Background: The quality of the reconstitution water, storage temperature, and brand-specific formulation critically influence the in-use stability of reconstituted azithromycin oral suspensions. This study investigated these factors using two generic brands (Azimax® and Zomax®) reconstituted with tap water, deionized water, and sterile distilled water, stored at room temperature (27°C) and under refrigeration (2-8°C) for seven days.

Objective: This study investigates azithromycin suspension stability using three reconstitution water types and two storage conditions across two generic brands.

Method: A validated HPLC method with UV detection at 210 nm was employed for analysis. We determined degradation kinetics using zero-order, first-order, and second-order models.

Results: Azimax® demonstrated superior stability across all conditions, remaining within USP specification (2022) (95- 105%) for up to six days with tap water at room temperature, compared to four days for Zomax®. Refrigeration did not consistently enhance stability, with Azimax® showing better stability at room temperature with tap water and deionized water. Degradation followed zero-order kinetics for both brands, with Zomax® exhibiting 2-5 times faster degradation rates (k = 6.10-11.98 %/day) than Azimax® (k = 1.16-2.80 %/day).

Conclusion: The observed degradation patterns highlight the critical importance of brand selection, reconstitution water quality, and appropriate storage recommendations while informing formulation development. This work provides critical baseline data that will guide the development of next-generation azithromycin nanosuspensions with enhanced stability profiles using nanoparticle engineering approaches.