***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
    ***DOCUMENTATION*** 
    ***EXAMPLES*** 
    Input: To assess the comparative efficacy of omeprazole 20 mg , a proton pump inhibitor , versus ranitidine 150 mg twice a day , an H2-receptor antagonist , in healing duodenal ulcers we performed a r and omized , double-blind , multicenter trial in 309 patients with endoscopically diagnosed ulcers . Patients were treated for up to four weeks and were seen at week 2 and at week 4 , if unhealed at week 2 , for determination of ulcer status by endoscopy , review of daily self- assessment symptom diaries , and clinical laboratory including fasting serum gastrin . Gastrin levels were repeated two weeks after cessation of study medication . Evaluation of baseline demographic and laboratory parameters demonstrated no significant differences between the two groups at entry . At week 2 , 42 % of the omeprazole and 34 % of the ranitidine-treated patients were healed ( P = NS ) . At week 4 , there was a 19 % advantage in ulcer healing for the omeprazole-treated patients in comparison to those treated with ranitidine ( 82 % vs 63 % , respectively , P<0.05 ) . Healing of ulcers ≥1.0 cm occurred in 83 % of those treated with omeprazole versus 37 % treated with ranitidine ( P<0.01 ) . There were no significant differences in rate of pain relief or incidence of clinical laboratory abnormalities . Mean fasting serum gastrin value during treatment increased over the baseline in both groups , ( P<0.05 ) . The percent change was significantly greater with omeprazole but few patients had elevations above the upper limit of normal for the assay . Both drugs were well tolerated . Omeprazole 20 mg demonstrated superiority in healing duodenal ulcers at four weeks in comparison to ranitidine 150 mg twice daily and was more effective in healing ulcers > -1.0 cm We performed a prospect i ve observational cohort study of the epidemiology and etiology of nosocomial pneumonia in 358 medical ICU patients in two university-affiliated hospitals .  Protected bronchoscopic techniques ( protected specimen brush and bronchoalveolar lavage ) were used for diagnosis to minimize misclassification . Risk factors for ventilator-associated pneumonia were identified using multiple logistic regression analysis . Twenty-eight cases of pneumonia occurred in 358 patients for a cumulative incidence of 7.8 % and incidence rates of 12.5 cases per 1 , 000 patient days and 20.5 cases per 1,000 ventilator days . Staphylococcus aureus , Streptococcus pneumoniae , Pseudomonas aeruginosa , and Hemophilus species made up 65 % of isolates from the lower respiratory tract , whereas only 12.5 % of isolates were enteric gram-negative bacilli . Daily surveillance cultures of the nares , oropharynx , trachea , and stomach demonstrated that tracheal colonization preceded ventilator-associated pneumonia in 93.5 % , whereas gastric colonization preceded tracheal colonization for only four of 31 ( 13 % ) eventual pathogens . By multiple logistic regression , independent risk factors for ventilator- associated pneumonia were admission serum albumin < = 2.2 g/dl ( odds ratio [ OR ] 5.9 ; 95 % confidence interval [ CI ] 2.0 - 17.6 ; p = 0.0013 ) , maximum positive end-expiratory pressure > = 7.5 cm H2O ( OR , 4.6 ; 95 % CI , 1.4 to 15.1 ; p = 0.012 ) , absence of antibiotic therapy ( OR , 6.7 ; 95 % CI , 1.8 to 25.3 ; p = 0.0054 ) , colonization of the upper respiratory tract by respiratory gram-negative bacilli ( OR , 3.4 ; 95 % CI , 1.1 to 10.1 ; p = 0.028 ) , pack-years of smoking ( OR , 2.3 for 50 pack-years ; 95 % CI , 1 . 2 to 4.2 ; p = 0.012 ) , and duration of mechanical ventilation ( OR , 3 . 4 for 14 d ; 95 % CI , 1.5 to 7.8 ; p = 0.0044 ) . Several of these risk factors for ventilator-associated pneumonia appear amenable to intervention BACKGROUND Critically ill patients who require mechanical ventilation are at increased risk for gastrointestinal bleeding from stress ulcers . There are conflicting data on the effect of histamine H2-receptor antagonists and the cytoprotective agent sucralfate on rates of gastrointestinal bleeding , ventilator-associated pneumonia , and mortality . METHODS In a multicenter , r and omized , blinded , placebo-controlled trial , we compared sucralfate with the H2-receptor antagonist ranitidine for the prevention of upper gastrointestinal bleeding in 1200 patients who required mechanical ventilation . Patients received either nasogastric sucralfate suspension ( 1 g every six hours ) and an intravenous placebo or intravenous ranitidine ( 50 mg every eight hours ) and a nasogastric placebo . RESULTS The patients in the two groups had similar base-line characteristics . Clinical ly important gastrointestinal bleeding developed in 10 of 596 ( 1.7 percent ) of the patients receiving ranitidine , as compared with 23 of 604 ( 3.8 percent ) of those receiving sucralfate ( relative risk , 0.44 ; 95 percent confidence interval , 0.21 to 0.92 ; P=0.02 ) . In the ranitidine group , 114 of 596 patients ( 19.1 percent ) had ventilator-associated pneumonia , as compared with 98 of 604 ( 16.2 percent ) in the sucralfate group ( relative risk , 1.18 ; 95 percent confidence interval , 0.92 to 1.51 ; P=0.19 ) . There was no significant difference between the groups in mortality in the intensive care unit ( ICU ) ( 23.5 percent in the ranitidine group and 22.9 percent in the sucralfate group ) or the duration of the stay in the ICU ( median , nine days in both groups ) . CONCLUSIONS Among critically ill patients requiring mechanical ventilation , those receiving ranitidine had a significantly lower rate of clinical ly important gastrointestinal bleeding than those treated with sucralfate . There were no significant differences in the rates of ventilator-associated pneumonia , the duration of the stay in the ICU , or mortality Two hundred thirty patients with reflux symptoms and endoscopically proven erosive esophagitis were enrolled from 15 U.S. centers into a r and omized , double-blind , dose-ranging study comparing placebo with omeprazole , 20 or 40 mg given once daily in the morning . Esophagitis grade 2 was present in 44 % of patients , grade 3 in 37 % of patients , and grade 4 in 19 % of patients . Endpoints , defined as complete relief of heartburn and complete esophageal mucosal healing , were assessed after 4 and 8 weeks of treatment . Both omeprazole doses were significantly superior to placebo in complete endoscopic healing . After 8 weeks of treatment , 73.5 % of patients in the 20-mg omeprazole group and 74.7 % in the 40-mg omeprazole group , compared with 14.0 % in the placebo group , had complete healing of the esophageal mucosa . At the end of the study , complete relief of daytime heartburn was obtained in 79.5 % of patients in the 20-mg omeprazole group , 81.6 % in the 40-mg omeprazole group , and 37.2 % in the placebo group ( P less than or equal to 0.05 ) . Complete relief of nighttime heartburn was noted by 79.5 % of patients in the 20-mg omeprazole group , 85.1 % in the 40-mg omeprazole group , and 34.9 % in the placebo group ( P less than or equal to 0.05 ) . The median time to complete relief of daytime and nighttime heartburn occurred earlier in the 40-mg group than in the 20-mg group ( 9 vs. 17 days and 9 vs. 20 days , respectively ) ; however , these differences were not statistically significant . Relief of acid regurgitation and dysphagia also occurred earlier in the 40-mg group . Omeprazole was well tolerated  in this group of patients . No unexpected adverse experiences occurred . The results of this study confirm those of six multicenter , international trials in which omeprazole in doses of 20 - 60 mg provided a degree of esophageal mucosal healing and complete relief of reflux symptoms superior to any other medical treatment BACKGROUND : It has been suggested that patients with Barrett 's esophagus ( BE ) are unusually resistant to the antisecretory effects of proton pump inhibitors ( PPIs ) . OBJECTIVES : To compare intragastric and intraesophageal acidity in patients with BE receiving esomeprazole 40 mg three times daily ( t.i.d . ) , esomeprazole 40 mg twice daily ( b.i.d . ) , and esomeprazole  20 mg t.i.d . METHODS : In this r and omized , double-blind , three-way crossover study , patients with long-segment BE received each of the three esomeprazole dosages for 5 days separated by 10–14-day washout periods . Intragastric and intraesophageal pHs were measured for 24 h on day 5 . RESULTS : Among 31 patients with evaluable pH data  , intragastric pH was > 4.0 for 88.4 % , 81.4 % , and 80.4 % of day 5 after treatment with esomeprazole 40 mg t.i.d . , 40 mg b.i.d . , and 20 mg t.i.d . , respectively . Esomeprazole 40 mg t.i.d . was significantly more effective than the other dosages ( p < 0.01 ) . Intraesophageal pH was < 4.0 for mean values of < 5 % of the monitoring period with all the three dosing regimens , but esophageal pH remained < 4.0 for > 5 % of the time in 16 % , 23 % , and 19 % of patients receiving esomeprazole 40 mg t.i.d . , 40 mg b.i.d . , and 20 mg t.i.d . , respectively . All dosages were well tolerated . CONCLUSIONS : All the three esomeprazole dosages significantly decreased intragastric acidity and reduced esophageal acid exposure to mean normal values in the total group of patients with BE . However , abnormal esophageal acid exposure continued in 16–23 % of patients despite the significant decrease in gastric acidity . These results suggest that the apparent “ PPI resistance ” described in patients with BE may be caused by their profound reflux diathesis rather than by gastric resistance to the antisecretory effects of PPIs Objectives To determine whether a continuous iv infusion of cimetidine , a histamine-2 ( H2 ) receptor antagonist , is needed to prevent upper gastrointestinal ( GI ) hemorrhage when compared with placebo and if that usage is associated with an increased risk of nosocomial pneumonia . Due to the importance of this latter issue , data were collected to examine the occurrence rate of nosocomial pneumonia under the conditions of this study . Design A multicenter , double-blind , placebocontrolled study . Interventions Patients were r and omized to receive cimetidine ( n = 65 ) as an iv infusion of 50 to 100 mg/hr or placebo  ( n = 66 ) . Setting Intensive care units in 20 institutions . Patients Critically ill patients ( n = 131 ) , all of whom had at least one acute stress condition that previously had been associated with the development of upper GI hemorrhage . Measurements and Main Results Sample s of gastric fluid from nasogastric aspirates were collected every 2 hrs for measurement of pH and were examined for the presence of blood . Upper GI hemorrhage was defined as bright red blood or persistent ( continuing for > 8 hrs ) “ coffee ground material ” in the nasogastric aspirate . Baseline chest radiographs were performed and sputum specimens were collected from all patients , and those patients without clear signs of pneumonia ( positive chest radiograph , positive cough , fever ) at baseline were followed prospec-tively for the development of pneumonia while receiving the study medication . Cimetidine-infused patients experienced significantly ( p = .009 ) less upper GI hemorrhage than placebo-infused patients : nine ( 14 % ) of 65 cimetidine vs. 22 ( 33 % ) of 66 placebo patients . Cimetidine patients demonstrated significantly ( p = .0001 ) higher mean intragastric pH ( 5.7 vs. 3.9 ) , and had intragastric pH values at > 4.0 for a significantly ( p = .0001 ) higher mean percentage of time ( 82 % vs.  
    Output:
    
Although a trend was evident in both a chi(2 ) analysis of individual studies and a meta- analysis , the present review and meta- analysis failed to show a conclusive association between PPIs and respiratory infections .