![]() The available treatment options according to the site of infection are shown in Figure PP39-2. In seriously ill patients with suspected or proven MRSA infection, a loading dose of vancomycin (25–30 mg/kg) may be considered followed by 15–20 mg/kg of actual body weight every 8–12h (not to exceed 2 g per dose). aureus (vancomycin MIC 4–8 mg/L and ≥16 mg/L, respectively) are rare. Methicillin-resistant Staphylococcus aureus (MRSA, oxacillin MIC >2 mg/L) remains one of the principal pathogens, whereas vancomycin-intermediate or vancomycin-resistant Staph. MRSE are now extremely common, as ICU surveillance by the CDC showed an 89% incidence in the US in 2003, 50 while a report from Taiwan in 2000 showed the incidence there was 84%. 52 There are at least five types of a mobile staphylococcal cassette chromosome mecA (SCC mec) gene that confers β-lactam resistance, 53 by virtue of encoding an altered penicillin-binding protein 2a (PBP2a) the SCC mec types I–III are associated with HA-MRSA. 50 Most current data on MRSA incidence is 60% in Taiwan, 49 74% in Hong Kong, 72% in Japan, 51 and 20% in Europe. aureus isolates collected from ICU patients, representing an 11% increase over the mean rate of resistance for the 5 prior years. 26 According to the CDC, the incidence of HA-MRSA in the US during 2003 was 59.5% of the S. ![]() 49 MRSA remain susceptible to vancomycin (with the exception of those strains noted below), quinupristin/dalfopristin (QD), and linezolid. MRSA (now defined as strains with an oxacillin minimum inhibitory concentration (MIC) ≥4 μg mL −1) are resistant to not only methicillin and oxacillin, but virtually all β-lactams, aminoglycosides, tetracyclines, chloramphenicol, lincosamides, macrolides, trimethoprim/sulfamethoxazole, and fluoroquinolone antibiotics. Brickner, in Comprehensive Medicinal Chemistry II, 2007 7.23.3.1 Hospital-Acquired Methicillin-Resistant Staphylococcus aureus and Staphylococcus epidermidis The procedure for extraction of the antibiotic oxacillin using oxacillin imprinted polymer involved the following steps: (i) spiked milk samples containing 0 and 50 μg/ml oxacillin were centrifuged at 11,000 rpm for 20 min and the pellet discarded (ii) the supernatants were adjusted to pH 4.5 with 5 N hydrochloric acid and then centrifuged as before (iii) the pH of the supernatants were raised to pH 7.5 with 5 N NaOH and methanol added (2 parts to 1 part aqueous phase) (iv) the supernatants were extracted twice with chloroform, each for 10 min under slight agitation (v) the top aqueous/methanol phases were dried under a stream of nitrogen (vi) the dried extracts were reconstituted in the mobile phase acetonitrile:0.001 M phosphate buffer, pH 3.5 (50:50) and then injected (20 μl per sample, 0.5 ml/min flow rate) onto the HPLC column and (vii) the bound fraction was eluted in the mobile phase and the elution profile monitored at 208–300 nm. ‘New configurations and applications of molecularly imprinted polymers’, 15–24 (2000), with permission from Elsevier Science. Chromatogram representing print molecule (oxacillin) and two other β-lactam antibiotics (penicillin G and V) on oxacillin MIP (a) compared with the control blank MIP (b). Methicillin-resistant Staphylococcus (e.g., MRSA or MRSP) are usually identified by using oxacillin break points (see “ Patient Monitoring and Laboratory Tests” section).įig. 4.5. Oxacillin is not valuable therapeutically, but is used as a marker to test for mec-A-mediated resistance of PBP2a in Staphylococcus. Because of a short half-life and low oral absorption, there are limitations to its use in animals. Limited pharmacokinetic data are available for animals. Staphylococci are susceptible because oxacillin is resistant to the bacterial beta-lactamase produced by Staphylococcus spp. ![]() Resistance is common, especially among enteric gram-negative bacilli. ![]() Oxacillin has a limited spectrum of activity that includes primarily gram-positive bacteria. ![]() Like other beta-lactams, this drug acts in a time-dependent manner (i.e., it is more effective when drug concentrations are maintained above the MIC during the dose interval). After binding to PBPs, the cell wall weakens or undergoes lysis. Oxacillin, like other beta-lactam antibiotics, binds penicillin-binding proteins (PBPs) that weaken or interfere with cell wall formation. Papich DVM, MS, DACVCP, in Saunders Handbook of Veterinary Drugs (Fourth Edition), 2016 Pharmacology and mechanism of actionīeta-lactam antibiotic. ![]()
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