Potential determinants of drug-drug interaction associated dispensing in community pharmacies

Although the number of clinically relevant drug-drug interactions (DDIs) is probably low, DDIs may be responsible for a substantial number of hospital admissions. In some countries, the pharmacist is responsible for preventing the use of unsafe or non-effective drug regimens. Specifically they should avoid the dispensing of combinations of drugs that may cause serious DDIs. In order to assess the determinants related to community pharmacies and associated with these dispensings, a systematic literature review was conducted. Medline and International Pharmaceutical Abstracts were searched for articles published in English between 1993 and 2003. Additional relevant articles were identified by screening the reference lists of relevant articles. Seven papers were located. The determinants described in the literature were divided into three groups. The first group focussed on the relationship between the pharmacist and the prescriber. The number of prescribers is of importance as well as the number of dispensing pharmacies. Both a high number of primary care physicians and multiple dispensing pharmacies increased the risk of DDIs. The availability, quality and sensitivity of the medication surveillance software appeared to be a second important determinant. Both too many and too few signals increased the risk of dispensing interacting drugs. The third group of determinants was related to the pharmacist and pharmacy organisation. Signals from the surveillance program are usually judged first by technicians and subsequently managed by the pharmacist. Consequently, knowledge, instructions and supervision are important determinants. A fourth group of determinants was identified in literature assessing interventions by pharmacists, including interventions for DDIs. A higher workload was associated with lower intervention rates, which indicated a higher risk of dispensing interacting drugs. The determinants identified in this review can be used to develop strategies to minimise patient harm resulting from DDIs. Further assessment of the relation between these determinants and the dispensing of DDIs and of the relation between DDI-associated dispensing and patient harm is recommended.