Antimicrobial therapy systemic infections

Bacterial cultures should be obtained prior to antimicrobial therapy in patients with a systemic inflammatory response, risk factors for antimicrobial resistance, or infections where diagnosis or antimicrobial susceptibility is uncertain. 

Bacterial colonization of pressure sores is common. Because infection impairs wound healing and may require systemic antimicrobial therapy, the clinician must be able to distinguish it from colonization. Table 70-8 describes the clinical presentation of infected pressure sores. 

Patients with GI infections should be evaluated for resolution of GI symptoms, as well as any related systemic signs and symptoms. If antimicrobial therapy was used, completion of the course of therapy should be assessed. Documented clearance of the offending microorganism is not necessary. 

Nitrofurantoin is administered orally and is rapidly and almost completely absorbed from the small intestine only low levels of activity are achieved in serum because the drug is rapidly metabolized. Relatively high protein binding (about 70%) also affects serum levels, reducing potential for systemic toxicity and alteration of intestinal flora. Relative tissue penetration is much lower than other antimicrobials for UTIs, and therefore, nitrofurantoin is not indicated in the therapy of infections such as pyelonephritis and renal cortical or perinephric abscesses. Nitrofurantoin is rapidly excreted by glomerular filtration and tubular secretion to yield effective urinary levels. In moderate to severe renal dysfunction, toxic blood levels may occur while urinary levels may be inadequate. The drug is inactivated in the liver. 

Oral therapy of infections is usually cheaper and avoids the risks associated with maintenance of intravenous access on the other hand, it may expose the gastrointestinal tract to higher local concentrations of antibiotic with consequently greater risks of antibiotic-associated diarrhoea. Some antimicrobial agents are available only for topical use to skin, anterior nares, eye or mouth in general it is better to avoid antibiotics that are also used for systemic therapy because topical use may be especially likely to select for resistant strains. Topical... 

Topical uses. Neomycin and framycetin, whilst too toxic for systemic use, are effective for topical treatment of infections of the conjunctiva or external ear. They are sometimes used in antimicrobial combinations selectively to decontaminate the bowel of patients who are to receive intense immunosuppressive therapy. Tobramycin is given by inhalation for therapy of infective exacerbations of cystic fibrosis. 

Deep bacterial infections, e.g. boils, generally do not require antimicrobial therapy but if they do it should be systemic. Cellulitis requires systemic chemotherapy initially with benzylpeniciUin and flucloxacillin. 

The search for useful inhaled antibiotics has been driven, in part, by a concern about the adequacy of systemic antimicrobial therapy for respiratory infections. Some agents, including aminoglycoside antibiotics, exhibit limited penetration into respiratory tract secretions. In fact, aminoglycosides may achieve sputum concentrations that are 12% of related serum concentrations. In addition, cystic fibrosis patients are often colonized with mucoid strains of Pseudomonas aeruginosa. This phenotype is associated with a further reduction in penetration of antibiotics. 

In the late 1970s and early 1980s, Peyman and Baum et al. (19,20) popularized the use of intraocular antibiotics and this route of administration became the mainstay of therapy for intraocular infection. Intraocular antimicrobials are now given in essentially all cases of endophthalmitis some patients are also treated with vitrectomy. In the EYS, all patients received intraocular antibiotics but only half the patients received systemic therapy. Systemic antimicrobials did not improve prognosis in the EYS, but amikacin, which has poor intraocular penetration, was used for gram-positive coverage in the study (1). 

As with all drugs, the specific side effects of the quinolones must be considered when they are chosen for treatment of bacterial infections [5]. Reactions of the gastrointestinal tract and the central neivous system are the most often observed adverse effects during therapy with quinolones. It should be underlined, however, that compared with many other antimicrobials, diarrhea is less frequently observed during quinolone treatment. Antibiotic-associated colitis has been observed rarely during quinolone therapy. Similarly, hypersensitivity reactions, as observed during therapy with penicillins and other (3-lactams, is less frequently caused by quinolones. Some other risks of quinolone therapy have been defined and must be considered if a drug from this class is chosen for treatment of bacterial infections. 

Cefazolin or cefuroxime are appropriate for prophylaxis in cardiothoracic and vascular surgeries. In the case of 3-lactam allergy, vancomycin or clindamycin are advised. Debate exists on the duration of antimicrobial prophylaxis. The National Surgical Infection Prevention Project cites data that extending prophylaxis beyond 24 hours does not decrease SSI rates and may increase bacterial resistance.1 American Society of Health-System Pharmacists guidelines from 1999 allow for the continuation of prophylaxis for up to 72 hours.22 Duration of therapy should be based on patient factors and risk of development of an SSI. SSIs are rare after cardiothoracic operations, but the potentially devastating consequences lead some clinicians to support longer periods of prophylaxis. 

Systemic therapy with a variety of (3-lactams, macro-lides and lincosamides (clindamycin) has been the cornerstone of skin infection therapy for many years [17]. However, topical antibiotics can play an important role in both treatment and prevention of many primary cutaneous bacterial infections commonly seen in the dermatological practice [18], Indeed, while systemic antimicrobials are needed in the complicated infections of skin and skin structure, the milder forms can be successfully treated with topical therapy alone [18], The topical agents used most often in the treatment of superficial cutaneous bacterial infections are tetracyclines, mupirocin, bacitracin, polymyxin B, and neomycin. 

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