Extremely long time stability study of selected antibiotic standards.

Area of Science:

• Pharmaceutical Sciences
• Analytical Chemistry
• Microbiology

Background:

• Reference standards are crucial for pharmaceutical quality control.
• Older standards predating modern purification and analysis techniques may have questionable quality.
• Assessing the long-term stability of these legacy standards is vital.

Purpose of the Study:

• To investigate the quality and antimicrobial activity of aged World Health Organization (WHO) and European Pharmacopoeia (EP) antibiotic reference standards.
• To evaluate the stability of oxytetracycline, doxycycline, colistin, and spiramycin standards stored for extended periods.

Main Methods:

• Assay and purity tests were performed following European Pharmacopoeia (Ph. Eur.) 6.0 guidelines.
• Antibacterial activity was assessed using the microbiological agar diffusion method (Ph. Eur. 4.0).
• High-performance liquid chromatography (HPLC) was employed for potency determination.

Main Results:

• Several reference standards demonstrated stability exceeding 40 years, with one remaining stable for over 50 years.
• Determined potency closely matched declared values, irrespective of whether HPLC or microbiological assays were used.
• Compositional analysis revealed significant differences in multi-substance antibiotics (colistin, spiramycin) compared to newer standards.
• No excessive degradation or significant changes in impurity levels were observed during the storage period.

Conclusions:

• Legacy antibiotic reference standards can exhibit exceptional long-term stability.
• Potency assays remain reliable indicators of quality for these aged substances.
• Differences in composition highlight the impact of evolving manufacturing and purification techniques on antibiotic reference materials.