Urticaria and Thyroid Medication: Key Insights for Patients

Urticaria and Thyroid Medications

Hello Doctor: At the end of March, I was diagnosed with hyperthyroidism and started taking methimazole in early April.
However, about three weeks into the treatment, I began experiencing widespread itching and hives.
The doctor prescribed one antihistamine per day along with three steroid pills, but I am still experiencing severe itching daily.
This has persisted for 1 to 2 weeks without improvement.
When I visited the doctor a few days ago, they mentioned that the areas of my body affected by the allergy change frequently and that the onset of symptoms three weeks after starting the medication makes it less likely to be drug-related.
Nevertheless, they switched my medication to Procil 50mg, to be taken three times a day, three pills each time.
Additionally, my FT4 levels have decreased to over 2.
Previously, I would occasionally experience hives and other allergic reactions, but they were not as severe or prolonged, and the symptoms improved with medication.
I would like to ask the following questions:
1.
The doctor mentioned that Procil is a short-acting medication with an effect lasting only 8 hours.
Does this mean I need to take it every 8 hours? The medication instructions indicate to take it after meals, which would mean the interval from dinner to breakfast exceeds 12 hours.
Sometimes on weekends, I sleep in and skip breakfast, taking only lunch, which could lead to a gap of over 16 hours without medication or missing a dose entirely.

2.
Is it necessary to take Procil after meals? Or is the instruction on the medication label just a reminder for patients to take their medication on time? Does it have no impact on the body whether taken before or after meals? (Sometimes I delay taking the medication for a long time just to wait until after meals.)
3.
Is it likely that the hives are caused by the medication? How can I determine if it is a side effect of the medication? Thank you!

Lin, 20~29 year old female. Ask Date: 2017/05/06

Dr. Xiao Yongxun reply Internal Medicine

Dear Ms.
Lin,
Please read the following explanation, primarily based on the recommendations from the U.S.
Food and Drug Administration for healthcare professionals in January 2016: Procil® (Propylthiouracil, PTU; 50mg/tablet) primarily works by inhibiting the production of thyroid hormones and can also inhibit the conversion of thyroxine (T4) to triiodothyronine (T3).
The recommended dosage is 50-100mg, taken after meals three times a day.
It typically takes about 8-10 weeks of treatment for thyroid function to return to normal.
Common antithyroid medications include Carbimazole, Methimazole, or Propylthiouracil, all of which may cause skin itching as a side effect within 90 days of treatment, and can even lead to agranulocytosis (white blood cell count <100 cells/mm3).
Skin itching may require the concurrent use of antihistamines, while agranulocytosis often necessitates discontinuation of the medication and hospitalization.

In clinical practice, we often start treatment for hyperthyroidism with Carbimazole or Methimazole, taken once daily; if skin itching is difficult to control, we may switch to PTU, which is taken three times a day (less convenient).
However, approximately 30-50% of patients may still experience skin itching.
Regardless of whether Carbimazole, Methimazole, or Propylthiouracil is used, a very small number of patients may experience hepatotoxicity or a metallic taste, as well as aplastic anemia or ANCA-positive vasculitis, which require clinical attention.
Therefore, Procil® is generally taken three times a day.
While the ideal situation is to space doses 8 hours apart, it is acceptable as long as the intervals are not excessively long or short.
Of course, if the intervals are too long, the concentration in the blood may significantly decrease, potentially affecting treatment efficacy.

In general, all medications are best absorbed on an empty stomach.
However, due to individual differences in constitution or experiences (e.g., gastrointestinal discomfort, nausea, bloating, etc.), physicians may sometimes recommend taking them after meals.
Almost all medications can potentially cause urticaria; however, the incidence varies widely.
Some medications are more likely to cause urticaria, such as certain pain relievers, urate-lowering drugs, antibiotics, and antiepileptic medications, while others, like antacids and antihistamines, are less likely to do so.
Nonetheless, it is often unpredictable, reflecting the strong uncertainty in medicine.
Clinically, it can be challenging to determine whether a specific medication is causing urticaria; it often requires discontinuation of the medication for a period to confirm.
However, this carries the inherent risk of disease recurrence.

The management by your attending physician appears very reasonable and is based on the latest guidelines and recommendations.
Therefore, it is advisable for you to discuss and decide on the treatment plan with them thoroughly.

Reply Date: 2017/05/06

More Info

Urticaria, commonly known as hives, is a skin condition characterized by raised, itchy welts that can appear anywhere on the body. It can be triggered by various factors, including medications, food, infections, and environmental factors. In your case, the onset of urticaria after starting methimazole for hyperthyroidism raises important considerations regarding the relationship between your medication and the allergic reaction you are experiencing.

1. Understanding Procil and Its Administration: Procil (also known as propylthiouracil or PTU) is indeed a medication used to manage hyperthyroidism, and it is classified as a short-acting drug. The typical dosing schedule for Procil is often three times a day, which means it should be taken approximately every 8 hours. However, the instruction to take it with meals is designed to enhance absorption and minimize gastrointestinal side effects. If you find yourself in a situation where you miss a dose, it is generally advisable to take it as soon as you remember, unless it is almost time for your next dose. In that case, skip the missed dose and continue with your regular schedule. It is not recommended to double up on doses.

2. Timing of Medication: While Procil is recommended to be taken after meals, the primary goal is to ensure that the medication is taken consistently. If you find that taking it after meals is causing significant delays, you may discuss with your physician the possibility of taking it at a different time, such as before meals, as long as it does not interfere with the absorption of the medication. The key is to maintain a regular dosing schedule to keep the medication levels stable in your bloodstream.

3. Assessing the Cause of Urticaria: The relationship between your medication and the urticaria is a critical aspect to evaluate. While it is true that urticaria can develop after starting a new medication, it is also possible that other factors could be contributing to your symptoms. To determine if Procil or any other medication is the cause of your urticaria, consider the following steps:
- Timing: Note when the urticaria began in relation to when you started taking Procil. If the hives appeared shortly after starting the medication, it could suggest a connection.

- Pattern: Observe if the urticaria correlates with taking the medication. If the hives appear consistently after taking Procil, this may indicate a reaction.

- Consultation: Discuss your symptoms with your healthcare provider. They may recommend stopping the medication temporarily to see if your symptoms improve, or they might suggest an alternative treatment for your hyperthyroidism.

4. Management of Urticaria: In the meantime, managing your urticaria is essential. Antihistamines are commonly prescribed to alleviate itching and reduce the severity of hives. If your current antihistamine is not providing relief, your doctor may consider adjusting the dosage or trying a different antihistamine. Corticosteroids may also be prescribed for more severe cases, but they are typically used for a short duration due to potential side effects.

5. Monitoring and Follow-Up: It is crucial to maintain regular follow-up appointments with your healthcare provider to monitor your thyroid levels and the effectiveness of your treatment. If your urticaria persists or worsens, further evaluation may be necessary, including allergy testing or referral to a specialist.

In summary, while urticaria can be a side effect of medications like Procil, it is essential to evaluate all potential causes and maintain open communication with your healthcare provider. Adjusting your medication schedule, understanding the timing of doses, and monitoring your symptoms will help you manage both your thyroid condition and the urticaria effectively.

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