Bioinfo Publications 217 DEVELOPMENT AND VALIDATION OF A STABILITY-INDICATIVE AGAR DIFFUSION ASSAY TO DETERMINE THE POTENCY OF FLUCLOXACILLIN SODIUM IN CAPSULES International Journal of Microbiology Research ISSN: 0975-5276 & E-ISSN:0975-9174, Volume 4, Issue 4, 2012, pp.-217-222. Available online at http://www.bioinfo.in/contents.php?id=27 FLÁVIA A.M. FIORENTINO* AND HÉRIDA R.N. SALGADO Post Graduation Program in Pharmaceutical Sciences, School of Pharmaceutical Sciences, Univ. Estadual Paulista, Araraquara, SP, Brazil. *Corresponding Author: Email- flafiorentino@ig.com.br Received: May 17, 2012; Accepted: May 24, 2012 Abstract- Flucloxacillin sodium (FLU) is a semi-synthetic penicillin active against many gram-positive bacteria such as streptococci and penicilinase-producing staphylococci, including methicillin-susceptible S. aureus. This study describes the development and validation of a microbiological assay, applying the diffusion agar method for the determination of FLU, as well as the evaluation of the ability of the method in determining the stability of FLU in capsules against acidic and basic hydrolysis, photolytic and oxidative degradations, using S. aureus ATCC 25923 as micro-organism test and 3 x 3 parallel line assay design (three doses of the standard and three doses of the sample in each plate), with six plates for each assay, according to the Brazilian Pharmacopoeia. The validation method showed good results including line- arity, precision, accuracy, robustness and selectivity. The assay is based on the inhibitory effect of FLU using Staphylococcus aureus ATCC 25923. The results of the assay were treated by analysis of variance (ANOVA) and were found to be linear (r = 0.9997) in the range from 1.5 to 6.0 μg/mL, precise (repeatability: R.S.D. = 1.63 and intermediate precision: R.S.D. = 1.64) and accurate (98.96%). FLU solution (from the capsules) exposed to direct UVC light (254 nm), alkaline and acid hydrolysis and hydrogen peroxide causing oxidation were used to evalu- ate the specificity of the bioassay. Comparison of bioassay and liquid chromatography by ANOVA showed no difference between methodol- ogies. The results demonstrated the validity of the proposed bioassay, which is a simple and useful alternative methodology for FLU deter- mination in routine quality control. Key words- Flucloxacillin, Bioassay, Penicillin, Pharmaceutical formulation, Quality control, Validation. International Journal of Microbiology Research ISSN: 0975-5276 & E-ISSN:0975-9174, Volume 4, Issue 4, 2012 Introduction Flucloxacillin (FLU) is a semi-synthetic and penicillinase-stable isoxazolyl penicillin active against many Gram-positive bacteria such as hemolytic streptococci and penicillinase-producing staph- ylococci, including methicillin-susceptible S. aureus (MSSA), but not active against methicillin-resistant S. aureus. It acts by the inhibition of transpeptidation, thus leading to the formation of a weakened peptidoglycan. As autolysins continue to act, the cell walls of Gram-positive organisms become progressively weaker, and osmotic lysis takes place [1,2]. FLU is chemically known as sodium (2S,5R,6R)-6-[[[3-(chloro-6-fluorophenyl)-5-methylisoxazol -4-yl]carbonyl]amino]-3,3-dimethyl-7-oxo-4-thia-1-azabicyclo [3.2.0]hepatane - 2 carboxylate monohydrate [3-5]. FLU is used for the treatment of skin, soft tissue and respiratory tract infections as well as endocarditis and osteomyelitis caused by methicillin- susceptible S. aureus [2]. The chemical structure of FLU sodium is presented in (Fig. 1). Fig. 1- Chemical structure of flucloxacillin sodium (CAS 1847-24- 1). Citation: Flávia A.M. Fiorentino and Hérida R.N. Salgado (2012) Development and Validation of a Stability-Indicative Agar Diffusion Assay to Determine the Potency of Flucloxacillin Sodium in Capsules. International Journal of Microbiology Research, ISSN: 0975-5276 & E- ISSN:0975-9174, Volume 4, Issue 4, pp.-217-222. Copyright: Copyright©2012 Flávia A.M. Fiorentino and Hérida R.N. Salgado. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the origi- nal author and source are credited.