Classifications: sulfonamide antibiotic;
Therapeutic: antibiotic, sulfonamide

Pregnancy Category: C (D if near term)


500 mg tablets


Short-acting derivative of sulfanilamide. Bacteriostatic action believed to be by competitive inhibition of p-aminobenzoic acid (PABA), thereby interfering with folic acid biosynthesis required for bacterial growth.

Therapeutic Effect

Exhibits broad antimicrobial spectrum against both gram-positive and gram-negative organisms.


Acute, recurrent, and chronic urinary tract infections and chancroid; adjunctive therapy in trachoma, chloroquine-resistant strains of malaria, acute otitis media due to Haemophilus influenzae, and meningococcal and H. influenzae meningitis. Ophthalmic preparations used in treatment of conjunctivitis, corneal ulcer, and other superficial eye infections and as adjunct to systemic sulfonamide therapy for trachoma. Topical vaginal preparation used for H. vaginalis vaginitis.


History of hypersensitivity to sulfonamides, salicylates, or chemically related drugs; use in treatment of group A beta-hemolytic streptococcal infections; infants <2 mo of age (except in treatment of congenital toxoplasmosis); neonates; porphyria; G6PD deficiency; advanced kidney or liver disease; intestinal and urinary obstruction; pregnancy (category C, category D if near term).

Cautious Use

Impaired kidney or liver function; severe allergy; bronchial asthma; blood dyscrasias.

Route & Dosage

Adult: PO 2–4 g initially, followed by 4–8 g/d in 4–6 divided doses
Child (>2 mo): PO 75 mg/kg initially, followed by 150 mg/kg/d in 4–6 divided doses (max: 6 g/d)


  • Give with full glass of water or other fluid; tablet may be crushed.
  • Store at 15°–30° C (59°–86° F) in tight, light-resistant containers.

Adverse Effects (≥1%)

CNS: Headache, peripheral neuritis, peripheral neuropathy, tinnitus, hearing loss, vertigo, insomnia, drowsiness, mental depression, acute psychosis, ataxia, convulsions, kernicterus (newborns). GI: Nausea, vomiting, diarrhea, abdominal pains, hepatitis, jaundice, pancreatitis, stomatitis. Hematologic: Acute hemolytic anemia (especially in patients with G6PD deficiency), aplastic anemia, methemoglobinemia, agranulocytosis, thrombocytopenia, leukopenia, eosinophilia, hypoprothrombinemia. Body as a Whole: Headache, fever, chills, arthralgia, malaise, allergic myocarditis, serum sickness, anaphylactoid reactions, lymphadenopathy, local reaction following IM injection, fixed drug eruptions, diuresis, overgrowth of nonsusceptible organisms, LE phenomenon. Skin: Pruritus, urticaria, rash, erythema multiforme including Stevens-Johnson syndrome exfoliative, dermatitis, alopecia, photosensitivity, vascular lesions. Urogenital: Crystalluria, hematuria, proteinuria, anuria, toxic nephrosis, reduction in sperm count. Metabolic: Goiter, hypoglycemia. Special Senses: Conjunctivitis, conjunctival or scleral infection, retardation of corneal healing (ophthalmic ointment).

Diagnostic Test Interference

Sulfonamides may interfere with BSP retention and PSP excretion tests and may affect results of thyroid function tests (I-131 may be decreased for about 7 d). Large doses of sulfonamides reportedly may produce false-positive urine glucose determinations with copper reduction methods (e.g., Benedict's and Clinitest). SULFONAMIDES may produce false-positive results for urinary protein (with sulfosalicylic acid test) and may interfere with urine urobilinogen determinations using Ehrlich's reagent or Urobilistix. Follow-up cultures are unreliable unless PABA is added to culture medium.


Drug: paba-containing local anesthetics may antagonize sulfa's effects; oral anticoagulants potentiate hypoprothrombinemia; may potentiate sulfonylurea-induced hypoglycemia; may decrease concentrations of cyclosporine; may increase levels of phenytoin.


Absorption: Readily from GI tract. Peak: 2–4 h. Distribution: Distributed in extracellular space; crosses blood–brain barrier and placenta; detected in breast milk. Metabolism: in liver. Elimination: 95% in urine in 24 h. Half-Life: 4.6–7.8 h.

Nursing Implications

Assessment & Drug Effects

  • Lab tests: Obtain a specimen for C&S prior to initiation of therapy. Perform frequent kidney function tests and urinalyses; complete blood counts and liver function tests, especially during regimens longer than 2 wk.
  • Monitor I&O. Report oliguria and changes in I&O ratio. Fluid intake should be adequate to support urinary output of at least 1500 mL/d to prevent crystalluria and stone formation.
  • Check urine pH daily with Nitrazine paper or Labstix; fall in urinary pH (more acidic) increases risk of crystalluria.
  • Report increasing urine acidity. If urine is highly acidic, physician may prescribe a urinary alkalinizer.
  • Monitor temperature. Sudden appearance of fever may signify sensitization (serum sickness) or hemolytic anemia (frequent in patients with G6PD deficiency, which is most common among black males and Mediterranean ethnic groups). Reactions generally develop within 10 d. Agranulocytosis may develop after 10 d–6 wk of therapy.
  • Report early manifestations of blood dyscrasias or hypersensitivity reactions immediately (fever with sore throat, malaise, unusual fatigue, joint pains, pallor, bleeding tendencies, rash, jaundice).
  • Be alert for skin lesions, papular or vesiculobullous lesions, especially on sun-exposed areas, Stevens-Johnson syndrome (severe erythema multiforme) may be preceded by high fever, severe headache, stomatitis, conjunctivitis, rhinitis, urticaria, balanitis (inflammation of penis or clitoris). Termination of drug therapy is indicated.
  • Observe diabetic patients receiving oral hypoglycemic agents closely for hypoglycemic reactions. Obtain blood glucose and HbA1C levels before and shortly after initiation of therapy.

Patient & Family Education

  • Do not take OTC medications without consulting physician. Many analgesic mixtures contain aspirin in combination with p-aminobenzoic acid; avoid to prevent crystallization in urine.
  • Use or add barrier contraceptives if using hormonal contraceptives, which may be unreliable while taking this drug.
  • Avoid exposure to ultraviolet light and excessive sunlight to prevent photosensitivity reaction during therapy and for several months after treatment is discontinued.
  • Inform dentist or new physician that you are taking a sulfonamide.

Common adverse effects in italic, life-threatening effects underlined; generic names in bold; classifications in SMALL CAPS; Canadian drug name; Prototype drug

© 2006-2022 Last Updated On: 11/20/2022 (0)
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