Pharmacogenetic testing in community pharmacies could improve drug selection and reduce adverse effects, study finds

Pharmacogenetic testing could improve drug or dose selection for one-fifth of patients who have been prescribed one of 56 common drugs, research shows.

Research at the University of East Anglia analyzed a large database of community pharmacies to estimate the number of times 56 medicines were first prescribed in the UK in 2019.

The 56 drugs included opioids, proton pump inhibitors and antidepressants. For each drug selected, only one drug-gene interaction was included in the analysis.

The researchers combined these early prescribing estimates with phenotypic frequency data to estimate the number of “actionable” drug-gene interactions that occur during daily practice in community pharmacies.

The study defined an “actionable” drug-gene interaction as one that requires intervention; whether it is a “direct action”, such as adjusting the dose or changing the drug, or an “indirect action”, such as carefully observing the patient’s condition or protecting against a maximum dose.

The researchers used guidelines produced by the Dutch Pharmacogenetics Working Group and the Clinical Pharmacogenetics Implementation Consortium to estimate that an actionable drug-gene interaction was present between 19.1% and 21.1% (5,233,353-5,780,595) of all new prescriptions for the 56 drugs.

They found that four genes (CYP2D6, CYP2C19, HLA-B, and SCLO1B1) accounted for 95.8% of all drugs initiated with an actionable drug-gene interaction.

“Yes [pharmacogenetic] testing has been done for all patients with a new prescription for any of the 56 commonly prescribed drugs, so one in five of these patients could potentially benefit from better drug or dose selection,” said David Wright, professor of pharmaceutical practice at the University of East Anglia and one of the study’s authors.

“These tests are now relatively cheap, and the government plans to make them routinely available through the NHS in the near future. If patients reach their treatment goals more quickly, are less likely to experience adverse drug reactions, or do not have to return to medical practice until the best treatment and dose are identified, then this could represent a great value for money for the NHS,” he said. noted.

“With a need to counsel patients on the use of any genetic test and to provide treatment advice once results are obtained, the pharmacist is the most appropriate healthcare professional to take on this role.”

Wright said the tests, which involve taking a cheek swab, could be done by the patient themselves and could easily be incorporated into the new medicine service within the community pharmacy or into clinical pathways in medical practice and in hospital environment.

“Pharmacogenetic testing has the potential to guide treatment decisions for a number of drugs,” said Dyfrig Hughes, professor of pharmacoeconomics at Bangor University and champion of pharmacogenetics for the Royal Pharmaceutical Society.

“They aim to identify patients most at risk of experiencing an adverse drug reaction and/or reduced treatment effect, and therefore can help determine whether alternative treatment or a change in dose is warranted.”

However, Hughes pointed out that it may “not be possible” to perform pharmacogenetic testing for the numbers highlighted in the article, and that “appropriate eligibility criteria” should be specified to contain the volume and costs, “such as prioritizing patients with other risk factors, or before prescribing high doses, or drugs associated with the most serious or common adverse effects”.

He continued: “A notable finding is that 4 genes (CYP2D6, CYP2C19, HLA-B and SCLO1B1) accounted for 95.8% of all pharmacogenetically actionable drugs. There may be advantages in panel testing, where a number of genes can be assessed simultaneously, and data stored in patients’ medical records as to when they might be eligible for one of these drugs at the time. to come up.

According to the study, NHS England recently announced plans to adopt a preemptive pharmacogenomics testing strategy for drug-gene pairs with the most evidence of clinical efficacy and cost-effectiveness, with the aim of integrating pharmacogenomics into practice by 2025.

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