Sulphadiazine

Indications

Sulphadiazine is a sulfonamide antibacterial taken by mouth. Today it is mainly used, together with Pyrimethamine and Folinic Acid, to treat toxoplasmosis, an infection caused by a parasite that can affect the eyes, brain or an unborn baby. It may also be used for some other infections such as nocardiosis, and to prevent rheumatic fever coming back in people who cannot take Penicillin.

How It Works

Germs need folic acid to grow. Sulphadiazine blocks the germ's ability to make folic acid, which stops it from multiplying so the body's defences can clear the infection. With Pyrimethamine, which blocks a later step in the same pathway, the effect is much stronger.

Dosage and Administration

Dose and length of treatment depend on the infection and the person's weight and kidney function, so it is taken as prescribed. Treatment for toxoplasmosis usually lasts several weeks and is supervised by a specialist. Take with a full glass of water and drink plenty of fluids every day (adults usually at least 2 to 3 litres) to protect the kidneys. Complete the full course. Children and newborns: only as prescribed by a specialist.

Interactions

It can increase the effect of Warfarin (more bleeding), Phenytoin, Methotrexate and sulfonylurea diabetes medicines such as Glibenclamide (low blood sugar). Combining with Trimethoprim, Pyrimethamine or Methotrexate increases the risk of low blood counts, so blood tests are needed. Avoid with Methenamine. It may make some vaccines that contain live bacteria (such as oral typhoid vaccine) less effective.

Contraindications

• Allergy to sulfonamides ("sulfa drugs"), including a past severe skin reaction.
• Porphyria.
• Severe kidney or liver disease.
• Babies under 2 months old (except under specialist care for congenital toxoplasmosis).
• Late pregnancy and breastfeeding of newborn, premature or jaundiced babies.

Side Effects

Common: nausea, loss of appetite, headache, skin rash and sensitivity to sunlight. Less common: crystals in the urine or kidney stones (pain in the side, blood in the urine), low blood counts, fever and joint pain.

Stop taking it and get urgent medical help for: a widespread rash, blisters, peeling skin or sores in the mouth, eyes or genitals; swelling of the face or difficulty breathing; yellow skin or eyes; sore throat, fever or mouth ulcers that may mean low white cells; unusual bleeding or bruising; very little urine, blood in the urine or severe pain in the side.

Pregnancy and Lactation

Used in pregnancy only when a specialist decides the benefit is greater than the risk, for example to protect the baby from toxoplasmosis. Folinic acid is usually given alongside. Avoid near delivery, as it can raise jaundice in the newborn. Small amounts pass into breast milk; avoid breastfeeding newborn, premature, ill or jaundiced babies, or babies with G6PD deficiency.

Precautions and Warnings

• Blood counts and kidney and liver tests are checked regularly during long treatment.
• Tell the doctor about G6PD deficiency, asthma, severe allergies, kidney or liver disease, or folate deficiency.
• Drink plenty of fluids and avoid strong sunlight.
• Older people and people with HIV are more likely to have side effects.

Overdose

Too much can cause nausea, vomiting, dizziness, confusion, blood in the urine, kidney problems and yellow skin. Seek urgent medical help.

Therapeutic Class

Sulfonamide antibacterial.

Storage

Store below 30°C in a dry place, away from light and out of the reach of children.