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Purpose: The purpose of this project was to evaluate selected drug-drug interactions with citalopram, escitalopram and agents capable of prolonging the QTc interval for disparities in inclusion and severity level classifications amongst and within various widely used drug compendia.
Methods: At the JLW College of Pharmacy, faculty, preceptors and students have access to 4 online drug compendia: Micromedex, E-Facts & Comparisons, Lexicomp and Clinical Pharmacology. Twenty-four medications known to prolong the QTc interval were identified and evaluated for interaction with either citalopram or escitalopram. The inclusion-status of each drug interaction was noted, and if applicable, the drug pair’s severity level classification was recorded as it appeared in the 4 drug databases.
Results: Each database varied in the number of drug interactions included, ranging from 21/24 citalopram-QTc prolonging drug interactions in E-Facts & Comparisons to 24/24 interactions in both Lexicomp and Clinical Pharmacology. For the escitalopram-QTc prolonging drug pairs, 0/24 interactions were found in Micromedex as compared to 24/24 interactions found in Lexicomp, while E-Facts & Comparisons yielded 1/24 interactions to Clinical Pharmacology’s 8/24 interactions. For those interactions included in the several drug databases, a degree of variability was seen in severity level classification, ranging from “major” or “severe,” to “contraindicated” and “avoid.”
Conclusion: Faced with variations in inclusion and classification of interaction severity when consulting popular drug compendia, the clinician’s ability to render important therapeutic decisions may be compromised. It would therefore be wise for healthcare professionals to be aware of the criteria used to classify drug-drug interactions in their particular database-of-choice, and to avail themselves of 2 or more drug databases when formulating important clinical decisions.