The different approaches of the UK and US drug regulators have been noted more than once in this column. A current case in point concerns the thyroid drugs and, in particular, thyroxine sodium, marketed in the UK as Eltroxin and, in the US, as Synth

In the US, the Food and Drug Administration (FDA) is seriously considering a withdrawal of the drug because it has "a history of problems" and cannot be recognised as "safe and effective". The drug is also the subject of a raft of class action suits in the US.

Despite this, the Committee for the Safety of Medicines, the UK drugs watchdog, appears to have no such qualms.

The drug treats hypothyroidism when the thyroid underperforms by drip feeding exact amounts of synthetic thyroxine. It's a delicate balance and one that often goes askew; when it does, the thyroid will either not do all it should or go into overdrive. The FDA noted that: "Synthroid has not been reliably potent and stable". As a result, "patients receive tablets that are filled with a product of unpredictable potency" and so "therapy with thyroxine sodium is neither safe

nor effective".

Most side effects of Synthroid and Eltroxin are related to overdosage, which causes symptoms of hyperthyroidism. These include heart pain, irregular heart rhythm, palpitations, muscle cramping, tremors, restlessness, excitability, insomnia, headache, sweating, excessive weight loss and muscular weakness.

In its 40 years of use in the US, Synthroid has been the subject of numerous product recalls because of dosage problems. Even so, it is the third most prescribed drug in America yet, the FDA is prepared to withdraw it if necessary.

We hope that the Committee for the Safety of Medicines is watching.