|
After hospital acquired pneumonia is diagnosed, it is absolutely essential that microbial therapy is begun promptly since delays in commencing antibiotics end up with worse results. One study in support of this observation confirmed a mortality rate of 30% in patients who received prompt, appropriate treatment as against 91% among patients who did not. The initial selection of an antimicrobial agent is mostly always made on an empiric basis and is determined by factors such as severity of infection, patient-specific risk factors, and the duration of stay in hospital before onset of infection.
All empiric treatment regimens must provide coverage against a group of core organism that includes gram negative bacilli (Escherichia coli, Enterobacter spp, Klebsiella spp, Serratia marcescens, Proteus spp, and Hemophilius influenzae) and gram-positive organisms such as streptococcus pneumonia and Staphylococcus aureus.
In patients with relatively mild and moderate infections and no particular risk factors for resistant or unusual pathogens, a nonpseudomonal third-generation cephalosporin such as ceftriaxone; monotherapy with a second-generation cephalosporin such as cefuroxime; or piperacillin/tazobactam; or a beta-lactam/beta-lactamase inhibitor such as ampicillin/sulbactam, ticarcillin/clavulanate may be appropriate. For patients in low risk category like this who are allergic to penicillin, it is recommended to start treatment with clindamycin or fluoroquinolone and aztreonam. While the use of flouroquinolone in the empiric regimen of patients with penicillin allergies is considered acceptable, a recent report studied the use of penicillin skin testing in such patients and concluded that most patients with a history of penicillin allergy could be safely treated with penicillin antibiotics. Therefore penicillin skin testing may be a method by which the administration of fluoroquinolones could be decreased.
Patients with mild or moderate infections having specific risk factors should have a wider empiric coverage. For patients with witnessed aspiration or in those having undergone recent thoracoabdominal surgery, adding clindamycin to cover anaerobes may be recommended, although even the use of a beta-lactam may be sufficient. For patients with head trauma, coma, recent influenza virus infections, chronic renal failure or diabetes, or those who are users of injection drugs, are vulnerable to infection by Staphylococcus aureus the addition of vancomycin to cover methicillin-resistant strains until sensitivities are known may be advised. Patients who have been on a prolonged course of steroids should include a macrolide as part of their initial therapy due to their heightened susceptibility to Legionella spp.
The severity of the infection notwithstanding, patients who have been on antibiotic medication prior to developing pneumonia, patients suffering from structural lung disease, those on steroids and those with a prolonged ICU course (more than 5 days) should be administered a combination of antibiotics to cover core pathogens along with infection from Pseudomonas aeruginosa or Acinetobacter spp. The high rate of acquired resistance among these organisms is the major reason why combination therapy is advised. For this category of patients, appropriate combinations include, ciprofloxacin, aminoglycoside in addition to a beta-lactam with antipseudomonal coverage. In case the patient shows risk factors that indicate that methicillin-resistant Staphylococcus aureus could be a likelypathogen, vancomycin could also be considered.
The criteria for pneumonia to be diagnosed as severe are if the patient needs to be shifted into the ICU, there is radiographic evidence of rapid progression, if mechanical ventilation or high level of inspired oxygen is required or if there is any evidence of sepsis. Patients suffering from severe pneumonias who have been hospitalized for less than 5 days, should be treated for empiric coverage to target the core group of organisms only; although monotherapy would in most cases not suffice for these patients and hence a combination therapy would be advised. Any patient diagnosed with severe pneumonia and having any one risk factor including a hospitalization of more than 5 days, should be re-administered with a combination of antibiotics that cover infections by P aeruginosa and Acinetobacter spp.
There happens to be no consensus about the duration of antibiotic therapy for patients suffering from hospital acquired pneumonia, but if the initial clinical suspicion was low, and if the clinical symptoms have not deviated drastically, antibiotics may be safely discontinued after 72 hrs. The Recommendations of the American Thoracic Society indicate that the duration of treatment should be determined by severity, the pathogenic organism and the time taken for clinical response. However a panel of experts differs with this view and states that the main factor determining the duration of therapy should be the time taken for clinical response and not the pathogen involved. They further state that patients be treated for a minimum of 72 hours after a clinical response is achieved.
Clinical response to antimicrobial therapy is not very likely to be achieved in the initial 48 to 72 hours, so the empiric antibiotic treatment should not be altered at this time unless prompted by results of microbiologic investigation. For patients failing to respond after the initial period, a broader antibiotic coverage may be recommended, invasive diagnostic testing may be performed and non infectious causes considered. Appropriate diagnostic testing may include radiographic tests to assess the possibility of pleural effusions or abscesses that hamper response, bronchoscopy with PSB and BAL, CTs of the sinuses to evaluate for sinusitis, as this may be a cause of recurring, persistent symptoms. After eliminating all other etiologies in the non responsive patient, an open lung biopsy for diagnostic purposes may be recommended although this method has not shown any marked improvement in the outcomes.
|
