Concurrent Use of Prescription Drugs and Herbal Medicinal Products Among Older Adults

Abstract

Background: Polypharmacy is a recognised patient safety risk, with older adults at greater risk due to co-morbidities and reduced clearance of drugs due to ageing. However, very little is known about the concurrent use of prescription drugs and herbal medicinal products (HMPs) among older adults. There is no common understanding of what HMPs are and no UK based studies among older adults completed in the last 15 years were identified. Aim: To understand the concurrent use of prescription drugs and HMPs among UK older adults. Research questions: The different phases of the study were guided by the following questions. Phase 1: Systematic Literature Review • What is the prevalence and pattern of concurrent use of prescription drugs and herbal medicinal products (HMPs) among older adults? • What patient and clinical characteristics are associated with concurrent use of prescription drugs and HMPs? • What are the range of prescription drugs and HMPs most concurrently used by older adults? • What safety issues and other factors are associated with concurrent prescription drug and HMPs use in older adults?

Phase 2: Questionnaire Survey • What is the prevalence and patterns of concurrent prescription drugs and HMPs use among UK community dwelling older adults? • What types of HMPs and prescription drugs are concurrently used? • What is the potential herb-drug interactions from the HMPs, and prescription drugs reported? • What patient and clinical characteristics are associated with concurrent HMPs and prescription drugs use? Phase 3: In-depth exploration of older adults’ experiences of using HMPs with prescribed medications • Why do older adults concurrently use prescription drugs, HMPs and dietary supplements (DS)? • What is the experience of concurrent users?

Methods: Three phased mixed method sequential explanatory study. Phase1 was a systematic literature review to evaluate and summarise available evidence. Phase 2 estimated the prevalence of concurrent use and identified the pattern and range of medicines combined using questionnaire survey among community dwelling older adults from two GP surgeries in Essex and London. Phase 3 Interviews with older people to gain in-depth understanding of the older peoples’ reasons for concurrently using HMPs with prescription medications, their experiences and views. Findings: Both the review and survey demonstrated that concurrent prescription drugs and HMPs use among older adults is widespread, with potentially serious herb-drug interactions from certain combinations. Prevalence among older adults varied widely between 5.3% and 88.3% among previous studies, while this study estimated it to be 33.5%. Dietary supplements (DS) are also concurrently used with prescribed medicines. The most commonly used HMPs were evening primrose oil, valerian, and Nytol Herbal® (a combination of hops, gentian, and passion flower) while cod liver oil, glucosamine, multivitamins and vitamin D were the dietary supplements most reported. The prescription drugs most commonly combined with HMPs are beta blockers, diuretics, antihyperlipidemic agents, anticoagulants, analgesics, antihistamines, antidiabetics, antihypertensive drugs, antidepressants, non-steroidal anti-inflammatory drugs (NSAIDs) and statins. Although most of the survey participants were not exposed to significant harm from concurrently using HMPs and DS with prescription medicines, the potential risk of herb-drug and supplement-drug interactions cannot be ignored.

The interviews revealed that older adults draw on different rationale and sources of information when making the decision to use HMPs or dietary supplements concurrently with prescription drugs. Six main themes captured the range of experience and underlying reasons for concurrent use. These were: older people’s values and beliefs, the decision to use HMPs and DS, sources of information and advice, self-management and taking control, disclosure and non-disclosure, awareness of potential herb-drug interactions.

Discussion: This study has provided the first estimate of the prevalence of concurrent HMPs and prescription drug use among UK older adults and established the range of HMPs and dietary supplements that older adults most commonly combine with prescribed medicines. It has highlighted potential interactions from certain combinations of prescription drugs, HMPs and dietary supplements which healthcare practitioners should routinely ask older adults about. As well as the need to systematically identify older people who may be at risk of potential herb-drug interactions, the range of reasons for concurrent use provided by this study adds to the literature on polypharmacy and interventions to support medicine management for older adults living at home with multiple health needs. Evidence from the study demonstrates the range of experience that reflects individual and system issues about accessing medical care and advice on medication. The findings highlight the difficulties that this population face in accessing the advice and support they need. It also indicates a need to revisit the responsibilities of clinicians and regulators with regards to the regulation and sale of HMPs. Likewise, accurate and key information regarding interactions with other products and possible adverse effects should be readily available. Future work could test what enables older consumers to make informed choices about the safe use of HMPs.