21 Mar 2014

Cold and flu drugs too strong, study reveals

9:26 am on 21 March 2014

A New Zealand pharmaceutical company says people around the world, including in this country, have been inadvertently taking over-the-counter cold and flu drugs that are twice as strong as they should be.

The study by AFT Pharmaceuticals, published in the New England Journal of Medicine, says there has been a major error in the formulation of 1300 products containing phenylephrine.

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AFT managing director Hartley Atkinson says many over-the-counter products combine phenylephrine and paracetemol.

Dr Atkinson says his company's research reveals that when the two are combined, the concentration of phenylephrine spikes because of the way the human body processes both drugs together.

He says while the standard dose of phenylephrine is limited to 10 milligrams, when taken with paracetemol it spikes to 20 - and there can be side-effects. These include an increase in feelings of being unwell, nervousness, dry mouth and sleeplessness.

AFT searched high and low for literature to confirm their results, but the widely held view was that no interaction was expected between the drugs, he says.

Previously, paracetemol was combined with pseudoephedrine. But in many countries, including New Zealand, pseudoephedrine-based products are now only available on prescription because the drug is used to make methamphetamine.