Microbiological stability and antimicrobial preservative effectiveness of a 5 mg/mL spironolactone oral suspension in Inorpha^®

Introduction
Spironolactone is used in pediatric patients to treat hypertension and nephrotic syndrom. In hospital pharmacies, coumpounded capsules are prepared. To reduce errors and facilitate administration, an oral suspension of spironolactone 5 mg/mL containing 0.25% of xanthan gum in Inorpha^® was formulated.

Objective
Evaluate the microbiological stability and efficacity of antimicrobial preservative effectiveness of the spironolactone 5 mg/mL oral suspension in order to determinate its shelf life.

Method
Method suitability was validated to determinate the smallest dilution capable to neutralize the potassium sorbate. Three dilutions were tested: microbial enumeration (Ph. Eur 2.6.12) and the detection of specified E. coli (Ph. Eur 2.6.13).
The microbiological stability of the suspension (Ph. Eur 5.1.4) was conducted over 3 months (M0, M1, M2 et M3) at 20±5°C and 5±3°C using 3 batches (n=3/batch) of opened and closed bottles. At M0, three bottles stored at 20±5°C and three at 5±3°C were opened to assess in-use stability. To reproduce the real-life use, daily withdrawal was performed from the opened bottles. Each month, microbial counts and E. coli research were carried out in these bottles (Ph. Eur acceptance limit: TAMC < 200 CFU/mL; TYMC < 20 CFU/mL and absence of E. coli). Antimicrobial preservative effectiveness (Ph. Eur 5.1.3) was studied in 5 bottles, each inoculated with one of the five microorganisms (MO) specified in the Ph. Eur. Microbial counts were performed on Days 0,14 and 28.

Results
All tested dilutions were validated during the method suitability testing. The lowest dilution was selected for the microbial enumeration (1:10) and E. coli (1:10). Several colonies were detected during the microbiological stability study. At M0,17 CFU/mL were found in the opened bottles stored at 5±3°C (Kocuria rhizophila) and in the unopened bottles stored at 20±5°C (Cladosporium cladosporioides). At M1, 117 CFU/mL (>20 CFU/mL, exceeding the Ph. Eur limit) identified as Cladosporium cladosporioides were detected in the opened bottles at 20±5°C. At M2, 17 CFU/mL of molds were detected in the unopened bottles stored at 5±3°C. At M3, no MO were detected. E. coli testing remained negative up to M3 at both storage temperatures. The antimicrobial preservative effectiveness test with the potassium sorbate demonstrated logarithmic reductions in microbial counts at Day 14 and 28 exceeding the requirements of the Ph. Eur.

Conclusion
At 20±5°C, the suspension is microbiologically stable for 3 months before opening but is not stable after opening. At 5±3°C, it remained microbiologically stable for 3 months both before and after opening. Potassium sorbate at the concentration present in the ready-to-use vehicule, provided effective antimicrobial preservation.

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