Optimization of drug prescribing in older populations is a priority due to the significant clinical and economic costs of drug related illness. Inappropriate prescribing in older people is associated with increases in morbidity, adverse drug events, hospitalization and mortality [1, 2]. However the selection of appropriate medication in older people is a challenging and complex process. Older people are particularly vulnerable to inappropriate prescribing because of their multiple drug regimens, co-morbid conditions and age associated physiological changes which can alter their pharmacokinetics and enhance their pharmacodynamic sensitivity to specific drugs . In general, medicines in older people are considered appropriate when they have a clear evidence-based indication, are well tolerated in the majority and are cost-effective. In contrast, medicines that are potentially inappropriate have no clear evidence-based indication, carry a substantially higher risk of adverse side-effects compared with use in younger people or are not cost effective .
Appropriateness of prescribing in older people can be assessed by process (i.e. what providers do) or outcome measures (i.e. patient outcomes) which are implicit or explicit . Implicit process measures are based on a clinician's judgment of appropriateness for the individual patient . Explicit process measures are criterion based and are developed from published reviews, expert opinion and/or consensus techniques and should be generalizable across countries . These measures consist of drugs to be avoided in older people, independent of diagnoses or in the context of certain diagnoses [7–9].
The US Beers criteria are the most frequently used and validated explicit process measure [10, 11]. However in the context of European prescribing Beers criteria have several limitations. Some of the limitations include the fact that almost half of the drugs that make up the criteria are unavailable for prescribers [12, 13], several of the drugs are not contra-indicated in older people as per the British National Formulary (BNF), e.g. doxazosin , whereas other contra-indicated drugs are omitted . The Beers criteria do not consider drug–drug interactions, duration of treatment, varying indications for certain drugs, e.g. low-dose amitriptyline and neuropathic pain (BNF) and underuse of indicated drugs [3, 4]. Given the limitations of the Beers criteria, a more comprehensive explicit process measure of potentially inappropriate prescribing (PIP) has recently been developed and validated for use in European countries, the Screening Tool of Older Peoples Prescriptions (STOPP) .
There have been few studies of PIP in the general population of older people [12, 15, 16]. Previous research is limited by having focused on specific groups in particular settings such as geriatric units, nursing homes and hospitals as well as having measured PIP using Beers criteria. There is also a limited understanding of the risk factors associated with PIP and results from previous studies have been inconclusive [11, 15, 17]. The overall aim of this study was to estimate the prevalence of PIP in the national Irish population aged ≥70 years, in 2007 using thirty STOPP criteria. Additional objectives included: (i) estimation of the prevalence of PIP per individual STOPP criteria by physiological system; (ii) investigation of the association between PIP, number of drug classes, gender and age and; (iii) establishing the total cost of PIP drugs and the cost in relation to overall national pharmaceutical expenditure.