Methimazole Should Be Held for 1 Week Prior to Surgery in Hyperthyroid Patients
For patients with hyperthyroidism requiring surgery, methimazole should be discontinued approximately 7 days before the procedure to minimize perioperative complications, though recent evidence suggests surgery can be safely performed in the hyperthyroid state with appropriate cardiovascular stabilization.
Evidence for Holding Methimazole
The traditional approach has been to achieve biochemical euthyroidism before surgery to prevent thyroid storm, though the supporting evidence for this practice is limited 1. However, there is no specific guideline-based recommendation for the exact duration to hold methimazole prior to surgery in the provided evidence.
Alternative Approach: Surgery in the Hyperthyroid State
Recent evidence challenges the necessity of achieving euthyroidism before surgery:
- Thyroidectomy can be safely performed during the hyperthyroid phase by experienced anesthesiologists and surgeons without precipitating thyroid storm or increasing intraoperative and postoperative complications 1
- Surgery does not need to be delayed until biochemical euthyroidism is achieved if the patient is cardiovascularly stable 1
- Preoperative treatment does not prevent thyroid storm whether the patient is euthyroid or hyperthyroid during surgery 1
Rapid Preoperative Preparation Protocol (When Surgery Cannot Be Delayed)
When surgery must proceed without achieving euthyroidism, a rapid 5-day preparation protocol can be used:
- Betamethasone 0.5 mg every 6 hours 2
- Iopanoic acid 500 mg every 6 hours 2
- Propranolol 40 mg every 8 hours 2
- Surgery performed on day 6 2
This regimen produces:
- Significant T3 reduction by 38.2% within 24 hours and 64.5% by day 5 2
- Clinical euthyroid state by day 5 2
- No anesthetic incidents or postoperative complications 2
Critical Preoperative Considerations
The patient's cardiovascular system must be stabilized regardless of thyroid status:
- Beta-blockers should be used to control heart rate and manage cardiovascular symptoms until thyroid hormone levels are reduced 3
- Particular attention must be paid to cardiovascular stability when surgery is performed in the hyperthyroid state 1
- The decision should involve collaborative evaluation by anesthesiologist, surgeon, and endocrinologist 1
Factors Determining Whether to Delay Surgery
Surgery may need to proceed without achieving euthyroidism when:
- Medication allergies or severe drug side effects occur 1
- Treatment-resistant disease is present 1
- Patient noncompliance prevents adequate medical management 1
- Urgency of definitive treatment outweighs risks 1
Monitoring During Methimazole Treatment
- Free T4 or Free Thyroxine Index should be monitored every 2-4 weeks to adjust dosing 3
- The goal is to maintain free T4 in the high-normal range using the lowest possible dose 3
Common Pitfalls to Avoid
- Do not assume that achieving biochemical euthyroidism is absolutely necessary before surgery - cardiovascular stability is more critical than thyroid hormone levels 1
- Do not delay urgent surgery solely to achieve euthyroidism if the patient is cardiovascularly stable 1
- Do not proceed with surgery in a hyperthyroid patient without adequate beta-blockade and cardiovascular assessment 3, 1