<prompt> A 26 year old patients presents with suspected pneumococcal meningitis.CSF culture is sent for antibiotic sensitivity. Which empirical antibiotic should be given till culture sensitivity result come?Penicillin GCeftriaxone metronidazoleDoxycyclineCefotaxime vancomycin  <response>: To achieve synergism Every AMA has a specific effect on selected microorganisms. Depending on the drug pair as well as the organism involved, either synergism supra-additive effect, additive action, indifference or antagonism may be observed when two AMAs belonging to different classes are used together. Antibiotics are the mainstay of treatment in S pneumoniae infections. Until the 1970s, essentially all pneumococcal isolates were sensitive to easily achievable levels of most commonly used antibiotics, including penicillins, macrolides, clindamycin, cephalosporins, rifampin, vancomycin, and trimethoprim-sulfamethoxazole The mechanism of pneumococcal resistance to penicillin and cephalosporins is through alteration in the molecular cell wall targets, penicillin-binding proteins PBPs. Mutations that alter the PBPs result in decreased affinity for binding to these agents, rendering them less effective. This type of resistance can be overcome if the antibiotic concentration at the site of infection exceeds the MIC of the organism for 40-50 of the dosing interval. Penicillin-resistant pneumococci are often resistant to multiple additional classes of antibiotics, including other penicillin derivatives, cephalosporins, sulfonamides, trimethoprim-sulfamethoxazole through amino acid changes, macrolides through methylation or an efflux pump, quinolones through decreased permeability, efflux pumps, and alteration of enzymes, and chloramphenicol through inactivating enzymes. Resistance is obtained as pa of a cassette of genetic information, or a transposon, that encodes resistance to multiple antibiotics. Resistance rates of pneumococcal isolates in the United States to trimethoprim-sulfamethoxazole, tetracycline, and the macrolides are relatively high. Some isolates 10 in the United States that are resistant to macrolides are also resistant to clindamycin. Vancomycin-resistant pneumococcal isolates have not been repoed in the United States. The phenomenon of tolerance survival but not growth in the presence of a given antibiotic has been observed, but its clinical relevance is unknown. Any strain with an in vitro MIC greater than 1 ugmL to vancomycin should be immediately repoed to the state health depament and arrangements made for confirmatory testing at the CDC. In the United States, most pneumococcal isolates remain susceptible to fluoroquinolones. In ceain countries and specific populations in whom the use of respiratory fluoroquinolones is more prevalent eg, nursing homes, an increase in resistance to these agents has been seen. REFERENCE: emedicine.medscape.com , ESSENTIALS OF MEDICAL PHARMACOLOGYK.D.TRIPATHI,SIXTH EDITION,PAGE NO:677 