Levothyroxine is used to treat hypothyroidism.

Dosage regimen

* Levothyroxine should be started at 50-100mcg per day, then titrated up by 25-50mcg every two to three months depending on response. Elderly patients should be started on a lower dose. The usual maintenance dose is 75-170mcg daily. Levothyroxine is best taken in the morning before breakfast.

Patient's knowledge of the medicine's use

* Ensure the patient understands the need for the dose of levothyroxine to be titrated and the fact that treatment is lifelong.

Is the medicine working?

* Does the patient feel restless or nervous, or report symptoms such as shortness of breath, tremor, sweating, palpitations or tachycardia? This can indicated that the levothyroxine dose is too high.

* Is the patient complaining about feeling cold or tired, weight gain or constipation? This can indicate insufficiently treated hypothyroidism.

Side effects

* Levothyroxine can cause diarrhoea, vomiting and arrhythmias, but usually only at excessive doses.

Monitoring

* The BNF recommends a baseline ECG before patients are started on levothyroxine as the changes induced by hypothyroidism can be confused with ischaemia. Patients should be monitored every two to three months while their dose is being titrated, then annually once stable.

Lifestyle

* Ensure patients with hypothyroidism know they are entitled to free prescriptions.

* Levothyroxine tablets should be taken on an empty stomach before breakfast. This is because some iron- or calcium-rich foods may interfere with the drug's absorption.

* Levothyroxine has a narrow therapeutic range and small changes in absorption or metabolism can substantially alter thyroid hormone levels. Particular drug interactions to look out for include iron or calcium supplements, liver enzyme inducers such as phenytoin, carbamazepine, phenobarbital and rifampicin, amiodarone, lithium and warfarin.