Propylthiouracil

About Propylthiouracil

Propylthiouracil blocks the thyroid’s production of hormone and also slows the conversion of thyroxine (T4) into triiodothyronine (T3) in the body’s tissues. The label approves it for Graves’ disease with hyperthyroidism or toxic multinodular goiter in people who cannot tolerate methimazole and for whom surgery or radioactive iodine is not an appropriate option, and, in the same group, for easing symptoms before thyroid surgery or radioactive iodine. Adults usually start at 300 mg a day, split into three doses about eight hours apart; severe disease or a very large goiter may call for 400 mg a day, and occasionally 600 to 900 mg, and the usual maintenance dose is 100 to 150 mg a day. Thyroid blood tests guide the dose, and a raised TSH once the overactivity has settled means a lower maintenance dose is needed.

The boxed warning describes severe liver injury and acute liver failure, sometimes fatal and including cases that needed a liver transplant, in adults and children. Routine liver blood tests are not expected to prevent it, because it comes on quickly and unpredictably, so patients are told to report loss of appetite, itching, yellow skin or eyes, pale stools, dark urine or pain in the upper right abdomen, especially in the first six months; the drug is then stopped at once. Agranulocytosis, a dangerous loss of white blood cells, typically appears in the first three months: a sore throat, fever, rash, headache or general feeling of illness should be reported right away so a white blood cell count can be done. Severe vasculitis, mostly ANCA-positive, has caused deaths, so a new rash, blood in the urine, less urine, shortness of breath or coughing up blood should be reported. It can also cause low prothrombin and bleeding, so clotting tests may be checked, especially before surgery. The only contraindication is an allergy to the drug; minor side effects include rash, itching, nausea, stomach upset, joint and muscle pain, loss of taste, hair loss and headache.

Because methimazole may be linked to rare birth defects, the label says propylthiouracil may be the preferred drug in the first trimester of pregnancy, and that switching to methimazole for the second and third trimesters may be better because of the liver risk to the mother. Untreated or undertreated Graves’ disease raises the risk of miscarriage, preterm birth, stillbirth and an overactive thyroid in the baby, yet the drug crosses the placenta and can cause goiter and cretinism in the fetus, so the dose should be sufficient but not excessive, and a lower dose may become possible as pregnancy goes on. Anyone who becomes pregnant or plans to should call the prescriber right away. Only small amounts pass into breast milk. It is not recommended for children unless methimazole is not well tolerated and surgery or radioactive iodine is not appropriate, since no liver failure has been reported with methimazole in children.

Taking Propylthiouracil

How to take it

Usually three times a day, about eight hours apart, at the same times each day, exactly as prescribed. Frequent thyroid blood tests guide the dose, so keep every appointment.

If you miss a dose

Take it as soon as you can, but skip the missed dose if it is almost time for the next one. Do not take two doses at one time.

Storage

At room temperature, away from moisture and heat.

Interactions to know about

It can strengthen the effect of warfarin and other oral blood thinners, so clotting tests may be checked more often. As the thyroid returns to normal, doses of beta blockers, digoxin and theophylline may need to be lowered. Tell the prescriber about any other medicine that can lower white blood cells.

This summarizes the official prescribing information. Your prescriber’s and pharmacist’s instructions, and the leaflet that comes with your medicine, take priority.

Why the cash price for Propylthiouracil differs from pharmacy to pharmacy

Propylthiouracil is an old generic, but its boxed warning reserves it for a narrow group of patients, so a pharmacy may not keep it on the shelf; one that rarely fills it may order it in and price it as a slow-moving item.

The tablet count matters too. A starting dose of 300 mg a day is six tablets a day, while the usual maintenance dose is two or three, so early fills are large and the quote depends on how each pharmacy prices volume.

Ways to pay less for Propylthiouracil without insurance

• Ask each pharmacy to confirm it has enough tablets in stock before the prescription is sent, so treatment is not interrupted.
• Ask whether propylthiouracil is on the pharmacy’s flat-price generic list, and compare more than one pharmacy.
• Once your dose is stable, ask for a ninety-day supply.
• If you are not pregnant and have not had a problem with methimazole, ask the prescriber whether methimazole would suit you, since the label reserves propylthiouracil for people who cannot take it.
• Upload the prescription to Script Unlock so licensed pharmacies can quote their cash price. You pay the pharmacy directly.

Questions to ask your pharmacist about Propylthiouracil

1. 1.Which signs of liver trouble mean I should stop it and call right away?
2. 2.If I get a sore throat or fever, how soon do I need a blood count?
3. 3.Does it interact with my warfarin, digoxin, theophylline or beta blocker?
4. 4.What should I do if I become pregnant or plan to?

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