Low attainment to PK/PD-targets for ß-lactams in a multi-center study on the first 72 h of treatment in ICU patients.

Severe infections are life-threatening conditions commonly seen in the intensive care units (ICUs). Antibiotic treatment with adequate concentrations is of great importance during the first days when the bacterial load is the highest. Therapeutic drug monitoring (TDM) of ß-lactam antibiotics has been suggested to monitor target attainment and to improve the outcome. This prospective multi-center study in seven ICUs in Sweden investigated pharmacokinetic/pharmacodynamic-target (PK/PD-target) attainment for cefotaxime, piperacillin-tazobactam and meropenem, commonly used ß-lactams in Sweden. A mid-dose and trough antibiotic concentration blood sample were taken from patients with severe infection daily during the first 72 h of treatment. Antibiotic plasma concentrations were analysed by liquid chromatography-mass spectrometry (LC-MS). Antibiotic concentrations 100% time above MIC (minimal inhibitory concentration), (100% T > MIC) and four times above MIC 50% of the time (50% T > 4xMIC) were used as PK/PD-targets. We included 138 patients with the median age of 67 years and the median Simplified Acute Physiology Score 3 (SAPS3) of 59. Forty-five percent of the study-population failed to reach 100% T > MIC during the first day of treatment. The results were similar the following two days. There was a three-fold risk of not meeting the PK/PD target if the patient was treated with cefotaxime. For the cefotaxime treated patients 8 out of 55 (15%) had at least one end-dose concentrations below the level of detection during the study. Low age, low illness severity, low plasma creatinine, lower respiratory tract infection and cefotaxime treatment were risk factors for not reaching 100% T > MIC. In Swedish ICU-patients treated with ß-lactam antibiotics, a high proportion of patients did not reach the PK/PD target. TDM could identify patients that need individual higher dosing regimens already on the first day of treatment. Further studies on optimal empirical start dosing of ß-lactams, especially for cefotaxime, in the ICU are needed.Trial registration: The protocol was retrospectively registered 100216 (ACTRN12616000167460).

Individualised dosing algorithm and personalised treatment of high-dose rifampicin for tuberculosis.

AIMS: To propose new exposure targets for Bayesian dose optimisation suited for high-dose rifampicin and to apply them using measured plasma concentrations coupled with a Bayesian forecasting algorithm allowing predictions of future doses, considering rifampicin's auto-induction, saturable pharmacokinetics and high interoccasion variability. METHODS: Rifampicin exposure targets for Bayesian dose optimisation were defined based on literature data on safety and anti-mycobacterial activity in relation to rifampicin's pharmacokinetics i.e. highest plasma concentration up to 24 hours and area under the plasma concentration-time curve up to 24 hours (AUC0-24h ). Targets were suggested with and without considering minimum inhibitory concentration (MIC) information. Individual optimal doses were predicted for patients treated with rifampicin (10 mg/kg) using the targets with Bayesian forecasting together with sparse measurements of rifampicin plasma concentrations and baseline rifampicin MIC. RESULTS: The suggested exposure target for Bayesian dose optimisation was a steady state AUC0-24h of 181-214 h × mg/L. The observed MICs ranged from 0.016-0.125 mg/L (mode: 0.064 mg/L). The predicted optimal dose in patients using the suggested target ranged from 1200-3000 mg (20-50 mg/kg) with a mode of 1800 mg (30 mg/kg, n = 24). The predicted optimal doses when taking MIC into account were highly dependent on the known technical variability of measured individual MIC and the dose was substantially lower compared to when using the AUC0-24h -only target. CONCLUSIONS: A new up-to-date exposure target for Bayesian dose optimisation suited for high-dose rifampicin was derived. Using measured plasma concentrations coupled with Bayesian forecasting allowed prediction of the future dose whilst accounting for the auto-induction, saturable pharmacokinetics and high between-occasion variability of rifampicin.

Serum levels of 25-hydroxyvitamin D and the CYP3A biomarker 4ß-hydroxycholesterol in a high-dose vitamin D supplementation study.

The primary aim was to study the relationship between individual serum levels of 25-hydroxyvitamin D and 4ß-hydroxycholesterol, which is an endogenous biomarker of the drug-metabolizing CYP3A enzymes. In addition, the relationship between this biomarker and inflammation, measured as C-reactive protein (CRP), was investigated. Serum samples were used from a recently performed clinical trial in patients with antibody deficiency or increased susceptibility to respiratory tract infections that were randomized to either placebo or high-dose (4000 IU/day) vitamin D for 12 months. One hundred sixteen patients were included in the final analyses, and serum samples collected 6 months after study start were analyzed. At this time point, 25-hydroxyvitamin D levels were found to range between 10 and 284 nM. Individual levels of 25-hydroxyvitamin D as well as CRP were compared with 4ß-hydroxycholesterol levels. In addition, all participants were genotyped for two polymorphisms (Taq1 and Foq1) in the vitamin D receptor gene. There was no significant correlation between individual serum levels of 25-hydroxyvitamin D and 4ß-hydroxycholesterol. However, a moderate, but statistically significant, negative correlation between CRP and 4ß-hydroxycholesterol levels was observed. This study in patients with highly variable serum levels of 25-hydroxyvitamin D could not reveal any relationship between vitamin D and 4ß-hydroxycholesterol, an endogenous biomarker of CYP3A activity. However, the negative correlation between CRP and 4ß-hydroxycholesterol supports earlier experimental results that inflammation may suppress hepatic CYP3A activity, a finding of potentially high clinical relevance that warrants further exploration.

Use of molecular simulation for mapping conformational CYP2E1 epitopes.

The identification of the epitopes recognized by autoantibodies against cytochrome P450s (CYPs) associated with drug-induced hepatotoxicity is difficult because of their conformational nature. In the present investigation, we used a novel approach based on the analysis of the whole molecule antigenic capacity following single amino acid substitutions to identify the conformational epitopes on CYP2E1. A molecular model of CYP2E1 was generated based on the CYP2C5 crystal structure, and potential motifs for amino acid exchanges were selected by computer simulation in the surface of alpha helices and beta sheets. Fourteen modified, apparently correctly folded CYP2E1 variants were produced in Escherichia coli and evaluated in immunoprecipitation experiments using sera with anti-CYP2E1 autoreactivity from 10 patients with halothane hepatitis and 12 patients with alcoholic liver disease. Ala substitution of Glu-248 and Lys-251 as well as of Lys-324, Lys-342, Lys-420, and Phe-421 severely decreased or abolished CYP2E1 recognition by the majority of both the halothane hepatitis and alcoholic liver disease sera, whereas the other substitutions had only minor effects. Based on the structural model, these substitutions identified two distinct epitopes on the CYP2E1 surface corresponding to the G-helix and an area formed by juxtaposition of the J' and K'' helices, respectively. The combined use of molecular modeling and single amino acid mutagenesis is thus a useful approach for the characterization of conformational epitopes recognized by autoantibodies.