Background Clarithromycin is a strong inhibitor especially of cytochrome-P450 3A4 in contrast to azithromycin. Clinicians may often not be aware of the importance of clarithromycin drug interactions. To date, we could not find published data directly comparing potential interactions of clarithromycin and azithromycin.

Purpose The aim of this study was to evaluate macrolide prescriptions with respect to the interaction potential of either clarithromycin or azithromycin, as well as the indication and duration of therapy by clinical pharmacists.

Material and methods From May 2018 to July 2018, a total of 48 patients for whom clarithromycin IV was ordered were identified at a German university hospital. Two clinical pharmacists independently evaluated drug therapy and performed database-based interaction checks^1–4 of the complete medication regimens with clarithromycin according to a German validated classification system (ABDA⁵) and compared them to azithromycin. The most important antibiotic-related interventions were discussed with the physician in charge. Complete medication regimens, indications, duration of therapy, number and severity of interactions as well as the implementation of the interventions were documented.

Results Interventions were necessary in 37/48 patients. Clarithromycin was combined with 166 different medications, and, in total, 548 combinations were checked with the following results:

• In 16 patients discontinuation of clarithromycin due to missing indication.

• In eight patients switch to azithromycin IV, in four patients switch to azithromycin PO.

• In seven patients continuation of clarithromycin under close monitoring.

• in two patients interventions regarding the comedication.

A complete switch from clarithromycin IV to azithromycin would have resulted in a reduction of clinically relevant drug interactions from 168/548 to 115/548, with a shift to lower severity of interaction according to the ABDA classification system:

• Contraindicated combination: reduction from 15 to 0.

• Dosage adjustment or close monitoring needed/not recommended combination: reduction from 72 to six.

• Consider some monitoring: increase from 81 to 109.

• Generally no action needed: increase from 380 to 433.

Conclusion Involvement of clinical pharmacists helps to optimize macrolide prescription with respect to the interaction potential of either clarithromycin or azithromycin as well as the indication and duration of therapy.

References and/or acknowledgements 1. https://mediq.ch

2. https://about.medicinescomplete.com, Stockleys Drug Interactions

3. https://www.fachinfo.de

4. https://www.uptodate.com, Lexicomp® Drug Interactions

5. https://www.pharmazeutische-zeitung.de/ausgabe-252013/zum-1-juli-neue-klassifikationsstufen/

No conflict of interest.