Proposal for a New Tool to Evaluate Drug Interaction Cases

TLDR

Assessing causation in drug interactions requires evaluating drug properties, patient factors, and concurrent medications, a task for which the Naranjo nomogram—designed for single‑drug adverse events—is ill‑suited because many of its questions are inapplicable or fail to distinguish object and precipitant drugs. The Drug Interaction Probability Scale was created to help clinicians assess causation of drug interaction–induced adverse outcomes in individual patients. The DIPS calculates a probability score through a series of questions that rely on knowledge of both drugs’ pharmacologic properties, making limited understanding a potential drawback. While the Naranjo nomogram has been misapplied to drug interactions, the DIPS offers a structured approach for both reporting and evaluating such cases.

Abstract

The assessment of causation for a potential drug interaction requires thoughtful consideration of the properties of both the object and precipitant drugs, patient-specific factors, and the possible contribution of other drugs that the patient may be taking. The Naranjo nomogram was designed to evaluate single-drug adverse events, not drug-drug interactions. Several of the questions on the Naranjo nomogram do not apply to potential drug-drug interactions, while others do not specify object or precipitant drug. Nevertheless, it has been inappropriately used to evaluate drug-drug interactions. The Drug Interaction Probability Scale (DIPS) was developed to provide a guide to evaluating drug interaction causation in a specific patient. It is intended to be used to assist practitioners in the assessment of drug interaction-induced adverse outcomes. The DIPS uses a series of questions relating to the potential drug interaction to estimate a probability score. An accurate assessment using the DIPS requires knowledge of the pharmacologic properties of both the object and precipitant drugs. Inadequate knowledge of either the drugs involved or the basic mechanisms of interaction will be a limitation for some users. The DIPS can also serve as a guide in the preparation of articles describing case reports of drug interactions, as well as in the evaluation of published case reports.