Sulfadiazine (Oral)

Sulfadiazine is an oral antibiotic available on prescription to treat a range of infections, most notably toxoplasmosis.


Sulfadiazine is a prescription-only medication that is used to prevent and treat a number of infections. It belongs to a family of drugs called the sulfa antibiotics, and it works by preventing the creation and growth of bacteria and other harmful organisms. It is often prescribed along with another drug, pyrimethamine.

Sulfadiazine is not used to treat common viral infections such as colds and flu.

One common use for sulfadiazine is to treat a condition called toxoplasmosis, an infection caused by a parasite called Toxoplasma gondii. This parasite usually resides in places such as undercooked meat, cat feces and contaminated water. These parasites can be very harmful, causing serious infections in both adults and children. They can also lead to birth abnormalities if an expectant mother contracts an infection during pregnancy.

Most people that contract toxoplasma do not experience any symptoms, so it is difficult to treat the disease early. It is estimated by the Centers for Disease Control and Prevention (CDC) that more than 60,000 people in the United States are currently living with toxoplasmosis - many without realizing it. Usually, the disease goes away on its own after a month or so. However, for those with weak immune systems, it can progress into several serious conditions, such as brain inflammation, eye infections and lung infections. These conditions can be fatal if left untreated. For pregnant women, the progression of the disease can be life-threatening for the baby shortly after birth; or alternatively, the child can develop symptoms as they get older.

Sulfadiazine is an effective and widely used oral treatment for the prevention of long-term health damage to those infected by the Toxoplasma gondii virus. However, it should not be used in babies that are under two months as there are risks of serious side effects.

Conditions treated

  • Conditions contracted from the parasite Toxoplasma gondii
  • Infection from birth due to the Nocardia bacteria
  • Encephalitis as a result of the Toxoplasma gondii bacteria
  • Bacterial urinary tract infection
  • ┬áRheumatic fever prevention

Type of medicine

  • Antibiotic

Side effects

As with most drugs, there is always the risk of experiencing several unwanted and unpleasant side effects. With sulfadiazine, you may experience any of the below - although many of these are very rare. If you have any severe symptoms, or if you are worried about how your body is reacting to the drug, you should contact your doctor right away for advice. These are the side effects that you may be vulnerable to when taking sulfadiazine:

  • headache
  • increased hunger
  • nausea
  • cold sweats
  • dizziness
  • anxiety or depression
  • blurry vision
  • changes in menstrual periods
  • chills
  • feeling cold
  • nightmares or vivid dreams
  • seizures and fits
  • dry skin
  • puffy skin
  • confusion
  • paler or washed out looking skin
  • loss of libido (sex drive) or inability to get an erection
  • unusual or extreme levels of tiredness or weakness
  • fast or irregular heartbeat
  • nervousness or agitation
  • shakiness
  • slurry speech
  • swelling of front part of the neck
  • sudden or sharp weight gain
  • back, leg, or stomach pains
  • bleeding gums or ulcers in the mouth
  • blistering
  • skin peeling
  • saggy skin
  • chest pain
  • cloudy urine
  • clumsiness or lack of balance
  • bloating
  • blood in the urine
  • constipation
  • buzzing sound in the ears
  • cough or hoarseness
  • cracked skin
  • dark urine
  • decrease in the amount of urine
  • diarrhea
  • difficulty with breathing
  • difficulty with moving
  • dizziness
  • lightheadedness
  • feeling of discomfort
  • fever with or without chills
  • general body swelling
  • general feeling of tiredness or weakness
  • headache
  • sudden or gradual loss of hearing
  • indigestion
  • itching
  • back pain, typically in the lower back region
  • stiffness in the muscles and joints
  • nosebleeds
  • burning sensation when passing urine
  • needing to urinate more often than normal
  • pale skin
  • red patches on the skin
  • pinpoint red or purple spots on the skin
  • rapid heart rate
  • bloodshot eyes
  • rashes or spots on any part of the body
  • skin lesions
  • scaly skin
  • shakiness
  • shortness of breath
  • pain in the throat
  • soreness of the muscles
  • sores, ulcers, or white spots on the lips or in the mouth
  • difficulty emptying the bladder
  • swollen or painful glands
  • tight feeling in the chest, or difficulty catching breath
  • unsteadiness, trembling, or other problems with muscle control or coordination
  • unknown bruising
  • upper right abdominal pain
  • poor vision, e.g. short or long sight
  • swelling of the face, including eye area or lips
  • weak feeling in the hands or feet
  • wheezing and coughing
  • jaundice (yellow skin or eyes)


Your doctor will decide on the appropriate dosage for you depending on a number of factors, such as your age, medical history, immune system and the type or progression of any infection.

For toxoplasmosis, the usual treatment dose is first a course of 200 mg of pyrimethamine, taken orally once per day. This initial dosage will likely be reduced as your treatment progresses, reaching a maintenance dose that is dependent on your body weight. For patients with body weights that are less than 60 kg, the dose will usually be set at 1 g of sulfadiazine taken every six hours, plus a dose of 50 mg pyrimethamine once per day.

For patients that weigh more than 60 kg, the maintenance dosage will be 1,500 mg taken orally every six hours, along with a dose of pyrimethamine 75 mg taken orally once per day.

For children, a starting dose of 2 mg per kilogram of body weight is advised, to be taken orally once per day. The maintenance dose is then 50 mg of sulfadiazine taken orally twice per day, along with 1 mg per kilogram of body weight taken orally once per day.

For other conditions, the dosage may vary. (ref 1)

Major drug interactions

Do not accept a prescription of sulfadiazine if you are taking any of the below medications. These drugs can cause a major reaction with sulfadiazine and impact on its effectiveness to treat your infection. They can also cause serious side effects when taken together, causing danger to your health. Drugs with major interactions to sulfadiazine are:

  • amyl nitrite, sodium nitrite, sodium thiosulfate
  • anisindione
  • benzoic acid, hyoscyamine, methenamine, methylene blue, phenyl salicylate
  • benzoic acid, methenamine, sodium salicylate
  • cholera vaccine, live
  • clozapine
  • cyclosporine
  • dicumarol
  • epinephrine, prilocaine
  • hyoscyamine, methenamine
  • hyoscyamine, methenamine, methylene blue, phenyl salicylate
  • hyoscyamine, methenamine, methylene blue, phenyl salicylate, sodium biphosphate
  • hyoscyamine, methenamine, methylene blue, sodium biphosphate
  • lidocaine, prilocaine topical
  • lomitapide
  • methenamine
  • methenamine, sodium acid phosphate
  • methenamine, sodium biphosphate
  • mipomersen
  • potassium aminobenzoate
  • prilocaine
  • sodium nitrite
  • sodium nitrite, sodium thiosulfate
  • warfarin

There are 125 drugs that have been found to have some level of reaction with sulfadiazine. Aside from those with major interactions listed above, there are 98 that have a moderate interaction and three that have a minor interaction. You may still be able to take sulfadiazine if you are taking another drug with a moderate or minor interaction, but your doctor may alter the dosage that is set to you. Alternatively, there may be other medications that are more suitable for you. (ref 2)


Other diseases and conditions

Like with other drugs, there are also other conditions and diseases that can interact with your prescription. You should always tell your doctor if you are suffering from any other condition at all - no matter how small. Your doctor will also want to know about your medical history as even previous conditions that you have suffered from can impact whether you are suitable for this medication.

There are nine conditions that interact with this prescription. They are:

  • Renal Dysfunction
  • Porphyria
  • Colitis
  • Hematologic Toxicity
  • Hypersensitivity Reactions
  • Crystalluria
  • Hemodialysis
  • Liver Disease
  • Urinary Obstruction

Women and pregnancy

Pregnant women should not take this medication. This is because it has been found to cause birth defects in babies when they are born. If you are pregnant, or expect that you may be pregnant, always tell your doctor. Do not attempt to become pregnant while taking this medication.

Breastfeeding mothers

Do not use this medication if you are breastfeeding. Sulfadiazine has been found to enter the breast milk and therefore could cause harm to a nursing baby.


Children can take this medication, but it should be given at a reduced dosage. Babies under two months old should not be given sulfadiazine as the side effects can be too severe for the infant's immune system to cope with.


Occasionally, sulfadiazine can cause serious allergic reactions that can become fatal. Always tell your doctor if you are allergic to any sulfa-based drugs or products, along with any other allergies, including to animals, foods and preservatives.


Do not attempt to increase the dosage set to you by your pharmacist or doctor. This can cause the effects of overdose and can be fatal. If you think you have taken too much of this drug, you should call your local poison control center.


You should always keep your medication out of the reach of children; do not let children access your prescription. Tens of thousands of children are admitted to hospital every year with potentially life-threatening conditions because of prescription drugs that they have been able to access. A lockable cabinet is the ideal place to keep your medication. Otherwise, a high shelf that children or pets cannot get to.

You should also keep your medication in the original packaging. Always make sure the drugs remain clearly labelled so that they do not get mixed up with other medication. If your drugs are supplied in a tub with a child-proof lid, make sure this is in the lock position at all times when you are not using the medication.

Keep your drugs out of any direct light or heat sources. Also keep them away from water or damp conditions; it is not advisable to keep medication in the bathroom as it can easily become damp. You should also keep your medication at room temperature (between 15 and 25 degrees centigrade).


Dispose of unwanted medication responsibly and safely. Do not flush or grind your tablets. You can visit the FDA's website for advice on how to properly get rid of unused prescription drugs, but as a general rule, you should mix the whole tablets with an inedible material such as cat litter or soil, or something else similar. You should then put the mixture into a sealable plastic bag, shut it tightly and then put it in the bin. (ref 3)

In the United States, there are dedicated take-back schemes that can collect your unwanted prescription directly from you. This is the safest way to dispose of medicine and it can be easily arranged. You can check whether there is one in your local area by visiting the website of the FDA.


Sulfadiazine is a safe medication in the majority of cases, provided all instructions are followed and the dosage is not altered. It can be a potentially life-saving treatment for those that are suffering from a condition related to the bacteria Toxoplasma gondii. Medical studies have found the drug to be highly effective in the reduction and prevention of the Toxoplasma gondii bacteria, and studies continue to be carried out to assess its impact on long-term health. (ref 4)

Studies have found the drug to be dangerous for those that are pregnant or breastfeeding, and therefore expectant or nursing mothers should not be given the prescription. An alternative medication will be sought in these cases unless the risk to the mother is so great that it outweighs the risk to the unborn child.

It is important that patients tell their doctors about their full medical history before they take this drug. This is because there can be potentially serious side effects for those that take sulfadiazine with some other drugs. If the instructions for taking the drug are not followed, the risk of side effects is also heightened. Patients should take care to take each dose at the recommended time of day and in the right way. Doctors should periodically monitor those that are taking sulfadiazine to check for any severe side effects. Those that have had previous health conditions that interact with this drug should also be closely monitored.

Overall, if taken responsibly and as recommended, sulfadiazine is a strong and effective treatment that will work for the majority of people in preventing or treating toxoplasma related diseases.

Last Reviewed:
December 24, 2017
Last Updated:
April 05, 2018
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