Influence of the assessment of the severity on the frequency of adverse drug reactions (ADRs).

Sometimes it is difficult to compare data coming from different drug monitoring studies because of differences in methods, training of the monitors and other reasons. Many algorithms have been designed for permitting the objective and reproducible assessment of the causality of ADRs, but there is a lack of this kind of assessment for the severity of ADRs. This work was developed in order to show how important the standardized assessment of the severity of ADRs could be. For that purpose the same drug surveillance data were used for obtaining the frequency, characteristics and predisposing factors of ADRs, first considering all definite and probable ADRs--independently of their severity (study I)--and excluding after those considered as mild (study II). By means of an intensive prospective drug surveillance program, 2,559 patients hospitalized at the Medicine Service of the Clinical Hospital of the University of Chile were surveyed. The found frequencies of ARDs were 34.2% and 20.6% for study I and II, respectively. In both studies gastrointestinal and metabolic systems were the most ADRs-affected systems but some differences on adverse signs and/or symptoms were observed. For example, in study I the three most frequent reactions were hyponatremia, hypochloremia and hypokalemia while in study II the three commonest reactions were hypokalemia, vomiting and hypochloremia. In both studies similar characteristics of beginning and probability of ADRs were found, and the highest part of the reactions was dose-dependent. But when mild reactions were excluded (study II) an increase on the proportion of dose-independent ADRs was observed.(ABSTRACT TRUNCATED AT 250 WORDS)