Adverse drug reactions and drug substitution in an arrhythmia clinic.
OBJECTIVE
To assess the impact of adverse drug reactions on antiarrhythmic drug substitution in ambulatory patients.


METHODS
Tertiary care dysrhythmia clinic.


METHODS
A total of 671 medical records were reviewed. Sex of the study population was equally distributed, with an average age of 53 years. Follow-up averaged 26 months for patients seen more than once. Suspected adverse drug reactions and substitution of antiarrhythmic agent were used to ascertain events in patients' charts. Patients were exposed to 1253 treatment courses. The number of successive antiarrhythmic agents per patient averaged 1.8 and varied from one to seven.


RESULTS
One hundred and thirty-nine (20%) patients experienced a total of 194 adverse events (15.5% of drug courses), of which only eight (4%) were serious. Ninety-four per cent of the mostly benign adverse drug reactions were followed by a therapeutic modification: discontinuation or replacement in 87% and dosage reduction in 7%. The influence of successive drug changes was evident: the risk of a reaction was 7% in patients exposed to one agent compared with 100% in patients exposed to a seventh agent.


CONCLUSIONS
First, therapeutic substitution in response to adverse drug reactions appears to be determined more by the combined expected benefit, the product of arrhythmia severity and drug efficacy, than by the severity alone of the adverse reaction; and second, the probability of an adverse drug reaction is proportional to the number of agents tried consecutively, possibly as a result of patient selection, drug selection and increased patient and doctor awareness.
Research Centre, Hôpital du Sacré Coeur, Montréal, Québec.
I
I
Sadek
T
T
Kus
P
P
Biron
K
K
Benabdesselam
D000328:Adult; D000368:Aged; D000889:Anti-Arrhythmia Agents / Q000009:adverse effects*; D001145:Arrhythmias, Cardiac / Q000188:drug therapy*; D002170:Canada; D002300:Cardiac Care Facilities; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D018570:Risk Assessment
D000889:Anti-Arrhythmia Agents