible on withdrawal of therapy but can reoccur on rechallenge), convulsions, peripheral neuritis, ataxia, vertigo, dizziness, tremor, lethargy, paresthesia, convulsions, peripheral neuritis, tinnitus[Ref]

Ocular
Very rare (less than 0.01%): Uveitis[Ref]

Psychiatric
Very rare (less than 0.01%): Depression, hallucination, confusional state, agitation, anxiety, abnormal behavior, insomnia, nightmares[Ref]

Renal
Very rare (less than 0.01%): Renal tubular acidosis, Impaired renal function (sometimes reported as renal failure), hematuria
Frequency not reported: Serum creatinine increased, blood urea nitrogen increased
Postmarketing reports:
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]

Respiratory
Very rare (less than 0.01%): Cough, dyspnea, lung infiltration, shortness of breath, wheezing, epistaxis[Ref]

References

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, XXXXXXX CA.

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