Pharmacoeconomics and Safe Medication Use
Appendix 2. Drug Interaction Probability Scale
The drug interaction probability scale (DIPS) is designed to assess the probability of a causal relationship between
a potential drug interaction and an event. It is patterned after the Naranjo ADR probability scale (Naranjo CA,
Busto U, Sellers EM, et al. A method for estimating the probability of adverse drug reactions. Clin Pharmacol Ther
1981;30:239-45).
Directions
| o | Circle the appropriate answer for each question and add up the total score. |
|---|---|
| o | Object drug = Drug affected by the interaction. |
| o | Precipitant drug = Drug that causes the interaction. |
| o | Use the Unknown (Unk) or Not Applicable (NA) category if (a) you do not have the information or (b) the question |
is not applicable (e.g., no dechallenge; dose not changed).
Questions
Yes
No
NA/Unk
Are there previous credible reports of this interaction in humans reported in
the literature?
+1
–1
of the precipitant drug?
+1
–1
Is the observed interaction consistent with the known interactive properties
of object drug?
+1
–1
Is the event consistent with the known or reasonable time course of the
interaction (onset or offset)?
+1
–1
Did the interaction remit upon dechallenge of the precipitant drug with no change
in the object drug?
+1
–2
(if no dechallenge, use Unknown or NA and skip question 6)
Did the interaction reappear when the precipitant drug was readministered in the
presence of continued use of object drug?
+2
–1
Are there reasonable alternative causes for the event?a
–1
+1
consistent with the proposed interaction?
+1
Was the drug interaction confirmed by any objective evidence consistent with the
effects on the object drug (other than drug concentrations from question 8)?
+1
10. Was the interaction greater when the precipitant drug dose was increased or less
when the precipitant drug dose was decreased?
+1
–1
aConsider clinical conditions, other interacting drugs, lack of adherence, risk factors (e.g., age, inappropriate doses of object drug). A NO answer presumes that enough
information was presented so that one would expect any alternative causes to be mentioned. When in doubt, use Unknown or NA designation.
| Total Score _____ | Highly Probable: > 8 |
|---|
Probable: 5–8
Possible: 2–4
Doubtful: < 2