Monotherapy should be used when possible since combination therapy is often expensive and exposes patients to unnecessary antibiotics, thereby increasing the risk of MDR pathogens and adverse outcomes. Patients that develop nosocomial pneumonia with no risk factors for drug-resistant organisms are likely to respond to monotherapy with the antibiotics listed in this algorithm (45). Monotherapy with ciprofloxacin has been successful in patients with mild HAP (defined as a CPIS score of ＜ 6) but is less effective in severe HAP (70,78). Agents that have been shown to be effective as monotherapy in patients with moderately severe HAP not due to MDR pathogens include ciprofloxacin, levofloxacin, imipenem, meropenem, cefepime, and piperacillin/tazobactam (78-84). CPIS=clinical pulmonary infection score.