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It is well known that the age, weight, height and sex of a person may influence the choice and dose of their medicines. And we accept that checking renal function using blood tests has an important role in determining which drugs and what doses are safe to use in some patients, and in subsequent monitoring and dose titration. However, knowledge about how the genetic make up of individual patients might affect their response to drugs is less well known.

Personalised or precision medicine enables the use of genetic information to better target healthcare. This is known as pharmacogenomics (PGx).

PGx testing has been available from community pharmacies in the USA, Canada and Australia for several years. UK consumers can now access this as some DNA tests are available that include information on ‘drug response’. While use of these tests is currently limited in the UK, future expansion seems inevitable. 

An early example

One of the first disorders where genetic factors were found to affect drug metabolism is glucose-6-phosphate dehydrogenase (G6PD) deficiency. This disease was first described by the ancient Greeks, who noticed that an illness resulting from fava bean consumption affected some individuals but not others. The cause was found in the 1950s when G6PD deficiency was identified in people with the illness and a hereditary association was determined. The antimalarial primaquine, nitrofurantoin, quinolones and some sulphonamides (such as co-trimoxazole) should be avoided in those with known G6PD deficiency as their use may precipitate a haemolytic crisis, requiring blood transfusion. Aspirin, quinine, chloroquine, hydroxychloroquine and sulfonylureas are less toxic, but should be used with caution.