Levothyroxine, Liothyronine[Unlicensed preparations of desiccated thyroid (e.g. ERFA thyroid) are outside the scope of this monograph] |
Issues for Surgery |
Hypothyroid patients undergoing surgery are predisposed to anaemia, hypotension (which can lead to cardiovascular collapse), reduced gastrointestinal motility (which can lead to post-operative ileus) and rarely life-threatening myxedema coma1. |
Advice in the Perioperative period |
Elective Surgery Continue. Patients with known hypothyroidism or who are on treatment for hypothyroidism should have thyroid-stimulating hormone (TSH) checked pre-operatively to determine if treatment is adequate or if dose optimisation is needed before surgery1. NB: It can take 4-6 weeks for thyroid function tests (TFTs) to reach steady state after thyroid hormone dose adjustment. If TSH is significantly outside the normal limits, it may be preferable to defer elective surgery until a euthyroid state is achieved1. Discuss with the patient’s Endocrinologist. Emergency Surgery Continue. If TSH indicates patient is not euthyroid the risks of proceeding with surgery must be balanced against the risks of delaying the surgery. It is suggested that patients with mild or moderate hypothyroidism can proceed with urgent surgery provided the patient is monitored closely for signs of post-operative complications1. Post-operative Advice Patients undergoing Thyroidectomy Patients undergoing Other Surgery If a long nil by mouth (NBM) period is anticipated or if there are concerns regarding enteral absorption see Further Information. |
Interaction(s) with Common Anaesthetic Agents |
Liothyronine – none relevant2, 3, 4, 5. Esketamine and Ketamine There have been isolated reports of marked hypertension and tachycardia when ketamine is given to patients taking levothyroxine3, 6, 7. Hypertension may occur with concomitant use of esketamine – bear the interaction in mind in case of an usual response to treatment3. Sympathomimetics Levothyroxine may enhance the effects of sympathomimetics (e.g. adrenaline / epinephrine, phenylephrine). This is possibly due to increased catecholamine receptor sensitivity6, 7. |
Interaction(s) with other Common Medicines used in the Perioperative Period |
Liothyronine – none relevant2, 3, 4, 5. Drug-disease interactions Many drugs are known to alter thyroid function by altering protein binding and could therefore affect disease control, including3:-
Effects on Absorption of Levothyroxine H2 antagonists Proton Pump inhibitors (PPIs) Iron Supplements Other Medicines |
Further Information |
Risks Associated with Pre-operative Omission and Prolonged NBM period There is a potential risk of exacerbation of hypothyroidism if thyroid hormones are omitted perioperatively. However, the actual risk is dependent on the patient’s TFTs on admission and the length of time that they are omitted. It takes 4 – 6 weeks from being euthyroid to the patient becoming hypothyroid once thyroid hormones are stopped. If there are any concerns regarding the omission or continuation of thyroid hormones during the perioperative period, the patient’s Endocrinologist should be consulted. If oral medications cannot be given post-operatively thyroid hormones can be safely omitted for a few days1. The action of liothyronine is expected to persist for 1 to 2 days after it is stopped4, 5 and levothyroxine has a long half-life, approximately 6-7 days in euthyroid patients4, 5. If after this time oral medication still cannot be taken consideration should be given to prescribing an intravenous preparation if there are any concerns regarding the patient’s euthyroid state – consult product literature for preparation and dose. Unlicensed indications e.g. Resistant Depression Whilst this monograph relates to the use of thyroid hormones for endocrinology indications, perioperative continuation of thyroid hormones for other indications is not anticipated to be problematic.
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References |
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