Antithyroid medicines, radioiodine and thyroid surgery

01Purpose and principlesWhat the treatment does and how it fits into care.

Treatment has two separate goals: control the immediate biochemical and cardiovascular effects, then select a durable strategy for the underlying cause. A titration or block-and-replace antithyroid course, radioiodine and surgery have different time courses, relapse risks and burdens. NICE NG145 supports shared decision-making that includes pregnancy intentions, comorbidity, goitre, eye disease and patient preference.

Antithyroid medicines inhibit new hormone synthesis, so improvement is not instantaneous while stored hormone remains. Radioiodine gradually damages functioning thyroid tissue. Thyroidectomy is immediate definitive anatomy but brings anaesthetic, bleeding, recurrent laryngeal nerve and hypoparathyroid risks. The safest option is therefore contextual rather than a universal hierarchy.

Local pathways matter for nuclear-medicine authorisation, peri-operative preparation and post-treatment monitoring. Exact doses and withdrawal intervals around radioiodine vary with indication and service protocol; coordinate rather than improvising from an examination mnemonic.

Key points

First establish the cause of thyrotoxicosis. Graves' disease, toxic nodular disease and destructive thyroiditis do not share the same response to antithyroid medicines or radioiodine.
Carbimazole is usual first-line antithyroid treatment for many non-pregnant adults; propylthiouracil is reserved for defined situations because serious hepatic injury is an important risk.
Before starting an antithyroid medicine, obtain full blood count and liver tests. Routine serial counts do not replace urgent testing when fever, sore throat or mouth ulcers develop.
Agranulocytosis warning advice must be verbal and written: stop the antithyroid medicine and obtain an urgent neutrophil count rather than taking another dose while awaiting routine review.
Radioiodine is a definitive option for suitable Graves' or toxic nodular hyperthyroidism, but is contraindicated in pregnancy and breastfeeding and requires local radiation-protection precautions.
Active thyroid eye disease, immediate pregnancy plans, suspected malignancy, large compressive goitre and inability to follow radiation rules may make radioiodine unsuitable or change preparation.
Thyroidectomy offers rapid definitive control and tissue diagnosis, especially for large goitre, compression, nodules or selected eye disease, but requires an experienced high-volume team and euthyroid preparation where possible.
Beta-blockers relieve adrenergic symptoms but do not correct hormone production. Destructive thyroiditis generally needs symptom control rather than carbimazole because synthesis is already low.
After radioiodine or total thyroidectomy, lifelong biochemical follow-up is required because hypothyroidism is expected or common; a definitive treatment does not mean discharge without replacement planning.

02Indications, selection and cautionsWho may benefit, who needs urgent treatment and important alternatives.

Graves' disease

Diffuse goitre, bruit, orbitopathy, dermopathy and positive TSH-receptor antibodies support Graves' disease. Smoking and active eye disease affect definitive-treatment counselling and specialist ophthalmic involvement.

Toxic nodular disease

A nodular gland, older age and focal or patchy autonomous uptake suggest toxic adenoma or multinodular goitre. Spontaneous remission is unlikely, so definitive radioiodine or surgery is commonly considered.

Destructive thyroiditis

Painful subacute thyroiditis or a painless/postpartum destructive phase releases stored hormone, often with low uptake. Antithyroid medicines have little mechanistic benefit because new synthesis is not the driver.

Medicine toxicityRed flag

Fever, sore throat, oral ulceration, jaundice, dark urine, severe pruritus or abdominal pain during antithyroid therapy demands urgent assessment. Agranulocytosis and hepatic injury can progress despite an apparently modest dose.

Compression or stormRed flag

Stridor, positional dyspnoea, dysphagia, venous congestion or vocal change indicates possible compression. Fever, agitation, heart failure and marked tachycardia with thyrotoxicosis indicate a clinical storm pathway rather than routine scoring alone.

03Assessment before treatmentTests and checks that guide safe selection.

Investigation order

Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.

01
TSH, free T4 and free T3First step
Why
Confirm biochemical severity and provide a baseline for response.
Interpretation and limitations
TSH may stay suppressed after free hormones normalise, so early titration should not chase TSH alone. T3-predominant disease can be missed if only free T4 is checked.
02
TSH-receptor antibodies
Why
Support Graves' diagnosis when the clinical picture is not definitive.
Interpretation and limitations
A positive result often removes the need for diagnostic isotope imaging. A negative result does not explain all thyrotoxicosis, so revisit nodular autonomy, thyroiditis and exogenous hormone.
03
Full blood count and liver profile
Why
Record pretreatment status and investigate toxicity promptly.
Interpretation and limitations
Baseline mild abnormalities can accompany thyrotoxicosis. New neutropenia or hepatic injury after treatment requires urgent specialist action and should not be dismissed as the underlying disease.
04
Radionuclide uptake scan
Why
Differentiate diffuse Graves' uptake, focal autonomy and low-uptake thyroiditis when antibodies and examination do not settle the cause.
Interpretation and limitations
Diffuse uptake supports Graves', focal hot activity suggests autonomy and low uptake suggests destructive or exogenous causes. Do not use in pregnancy or breastfeeding.
05
Thyroid ultrasound
Why
Evaluate a palpable nodule, structural asymmetry, compression or malignancy concern rather than routine biochemical thyrotoxicosis.
Interpretation and limitations
Ultrasound does not determine functional activity. Suspicious structural findings enter the thyroid nodule pathway and may shift definitive treatment toward surgery.
06
ECG and cardiovascular assessment
Why
Identify atrial fibrillation, ischaemia or heart failure that changes urgency and treatment risk.
Interpretation and limitations
Treat instability immediately. Anticoagulation decisions in atrial fibrillation follow the usual validated stroke and bleeding assessment rather than assuming hyperthyroidism removes risk.

04Treatment approachPreparation, options, escalation and aftercare.

01Antithyroid courseStart, educate and titrate safelyFirst stepDefinitiveSynthesis-driven Graves' disease or temporary control of nodular hyperthyroidism while definitive care is arranged.

1Confirm cause, obtain baseline blood count and liver tests, review pregnancy possibility and interactions, then select carbimazole or a defined propylthiouracil indication.
2Give written agranulocytosis and hepatic warning advice. Recheck free hormones at the local early interval and adjust by titration or a specialist-agreed block-and-replace plan.
3At the planned course end, assess remission or relapse risk. Recurrent Graves' disease and persistent nodular autonomy prompt shared discussion of further medicine, radioiodine or surgery rather than indefinite drift.

02RadioiodineDefinitive nuclear-medicine pathwayDefinitiveSuitable Graves' or autonomous nodular disease after contraindication and preference review.

1Exclude pregnancy and breastfeeding, assess eye disease and compression, review recent iodine exposure and agree antithyroid withdrawal/restart with the administering service.
2Provide written contact restriction, conception avoidance and radiation-safety instructions tailored to the administered activity and household circumstances.
3Monitor thyroid function at defined intervals because transient worsening and later hypothyroidism can occur; start levothyroxine promptly when criteria are met.

03ThyroidectomyPrepare for safe definitive surgeryDefinitiveLarge/compressive goitre, suspected cancer, selected eye disease, patient preference or unsuitable/failed alternatives.

1Refer to an experienced thyroid surgeon and define extent of surgery from cause, nodules and cancer risk; document voice, calcium/vitamin D context and anaesthetic risk.
2Achieve biochemical control where possible with specialist antithyroid treatment, beta-blockade and, in selected protocols, short pre-operative iodine; urgent surgery requires individual risk management.
3After surgery, observe for neck haematoma, airway change, hypocalcaemia and voice dysfunction, then establish levothyroxine and pathology-led follow-up.

05Regimens, contraindications and interactionsTreatment details and the circumstances that modify them.

Preferred synthesis inhibitor for many non-pregnant adults with Graves' disease and for temporary control of toxic nodular disease.

Carbimazole

Initial and maintenance dose depend on biochemical severity and whether titration or block-and-replace is chosen; follow BNF and specialist review.

Stop and obtain urgent full blood count for fever, sore throat or mouth ulcers. Review liver symptoms, pregnancy potential and cross-reaction after a serious thionamide adverse effect.

Alternative around early pregnancy, after selected carbimazole intolerance, or in specialist emergency regimens because it also reduces peripheral T4 conversion.

Propylthiouracil

Use a specialist-selected divided regimen only for a defined indication, with dose reduction as free hormones improve.

Potential severe hepatotoxicity limits routine use. Give liver and agranulocytosis warnings; do not switch casually after a life-threatening class reaction.

Bridges tremor, palpitations and adrenergic distress while antithyroid or definitive therapy begins to work.

Propranolol

Individualise a short oral regimen to heart rate and symptoms while accounting for comorbidity and concurrent cardiovascular treatment.

Avoid or seek alternatives in asthma, severe bradycardia, decompensated heart failure or relevant conduction disease. It does not treat destructive hormone release or replace definitive care.

Definitive ablation for suitable Graves' disease or autonomously functioning nodular tissue.

Radioactive iodine-131

Single authorised activity selected and administered by nuclear medicine under local dosimetry, preparation and radiation-protection procedures.

Contraindicated in pregnancy and breastfeeding; active eye disease can worsen. Apply conception intervals, iodine/medicine preparation and household restrictions exactly as the treating service specifies.

06Complications, monitoring and follow-upAdverse effects, response and longer-term review.

During antithyroid titration, follow free T4 and free T3 at the local interval; use TSH later because its recovery can lag for months.
Do not schedule routine serial full blood counts as a substitute for symptom-triggered urgent neutrophils; repeat liver tests when clinical or baseline findings justify them.
After radioiodine, arrange proactive thyroid-function testing until stable and then lifelong surveillance for hypothyroidism or persistent disease.
After thyroidectomy, monitor the airway and wound immediately, check calcium according to the surgical pathway, document voice change and establish replacement review.
For Graves' orbitopathy, monitor eye pain, colour vision, diplopia, exposure and visual acuity; reduced vision or impaired colour perception needs urgent ophthalmic assessment.

07Special situationsVariants, exceptions and circumstances that change the usual approach.

Cause predicts drug value

Thionamides stop synthesis, not release. A low-uptake destructive thyroiditis therefore improves with time and symptom control, while extra carbimazole adds risk without addressing the mechanism.

TSH is a late reporter

Suppressed TSH may persist after circulating free hormones normalise. Using it as the sole early target can create iatrogenic hypothyroidism.

Definitive means planned follow-up

Radioiodine and total thyroidectomy exchange recurrent hyperthyroidism for a high likelihood or certainty of replacement. Reliable testing and access to levothyroxine are part of treatment success.

Eye disease changes the balance

Smoking cessation, activity and severity assessment matter when comparing radioiodine with surgery or medicine. Threatened sight is an ophthalmic emergency, not a cosmetic side issue.

Surgery has unique information

Thyroidectomy both treats hormone excess and yields histology, which becomes especially valuable when a suspicious nodule coexists with autonomy or Graves' disease.

08Common pitfallsFrequent interpretation and management errors.

01
Starting carbimazole for low-uptake destructive thyroiditis without confirming synthesis-driven disease.
02
Telling a patient to continue antithyroid tablets despite fever and sore throat until a routine appointment.
03
Choosing radioiodine without checking pregnancy, breastfeeding, eye disease or ability to comply with radiation precautions.
04
Escalating medicine because TSH remains suppressed while free hormone is already low-normal.
05
Referring compressive goitre for slow outpatient control without assessing airway or vocal symptoms.
06
Discharging after definitive therapy without lifelong thyroid-function and replacement arrangements.