Mahidol University Journal of Pharmaceutical Sciences 2008; 35(1-4): 18-23. Original Article Development of Guava Extract Chewable Tablets for Anticariogenic Activity against Streptococcus mutans S. Saraya, 1* J. Kanta, 1 N. Sarisuta, 1 R. Temsiririrkkul, 1 Y. Suvathi, 2 K. Samranri 1 and S. Chumnumwat 1 1 Faculty of Pharmacy, Mahidol University, Bangkok, 2 Research and Development Institute, The Government Pharmaceutical Organization (GPO), Bangkok, Thailand. Abstract Streptococcus mutans is a normal flora bacteria found in human oral cavity. This bacterium has been known to cause dental caries and bad breath odor. This study was conducted to develop the guava extract chewable tablets against S. mutans ATCC 25175. The guava leaves obtained from Psidium guajava L. were extracted with water by boiling 15 minutes and lyophilized to be the powder. The reconstituted crude extract was varied in concentration over the approximate 8×, 16×, 32× MIC and investigated for antibacterial activity. The minimal inhibitory concentration (MIC) against S. mutans of crude extract was 5 mg/ml which was equal to minimum bactericidal concentration (MBC). Crude extract was also tested for antimicrobial susceptibility compared with standard antibiotic kanamycin. The largest clear zone of 12.50 ± 0.71 mm in diameter was observed in crude 32× MIC comparing to 13 mm in kanamycin. The negative control gave no clear zone. The guava chewable tablets were formulated as complied with commercial chewable tablets. The tablets were tested for their antimicrobial susceptibility test and largest clear zone of 11.50 ± 0.71 mm in diameter was observed in the 32× MIC tablet. Moreover, measurement of bactericidal activity (time kill study) of 32× MIC tablet demonstrated the killing effect against S. mutans, the results showed that colony counts of tested bacteria were declined to zero within 2-3 hours. Although, those results support the traditional use of P. guava for the treatment of dental caries, further study is required for this medicinal plant. ©All right reserved. Keywords: chewable tablet; dental caries; Psidium guajava; Streptococcus mutans INTRODUCTION Dental infections such as dental caries is an infectious disease in which the oral bacterium Streptococcus mutans has been implicated as a principal etiological agent, although other oral bacterial species probably contribute to this disease. These bacteria are known to cause bad breath odor. Among the various oral micro-organisms, S. mutans has been identified as a plaque-forming bacterium capable of producing dental caries in experimental animals and in humans. 1 The ability of S. mutans to adhere firmly to tooth surfaces in the presence of sucrose and to release acids by fermenting various dietary sugars has been associated with its caries- inducing potential. Many attempts have been made to eliminate S. mutans from the oral flora. Antibiotics such as chlorhexidine, penicillin, ampicillin, tetracycline, erythromycin and vancomycin are very effective in preventing dental caries in vivo and in vitro. However, their excessive use can result in alterations of the oral and intestinal flora and cause undesirable side effects such as the development of bacterial tolerance, vomiting, diarrhea and teeth stains. These problems necessitate further search for natural antimicrobial agents that are safe for humans and specific for oral pathogens. 2 * Corresponding author: Faculty of Pharmacy, Mahidol University, 447 Sri-Ayudhaya Road, Bangkok 10400, Thailand. Fax: (662) 354-4326 E-mail: pyssr@mahidol.ac.th