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The need for prophylactic antibiotics in contaminated head and neck surgery is generally accepted. In contaminated cases, it has been shown that the wound infection rate with placebo approaches 100% through many prospective randomized clinical trials. When considering use of any antibiotic therapy, cost must be considered. Johnson, et al. in a retrospective analysis found that the cost per infection per person was $12,155.05 (1987 dollars). In a study by Blair in 1992, the excess cost to each patient who developed a wound infection was $36,000 (1992 dollars). The cost of administrating antibiotic prophylaxsis was much less than the cost of treating the infection. Wound infections are usually polymicrobial and treatment is with appropriate drainage and multi-antibiotic regime. In addition to cost,. One must also consider other issues associated with antibiotic therapy such as side effects and development of resistant strains.
Virtually all bacterial pathogens have the ability to acquire resistance to antibiotic therapy. This problem is more common in nocosomial pathogens such as VRE and MRSA. More recently, community acquired pathogens, such as Strept. pnuemoniae have developed resistant strains. Resistance to penicillin is found in 30-70 % of isolates depending on the hospital. Some strains are also found to be resistant to one of the following: cephalosporins, Bactrim, chloramphenicol, or a macrolide. Children are more likely than adults to be infected with strains resistant to chloramphenicol, erythromycin, or Bactrim.
Parenteral administration of antibiotics in head and neck surgery is the traditional route. Alexander and Alexander demonstrated that IV administration achieves the earliest level of antibiotic coverage in wound fluid. However, IM injections achieve the highest sustained level. Therefore it is recommended in contaminated cases to administer IV and IM loading doses followed by continuous IV or intermittent IM injections. The efficacy of topical antibiotics in contaminated head and neck surgery is still under investigation. Many studies show that the number of bacteria in the wound are reduced when using topical antibiotics however it has not been shown that this reduction is associated with a reduced number of wound infections.
Penicillins work by causing abnormal cell wall development in actively dividing bacterial cells. Drug resistance is achieved by alterations in penicillin binding proteins which hinders the ability of the drug to penetrate into the bacterial cell wall.
Natural penicillins are extracted from Penicillium chrypogenum. Penicillin G is the major natural penicllin. It has a half life of 30 minutes . However, penicillin G may be combined with procaine or benzathine to make a longer acting repository penicillin. Penicillin is the drug of choice for the treatment of St.pyogens and St. pneumoniae. However, 30% of isolates of St. pneumoniae are penicillin resistant. In penicillin resistant St. pnuemoniae, erythromycin or pediazole is used. It also has a good anaerobic spectrum and is the drug of choice for Clostridia perfringens. It does not have good activity for B. fragilis. Penicillin V is the oral form and has in general the same spectrum of activity.
The synthetic penicillins are prepared by mixing precursors in mold culture, by modifying a natural penicillin, or by adding side chains to 6-aminopenicillanic acid. The parenteral semi-synthetic penicllins are nafcillin, oxacillin, and methicillin. These drugs are used when S. aureus is suspected as they are resistant to staphlococcal B-lactamase. They also have good activity against St. pyogenes and St. pneumoniae. The most active pencillins are nafcillin and oxacillin. However, these drugs may cause interstitial nephritis, leukopenia, and reversible hepatic dysfunction. Methicillin carries the greatest potential for producing interstitial nephritis. Cloxacillin and dicloxacillin are the oral forms of synthetic penicillins.
The aminopenicillins include ampicillin(oral or iv form) and amoxicillin(oral form only). The aminopenicillins are not effective in the presence of B-lactamase. They are the antibiotics of choice for Enterococcus sp. and are active against some gram negative rods(E.coli and P. mirabilis). They are less active than PenG against Strept. species.
The antipsuedomonal penicillins include carbenicillin and ticarcillin. These are also susceptible to B-lactamase. These drugs have a similar gram negative spectrum of activity however are more active against Pseudomonas sp., Enterobacter sp. Serratia sp. and strains of B. fragilis group. They have poor activity against Klebsiella sp. They are synergistic with aminoglycosides against Ps. aeruginosa and some enterobacteriaccae. Ticarcillin is more active than carbenicillin. Side effects include sodium loading and platelet dysfunction.
The extended spectrum penicillins include mezlocillin and piperacillin. These drugs have sensitivities and side effects similar to the anti-psuedomonal penicillins. However, in vitro they are more active against the Streptococcus species and the Klebsiella species.
The first generation agents include cephalothin, cephapirin, cephradine, and cefazolin. They are active against Streptococcus sp. and Staph. aureus and Staph. epidermidis. They have limited gram negative activity but are active against E. coli, Klebsiella sp., and Proteus mirabilis. Associated adverse effects include allergic reactions, drug eruptions, phlebitis, and diarrhea. Large amounts of B-lactamase will inactivate cefazolin. The rest of the first generation cephalosporins are more resistant to B-lactamase.
The major second generation cephalosporins are cefoxitin, cefotetan, and cefuroxime., They have increase activity against the gram negative organisms. Cefoxitin and cefotetan are more active against the anaerobes. In one study by Maier et al. cefuroxime was found to have an advantage of better tissue penetration in the parotid gland, sinuses, and soft tissue of the neck when compared to other second generation cephalosporins.
The third generation cephalosporins include cefotaxime, ceftizoxime, ceftriaxone, ceftazidime, and cefoperazone. They are less active against Gram positive organisms but are more active than the enterobacteriaceae. Cefotaxime, ceftizoxime, and ceftriaxone are called the triplets and are very resistant to B-lactamase. They also have good activity against the Gram positive organisms with the exception of Enterococcus sp. They have good activity against Gram negative organisms except Pseudomonas sp. Ceftazadime has similar but less activity against the Enterobacter sp when compared to the triplets. It has superior activity against Pseudomonas sp. However, for serious Psuedomonas infections it should be combined with an aminoglycoside. Adverse reactions to cephalosporins include hypersensitivity reaction, hematological disturbances, GI complaints and reversible renal impairment.
Vancomycin has great activity against Staphlococcus aureus Staph. epidermidis, and Enterococcus. It is the antibiotic of choice for methicillin resistant Staph. aureus. It can be associated with nephrotoxicity or ototoxicity especially when given along with an aminoglycoside. Vancomycin use is also associated with the emergence of vancomycin resistant enterococcus which is often seen in immunocompromised patients in the ICU.
Metronidazole is a good antibiotic for the treatment of anaerobic organisms. It acts by producing toxic oxygen radicals that are lethal for anaerobic organisms. It is well absorbed into abscesses. Side effects are rare but include seizures, cerebellar dysfunction, disulfiram reaction with alcohol, and psuedomembranous colitis.
Recently, increasing concern has emerged over the development of resistance of Pseudomonas to many commonly used antimicrobial ear drops. In a study done at the Childrens Hospital in Pittsburgh, only 17% of the aural isolates of Psuedomonas were found to be sensitive to neomycin. Further studies need to be carried out in the area.
In other otologic surgery, there has been no significant difference shown in infection rates post-operatively between those patients treated with peri-operative antibiotics and those who have not been treated. In the surgical treatment of ears with chronic drainage by tympanomastoidectomy, pathogenic microorganisms may remain in the middle ear even after surgery and may cause recurrent infection. One study showed that the postoperative secretions from a tympanostomy tube placed after mastoid surgery was still colonized by bacteria. Even with prophylaxis, the isolates remained. The bacterial isolates found were Psuedomonas and Staph. epidermidis. Studies to date show no statistically significant influence upon post-operative otologic infection or colonization rates as a result of using prophylactic antibiotics. Although studies show that there is a higher incidence of infection and graft failure in those ears infected preoperatively, the use of preoperative antibiotics did not alter this outcome.
When placing prosthetic devices, especially cochlear implants, there is always temptation to use prophylactic antibiotics. However, according to studies to date, infection resulting in removal of the implant does not seem to be dependent on prophylactic antibiotic use. Therefore, aside from otologic drops, prophylactic antibiotic use does not appear useful in otologic surgery. Wound infection is prevented more effectively by starting with a dry ear and observing good surgical technique.
Neurotological procedures that are long in duration and often require exposure of the dura and CNS are associated with a risk of CSF leak, meningitis, and wound infection. In a study by Kartush, et al., the result suggested that bacitracin irrigation intraoperatively alone is sufficient to prevent infectious complications however further studies need to be performed.
Several studies show that antibiotics given for 5-7 days post-operatively from a tonsillectomy are beneficial. Dysphagia, fever, pain, mouth odor and poor oral intake in the post-operative period can be reduced by giving a therapeutic regime of ampicillin or amoxicillin in children and ampicillin plus a beta lactamase inhibitor in adults. The duration of antibiotic treatment is unknown, and currently a 7 day course is recommended.
For animal bites, the antibiotic therapy is based on the type of animal. For example, 5% of dog bites usually result in infection with Strept. viridans, P. multocida, S. aureus, E. correndens, Bacteroides, Fusobacterium, and Caphocytophaga and is treated with Augmentin. Human bites usually result with infection with S.viridans, S. epidermidis, cornnebacterium, S. aureua, eikenella, bacteroides, and peptostrep and treatment is based on the length of time of contamination as well as the etiology. Studies show conflicting results on the use of antibiotics in animal bites reducing the incidence of wound infection. Some studies suggest that there is a strong correlation of amount of devitalized tissue and would infection. Current recommendations are to give empiric therapy to all human bites to the head and neck. Empiric antibiotic therapy is also recommended in animal bites where debridement of devitalized tissue is insufficient.
Contaminated head and neck cases should also receive prophylactic antibiotics. Most of these infections are polymicrobial. Studies have shown that maximal effectiveness of the treatment is achieved if the antibiotics are given prior to contamination. If they are given more that 3 hours after contamination, they are of minimal benefit. Clindamycin is a good choice for most surgeries however this should be based on the individual case.
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