A simple method for measuring drug concentrations in vivo could be used in medical and drug tests, claim Canadian chemists.

Janusz Pawliszyn and colleagues from the University of Waterloo, developed their method, based on a technique called solid phase microextraction (SPME), to offer fast sampling and more accurate sample analysis. 

The chemists used bio-compatible SPME probes to measure diazepam levels in beagle bloodstreams - as a probe is placed in contact with the blood, it adsorbs a fraction of the diazepam, which can then be extracted and measured. 'The major contributions of our group were to develop the calibration procedure, which determines how the amount of compound found on the probe relates to the concentration in the sample, and to develop an automated analysis system that can handle large amounts of samples at a time,' said Pawliszyn. 

According to Pawliszyn, a major advantage of SPME is that it measures the concentration of free compounds only. Methods that use whole blood samples also measure the amount of compound bound to, for example, blood proteins, but normally only the free compound determines the biological activity and is medically significant. 

'We have developed this technology to facilitate applications elsewhere,' Pawliszyn said. The technique can be adapted to almost any compound in any biological sample, he added. 'You can design probes that are very specific, for example, by using antibodies.'

'For some types of medical test, a patient could do his own sampling at home and then send the probes to the lab for analysis,' said Pawliszyn, highlighting the portability of the probes. The method could be used to determine compound metabolism rates and even be modified to measure compound concentrations in breath, he said. 

Danièle Gibney