As the number of effective medications expands and the population ages, patients are increasingly being prescribed complicated drug regimes containing multiple medications. A potential risk of this is the risk of drug-drug interactions where the effect of taking one medication is adversely affected by other medications the patient is also taking. Drug-drug interactions can cause considerable harm, accounting for 1% of all accident and emergency admissions in one study.
The purpose of this study is to look at how frequently drug pairs with a potential drug-drug interaction are prescribed in primary care, which drug pairs are most commonly implicated and whether this has changed over time.
This work will help find out how many patients might be at risk from drug-drug interactions and which drug pairs are responsible. This will be useful to both guide prescribing behaviour and also to guide future research in this area.
This descriptive observational study will explore the prescribing patterns of drug pairs with a potential drug-drug interaction in primary care over the past two decades by means of repeated cross-sectional studies. The primary outcome will be the proportion of patients in each year exposed to a potential drug-drug interaction. This will be broken down by drug class involved. Time trends between years will be compared by age standardisation and the effects of age, sex, number of concurrent medications and deprivation on the risk of being exposed to a potential drug-drug interaction in 2014 will be investigated by logistic regression. These factors have been associated with risk of potential drug-drug interactions in previous studies. Finally for each drug class, defined by British National Formulary chapter, the proportion of patients prescribed a drug of that class that were exposed to a potential drug-drug interaction will be described as a secondary outcome. This will be compared to the primary outcome to determine the proportion of the absolute variation in exposure to potential drug-drug interactions that is due to variation in the prescription rates of the drugs involved.
Primary outcome: the proportion of all registered patients concurrently prescribed a drug pair with a potential drug-drug interaction within the study year. Secondary outcome: the proportion of patients taking a specific drug class who are concurrently prescribed another drug with a potential drug-drug interaction with this drug class in the study year.
Ian Douglas - Chief Investigator - London School of Hygiene & Tropical Medicine ( LSHTM )
Adrian Root - Corresponding Applicant - London School of Hygiene & Tropical Medicine ( LSHTM )
Bruce Guthrie - Collaborator - University of Edinburgh
Liam Smeeth - Collaborator - London School of Hygiene & Tropical Medicine ( LSHTM )
Rupert Payne - Collaborator - University of Bristol
Patient Level Index of Multiple Deprivation;Practice Level Index of Multiple Deprivation