What is the recommended initial management for a newly diagnosed hyperthyroid patient, including propranolol dosing, methimazole dosing, baseline investigations, and follow‑up plan?

Initial Management of Newly Diagnosed Hyperthyroidism

Start methimazole 15-40 mg daily (divided into three doses every 8 hours) based on severity, plus propranolol 20-40 mg three times daily for symptom control, after obtaining baseline complete blood count (CBC), comprehensive metabolic panel (CMP), and thyroid function tests (TSH, free T4, free T3). 1, 2

Immediate Assessment and Baseline Investigations

Before initiating treatment, obtain the following baseline tests:

• Complete blood count (CBC) with differential – essential to establish baseline white blood cell count before methimazole, as agranulocytosis is a life-threatening complication 1
• Comprehensive metabolic panel (CMP) – to assess liver function (AST, ALT, bilirubin) and detect baseline hepatic abnormalities, as methimazole can cause cholestatic jaundice 3, 4
• Prothrombin time (PT/INR) – methimazole may cause hypoprothrombinemia and bleeding 1
• TSH, free T4, and free T3 – to confirm diagnosis and establish severity 2, 5
• TSH receptor antibodies (TRAb) – if Graves' disease is suspected, though treatment should not be delayed for results 6

Methimazole Dosing Based on Severity

Dose methimazole according to hyperthyroidism severity, divided into three doses at 8-hour intervals: 1

• Mild hyperthyroidism: 15 mg daily (5 mg every 8 hours)
• Moderately severe hyperthyroidism: 30-40 mg daily (10-13 mg every 8 hours)
• Severe hyperthyroidism: 60 mg daily (20 mg every 8 hours)

The FDA-approved dosing explicitly requires three divided doses at 8-hour intervals, not once-daily dosing. 1

Propranolol for Symptom Control

Start propranolol 20-40 mg three times daily (every 8 hours) for immediate symptom relief. 5, 7

Propranolol controls the peripheral manifestations of hyperthyroidism including:

• Nervousness and anxiety
• Palpitations and tachycardia
• Tremor
• Increased cardiac output 7

Critical caveat: Propranolol does not affect the underlying thyrotoxic process itself—it only provides symptomatic relief while methimazole reduces thyroid hormone synthesis. 7

Patient Safety Counseling and Monitoring

Instruct patients to report immediately: 1

• Sore throat or fever – may indicate agranulocytosis
• Skin eruptions or rash – may indicate vasculitis
• Jaundice or dark urine – may indicate cholestatic hepatitis 3
• New hematuria or decreased urine output – may indicate vasculitis 1

Obtain CBC with differential if any of these symptoms occur. 1

Follow-Up Monitoring Schedule

Monitor thyroid function tests (TSH, free T4) every 2-4 weeks initially: 1

• Once clinical hyperthyroidism resolves and TSH begins rising, reduce methimazole to maintenance dose of 5-15 mg daily 1
• Continue monitoring every 4-6 weeks during dose titration
• Once stable on maintenance dose, monitor every 2-3 months 1

Recheck PT/INR before any surgical procedures in patients on methimazole, as it may cause hypoprothrombinemia. 1

Special Populations and Contraindications

Pregnancy considerations: 1

• Methimazole is Pregnancy Category D due to risk of congenital malformations, particularly in the first trimester
• If methimazole must be used in pregnancy, use the lowest effective dose
• Consider switching to propylthiouracil (PTU) in first trimester, then back to methimazole for second and third trimesters 1

Patients on anticoagulants: 1

• Methimazole may increase warfarin activity through inhibition of vitamin K
• Monitor PT/INR more frequently, especially before surgical procedures

Patients on beta-blockers for other indications: 1

• Hyperthyroidism increases clearance of beta-blockers with high extraction ratios
• As patient becomes euthyroid, beta-blocker dose may need reduction to avoid bradycardia

Common Pitfalls to Avoid

• Never use once-daily methimazole dosing initially – FDA labeling explicitly requires three divided doses at 8-hour intervals for optimal efficacy 1
• Never delay treatment waiting for TRAb results – start empiric therapy based on clinical presentation and thyroid function tests 2
• Never start methimazole without baseline CBC – you must have a baseline to compare if agranulocytosis is suspected 1
• Never ignore early warning signs of agranulocytosis (sore throat, fever) – this is a medical emergency requiring immediate CBC and potential methimazole discontinuation 1
• Never assume propranolol alone is sufficient – it only controls symptoms and does not treat the underlying hyperthyroidism 7

When to Hospitalize

Admit immediately if: 4

• Thyroid storm suspected (Burch-Wartofsky score ≥45)
• Multiorgan dysfunction develops
• Severe tachycardia (heart rate >140 bpm) with hemodynamic instability
• Acute liver failure or severe jaundice develops on methimazole 4

Transition to Maintenance Therapy

Once TSH begins rising above normal range with declining free T4: 1

• Reduce methimazole to maintenance dose of 5-15 mg daily
• Continue monitoring every 2-3 months
• Typical duration of therapy is 12-18 months before considering discontinuation 2