Early detection of drug interactions utilizing a computerized drug prescription handling system-focus on cerivastatin-gemfibrozil

Detection of potential drug interactions - a model for a national pharmacy register

OBJECTIVE

The widespread use of pharmaceuticals prescribed by different physicians has caused the Swedish government to propose a new legislation with registration of all prescriptions dispensed at the Swedish pharmacies. In the present study, we wanted to examine the frequency, distribution and determinants of potential drug interactions.

METHODS

The prescriptions from all individuals (n=8,214) with two or more prescriptions during October 2003 to December 2004 were collected from the ongoing Jämtland cohort study of a total of about 11,000 individuals. Potential drug-drug interactions were detected with a computerized interaction detection system and classified according to clinical relevance (types A-D).

RESULTS

On average each individual filled 14.6 (men 14.3, women 14.8) prescriptions during the study period. 3.6% of the individuals used more than 15 different drugs. The number of detected potential drug interactions type A-D was 4,941 (men 1,949, women 2,992). The risk of receiving a potential interaction type A-D was estimated as the cumulative incidence 0.26 (2,116/8,214) overall, 0.22 (748/3,467) for men and 0.29 (1,368/4,747) for women during the 15-month study period. The age adjusted risk, RR(adj), for women was estimated as 1.30. Excluding sex hormones and modulators of the genital system, the RR(adj) was 0.96, with no elevated risk for women. For potential interactions type D, that might have serious clinical consequences, 167 (cumulative incidence 0.0203) individuals (72 men, cumulative incidence 0.0208, 95 women cumulative incidence 0.0200) were detected. The risk of receiving a combination of potentially interacting drugs was positively correlated to age and polypharmacy. The cumulative incidence for elderly was estimated as 0.36 (65-84 years) and 0.39 (85 years and above). The relative risk for individuals with 15 drugs or more was estimated as 3.67 (95% CI 3.46-3.90).

CONCLUSION

In a general population there were relatively few severe potential drug interactions. The new Swedish national pharmacy register will provide health care professionals with a powerful tool to systematically review all prescriptions. An alert system should focus on the more potential drug interactions, type C-D, with close monitoring of elderly and patients with polypharmacy.

Evaluation of a Drug-Drug Interaction Alert Structure through the Retrospective Analysis of Statins-Macrolides Co-Prescriptions

The aim of this work was the evaluation of the existent drug interaction alert structure in Spain, which is based on yellow cards notifications and circulation of drug alert letters, through the retrospective analysis of CYP3A-metabolized statins and macrolides co-prescriptions in the Spanish province of Badajoz between May and September 2001. The period of study was planned to include the release of 2 drug alert letters released by the Spanish Drug Agency in June and July, addressed to all healthcare professionals, which warned against the concomitant prescription of statins and inhibitors of their metabolism, e.g. macrolides antibacterials. 4,600,764 prescriptions were examined, 664 of which corresponded to combinations of statins and macrolides. Although a decrease was detected in the number of these co-prescriptions throughout the study, 80 of these corresponding to 67 patients were still being prescribed in September, after the warnings by the Spanish Drug Agency had been released. 431 physicians prescribed these drugs simultaneously, with 22.9% of them having more than one patient at potential risk. Doctors working at rural healthcare centres or not directly attached to any healthcare facility were more prone to prescribe unsafe coprescriptions than those working at urban health centre. This study shows that the present drug alert system is not fully efficient when facing a situation like the one retrospectively reviewed in this study, in which a prompt action, in this case termination of potentially hazardous coprescriptions, was required. New systems developed to improve prescribing, including a new method based on personal contact between Drug Surveillance Centres and general practitioners, are discussed.