Are incorrectly used drugs more frequently involved in adverse drug reactions? A prospective study

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Abstract
Objectives The aims of this study were to identify and evaluate the frequency of drugs involved in adverse drug reactions (ADRs) for which recommendations of the Summary of Product Characteristics (SPC) had not been respected and to compare the percentages of drugs suspected of being the cause of ADRs when correctly and incorrectly used. Methods All ADRs reported to the Regional Pharmacovigilance Centre of Tours (RPC) over a period of 5 months were analysed to identify drugs used “incorrectly” defined by drug use beyond the recommendations of the SPC, i.e. drugs used when contra-indicated and/or drugs used for an off-label indication, and/or drugs used at an inappropriate dose, and/or inappropriate duration of treatment, and/or drugs used in the presence of a potentially or definitely interacting drug. Results Included in the study were 182 ADRs involving 182 patients. Of 642 drugs, 169 (26%) were incorrectly used and for 81 patients (44.5%) ADRs involved at least one “incorrectly” used drug. These included 10% (64 of 642) drug interactions, 7.3% (47 of 642) off-licence indications, 5% (32 of 642) inadequate dosage, 3% (20 of 642) incorrect duration of treatment and 1% (6 of 642) contraindications. “Correctly” used drugs appeared to be less often the cause of the ADRs than “incorrectly” used drugs (59.4% versus 75%, P=0.0001). Conclusion “Incorrectly” used drugs were more often causally linked to ADR than correctly used drugs. A meaningful number of ADRs could probably be avoided if SPC guidelines for a safe and effective drug use are carefully adhered to.