A prospective study on causality assessment rating, mortality rate, and case fatality rate for adverse drug reactions among medical inpatients at the University of Benin Teaching Hospital, Nigeria

Abstract

Background: An adverse drug reaction (ADR) is a special form of adverse drug event (ADE) in which a causative relationship can be shown or established and is attributable to the offending/precipitating medication. ADR causality assessment is used to determine the likelihood that a particular drug caused a suspected ADR. Causality assessment rating evaluates the relationship between drug treatment and the occurrence of an ADE. It is also used to evaluate, check, confirm, and ascertain that the particular treatment is the cause of an observed adverse event or not. Aim: This study was designed to evaluate the causality assessment rating, mortality rate, and case fatality rate for ADRs among adult medical inpatients in clinical practice setting with the goal of preventing them and improving their treatment outcome. Methods: The patients admitted to the adult medical wards of a Nigerian University Teaching Hospital over 9 months from December 2013 to August 2014 were prospectively recruited for the study and followed up till discharge. Results: Five hundred and seven patients were evaluated during the study, of which 269 (53.1%) of them were male and 238 (46.9%) were female. The mean age of the study population was 48.9 ± 17.8 years (median of 46 years). In this study, the causality assessment rating for the observed ADRs was evaluated using both the World Health Organization (WHO) causality rating criteria and the Naranjo algorithm. Using the WHO causality rating criteria, certain cases were 10 (19.6%), probable cases were 17 (33.3%), and possible cases were 24 (47.1%). Using the Naranjo algorithm, definite cases were 9 (17.6%), probable cases were 19 (37.3%), and possible cases were 23 (45.1%). The number of patients admitted solely because of ADRs (ADR-out) was 18 (3.6%) patients, whereas those that experienced ADRs during admission (ADR-in) stood at 33 (6.5%) patients. Furthermore, the case fatality rate for ADRs was 7.8% (4/51), while the ADR-associated overall mortality rate was 0.8% (4/507). Conclusion: In this study, the two methods used to ascertain causality rate for ADRs caused by a suspected drug; both the WHO causality rating criteria and Naranjo algorithm, showed similar causality ratings, which strengthening the ascribed ADR causality rating. In addition, the mortality rate and case fatality rate for ADRs were significantly high among these adult medical inpatients.