Phase I,Open-Label,Safety and Pharmacokinetic Study To Assess Bronchopulmonary Disposition of Intravenous Eravacycline in Healthy Men and Women

This study evaluated the pulmonary disposition of eravacycline in 20 healthy adult volunteers receiving 1.0 mg of eravacycline/kg intravenously every 12 h for a total of seven doses over 4 days. Plasma samples were collected at 0, 1, 2, 4, 6, and 12 h on day 4, with each subject randomized to undergo a single bronchoalveolar lavage (BAL) at 2, 4, 6, or 12 h. Drug concentrations in plasma, BAL fluid, and alveolar macrophages (AM) were determined by liquid chromatography-tandem mass spectrometry, and the urea correction method was used to calculate epithelial lining fluid (ELF) concentrations. Pharmacokinetic parameters were estimated by noncompartmental methods. Penetration for ELF and AM was calculated by using a ratio of the area under the concentration time curve (AUC_0–12) for each respective parameter against free drug AUC (fAUC_0–12) in plasma. The total AUC_0–12 in plasma was 4.56 ± 0.94 μg·h/ml with a mean fAUC_0–12 of 0.77 ± 0.14 μg·h/ml. The eravacycline concentrations in ELF and AM at 2, 4, 6, and 12 h were means ± the standard deviations (μg/ml) of 0.70 ± 0.30, 0.57 ± 0.20, 0.34 ± 0.16, and 0.25 ± 0.13 with a penetration ratio of 6.44 and 8.25 ± 4.55, 5.15 ± 1.25, 1.77 ± 0.64, and 1.42 ± 1.45 with a penetration ratio of 51.63, respectively. The eravacycline concentrations in the ELF and AM achieved greater levels than plasma by 6- and 50-fold, respectively, supporting further study of eravacycline for patients with respiratory infections.     

Disposition and Elimination of Meropenem in Cerebrospinal Fluid of Hydrocephalic Patients with External Ventriculostomy

The broad antibacterial spectrum and the low incidence of seizures in meropenem-treated patients qualifies meropenem for therapy of bacterial meningitis. The present study evaluates concentrations in ventricular cerebrospinal fluid (CSF) in the absence of pronounced meningeal inflammation. Patients with occlusive hydrocephalus caused by cerebrovascular diseases, who had undergone external ventriculostomy (n = 10, age range 48 to 75 years), received 2 g of meropenem intravenously over 30 min. Serum and CSF were drawn repeatedly and analyzed by liquid chromatography-mass spectroscopy. Pharmacokinetics were determined by noncompartmental analysis. Maximum concentrations in serum were 84.7 ± 23.7 μg/ml. A CSF maximum (C_maxCSF) of 0.63 ± 0.50 μg/ml (mean ± standard deviation) was observed 4.1 ± 2.6 h after the end of the infusion. C_maxCSF and the area under the curve for CSF (AUC_CSF) depended on the AUC for serum (AUC_S), the CSF-to-serum albumin ratio, and the CSF leukocyte count. Elimination from CSF was considerably slower than from serum (half-life at β phase [t_1/2β] of 7.36 ± 2.89 h in CSF versus t_1/2β of 1.69 ± 0.60 h in serum). The AUC_CSF/AUC_S ratio for meropenem, as a measure of overall CSF penetration, was 0.047 ± 0.022. The AUC_CSF/AUC_S ratio for meropenem was similar to that for other β-lactam antibiotics with a low binding to serum proteins. The concentration maxima of meropenem in ventricular CSF observed in this study are high enough to kill fully susceptible pathogens. They may not be sufficient to kill bacteria with a reduced sensitivity to carbapenems, although clinical success has been reported for patients with meningitis caused by penicillin-resistant pneumococci and Pseudomonas aeruginosa.     

Daptomycin Pharmacokinetics in Adult Oncology Patients with Neutropenic Fever

Daptomycin is the first antibacterial agent of the cyclic lipopeptides with in vitro bactericidal activity against gram-positive organisms, including vancomycin-resistant enterococci, methicillin-resistant staphylococci, and glycopeptide-resistant Staphylococcus aureus. The pharmacokinetics of daptomycin were determined in 29 adult oncology patients with neutropenic fever. Serial blood samples were drawn at 0, 0.5, 1, 2, 4, 8, 12, and 24 h after the initial intravenous infusion of 6 mg/kg of body weight daptomycin. Daptomycin total and free plasma concentrations were determined by high-pressure liquid chromatography. Concentration-time data were analyzed by noncompartmental methods. The results (presented as means ± standard deviations and ranges, unless indicated otherwise) were as follows: the maximum concentration of drug in plasma (C_max) was 49.04 ± 12.42 μg/ml (range, 21.54 to 75.20 μg/ml), the 24-h plasma concentration was 6.48 ± 5.31 μg/ml (range, 1.48 to 29.26 μg/ml), the area under the concentration-time curve (AUC) from time zero to infinity was 521.37 ± 523.53 μg·h/ml (range, 164.64 to 3155.11 μg·h/ml), the volume of distribution at steady state was 0.18 ± 0.05 liters/kg (range, 0.13 to 0.36 liters/kg), the clearance was 15.04 ± 6.09 ml/h/kg (range, 1.90 to 34.76 ml/h/kg), the half-life was 11.34 ± 14.15 h (range, 5.17 to 83.92 h), the mean residence time was 15.67 ± 20.66 h (range, 7.00 to 121.73 h), and the median time to C_max was 0.6 h (range, 0.5 to 2.5 h). The fraction unbound in the plasma was 0.06 ± 0.02. All patients achieved C_max/MIC and AUC from time zero to 24 h (AUC_0-24)/MIC ratios for a bacteriostatic effect against Streptococcus pneumoniae. Twenty-seven patients (93%) achieved a C_max/MIC ratio for a bacteriostatic effect against S. aureus, and 28 patients (97%) achieved an AUC_0-24/MIC ratio for a bacteriostatic effect against S. aureus. Free plasma daptomycin concentrations were above the MIC for 50 to 100% of the dosing interval in 100% of patients for S. pneumoniae and 90% of patients for S. aureus. The median time to defervescence was 3 days from the start of daptomycin therapy. In summary, a 6-mg/kg intravenous infusion of daptomycin every 24 h was effective and well tolerated in neutropenic cancer patients.     

Meropenem-RPX7009 Concentrations in Plasma,Epithelial Lining Fluid,and Alveolar Macrophages of Healthy Adult Subjects

The steady-state concentrations of meropenem and the β-lactamase inhibitor RPX7009 in plasma, epithelial lining fluid (ELF), and alveolar macrophage (AM) concentrations were obtained in 25 healthy, nonsmoking adult subjects. Subjects received a fixed combination of meropenem (2 g) and RPX7009 (2 g) administered every 8 h, as a 3-h intravenous infusion, for a total of three doses. A bronchoscopy and bronchoalveolar lavage were performed once in each subject at 1.5, 3.25, 4, 6, or 8 h after the start of the last infusion. Meropenem and RPX7009 achieved a similar time course and magnitude of concentrations in plasma and ELF. The mean pharmacokinetic parameters ± the standard deviations of meropenem and RPX7009 determined from serial plasma concentrations were as follows: C_max = 58.2 ± 10.8 and 59.0 ± 8.4 μg/ml, V_ss = 16.3 ± 2.6 and 17.6 ± 2.6 liters; CL = 11.1 ± 2.1 and 10.1 ± 1.9 liters/h, and t_1/2 = 1.03 ± 0.15 and 1.27 ± 0.21 h, respectively. The intrapulmonary penetrations of meropenem and RPX7009 were ca. 63 and 53%, respectively, based on the area under the concentration-time curve from 0 to 8 h (AUC_0–8) values of ELF and total plasma concentrations. When unbound plasma concentrations were considered, ELF penetrations were 65 and 79% for meropenem and RPX7009, respectively. Meropenem concentrations in AMs were below the quantitative limit of detection, whereas median concentrations of RPX7009 in AMs ranged from 2.35 to 6.94 μg/ml. The results from the present study lend support to exploring a fixed combination of meropenem (2 g) and RPX7009 (2 g) for the treatment of lower respiratory tract infections caused by meropenem-resistant Gram-negative pathogens susceptible to the combination of meropenem-RPX7009.     

In Vivo Activity of Cefquinome against Escherichia coli in the Thighs of Neutropenic Mice

Cefquinome is a cephalosporin with broad-spectrum antibacterial activity, including activity against enteric Gram-negative bacilli such as Escherichia coli. We utilized a neutropenic mouse model of colibacillosis to examine the pharmacodynamic (PD) characteristics of cefquinome, as measured by organism number in homogenized thigh cultures after 24 h of therapy. Serum drug levels following 4-fold-escalating single doses of cefquinome were measured by liquid chromatography-tandem mass spectrometry (LC-MS/MS). The pharmacokinetic (PK) properties of cefquinome were linear over a dose range of 10 to 640 mg/kg of body weight. Serum half-lives ranged from 0.29 to 0.32 h. Dose fractionation studies over a 24-h dose range of 2.5 to 320 mg/kg were conducted every 3, 6, 12, or 24 h. Nonlinear regression analysis was used to determine which pharmacodynamic parameter best correlated with efficacy. The free percentage of the dosing interval that the serum levels exceed the MIC (fT_>MIC) was the PK-PD index that best correlated with efficacy (R² = 73% for E. coli, compared with 13% for the maximum concentration of the free drug in serum [fC_max]/MIC and 45% for the free-drug area under the concentration-time curve from 0 to 24 h [fAUC_0-24]/MIC). Subsequently, we employed a similar dosing strategy by using 4-fold-increasing total cefquinome doses administered every 4 h to treat animals infected with four additional E. coli isolates. A sigmoid maximum-effect (E_max) model was used to estimate the magnitudes of the %fT_>MIC associated with net bacterial stasis, a 1-log₁₀ CFU reduction from baseline, and a 2-log₁₀ CFU reduction from baseline; the corresponding values were 28.01% ± 2.27%, 37.23% ± 4.05%, and 51.69% ± 9.72%. The potent bactericidal activity makes cefquinome an attractive option for the treatment of infections caused by E. coli.     

An Open,Randomized, Single-Center,Crossover Pharmacokinetic Study of Meropenem after Intraperitoneal and Intravenous Administration in Patients Receiving Automated Peritoneal Dialysis

The objective of this study was to determine the pharmacokinetic profile of meropenem in automated peritoneal dialysis (APD) patients. In 6 patients without peritonitis, a single dose of 0.5 g of meropenem was applied intraperitoneally (i.p.) or intravenously (i.v.) and concentrations in serum and dialysate were measured at specified intervals over 24 h with high-performance liquid chromatography-mass spectrometry. The mean maximum concentrations of meropenem in serum (C_max) were 27.2 mg/liter (standard deviation [SD], ±6.9) and 10.1 mg/liter (SD, ±2.5) and in dialysate were 3.6 mg/liter (SD, ±2.3) and 185.8 mg/liter (SD, ±18.7) after i.v. and i.p. administrations, respectively. The mean areas under the curve from 0 to 24 (AUC_0–24) of meropenem in serum were 173.5 mg · h/liter (SD, ±29.7) and 141.4 mg · h/liter (SD, ±37.5) (P = 0.046) and in dialysate were 42.6 mg · h/liter (SD, ±20.0) and 623.4 mg · h/liter (SD, ±84.1) (P = 0.028) after i.v. and i.p. administrations, respectively. The ratios for dialysate exposure over plasma exposure after i.v. and i.p. treatments were 0.2 (SD, ±0.1) and 4.6 (SD, ±0.9), respectively (P = 0.031). A mean target value of 40% T>MIC (time for which the free meropenem concentration exceeds the MIC) for clinically relevant pathogens with EUCAST susceptibility breakpoints of 2 mg/liter was reached in serum after i.p. and i.v. administrations and in dialysate after i.p. but not after i.v. administration. The present data indicate that low i.p. exposure limits the i.v. use of meropenem for PD-associated peritonitis. In contrast, i.p. administration not only results in superior concentrations in dialysate but also might be used to treat systemic infections.     

Repeated-Dose Pharmacokinetics of an Oral Solution of Itraconazole in Infants and Children

The safety, tolerability, and pharmacokinetics of an oral solution of itraconazole and its active metabolite hydroxyitraconazole were investigated in an open multicenter study of 26 infants and children aged 6 months to 12 years with documented mucosal fungal infections or at risk for the development of invasive fungal disease. The most frequent underlying illness was acute lymphoblastic leukemia, except in the patients aged 6 months to 2 years, of whom six were liver transplant recipients. The patients were treated with itraconazole at a dosage of 5 mg/kg of body weight once daily for 2 weeks. Blood samples were taken after the first dose, during treatment, and up to 8 days after the last itraconazole dose. On day 1, the mean peak concentrations in plasma after the first and last doses (C_max) and areas under the concentration-time curve from 0 to 24 h (AUC_0–24) for itraconazole and hydroxyitraconazole were lower in the children aged 6 months to 2 years than in children aged 2 to 12 years but were comparable on day 14. The mean AUC_0–24-based accumulation factors of itraconazole and hydroxyitraconazole from day 1 to 14 ranged from 3.3 to 8.6 and 2.3 to 11.4, respectively. After 14 days of treatment, C_max, AUC_0–24, and the half-life, respectively, were (mean ± standard deviation) 571 ± 416 ng/ml, 6,930 ± 5,830 ng · h/ml, and 47 ± 55 h in the children aged 6 months to 2 years; 534 ± 431 ng/ml, 7,330 ± 5,420 ng · h/ml, and 30.6 ± 25.3 h in the children aged 2 to 5 years; and 631 ± 358 ng/ml, 8,770 ± 5,050 ng · h/ml, and 28.3 ± 9.6 h in the children aged 5 to 12 years. There was a tendency to have more frequent low minimum concentrations of the drugs in plasma for both itraconazole and hydroxyitraconazole for the children aged 6 months to 2 years. The oral bioavailability of the solubilizer hydroxypropyl-β-cyclodextrin was less than 1% in the majority of the patients. In conclusion, an itraconazole oral solution given at 5 mg/kg/day provides potentially therapeutic concentrations in plasma, which are, however, substantially lower than those attained in adult cancer patients, and is well tolerated and safe in infants and children.     

Intracellular time course, pharmacokinetics, and biodistribution of isoniazid and rifabutin following pulmonary delivery of inhalable microparticles to mice

Intracellular concentrations of isoniazid and rifabutin resulting from administration of inhalable microparticles of these drugs to phorbol-differentiated THP-1 cells and the pharmacokinetics and biodistribution of these drugs upon inhalation of microparticles or intravenous administration of free drugs to mice were investigated. In cultured cells, both microparticles and dissolved drugs established peak concentrations of isoniazid (~1.4 and 1.1 μg/10⁶ cells) and rifabutin (~2 μg/ml and ~1.4 μg/10⁶ cells) within 10 min. Microparticles maintained the intracellular concentration of isoniazid for 24 h and rifabutin for 96 h, whereas dissolved drugs did not. The following pharmacokinetic parameters were calculated using WinNonlin from samples obtained after inhalation using an in-house apparatus (figures in parentheses refer to parameters obtained after intravenous administration of an equivalent amount, i.e., 100 μg of either drug, to parallel groups): isoniazid, serum half-life (t_1/2) = 18.63 ± 5.89 h (3.91 ± 1.06 h), maximum concentration in serum (C_max) = 2.37 ± 0.23 μg·ml⁻¹ (3.24 ± 0.57 μg·ml⁻¹), area under the concentration-time curve from 0 to 24 h (AUC_0-24) = 55.34 ± 13.72 μg/ml⁻¹ h⁻¹ (16.64 ± 1.80 μg/ml⁻¹ h⁻¹), and clearance (CL) = 63.90 ± 13.32 ml·h⁻¹ (4.43 ± 1.85 ml·h⁻¹); rifabutin, t_1/2 = 119.49 ± 29.62 h (20.18 ± 4.02 h), C_max = 1.59 ± 0.01 μg·ml⁻¹ (3.47 ± 0.33 μg·ml⁻¹), AUC_0-96 = 109.35 ± 14.78 μg/ml⁻¹ h⁻¹ (90.82 ± 7.46 μg/ml⁻¹ h⁻¹), and CL = 11.68 ± 7.00 ml·h⁻¹ (1.03 ± 0.11 ml·h⁻¹). Drug targeting to the lungs in general and alveolar macrophages in particular was observed. It was concluded that inhaled microparticles can reduce dose frequency and improve the pharmacologic index of the drug combination.     

Moxifloxacin Pharmacokinetics and Pleural Fluid Penetration in Patients with Pleural Effusion

The aim of this study was to evaluate the pharmacokinetics and penetration of moxifloxacin (MXF) in patients with various types of pleural effusion. Twelve patients with empyema/parapneumonic effusion (PPE) and 12 patients with malignant pleural effusion were enrolled in the study. A single-dose pharmacokinetic study was performed after intravenous administration of 400 mg MXF. Serial plasma (PL) and pleural fluid (PF) samples were collected during a 24-h time interval after drug administration. The MXF concentration in PL and PF was determined by high-performance liquid chromatography, and main pharmacokinetic parameters were estimated. Penetration of MXF in PF was determined by the ratio of the area under the concentration-time curve from time zero to 24 h (AUC₂₄) in PF (AUC_24PF) to the AUC₂₄ in PL. No statistically significant differences in the pharmacokinetics in PL were observed between the two groups, despite the large interindividual variability in the volume of distribution, clearance, and elimination half-life. The maximum concentration in PF (Cmax_PF) in patients with empyema/PPE was 2.23 ± 1.31 mg/liter, and it was detected 7.50 ± 2.39 h after the initiation of the infusion. In patients with malignant effusion, Cmax_PF was 2.96 ± 1.45 mg/liter, but it was observed significantly earlier, at 3.58 ± 1.38 h (P < 0.001). Both groups revealed similar values of AUC_24PF (31.83 ± 23.52 versus 32.81 ± 12.66 mg · h/liter). Penetration of MXF into PF was similarly good in both patient groups (1.11 ± 0.74 versus 1.17 ± 0.39). Despite similar plasma pharmacokinetics, patients with empyema/parapneumonic effusion showed a significant delay in achievement of PF maximum MXF levels compared to those with malignant effusion. However, in both groups, the degree of MXF PF penetration and the on-site drug exposure, expressed by AUC_24PF, did not differ according to the type of pleural effusion.     

Pharmacokinetics of Antituberculosis Drugs in HIV-Positive and HIV-Negative Adults in Malawi

Limited data address the impact of HIV coinfection on the pharmacokinetics (PK) of antituberculosis drugs in sub-Saharan Africa. A total of 47 Malawian adults underwent rich pharmacokinetic sampling at 0, 0.5, 1, 2, 3, 4, 6, 8, and 24 h postdose. Of the subjects, 51% were male, their mean age was 34 years, and 65% were HIV-positive with a mean CD4 count of 268 cells/μl. Antituberculosis drugs were administered as fixed-dose combinations (150 mg rifampin, 75 mg isoniazid, 400 mg pyrazinamide, and 275 mg ethambutol) according to recommended weight bands. Plasma drug concentrations were determined by high-performance liquid chromatography (rifampin and pyrazinamide) or liquid chromatography-mass spectrometry (isoniazid and ethambutol). Data were analyzed by noncompartmental methods and analysis of variance of log-transformed summary parameters. The pharmacokinetic parameters were as follows (median [interquartile range]): for rifampin, maximum concentration of drug in plasma (C_max) of 4.129 μg/ml (2.474 to 5.596 μg/ml), area under the curve from 0 to 24 h (AUC_0–∞) of 21.32 μg/ml · h (13.57 to 28.60 μg/ml · h), and half-life of 2.45 h (1.86 to 3.08 h); for isoniazid, C_max of 3.97 μg/ml (2.979 to 4.544 μg/ml), AUC_0–24 of 22.5 (14.75 to 34.59 μg/ml · h), and half-life of 3.93 h (3.18 to 4.73 h); for pyrazinamide, C_max of 34.21 μg/ml (30.00 to 41.60 μg/ml), AUC_0–24 of 386.6 μg/ml · h (320.0 to 463.7 μg/ml · h), and half-life of 6.821 h (5.71 to 8.042 h); and for ethambutol, C_max of 2.278 μg/ml (1.694 to 3.098 μg/ml), AUC_0–24 of 20.41 μg/ml · h (16.18 to 26.27 μg/ml · h), and half-life of 7.507 (6.517 to 8.696 h). The isoniazid PK data analysis suggested that around two-thirds of the participants were slow acetylators. Dose, weight, and weight-adjusted dose were not significant predictors of PK exposure, probably due to weight-banded dosing. In this first pharmacokinetic study of antituberculosis drugs in Malawian adults, measures of pharmacokinetic exposure were comparable with those of other studies for all first-line drugs except for rifampin, for which the C_max and AUC_0–24 values were notably lower. Contrary to some earlier observations, HIV status did not significantly affect the AUC of any of the drugs. Increasing the dose of rifampin might be beneficial in African adults, irrespective of HIV status. Current co-trimoxazole prophylaxis was associated with an increase in the half-life of isoniazid of 41% (P = 0.022). Possible competitive interactions between isoniazid and sulfamethoxazole mediated by the N-acetyltransferase pathway should therefore be explored further.     

Nutritional Supplementation Increases Rifampin Exposure among Tuberculosis Patients Coinfected with HIV

Nutritional supplementation to tuberculosis (TB) patients has been associated with increased weight and reduced mortality, but its effect on the pharmacokinetics of first-line anti-TB drugs is unknown. A cohort of 100 TB patients (58 men; median age, 35 [interquartile range {IQR}, 29 to 40] years, and median body mass index [BMI], 18.8 [17.3 to 19.9] kg/m²) were randomized to receive nutritional supplementation during the intensive phase of TB treatment. Rifampin plasma concentrations were determined after 1 week and 2 months of treatment. The effects of nutritional supplementation, HIV, time on treatment, body weight, and SLCO1B1 rs4149032 genotype were examined using a population pharmacokinetic model. The model adjusted for body size via allometric scaling, accounted for clearance autoinduction, and detected an increase in bioavailability (+14%) for the patients in the continuation phase. HIV coinfection in patients not receiving the supplementation was found to decrease bioavailability by 21.8%, with a median maximum concentration of drug in serum (C_max) and area under the concentration-time curve from 0 to 24 h (AUC_0–24) of 5.6 μg/ml and 28.6 μg · h/ml, respectively. HIV-coinfected patients on nutritional supplementation achieved higher C_max and AUC_0–24 values of 6.4 μg/ml and 31.6 μg · h/ml, respectively, and only 13.3% bioavailability reduction. No effect of the SLCO1B1 rs4149032 genotype was observed. In conclusion, nutritional supplementation during the first 2 months of TB treatment reduces the decrease in rifampin exposure observed in HIV-coinfected patients but does not affect exposure in HIV-uninfected patients. If confirmed in other studies, the use of defined nutritional supplementation in HIV-coinfected TB patients should be considered in TB control programs. (This study has the controlled trial registration number ISRCTN 16552219.)     

Ceftolozane-Tazobactam Pharmacokinetics in a Critically Ill Patient on Continuous Venovenous Hemofiltration

Extended-infusion ceftolozane-tazobactam treatment at 1.5 g every 8 h was used to treat multidrug-resistant Pseudomonas aeruginosa in a critically ill patient on continuous venovenous hemofiltration. Serum drug concentrations were measured at 1, 4, 5, 6, and 8 h after the start of infusion. Prefilter levels of ceftolozane produced a maximum concentration of drug (C_max) of 38.57 μg/ml, concentration at the end of the dosing interval (C_min) of 31.63 μg/ml, time to C_max (T_max) of 4 h, area under the concentration-time curve from 0 to 8 h (AUC_0–8) of 284.38 μg · h/ml, and a half-life (t_1/2) of 30.7 h. The concentrations were eight times the susceptibility breakpoint for the entire dosing interval.     

Pharmacokinetics and Safety of Ofloxacin in Children with Drug-Resistant Tuberculosis

Ofloxacin is widely used for the treatment of multidrug-resistant tuberculosis (MDR-TB). Data on its pharmacokinetics and safety in children are limited. It is not known whether the current internationally recommended pediatric dosage of 15 to 20 mg/kg of body weight achieves exposures reached in adults with tuberculosis after a standard 800-mg dose (adult median area under the concentration-time curve from 0 to 24 h [AUC_0–24], 103 μg · h/ml). We assessed the pharmacokinetics and safety of ofloxacin in children <15 years old routinely receiving ofloxacin for MDR-TB treatment or preventive therapy. Plasma samples were collected predose and at 1, 2, 4, 8, and either 6 or 11 h after a 20-mg/kg dose. Pharmacokinetic parameters were calculated using noncompartmental analysis. Children with MDR-TB disease underwent long-term safety monitoring. Of 85 children (median age, 3.4 years), 11 (13%) were HIV infected, and of 79 children with evaluable data, 14 (18%) were underweight. The ofloxacin mean (range) maximum concentration (C_max), AUC_0–8, and half-life were 8.97 μg/ml (2.47 to 14.4), 44.2 μg · h/ml (12.1 to 75.8), and 3.49 h (1.89 to 6.95), respectively. The mean AUC_0–24, estimated in 72 participants, was 66.7 μg · h/ml (range, 18.8 to 120.7). In multivariable analysis, AUC_0–24 was increased by 1.46 μg · h/ml for each 1-kg increase in body weight (95% confidence interval [CI], 0.44 to 2.47; P = 0.006); no other assessed variable contributed to the model. No grade 3 or 4 events at least possibly attributed to ofloxacin were observed. Ofloxacin was safe and well tolerated in children with MDR-TB, but exposures were well below reported adult values, suggesting that dosage modification may be required to optimize MDR-TB treatment regimens in children.     

Pharmacokinetics of Hydroxymethylnitrofurazone,a Promising New Prodrug for Chagas' Disease Treatment

Hydroxymethylnitrofurazone (NFOH) is a trypanocidal prodrug of nitrofurazone (NF), devoid of mutagenic toxicity. The purpose of this work was to study the chemical conversion of NFOH into NF in sodium acetate buffer (pH 1.2 and 7.4) and in human plasma and to determine preclinical pharmacokinetic parameters in rats. At pH 1.2, the NFOH was totally transformed into NF, the parent drug, after 48 h, while at pH 7.4, after the same period, the hydrolysis rate was 20%. In human plasma, 50% of NFOH was hydrolyzed after 24 h. In the investigation of kinetic disposition, the concentration of drug in serum versus time curve was used to calculate the pharmacokinetic parameters after a single-dose regimen. NFOH showed a time to maximum concentration of drug in serum (T_max) as 1 h, suggesting faster absorption than NF (4 h). The most important results observed were the volume of distribution (V) of NFOH through the tissues, which showed a rate that is 20-fold higher (337.5 liters/kg of body weight) than that of NF (17.64 liters/kg), and the concentration of NF obtained by in vivo metabolism of NFOH, which was about four times lower (maximum concentration of drug in serum [C_max] = 0.83 μg/ml; area under the concentration-time curve from 0 to 12 h [AUC_0–12] = 5.683 μg/ml · h) than observed for administered NF (C_max = 2.78 μg/ml; AUC_0–12 = 54.49 μg/ml · h). These findings can explain the superior activity and lower toxicity of the prodrug NFOH in relation to its parent drug and confirm NFOH as a promising anti-Chagas'' disease drug candidate.     

Metronidazole and Hydroxymetronidazole Central Nervous System Distribution: 1. Microdialysis Assessment of Brain Extracellular Fluid Concentrations in Patients with Acute Brain Injury

The distribution of metronidazole in the central nervous system has only been described based on cerebrospinal fluid data. However, extracellular fluid (ECF) concentrations may better predict its antimicrobial effect and/or side effects. We sought to explore by microdialysis brain ECF metronidazole distribution in patients with acute brain injury. Four brain-injured patients monitored by cerebral microdialysis received 500 mg of metronidazole over 0.5 h every 8 h. Brain dialysates and blood samples were collected at steady state over 8 h. Probe recoveries were evaluated by in vivo retrodialysis in each patient for metronidazole. Metronidazole and OH-metronidazole were assayed by high-pressure liquid chromatography, and a noncompartmental pharmacokinetic analysis was performed. Probe recovery was equal to 78.8% ± 1.3% for metronidazole in patients. Unbound brain metronidazole concentration-time curves were delayed compared to unbound plasma concentration-time curves but with a mean metronidazole unbound brain/plasma AUC_0–τ ratio equal to 102% ± 19% (ranging from 87 to 124%). The unbound plasma concentration-time profiles for OH-metronidazole were flat, with mean average steady-state concentrations equal to 4.0 ± 0.7 μg ml⁻¹. This microdialysis study describes the steady-state brain distribution of metronidazole in patients and confirms its extensive distribution.     

Double-Blind Evaluation of the Safety and Pharmacokinetics of Multiple Oral Once-Daily 750-Milligram and 1-Gram Doses of Levofloxacin in Healthy Volunteers

The safety and pharmacokinetics of once-daily oral levofloxacin in 16 healthy male volunteers were investigated in a randomized, double-blind, placebo-controlled study. Subjects were randomly assigned to the treatment (n = 10) or placebo group (n = 6). In study period 1, 750 mg of levofloxacin or a placebo was administered orally as a single dose on day 1, followed by a washout period on days 2 and 3; dosing resumed for days 4 to 10. Following a 3-day washout period, 1 g of levofloxacin or a placebo was administered in a similar fashion in period 2. Plasma and urine levofloxacin concentrations were measured by high-pressure liquid chromatography. Pharmacokinetic parameters were estimated by model-independent methods. Levofloxacin was rapidly absorbed after single and multiple once-daily 750-mg and 1-g doses with an apparently large volume of distribution. Peak plasma levofloxacin concentration (C_max) values were generally attained within 2 h postdose. The mean values of C_max and area under the concentration-time curve from 0 to 24 h (AUC_0–24) following a single 750-mg dose were 7.1 μg/ml and 71.3 μg · h/ml, respectively, compared to 8.6 μg/ml and 90.7 μg · h/ml, respectively, at steady state. Following the single 1-g dose, mean C_max and AUC_0–24 values were 8.9 μg/ml and 95.4 μg · h/ml, respectively; corresponding values at steady state were 11.8 μg/ml and 118 μg · h/ml. These C_max and AUC_0–24 values indicate modest and similar degrees of accumulation upon multiple dosing at the two dose levels. Values of apparent total body clearance (CL/F), apparent volume of distribution (V_ss/F), half-life (t_1/2), and renal clearance (CL_R) were similar for the two dose levels and did not vary from single to multiple dosing. Mean steady-state values for CL/F, V_ss/F, t_1/2, and CL_R following 750 mg of levofloxacin were 143 ml/min, 100 liters, 8.8 h, and 116 ml/min, respectively; corresponding values for the 1-g dose were 146 ml/min, 105 liters, 8.9 h, and 105 ml/min. In general, the pharmacokinetics of levofloxacin in healthy subjects following 750-mg and 1-g single and multiple once-daily oral doses appear to be consistent with those found in previous studies of healthy volunteers given 500-mg doses. Levofloxacin was well tolerated at either high dose level. The most frequently reported drug-related adverse events were nausea and headache.     

Therapy of Pseudomonas aeruginosa Infections with Tobramycin

The efficacy of tobramycin in doses of 2.7 to 5.6 mg/kg per day in 29 courses of therapy in 25 hospitalized patients with serious Pseudomonas aeruginosa infections was studied. Eighty-three percent of the P. aeruginosa strains showed zones of inhibition of 16 mm or more around a 10-μg tobramycin disk in the Bauer-Kirby disk method. Tobramycin minimal inhibitory concentration ranged from <0.05 to 1.5 μg/ml (microtiter twofold dilution method); for gentamicin they ranged from 0.05 to 6.2 μg/ml; corresponding geometric means were 0.19 and 0.49 μg/ml. Therapy was given for a median of 10 days (mean 19, range 1 to 83). The clinically satisfactory response rate for the 29 courses of therapy was 52%: critically ill, 44%; seriously ill, 50%; moderately ill, 80%. The response rates for various sites of infection were bone and cartilage, 100%; urinary tract infection, 56%; wound, 50%; respiratory tract, 67%; septicemia, 40%; abscess, 0%; burns, 44%. No adverse reactions were seen. Serum concentration (μg/ml ± standard deviation) of tobramycin determined by an agar-well plate method, were 4.81 ± 2.17 (1 h); 3.24 ± 1.43 (2 h); 2.35 ± 1.30 (4 h); and 1.40 ± 1.09 (8 h). Tobramycin appears to be as effacacious as gentamicin in the treatment of serious P. aeruginosa infections and has a theoretical advantage of lower minimal inhibitory concentration for P. aeruginosa. The data suggest that, for life-threatening infections, dosages of tobramycin may need to be increased over those used in this study.     

Penetration of GSK1322322 into Epithelial Lining Fluid and Alveolar Macrophages as Determined by Bronchoalveolar Lavage

GSK1322322 is a potent peptide deformylase inhibitor with in vitro and in vivo activity against multidrug-resistant skin and respiratory pathogens. This report provides plasma and intrapulmonary pharmacokinetics, safety, and tolerability of GSK1322322 after repeat (twice daily intravenous dosing for 4 days) dosing at 1,500 mg. Plasma samples were collected over the last 12-hour dosing interval of repeat dosing following the day 4 morning dose (the last dose). Bronchoalveolar lavage samples were collected once in each subject, either before or at 2 or 6 h after the last intravenous dose. Plasma area under the concentration-time curve (AUC_0–τ) was 66.7 μg · h/ml, and maximum concentration of drug in serum (C_max) was 25.4 μg/ml following repeat doses of intravenous GSK1322322. The time course of epithelial lining fluid (ELF) and alveolar macrophages (AM) mirrored the plasma concentration-time profile. The AUC_0–τ for ELF and AM were 78.9 μg · h/ml and 169 μg · h/ml, respectively. The AUC_0–τ ratios of ELF and AM to total plasma were 1.2 and 2.5, respectively. These ratios increased to 3.5 and 7.4, respectively, when unbound plasma was considered. These results are supportive of GSK1322322 as a potential antimicrobial agent for the treatment of lower respiratory tract bacterial infections caused by susceptible pathogens. (This study has been registered at ClinicalTrials.gov under registration number {"type":"clinical-trial","attrs":{"text":"NCT01610388","term_id":"NCT01610388"}}NCT01610388.)     

Metronidazole and Hydroxymetronidazole Central Nervous System Distribution: 2. Cerebrospinal Fluid Concentration Measurements in Patients with External Ventricular Drain

This study explored metronidazole and hydroxymetronidazole distribution in the cerebrospinal fluid (CSF) of brain-injured patients. Four brain-injured patients with external ventricular drain received 500 mg of metronidazole over 0.5 h every 8 h. CSF and blood samples were collected at steady state over 8 h, and the metronidazole and hydroxymetronidazole concentrations were assayed by high-pressure liquid chromatograph. A noncompartmental analysis was performed. Metronidazole is distributed extensively within CSF, with a mean CSF to unbound plasma AUC_0–τ ratio of 86% ± 16%. However, the concentration profiles in CSF were mostly flat compared to the plasma profiles. Hydroxymetronidazole concentrations were much lower than those of metronidazole both in plasma and in CSF, with a corresponding CSF/unbound plasma AUC_0–τ ratio of 79% ± 16%. We describe here for the first time in detail the pharmacokinetics of metronidazole and hydroxymetronidazole in CSF.     

Theory-based analysis of clinical efficacy of triptans using receptor occupancy

Background

Triptans, serotonin 5-HT_1B/1D receptor agonists, exert their action by targeting serotonin 5-HT_1B/1D receptors, are used for treatment of migraine attack. Presently, 5 different triptans, namely sumatriptan, zolmitriptan, eletriptan, rizatriptan, and naratriptan, are marketed in Japan. In the present study, we retrospectively analyzed the relationships of clinical efficacy (headache relief) in Japanese and 5-HT_1B/1D receptor occupancy (Φ_1B and Φ_1D). Receptor occupancies were calculated from both the pharmacokinetic and pharmacodynamic data of triptans.

Methods

To evaluate the total amount of exposure to drug, we calculated the area under the plasma concentration-time curve (AUC_cp) and the areas under the time curves for Ф_1B and Ф_1D (AUC_Ф^1B and AUC_Ф^1D). Moreover, parameters expressing drug transfer and binding rates (A _cp , A _Ф ^1B , A _Ф ^1D ) were calculated.

Results

Our calculations showed that Ф_max^1B and Ф_max^1D were relatively high at 32.0-89.4% and 68.4-96.2%, respectively, suggesting that it is likely that a high occupancy is necessary to attain the clinical effect. In addition, the relationships between therapeutic effect and AUC_cp, AUC_Φ^1B, AUC_Φ^1D, and A _cp  · AUC_cp differed with each drug and administered form, whereas a significant relationship was found between the therapeutic effect and A _Φ ^1B  · AUC_Φ^1B or A _Φ ^1D  · AUC_Φ^1D that was not affected by the drug and the form of administration.

Conclusions

These results suggest that receptor occupancy can be used as a parameter for a common index to evaluate the therapeutic effect. We considered that the present findings provide useful information to support the proper use of triptans.