Safety,Tolerability, and Pharmacokinetics of PA-824 in Healthy Subjects

PA-824 is a novel antibacterial agent that has shown in vitro activity against both drug-sensitive and drug-resistant Mycobacterium tuberculosis. The compound''s MIC is between 0.015 and 0.25 μg/ml for drug-sensitive strains and between 0.03 and 0.53 μg/ml for drug-resistant strains. In addition, it is active against nonreplicating anaerobic Mycobacterium tuberculosis. The safety, tolerability, and pharmacokinetics of PA-824 were evaluated in two escalating-dose clinical studies, one a single-dose study and the other a multiple-dose study (up to 7 days of daily dosing). In 58 healthy subjects dosed with PA-824 in these studies, the drug candidate was well tolerated, with no significant or serious adverse events. In both studies, following oral administration PA-824 reached maximal plasma levels in 4 to 5 h independently of the dose. Maximal blood levels averaged approximately 3 μg/ml (1,500-mg dose) in the single-dose study and 3.8 μg/ml (600-mg dose) in the multiple-dose study. Steady state was achieved after 5 to 6 days of daily dosing, with an accumulation ratio of approximately 2. The elimination half-life averaged 16 to 20 h. Overall, PA-824 was well tolerated following oral doses once daily for up to 7 days, and pharmacokinetic parameters were consistent with a once-a-day regimen. The results of these studies, combined with the demonstrated activity of PA-824 against drug-sensitive and multidrug-resistant Mycobacterium tuberculosis, support the investigation of this novel compound for the treatment of tuberculosis.According to the World Health Organization, there were 9.27 million new tuberculosis (TB) cases worldwide in 2007, which claimed the lives of approximately 1.77 million people, including 456,000 patients coinfected with human immunodeficiency virus (11). In addition, global increases in cases of multidrug-resistant TB and, more recently, extensively drug-resistant TB pose serious treatment challenges (12). New anti-TB drugs are needed that can shorten the duration of treatment, improve the treatment of resistant disease, facilitate the treatment of TB patients coinfected with human immunodeficiency virus, and shorten the treatment of latent TB infection.The 4-nitroimidazo-oxazoles (a subclass of nitroimidazoles) have potent sterilizing activity against Mycobacterium tuberculosis, as first demonstrated in 1993 (1). The further investigation of nitroimidazoles in an anaerobic model of M. tuberculosis dormancy demonstrated that metronidazole is active against slow-growing M. tuberculosis, suggesting the potential for the treatment of latent TB infection and for shortening the treatment of active TB disease (10). The further development of the nitroimidazole class by Pathogenesis, Inc., led to the discovery of another subclass, 4-nitroimidazo-oxazines, with promising activity against M. tuberculosis. PA-824, with the full chemical name (S)-2-nitro-6-[4-(trifluoromethoxy)benzyloxy]-6,7-dihydro-5H-imidazo[2,1-b][1,3]oxazine), was identified as the lead 4-nitroimidazo-oxazine. Stover et al. (8) reported that the MIC of PA-824 under aerobic conditions against a variety of drug-sensitive clinical isolates was similar to the MIC of isoniazid (MIC of PA-824, 0.015 to 0.25 μg/ml; MIC of isoniazid, 0.03 to 0.06 μg/ml). PA-824 also was found to be active against all single-drug- and multidrug-resistant clinical isolates of M. tuberculosis tested, with MICs of 0.03 to 0.53 μg/ml. Additional studies using microaerophilic and anaerobic culture models indicated that PA-824 also is active against both replicating and nonreplicating or infrequently replicating M. tuberculosis isolates (3, 8).Like metronidazole, PA-824 requires metabolic activation by M. tuberculosis through an F420-dependent nitroreduction (4, 5, 8). Although not thoroughly elucidated at this time, PA-824''s novel mechanism of action involves the inhibition of the synthesis of both protein and lipids but not nucleic acid. Studies by Stover et al. (8) demonstrated that PA-824 inhibits the oxidation of hydroxymycolate to ketomycolate, an essential lipid for M. tuberculosis cell wall function. Recent work by Singh et al. (7) indicates that the reduction of PA-824 to its des-nitroimidazole metabolite by a deazaflavin (F420)-dependent nitroreductase is associated with the generation of reactive nitrogen species, including nitric oxide, which may represent important effectors of PA-824 killing of M. tuberculosis under anaerobic conditions. In an experimental mouse model of infection, Tyagi et al. (9) demonstrated that, at a dose of 100 mg/kg of body weight, PA-824 has substantial bactericidal activity during both the initial and continuation phases of TB treatment. Using a short-course mouse infection model that employs 9 days of the drug treatment of gamma-interferon knockout mice infected with M. tuberculosis 14 days before treatment initiation, Lenaerts et al. (3) found that at 100 mg/kg PA-824 was as active as isoniazid at 25 mg/kg, rifampin (rifampicin) at 10 mg/kg, and moxifloxacin at 100 mg/kg. Additional studies of a mouse model of TB examined the activity of PA-824 administered in combination with current TB drugs. When substituted for isoniazid in standard therapy, PA-824 resulted in significantly fewer CFU after 2 months of therapy and a higher rate of conversion to culture negativity than that of the standard drug combination. Relapse rates after 6 months of treatment were not different in the experimental and control treatment arms in this study, but the study design was such that an improved relapse rate relative to the control could not have been demonstrated (6). Pharmacokinetic analyses reported by Nuermberger et al. (6) demonstrated in mice that the standard rifampin-isoniazid-pyrazinamide regimen does not affect core PA-824 pharmacokinetic parameters, such as C_max (maximum concentration observed), AUC_0—24 (total area under concentration-time curve from 0 to 24 h), or t_1/2 (half-life). Further nonclinical studies are under way to characterize PA-824''s activity and interactions in novel drug combinations.     

The Emergency Severity Index Triage Algorithm Version 2 Is Reliable and Valid

OBJECTIVES: Initial studies have shown improved reliability and validity of a new triage tool, the Emergency Severity Index (ESI), over conventional three-level scales at two university medical centers. After pilot implementation and validation, the ESI was revised to include pediatric and updated vital signs criteria. The goal of this study was to assess ESI version (v.) 2 reliability and validity at seven emergency departments (EDs) in three states. METHODS: In part 1, interrater reliability was assessed using weighted kappa analysis of written training cases and postimplementation by a random sampling of actual patient triages. In part 2, validity was analyzed using a prospective cohort with stratified random sampling at each site. The ESI was compared with outcomes including resource consumption, inpatient admission, ED length of stay, and 60-day all-cause mortality. RESULTS: Weighted kappa analysis of interrater reliability ranged from 0.70 to 0.80 for the written scenarios (n = 3289) and 0.69 to 0.87 for patient triages (n = 386). Outcomes for the validity cohort (n = 1042) included hospitalization rates by ESI triage level: level 1, 83%; 2, 67%; 3, 42%; 4, 8%; level 5, 4%. Sixty-day all-cause mortality by triage level was as follows: level 1, 25%; 2, 4%; 3, 2%; 4, 1%; and 5, 0%. CONCLUSIONS: ESI v. 2 triage produced reliable, valid stratification of patients across seven sites. ESI triage should be evaluated as an ED casemix identification system for uniform data collection in the United States and compared with other major ED triage methods.     

Talin is required for integrin-mediated platelet function in hemostasis and thrombosis

Integrins are critical for hemostasis and thrombosis because they mediate both platelet adhesion and aggregation. Talin is an integrin-binding cytoplasmic adaptor that is a central organizer of focal adhesions, and loss of talin phenocopies integrin deletion in Drosophila. Here, we have examined the role of talin in mammalian integrin function in vivo by selectively disrupting the talin1 gene in mouse platelet precursor megakaryocytes. Talin null megakaryocytes produced circulating platelets that exhibited normal morphology yet manifested profoundly impaired hemostatic function. Specifically, platelet-specific deletion of talin1 led to spontaneous hemorrhage and pathological bleeding. Ex vivo and in vitro studies revealed that loss of talin1 resulted in dramatically impaired integrin αIIbβ3-mediated platelet aggregation and β1 integrin–mediated platelet adhesion. Furthermore, loss of talin1 strongly inhibited the activation of platelet β1 and β3 integrins in response to platelet agonists. These data establish that platelet talin plays a crucial role in hemostasis and provide the first proof that talin is required for the activation and function of mammalian α2β1 and αIIbβ3 integrins in vivo.     

The role of endoscopic ultrasound in inflammatory bowel disease

Ultrasonography has been applied to the diagnosis and management of inflammatory bowel disease for over 20 years. The combination of endoscopy with ultrasound has resulted in the application of intraluminal sonographic imaging to multiple diseases, including inflammatory bowel disease. Initial efforts were focused on the sonographic assessment of disease severity as based on bowel wall thickness, but this has been inconsistently demonstrated. Furthermore, disease severity is a clinical assessment that is based on both clinical and imaging studies. Recognizing that Crohn's disease tends to be transmural and ulcerative colitis a superficial mucosal inflammatory process, hopes were raised that endosonography would be effective in discriminating cases of otherwise indeterminate colitis. Efforts to demonstrate this, however, have been largely disappointing, and EUS plays a limited role in discriminating ulcerative colitis from Crohn's disease. On a more positive note, EUS evaluation of perirectal and perianal complications of Crohn's disease has been demonstrated to be superior to fistulography, CT, and equal to or superior to MRI. Because accurate anatomic information is required to guide surgical therapy of these lesions, EUS has the potential to emerge as a powerful imaging tool in the management of perianorectal Crohn's disease.     

Jimson Weed Extract as a Protective Agent in Severe Organophosphate Toxicity

Treatment of patients following an organophosphate (OP) exposure can deplete a hospital's entire supply of atropine. Given the possibility of multiple severe exposures after a terrorist attack using OP nerve agents, there exists a need for either greater atropine stores or the development of alternative antidotes. Jimson weed (Datura stramonium) contains atropine and other anticholinergic compounds and is common and readily available. It is used recreationally for its central anticholinergic effects and is made easily into an extract by boiling the crushed seeds. The extract has rapid onset of effects and may be useful for treatment of OP poisoning. OBJECTIVES: To determine whether pretreatment with an easily stored and prepared Datura seed extract (DSE) will increase survival following a severe OP poisoning. METHODS: Datura stramonium seeds were collected, crushed, and then heated in water to make a 2-mg/mL atropine solution (100 seeds contain approximately 6 mg of atropine or 0.007 mg/seed). Male rats were randomized to pretreatment with either saline (n = 10) or 7.5 mg/kg DSE (n = 10) given as a single intraperitoneal injection 5 minutes prior to a subcutaneous injection of 25 mg/kg of dichlorvos. The endpoint was time to death recorded by a blinded observer. RESULTS: The Kaplan-Meier estimates of the 24-hour survival rate was 90% (95% CI = 56% to 100%) for the DSE-pretreated group and 10% (95% CI = 0% to 45%) for the control group. The log-rank test revealed a statistically significant longer survival for the Datura-treated animals (p = 0.0002). Median survival time was 22 minutes 30 seconds for the control group and greater than 24 hours for the DSE-pretreated group. CONCLUSIONS: Pretreatment with DSE significantly increases survival following severe dichlorvos exposure.     

The formation of cocaethylene and clinical presentation of ED patients testing positive for the use of cocaine and ethanol

The purpose of this investigation was to document the clinical presentation of emergency department (ED) patients who tested positive for concurrent cocaine (COC) and ethanol (EtOH) use and the incidence of cocaethylene (CE) formation in this study population. Four study groups were evaluated: (1) drug-free, (2) EtOH-only, (3) COC-only, and (4) COC plus EtOH. CE was detected in plasma or urine specimens in 88% of the COC/EtOH-positive patients, and correlated directly with plasma COC and its metabolite benzoylecognine. Blood pressure and body temperature did not vary across study groups. COC/EtOH-positive patients displayed a significantly higher mean respiratory rate while the EtOH-only study group had an elevated mean heart rate. No significant differences were detected with respect to cardiac and neurological complaints between study groups. Trauma complaints in the drug-positive groups were more frequent than the incidence reported in the drug-free population. COC/EtOH-positive patients had the greatest percentage of trauma complaints (34.6%). Nearly half of the patients who tested positive for CE cited trauma as the primary reason for reporting to the ED. We conclude that ED patients who have concurrently used COC and EtOH are more closely associated with presentations related to traumatic injury than to those related to toxicologic complications.     

Interrater Reliability of Criteria Used in Assessing Blunt Head Injury Patients for Intracranial Injuries

OBJECTIVE: To determine the interrater reliability of potential predictor variables that may be used to construct a clinical decision rule for emergency computed tomography of the head in blunt head injury victims. METHODS: As a substudy of the NEXUS II study of blunt head trauma, physicians from 21 different emergency departments performed paired evaluations of patients undergoing computed tomography of the head after blunt head injury. Each physician independently determined, for each subject, the presence or absence of each of 19 separate clinical characteristics. The physicians were either residents or attending physicians in the participating emergency departments. Paired responses on a sample of 3,951 patients were compared for raw level of agreement and for interrater concordance using the kappa statistic. If the lower margin of the 95% confidence interval for raw agreement was at least 85% and was equal to or greater than 0.50 for kappa, this was predetermined to represent substantial interrater agreement. RESULTS: There was substantial interobserver agreement by both measures for 17 of the 19 candidate variables in patients with blunt head trauma. Interobserver agreement was substantial for all candidate variables except presence of seizure (kappa = 0.57 [95% CI = 0.47 to 0.67]; raw agreement = 96.5%) and abnormal cerebellar function (kappa = 0.54 [95% CI = 0.41 to 0.67]; raw agreement = 96.5%). CONCLUSIONS: The clinicians in our study had a substantial level of agreement regarding most clinical criteria assessed in this large sample of patients with blunt head injury.