Population Pharmacokinetics of Meropenem in Plasma and Subcutis from Patients on Extracorporeal Membrane Oxygenation Treatment.

The objectives of this study were to describe meropenem pharmacokinetics (PK) in plasma and/or subcutaneous adipose tissue (SCT) in critically ill patients receiving extracorporeal membrane oxygenation (ECMO) treatment and to develop a population PK model to simulate alternative dosing regimens and modes of administration. We conducted a prospective observational study. Ten patients on ECMO treatment received meropenem (1 or 2 g) intravenously over 5 min every 8 h. Serial SCT concentrations were determined using microdialysis and compared with plasma concentrations. A population PK model of SCT and plasma data was developed using NONMEM. Time above clinical breakpoint MIC for Pseudomonas aeruginosa (8 mg/liter) was predicted for each patient. The following targets were evaluated: time for which the free (unbound) concentration is maintained above the MIC of at least 40% (40% fT>MIC), 100% fT>MIC, and 100% fT>4×MIC. For all dosing regimens simulated in both plasma and SCT, 40% fT>MIC was attained. However, prolonged meropenem infusion would be needed for 100% fT>MIC and 100% fT>4×MIC to be obtained. Meropenem plasma and SCT concentrations were associated with estimated creatinine clearance (eCLCr). Simulations showed that in patients with increased eCLCr, dose increment or continuous infusion may be needed to obtain therapeutic meropenem concentrations. In conclusion, our results show that using traditional targets of 40% fT>MIC for standard meropenem dosing of 1 g intravenously every 8 h is likely to provide sufficient meropenem concentration to treat the problematic pathogen P. aeruginosa for patients receiving ECMO treatment. However, for patients with an increased eCLCr, or if more aggressive targets, like 100% fT>MIC or 100% fT>4×MIC, are adopted, incremental dosing or continuous infusion may be needed.

Penicillin G Treatment in Infective Endocarditis Patients - Does Standard Dosing Result in Therapeutic Plasma Concentrations?

Penicillin G is frequently used to treat infective endocarditis (IE) caused by streptococci, penicillin-susceptible staphylococci and enterococci. Appropriate antibiotic exposure is essential for survival and reduces the risk of complications and drug resistance development. We determined penicillin G plasma concentration [p-penicillin] once weekly in 46 IE patients. The aim was to evaluate whether penicillin G 3 g every 6 hr (q6 h) resulted in therapeutic concentrations and to analyse potential factors that influence inter- and intra-individual variability, using linear regression and a random coefficient model. [P-penicillin] at 3 hr and at 6 hr was compared with the minimal inhibitory concentration (MIC) of the bacteria isolated from blood cultures to evaluate the following PK/PD targets: 50% fT > MIC and 100% fT > MIC. [P-penicillin] varied notably between patients and was associated with age, weight, p-creatinine and estimated creatinine clearance (eCLcr). Additionally, an increase in [p-penicillin] during the treatment period showed strong correlation with age, a low eCLcr, a low weight and a low p-albumin. Of the 46 patients, 96% had [p-penicillin] that resulted in 50% fT > MIC, while 71% had [p-penicillin] resulting in 100% fT > MIC. The majority of patients not achieving the 100% fT > MIC target were infected with enterococci. Streptococci and staphylococci isolated from blood cultures were highly susceptible to penicillin G. Our results suggest that penicillin G 3 g q6 h is suitable to treat IE caused by streptococci and penicillin-susceptible staphylococci, but caution must be taken when the infection is caused by enterococci. When treating enterococci, therapeutic drug monitoring should be applied to optimize penicillin G dosing and exposure.

Artemether-Lumefantrine Concentrations in Tablets and Powders from Ghana Measured by a New High-Performance Liquid Chromatography Method.

We developed and validated a new analytical method for the simultaneous quantification of artemether and lumefantrine in fixed-dose tablets and powders for reconstitution into pediatric suspensions (PSs). The method showed linearity (r(2) > 0.9947), precision (coefficient of variation < 2%), accuracy (deviation of mean from actual concentrations < 4%), and specificity (peak purities > 99%). The validated method was used to analyze 24 batches of fixed-dose tablets and PSs of artemether and lumefantrine. Of the samples, 23 were obtained using convenience sampling of commonly available brands within Accra in Ghana and one was obtained from Aarhus University Hospital. In all, 83.3% (confidence interval: 80-120%) passed for both artemether and lumefantrine contents, 16.7% failed by the U.S. Pharmacopoeia standards, 8.3% failed for one content, and 8.3% failed for both contents. All four products (16.7%) that failed were PSs, and two (8.3%) showed higher levels of artemether than prescribed (222% and 756%).

Population pharmacokinetics of piperacillin in the early phase of septic shock: does standard dosing result in therapeutic plasma concentrations?

Antibiotic dosing in septic shock patients poses a challenge for clinicians due to the pharmacokinetic (PK) variability seen in this patient population. Piperacillin-tazobactam is often used for empirical treatment, and initial appropriate dosing is crucial for reducing mortality. Accordingly, we determined the pharmacokinetic profile of piperacillin (4 g) every 8 h, during the third consecutive dosing interval, in 15 patients treated empirically for septic shock. We developed a population pharmacokinetic model to assess empirical dosing and to simulate alternative dosing regimens and modes of administration. Time above the MIC (T>MIC) predicted for each patient was evaluated against clinical breakpoint MIC for Pseudomonas aeruginosa (16 mg/liter). Pharmacokinetic-pharmacodynamic (PK/PD) targets evaluated were 50% fT>4×MIC and 100% fT>MIC. A population PK model was developed using NONMEM, and data were best described by a two-compartment model. Central and intercompartmental clearances were 3.6 liters/h (relative standard error [RSE], 15.7%) and 6.58 liters/h (RSE, 16.4%), respectively, and central and peripheral volumes were 7.3 liters (RSE, 11.8%) and 3.9 liters (RSE, 9.7%), respectively. Piperacillin plasma concentrations varied considerably between patients and were associated with levels of plasma creatinine. Patients with impaired renal function were more likely to achieve predefined PK/PD targets than were patients with preserved or augmented renal function. Simulations of alternative dosing regimens showed that frequent intermittent bolus dosing as well as dosing by extended and continuous infusion increases the probability of attaining therapeutic plasma concentrations. For septic shock patients with preserved or augmented renal function, dose increment or prolonged infusion of the drug needs to be considered. (This study has been registered at ClinicalTrials.gov under registration no. NCT02306928.).

Moxifloxacin pharmacokinetic profile and efficacy evaluation in empiric treatment of community-acquired pneumonia.

When antimicrobials are used empirically, pathogen MICs equal to clinical breakpoints or epidemiological cutoff values must be considered. This is to ensure that the most resistant pathogen subpopulation is appropriately targeted to prevent emergence of resistance. Accordingly, we determined the pharmacokinetic (PK) profile of moxifloxacin at 400 mg/day in 18 patients treated empirically for community-acquired pneumonia. We developed a population pharmacokinetic model to assess the potential efficacy of moxifloxacin and to simulate the maximal MICs for which recommended pharmacokinetic-pharmacodynamic (PK-PD) estimates are obtained. Moxifloxacin plasma concentrations were determined the day after therapy initiation using ultra-high-performance liquid chromatography. Peak drug concentrations (Cmax) and area under the free drug concentration-time curve from 0 to 24 h (fAUC0-24) values predicted for each patient were evaluated against epidemiological cutoff MIC values for Streptococcus pneumoniae, Haemophilus influenzae, and Legionella pneumophila. PK-PD targets adopted were a Cmax/MIC of ≥12.2 for all pathogens, an fAUC0-24/MIC of >34 for S. pneumoniae, and an fAUC0-24/MIC of >75 for H. influenzae and L. pneumophila. Individual predicted estimates for Cmax/MIC and fAUC0-24/MIC as well as simulated maximal MICs resulting in target attainment for oral and intravenous administration of the drug were suitable for S. pneumoniae and H. influenzae but not for L. pneumophila. These results indicate that caution must be taken when moxifloxacin is used as monotherapy to treat community-acquired pneumonia caused by L. pneumophila. In conclusion, this report reveals key information relevant to the empirical treatment of community-acquired pneumonia while highlighting the robust and flexible nature of this population pharmacokinetic model to predict therapeutic success. (Clinical Trials Registration no. NCT01983839.).

Pharmacokinetics of cefuroxime in porcine cortical and cancellous bone determined by microdialysis.

Traditionally, the pharmacokinetics of antimicrobials in bone have been investigated using bone biopsy specimens, but this approach suffers from considerable methodological limitations. Consequently, new methods are needed. The objectives of this study were to assess the feasibility of microdialysis (MD) for measuring cefuroxime in bone and to obtain pharmacokinetic profiles for the same drug in porcine cortical and cancellous bone. The measurements were conducted in bone wax sealed and unsealed drill holes in cortical bone and in drill holes in cancellous bone and in subcutaneous tissue. As a reference, the free and total plasma concentrations were also measured. The animals received a bolus of 1,500 mg cefuroxime over 30 min. No significant differences were found between the key pharmacokinetic parameters for sealed and unsealed drill holes in cortical bone. The mean ± standard error of the mean area under the concentration-time curve (AUC) values from 0 to 5 h were 6,013 ± 1,339, 3,222 ± 1086, 2,232 ± 635, and 952 ± 290 min · µg/ml for free plasma, subcutaneous tissue, cancellous bone, and cortical bone, respectively (P < 0.01, analysis of variance). The AUC for cortical bone was also significantly different from that for cancellous bone (P = 0.04). This heterogeneous tissue distribution was also reflected in other key pharmacokinetic parameters. This study validates MD as a suitable method for measuring cefuroxime in bone. Cefuroxime penetration was impaired for all tissues, and bone may not be considered one distinct compartment.

Cobalamin analogues in humans: a study on maternal and cord blood.

BACKGROUND: Haptocorrin (HC) carries cobalamin analogues (CorA), but whether CorA are produced in the body is unknown. All cobalamins (Cbl) to the foetus are delivered by the Cbl-specific protein transcobalamin (TC), and therefore analysis of cord serum for CorA may help to clarify the origin of CorA. METHODS: HC-CorA were quantified in paired samples of cord serum from newborns and serum from mothers (n = 69). RESULTS: The CorA-concentration was higher in cord serum (median = 380, range: 41-780 pmol/L) than in serum from the mothers (median = 160, range: 64-330 pmol/L), (p<0.0001). HPLC-analysis showed CorA-peaks with retention times of 13.5, 14,5 and 16.5 min in samples from both the mother and cord serum. The peak with retention time 16.5 min constituted 24% (mother) and 45% (cord serum) of the total amount CorA, and eluted as does dicyanocobinamide. CONCLUSION: Our results support that CorA in the human body are derived from Cbl.

Assessment of vitamin B(12) absorption based on the accumulation of orally administered cyanocobalamin on transcobalamin.

BACKGROUND: Vitamin B(12), or cobalamin (Cbl), is absorbed in the intestine and transported to the cells bound to transcobalamin (TC). We hypothesize that cyanocobalamin (CNCbl) is absorbed unchanged, thereby allowing measurement of the complex of CNCbl bound to TC (TC-CNCbl) to be used for studying the absorption of the vitamin. METHODS: TC was immunoprecipitated from serum samples obtained from healthy donors at baseline and at 24 h after oral administration of three 9-microg CNCbl doses over 1 day. Cbl was released by treatment with subtilisin Carlsberg. The different forms of Cbl were isolated by HPLC and subsequently quantified with an ELISA-based Cbl assay. RESULTS: At baseline, the median TC-CNCbl concentration was 1 pmol/L (range, 0-10 pmol/L); the intraindividual variation (SD) was 1.6 pmol/L (n = 31). After CNCbl administration, the TC-CNCbl concentration increased significantly (P = 0.0003, paired t-test), whereas no major changes were observed in any of the other Cbl forms bound to TC (n = 10). Only a moderate additional increase in TC-CNCbl was observed with prolonged (5 days) CNCbl administration (n = 10). We designed an absorption test based on measuring TC-CNCbl at baseline and 24 h after CNCbl intake and established a reference interval for the increase in TC-CNCbl (n = 78). The median absolute increase was 23 pmol/L (range, 6-64 pmol/L), and the relative increase was >3-fold. CONCLUSIONS: Our data demonstrate that CNCbl is absorbed unchanged and accumulates on circulating TC. We suggest that measuring TC-CNCbl will improve the assessment of vitamin B(12) absorption.

A new principle for measurement of cobalamin and corrinoids, used for studies of cobalamin analogs on serum haptocorrin.

BACKGROUND: Transcobalamin (TC) and haptocorrin (HC) are serum corrinoid-binding proteins. We developed new methods for measurement of the corrinoids bound to HC and TC. METHODS: TC (n = 10) or HC (n = 138) was immunoprecipitated, and corrinoids were released by enzymatic degradation [subtilisin Carlsberg (EC 3.4.21.62)] of the binding proteins. Binding of the released corrinoids to added unsaturated TC (apoTC) or HC (apoHC) created holoTC (as measure of cobalamins) and holoHC (as measure of corrinoids). holoTC and holoHC were measured by use of ELISA. The amounts of analogs were calculated as the difference between corrinoids and cobalamins. Corrinoids extracted from HC were separated with HPLC after addition of potassium cyanide (n = 3). RESULTS: The corrinoid- and cobalamin-specific assays had a positive linear relation between analyte concentration and assay signal, detection limits of 8 and 4 pmol/L, and imprecision values (CV) of

Enzymatic extraction of cobalamin from monoclonal antibody captured haptocorrin and transcobalamin.

OBJECTIVES: Current extraction methods for cobalamins from serum influence the molecular characteristics of the vitamin. Therefore, an extraction procedure that leaves the cobalamins unchanged is needed. DESIGN AND METHODS: Monoclonal antibodies towards transcobalamin (TC) and haptocorrin (HC) (in house) linked to magnetic microspheres were used for precipitation of the proteins. The cobalamins were subsequently released by degradation of TC or HC with subtilisin Carlsberg (EC.3.4.21.14). RESULTS: Recovery for the extraction of (57)Co-cyanocobalamin ((57)Co-hydroxycobalamin) was higher than 99 (93)% and 92 (93)% from TC and HC respectively (n=10 (3)). No change in retention time and recovery was observed for (57)Co-hydroxycobalamin analyzed with HPLC before and after extraction with subtilisin Carlsberg. Endogenous cobalamin in serum was extracted from TC and HC and measured with routine methods. Enzymatic extracted cobalamin constituted 118-187% of that measured in serum with routine methods (n=16). CONCLUSION: We present a method that allows extraction of cobalamins from their binding proteins without modifying the vitamin. The procedure may be useful especially for extractions aiming at characterizing the cobalamins bound to individual cobalamin binding proteins.