Researchers hope that soon maybe even a simple urine test may help predict patients' response to particular drugs.
The research team from Imperial College London and Pfizer Research and Development showed that it was possible to predict how different individuals would deal with one drug by looking at the levels of different products of metabolism, known as metabolites, in their urine before they took a dose of the drug.
The researchers have shown evidence that gut microbes can have a crucial role in determining a person's response to a particular drug.
They looked at 99 healthy male volunteers aged between 18 and 64, taking one dose of the commonly used painkiller acetaminophen, widely known as paracetamol.
The researchers took urine samples from the men before they took the paracetamol dose and for six hours afterwards and analysed the metabolites in the samples.
The results revealed that a compound called para-cresol sulphate, which is derived from para-cresol produced by bacteria in the gut, was an indicator of how the men would metabolise the dose of paracetamol.
Those with higher levels of para-cresol sulphate metabolised the drug in a different way from those with lower levels. The scientists suggest that this is because the body uses compounds containing sulphur to process drugs like paracetamol effectively and para-cresol can deplete sulphur compounds in the body.
The body uses sulphur to process a variety of drugs, not just paracetamol, so the new findings about para-cresol could have significant implications for a whole group of drugs, said the researchers.
"This result is very encouraging. Pre-clinical studies had suggested it might be possible to predict how individuals would react to drugs by looking at their pre-dose metabolite profiles, but this is the first time that anyone has been able to show convincingly that such a test could work in humans," said Professor Jeremy Nicholson, senior author of the study from the Department of Biomolecular Medicine at Imperial College London.