Britt Jansson

Application of a Loading Dose of Colistin Methanesulfonate in Critically Ill Patients: Population Pharmacokinetics, Protein Binding, and Prediction of Bacterial Kill

ABSTRACT A previous pharmacokinetic study on dosing of colistin methanesulfonate (CMS) at 240 mg (3 million units [MU]) every 8 h indicated that colistin has a long half-life, resulting in insufficient concentrations for the first 12 to 48 h after initiation of treatment. A loading dose would therefore be beneficial. The aim of this study was to evaluate CMS and colistin pharmacokinetics following a 480-mg (6-MU) loading dose in critically ill patients and to explore the bacterial kill following the use of different dosing regimens obtained by predictions from a pharmacokinetic-pharmacodynamic model developed from an in vitro study on Pseudomonas aeruginosa. The unbound fractions of colistin A and colistin B were determined using equilibrium dialysis and considered in the predictions. Ten critically ill patients (6 males; mean age, 54 years; mean creatinine clearance, 82 ml/min) with infections caused by multidrug-resistant Gram-negative bacteria were enrolled in the study. The pharmacokinetic data collected after the first and eighth doses were analyzed simultaneously with the data from the previous study (total, 28 patients) in the NONMEM program. For CMS, a two-compartment model best described the pharmacokinetics, and the half-lives of the two phases were estimated to be 0.026 and 2.2 h, respectively. For colistin, a one-compartment model was sufficient and the estimated half-life was 18.5 h. The unbound fractions of colistin in the patients were 26 to 41% at clinical concentrations. Colistin A, but not colistin B, had a concentration-dependent binding. The predictions suggested that the time to 3-log-unit bacterial kill for a 480-mg loading dose was reduced to half of that for the dose of 240 mg.

Artemisinin autoinduction is caused by involvement of cytochrome P450 2B6 but not 2C9

Our goal was to investigate whether artemisinin autoinduction is caused by an increase in cytochrome P450 (CYP) 2B6 or CYP2C9 activities, we evaluated the effects of multiple‐dose artemisinin administration on S‐mephenytoin N‐demethylation in healthy subjects.

Quantitative analysis of colistin A and colistin B in plasma and culture medium using a simple precipitation step followed by LC/MS/MS

An analytical method for quantitation of colistin A and colistin B in plasma and culture medium is described. After protein precipitation with acetonitrile (ACN) containing 0.1% trifluoroacetic acid (TFA), the supernatants were diluted with 0.03% TFA. The compounds were separated on an Ultrasphere C18 column, 4.6 mm x 250 mm, 5 microm particle size with a mobile phase consisting of 25% ACN in 0.03% TFA and detected with tandem mass spectrometry. The instrument was operating in ESI negative ion mode and the precursor-product ion pairs were m/z 1167.7-->1079.6 for colistin A and m/z 1153.7-->1065.6 for colistin B. The lower limit of quantification (LLOQ) for 100 microL plasma was 19.4 and 10.5 ng/mL for colistin A and B, respectively, with CV <6.2% and accuracy <+/-12.6%. For culture medium (50 microL+50 microL plasma), LLOQ was 24.2 and 13.2 ng/mL for colistin A and B, respectively, with CV <11.4% and accuracy <+/-8.1%. The quick sample work-up method allows for determination of colistin A and B in clinical samples without causing hydrolysis of the prodrug colistin methanesulfonate (CMS).

Artemisinin antimalarials moderately affect cytochrome P450 enzyme activity in healthy subjects

The aim of this study was to investigate which principal human cytochrome P450 (CYP450) enzymes are affected by artemisinin and to what degree the artemisinin derivatives differ with respect to their respective induction and inhibition capacity. Seventy‐five healthy adults were randomized to receive therapeutic oral doses of artemisinin, dihydroartemisinin, arteether, artemether or artesunate for 5 days (days 1–5). A six‐drug cocktail consisting of caffeine, coumarin, mephenytoin, metoprolol, chlorzoxazone and midazolam was administered orally on days −6, 1, 5 and 10 to assess the activities of CYP1A2, CYP2A6, CYP2C19, CYP2D6, CYP2E1 and CYP3A, respectively. Four‐hour plasma concentrations of parent drugs and corresponding metabolites and 7‐hydroxycoumarin urine concentrations were quantified by liquid chromatography‐tandem mass spectrometry. The 1‐hydroxymidazolam/midazolam 4‐h plasma concentration ratio (CYP3A) was increased on day 5 by artemisinin [2.66‐fold (98.75% CI: 2.10–3.36)], artemether [1.54 (1.14–2.09)] and dihydroartemisinin [1.25 (1.06–1.47)] compared with day −6. The S‐4′‐hydroxymephenytoin/S‐mephenytoin ratio (CYP2C19) was increased on day 5 by artemisinin [1.69 (1.47–1.94)] and arteether [1.33 (1.15–1.55)] compared with day −6. The paraxanthine/caffeine ratio (CYP1A2) was decreased on day 1 after administration of artemisinin [0.27 (0.18–0.39)], arteether [0.70 (0.55–0.89)] and dihydroartemisinin [0.73 (0.59–0.90)] compared with day −6. The α‐hydroxymetoprolol/metoprolol ratio (CYP2D6) was lower on day 1 compared with day −6 in the artemisinin [0.82 (0.70–0.96)] and dihydroartemisinin [0.83 (0.71–0.96)] groups, respectively. In the artemisinin‐treated subjects this decrease was followed by a 1.34‐fold (1.14–1.58) increase from day 1 to day 5. These results show that intake of artemisinin antimalarials affect the activities of several principal human drug metabolizing CYP450 enzymes. Even though not significant in all treatment groups, changes in the individual metrics were of the same direction for all the artemisinin drugs, suggesting a class effect that needs to be considered in the development of new artemisinin derivatives and combination treatments of malaria.

Diphenhydramine Active Uptake at the Blood–Brain Barrier and Its Interaction with Oxycodone in vitro and in Vivo

Diphenhydramine (DPHM) and oxycodone are weak bases that are able to form cations. Both drugs show active uptake at the blood-brain barrier (BBB). There is thus a possibility for a pharmacokinetic interaction between them by competition for the same uptake transport system. The experiments of the present study were designed to study the transport of DPHM across the BBB and its interaction with oxycodone in vitro and in vivo. In vitro, the interaction between the drugs was studied using conditionally immortalized rat brain capillary endothelial cells (TR-BBB13 cells). The in vivo relevance of the in vitro findings was studied in rats using brain and blood microdialysis. DPHM was actively transported across the BBB in vitro (TR-BBB13 cells). Oxycodone competitively inhibited DPHM uptake with a K(i) value of 106 μM. DPHM also competitively inhibited oxycodone uptake with a K(i) value of 34.7 μM. In rats, DPHM showed fivefold higher unbound concentration in brain interstitial fluid (ISF) than in blood, confirming a net active uptake. There was no significant interaction between DPHM and oxycodone in vivo. This accords with the results of the in vitro experiments because the unbound plasma concentrations that could be attained in vivo, without causing adverse effects, were far below the K(i) values.

Serum and Cerebrospinal Fluid Levels of Colistin in Pediatric Patients

ABSTRACT Using a liquid chromatography-tandem mass spectrometry method, the serum and cerebrospinal fluid (CSF) concentrations of colistin were determined in patients aged 1 months to 14 years receiving intravenous colistimethate sodium (60,000 to 225,000 IU/kg of body weight/day). Only in one of five courses studied (a 14-year-old receiving 225,000 IU/kg/day) did serum concentrations exceed the 2 μg/ml CLSI/EUCAST breakpoint defining susceptibility to colistin for Pseudomonas and Acinetobacter. CSF colistin concentrations were <0.2 μg/ml but increased in the presence of meningitis (∼0.5 μg/ml or 34 to 67% of serum levels).

In-depth neuropharmacokinetic analysis of antipsychotics based on a novel approach to estimate unbound target-site concentration in CNS regions: link to spatial receptor occupancy

The current study provides a novel in-depth assessment of the extent of antipsychotic drugs transport across the blood–brain barrier (BBB) into various brain regions, as well as across the blood–spinal cord barrier (BSCB) and the blood–cerebrospinal fluid barrier (BCSFB). This is combined with an estimation of cellular barrier transport and a systematic evaluation of nonspecific brain tissue binding. The study is based on the new Combinatory Mapping Approach (CMA), here further developed for the assessment of unbound drug neuropharmacokinetics in regions of interest (ROI), referred as CMA-ROI. We show that differences exist between regions in both BBB transport and in brain tissue binding. The most dramatic spatial differences in BBB transport were found for the P-glycoprotein substrates risperidone (5.4-fold) and paliperidone (4-fold). A higher level of transporter-mediated protection was observed in the cerebellum compared with other brain regions with a more pronounced efflux for quetiapine, risperidone and paliperidone. The highest BBB penetration was documented in the frontal cortex, striatum and hippocampus (haloperidol, olanzapine), indicating potential influx mechanisms. BSCB transport was in general characterized by more efficient efflux compared with the brain regions. Regional tissue binding was significantly different for haloperidol, clozapine, risperidone and quetiapine (maximally 1.9-fold). Spatial differences in local unbound concentrations were found to significantly influence cortical 5-HT2A receptor occupancy for risperidone and olanzapine. In conclusion, the observed regional differences in BBB penetration may potentially be important factors contributing to variations in therapeutic effect and side effect profiles among antipsychotic drugs.

Quantitative analysis of the opioid peptide DAMGO in rat plasma and microdialysis samples using liquid chromatography–tandem mass spectrometry

A liquid chromatography-electrospray ionization-tandem mass spectrometry (LC-ESI-MS/MS) method for the quantification of the opioid peptide DAMGO in rat plasma, as well as DAMGO and the microdialysis recovery calibrator [(13)C(2),(15)N]-DAMGO in microdialysis samples, is described. The microdialysis samples consisted of 15 μL Ringer solution containing 0.5% bovine serum albumin. Pretreatment of the samples involved protein precipitation with acetonitrile followed by dilution with 0.01% formic acid. The lower limits of quantification were 0.52 ng/mL and 0.24 ng/mL for DAMGO and [(13)C(2),(15)N]-DAMGO respectively and the response was linear up to 5000 fold higher concentrations. The plasma samples (50 μL) were precipitated with acetonitrile containing the isotope labeled analog [(13)C(2),(15)N]-DAMGO as internal standard. The method was linear in the range of 11-110,000 ng/mL. The separations were conducted on a HyPurity C18 column, 50×4.6 mm, 3 μm particle size, with a mobile phase consisting of acetonitrile, water and formic acid to the proportions of 17.5:82.5:0.01. Low energy collision dissociation tandem mass spectrometric (CID-MS/MS) analysis was carried out in the positive ion mode using multiple reaction monitoring (MRM) of the following mass transitions: m/z 514.2→453.2 for DAMGO and m/z 517.2→456.2 for [(13)C(2),(15)N]-DAMGO. The intra-day precision and accuracy did not exceed 5.2% and 93-104% for both compounds and sample types described. The inter-day precision an accuracy were <6.8% and 95-105% respectively. The method described is simple, reproducible and suitable for the analysis of small sample volumes at low concentrations.

Improved method for quantitative analysis of the cyclotide kalata B1 in plasma and brain homogenate.

This study provides a new method for quantifying the cyclotide kalata B1 in both plasma and brain homogenate. Cyclotides are ultra‐stable peptides with three disulfide bonds that are interesting from a drug development perspective as they can be used as scaffolds. In this study we describe a new validated LC‐MS/MS method with high sensitivity and specificity for kalata B1. The limit of quantification was 2 ng/mL in plasma and 5 ng/gmL in brain homogenate. The method was linear in the range 2–10,000 ng/mL for plasma and 5–2000 ng/g for brain. Liquid Chromatographic separation was performed on a HyPurity C18 column, 50 × 4.6 mm, 3 µm particle size. The method had inter‐ and intra‐day precision and accuracy levels <15% and 12% respectively. Applying the method to in vivo plasma samples and brain homogenate samples from equilibrium dialysis yielded satisfying results and was able to describe the plasma pharmacokinetics and brain tissue binding of kalata B1. The described method is quick, reproducible and well suited to quantifying kalata B1 in biological matrices.