Generic name: Sulfisoxazole.

Gantrisin is a sulfa drug and an antibiotic. It inhibits the growth of bacteria by chemically interfering with their ability to survive. 

Quick Facts About Gantrisin


Used to treat severe, repeated, or long-lasting urinary tract infections. Also used to treat bacterial meningitis, and as a preventive measure for people exposed to meningitis. May also be used in combination with other medications to treat some middle ear infections, toxoplasmosis (parasite from cats, cat feces, or uncooked meat), malaria, eye infections, bacterial disease of the lungs, skin, and brain (nocardiosis), and chancroid (venereal disease of the groin).

Gantrisin Dosage

Drink lots of liquids to avoid crystals in the urine and stone formation. Shake suspension well before each use; use marked measuring spoon from your pharmacist Take at evenly spaced intervals to keep level of this medication constant.

  • Usual adult dose: 2 to 4 grams per day. Doctor may prescribe up to 4 to 8 grams per day divided into 4 to 6 doses.
  • Usual child dose: for children 2 months or older — Starting dose — 75 milligrams per 2.2 pounds of body weight divided into 4 to 6 doses in 24 hours. Regular dose — 120 to 150 milligrams per 2.2 pounds of body weight divided into 4 to 6 doses in 24 hours. Not for children under 2 years except to treat toxoplasmosis. Maximum dose is 6 grams per day.
  • Missed dose: take as soon as possible, unless almost time for next dose. In that case, do not take missed dose; go back to regular schedule. Do not double doses.

Gantrisin Side Effects

Overdose symptoms:

blood or sediment in urine, blue tinge to the skin, colic, dizziness, drowsiness, fever, headache, lack of or loss of appetite, nausea, unconsciousness, vomiting, yellowing of skin and eyes. If you suspect an overdose, immediately seek medical attention.

More common side effects: abdominal bleeding, abdominal pain, allergic reactions, anemia and other blood disorders, angioedema (swelling of the face, lips, tongue, and throat), anxiety, bluish tinge to the skin, chills, colitis, convulsions, cough, dark or tarry stools, depression, diarrhea, disorientation, dizziness, drowsiness, enlarged salivary glands, enlarged thyroid gland, exhaustion, fainting, fatigue, fever, flushing, gas, hallucinations, headache, hearing loss, hepatitis, hives, inability to fall or stay asleep, inability to urinate, increased urination, inflammation of the mouth or tongue, itching, joint pain, kidney failure, lack of feeling or concern, lack of muscle coordination, lack or loss of appetite, low blood sugar, muscle pain, nausea, palpitations, presence of blood or crystals in urine, rapid heartbeat, reddish or purplish skin spots, retention of urine, ringing in the ears, sensitivity to light, serum sickness (fever, painful joints, enlarged lymph nodes, skin rash), severe skin welts or swelling, shortness of breath, skin eruptions, skin rash, swelling due to fluid retention, tingling or pins and needles, vertigo, vomiting, weakness, yellow eyes and skin.

No known less common or rare Gantrisin side effects.


Inform your doctor before combining Gantrisin with:

blood thinners such as Coumadin; methotrexate, an anticancer medication; oral contraceptives; oral diabetes medications such as Micronase.

No known food/other substance interactions. 

Special Cautions

If pregnant or planning to become pregnant, inform your doctor immediately. Appears in breast milk; could affect a nursing infant. Should not take near the end of pregnancy or when nursing a baby under 2 months.

No special precautions apply to seniors.

Follow doctor’s instructions carefully for children.

  • Severe and fatal reactions have occurred with sulfa medications such as Gantrisin. Monitor for: sudden and severe liver damage, agranulocytosis (severe blood disorder), aplastic anemia (lack of red and white blood cells due to bone marrow disorder), and Stevens-Johnson syndrome (severe blistering).
  • Doctor should take blood counts and urine and kidney function analysis frequently.
  • Immediately contact your doctor if you experience reactions such as: skin rash, sore throat, fever, joint, pain, cough, shortness of breath or other breathing problems, abnormal skin paleness, reddish or purplish spots, yellowing of skin or eyes, or diarrhea.
  • Should not take if sensitive to or allergic to this or other sulfa medications.
  • Inform your doctor and use with caution if you have impaired kidney or liver function, severe allergies, or bronchial asthma.

Note: provides accurate and independent information prescription pills, over-the-counter medicines and natural products. This material is provided for educational purposes only and is not intended for medical advice, diagnosis or treatment. If you have questions about  dosage, or Gantrisin side effects, please contact your healthcare provider.