Evaluation of compounded aqueous milbemycin oxime: issues with formulation potency and reproducibility

Area of Science:

• Veterinary Pharmacy
• Compounding Science
• Analytical Chemistry

Background:

• Milbemycin oxime is used in veterinary medicine.
• Compounded medications require rigorous quality control.
• Assessing the stability and potency of compounded drugs is crucial for patient safety.

Purpose of the Study:

• To evaluate the potency and reproducibility of compounded milbemycin oxime aqueous suspensions (20 mg/mL).
• To assess the stability of these suspensions under different storage conditions over 28 days.

Main Methods:

• Samples of compounded milbemycin oxime suspensions were obtained from two veterinary compounding pharmacies.
• Milbemycin oxime recovery was performed using solid-phase extraction.
• Concentration was measured using high-performance liquid chromatography (HPLC) at multiple time points over 28 days.

Main Results:

• On day 7, concentrations varied significantly between pharmacies, with coefficients of variation (CV) of 11% and 22%.
• Over 28 days, mean concentration decreases ranged from 18% to 22%.
• Five out of six lots deviated by more than 10% from their labeled strength.

Conclusions:

• Compounded milbemycin oxime suspensions frequently deviate from their labeled potency.
• The clinical efficacy of these compounded products is not established.
• Current evidence suggests caution and discourages the use of these compounded suspensions.