Tramadol blood test tags painkiller response

Tramadol is commonly used as a painkiller and has been on the market since 1977 for the treatment of moderate to severe pain. It is a synthetic opioid and can be very effective, but doesn't work in all patients because they cannot metabolize it very well to its active form, O-demethyltramadol, leaving them without effective pain control. In a French study presented at Euroanaesthesia 2012, researchers showed that patients' ratio of tramadol to O-demethyltramadol could be used as a simple biomarker blood test to predict their response, allowing doctors to switch painkillers as soon as possible.

Dr. Laurent Varin of the Caen Teaching Hospital said: "In our hospital we frequently use tramadol after surgery--about 50-60% of patients are treated with it, while the rest are treated with nefopam, which is a non-opioid painkiller. However, in about 5-10% of Caucasian patients the CYP2D6 enzyme is inefficient and does not produce enough ODT to bind effectively to the opioid receptors; these patients are known as 'poor metabolizers' and will have poorly controlled pain unless the problem is identified quickly and they are switched to morphine or nefopam."

The researchers measured the ratio 24 and 48 hours after surgery in 294 Caucasian patients who were receiving tramadol, as well as checking their genetic make-up. They found that 8% of the patients were genetically poor metabolizers, and that the blood ratio could detect this with good levels of sensitivity and specificity.

The team has created a relatively low-cost blood test based on these results, which will allow physicians to profile patients whose pain is not relieved by tramadol after surgery and switch them to an alternative painkiller, such as morphine. The test could also identify those patients who will not respond to codeine, oxycodone and related drugs.

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- see the abstract