Selection of perioperative antibiotics reduces the risk of surgical site infection (SSI) caused by direct inoculation of skin flora during the index procedure. Our skin flora is polymicrobial, however, the most common bacteria are staphylococcus, streptococcus, and p.acnes (all gram-positive bacteria) and are also the most common bacteria associated with SSI and PJI  . Polymicrobial and gram-negative infections account for 20-30% of PJI.
AAOS recommends 1st and 2nd generation cephalosporins as first line antibiotic prophylaxis to target gram-positive bacteria and about 40% of gram-negative bacteria.  The studies published to demonstrate the efficacy of perioperative antibiotics, going back to the 1950s, show reduction of surgical site infections from about 10% to 1%[4-6].
Cefazolin (ancef) and cefuroxime (ceftin) are the most common prophylactic antibiotics. Cefazolin is given at 1 g for patients < 170 lbs and 2 g for those < 260 lbs (3 g can be considered for those higher). Ceftin is given as 1.5 g for all patients. Optimal timing of administration is within 1 hour of incision per AAOS guidelines, although within 30 minutes gives highest concentration as cefazolin has rapid tissue penetration[7, 8]. Antibiotics should be re-dosed intraoperatively in cases >4 hours as tissue concentrations should remain above the MIC thru the critical parts of the procedure to avoid higher infection rates .
Penicillin (PCN) allergy is rarely a contraindication to 2nd generation cephalosporins because the cross-reactivity is < 1% in patients with self-reported allergy, and <2.5% in patients with confirmed PCN allergy  . The misconception that cross-reactivity is 10% stems from articles published in the 1960s where there was likely PCN contamination of other antibiotics due to processing in the same manufacturing plant and because 1st generation cephalosporins were examined, which do have a higher cross-reactivity . Patients with anaphylactic PCN allergy should receive alterative antibiotic because the complication is too significant.
24 hours postoperative dosing is recommended (studies show no benefit to 3 or 7 days antibiotics for clean, primary TJA). [13-15] 
Clindamycin and Vancomycin are alternatives antibiotics. They can be given to patients with a beta-lactam allergy or to high-risk patients (MRSA history, institutionalized patients, and healthcare workers). While both offer MRSA coverage, Vancomycin covers a higher percentage of MRSA species, furthermore, Clindamycin is only bacteriostatic, and most surgeons prefer bacteriocidal antibiotics. Clindamycin is recommended at 900 mg dose.
Vancomycin is recommended at a weight-based dose (15 mg/kg) not a default 1 g to all comers. Studies suggest that patients given a default 1 g are under dosed in 70% of cases as 1 g only covers people weighing up to ~150 lbs . Vancomycin has slower tissue penetration, and rapid infusion risks histamine release causing hypotension and a skin reaction, and thus should be given 1 hr before incision. Therefore recommendations are for infusion within 2 hours of incision, and infusion must be completed before use of a tourniquet. Routine use of Vancomycin for primary TJA is controversial. While some studies have shown lower surgical site infection (SSI) rates (1.0% vs. 0.5%) and better eradication of infections with I&D alone for those infections that do occur(22% vs 77%), others have found no significant difference in SSI [18, 19]. Due to conflicting data, AAOS recommends consideration for routine use of vancomycin only if hospitals report a high rate of MRSA prevalence (although there is no definition of a high rate). Patients with prior history of MRSA, but screened negative for MRSA, should be given routine antibiotics. Active MRSA carriers should receive Vancomycin.
Teicoplanin is a glycopeptide antibiotic similar to vanomycin that is commonly used for TJA prophylaxis in Europe, yet it is not currently available in North America. This medication has a long half-life (32-176 hours), low toxicity and excellent tissue penetration.
Routine use of dual antibiotics is not recommended.
Other Considerations .
- Primary and Revision TJA (include megaprosthesis) get the same perioperative antibiotics, although patients being revised at second-stage TJA for infection should received antibiotics to cover cultured organism.
- Patients with poor immune function, either poorly controlled diabetes, on immunosuppressive medication, or autoimmune disease, do not require different antibiotics.
- Patients with asymptomatic bacteriuria can be treated with routine antibiotic prophylaxis. Patients with acute UTI require treatment prior to TJA. Three studies comparing preoperative bacteriuria with risk for PJI found no correlation. Incidence of bacteriuira increases from 0.5% to 1.0% with a single catheterization, and increases to 10-30% for catheters left for 4 days, and 95% in catheters left for 30 days.
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