Metabolism by the Cytochrome P450 system and its importance in family medicine

Abstract

Objective: To describe the frequency and type of interactions between the cytochrome system and drug metabolism, as well as the corresponding reports to the National Pharmacovigilance System (NPS). Type of Study: Post-hoc observational study carried out on 45 consultation days. Setting: Marco dos Pereiros Health Centre Outpost, Coimbra Health Authority. Population: Patients from one GP roster. Methodology: Database elaborated from a systematic record of all the medicines taken by each patient during a given time period. An up-to-date chart of drug interactions and descriptive statistical methods were used. Results: A prescription was given in 661 (75%) consultations with 114 cases (17.2%) of drug interactions, of which 82 (12.4%) associated with metabolism and 32 (4.8%) with inhibition by the same isoform. The number of cases increased from 2001 (n=15; 4.6%) to 2002 (n=17; 5%). A mean of 4.2 different active ingredients were recorded in interaction cases against 2.7 for cases in which no interaction was identified. Females were predominantly affected. Reports were sent to the NPS in four cases. Discussion: Although not sufficient data are available concerning the metabolism of involved isoforms, pharmacokinetic and pharmacodynamic interactions of clinical significance that may occur when multiple drugs are prescribed seem to be more frequent when compared with reports from other countries and contexts. Conclusions: Drug interactions were identified in 17.2% of consultations. They increased from 2001 to 2002, Reporting rates were low (4 out of 82). This problem should be more vigorously highlighted, namely in the Summaries of Products Characteristics.