Effect of albumin substitution on pharmacokinetics of piperacillin/tazobactam in patients with severe burn injury admitted to the ICU.

BACKGROUND: Pathophysiological changes in severely burned patients alter the pharmacokinetics (PK) of anti-infective agents, potentially leading to subtherapeutic concentrations at the target site. Albumin supplementation, to support fluid resuscitation, may affect pharmacokinetic properties by binding drugs. This study aimed to investigate the PK of piperacillin/tazobactam in burn patients admitted to the ICU before and after albumin substitution as total and unbound concentrations in plasma. PATIENTS AND METHODS: Patients admitted to the ICU and scheduled for 4.5 g piperacillin/tazobactam administration and 200 mL of 20% albumin substitution as part of clinical routine were included. Patients underwent IV microdialysis, and simultaneous arterial plasma sampling, at baseline and multiple timepoints after drug administration. PK analysis of total and unbound drug concentrations under steady-state conditions was performed before and after albumin supplementation. RESULTS: A total of seven patients with second- to third-degree burns involving 20%-60% of the total body surface were enrolled. Mean (SD) AUC0-8 (h·mg/L) of total piperacillin/tazobactam before and after albumin substitution were 402.1 (242)/53.2 (27) and 521.8 (363)/59.7 (32), respectively. Unbound mean AUC0-8 before and after albumin supplementation were 398.9 (204)/54.5 (25) and 456.4 (439)/64.5 (82), respectively. CONCLUSIONS: Albumin supplementation had little impact on the PK of piperacillin/tazobactam. After albumin supplementation, there was a numerical increase in mean AUC0-8 of total and unbound piperacillin/tazobactam, whereas similar Cmax values were observed. Future studies may investigate the effect of albumin supplementation on drugs with a higher plasma protein binding.

Comparison of ultrafiltration and microdialysis for ceftriaxone protein-binding determination.

BACKGROUND: High protein binding (PB) of antibiotics has an impact on their antimicrobial activity. It has been questioned whether in vitro PB determination can capture the dynamic and concentration-dependent PB of highly bound antibiotics. OBJECTIVES: This clinical study compared in vitro ultrafiltration (UF) and in vivo IV microdialysis (MD) methods to determine ceftriaxone PB. METHODS: Six healthy male volunteers received a single IV 2 g dose of ceftriaxone. Unbound ceftriaxone plasma concentrations were measured with MD and venous plasma sampling with subsequent UF. Pharmacokinetic parameters were determined using non-compartmental pharmacokinetic analysis. Non-linear mixed-effects modelling was used to quantify the PB. The PTA was estimated. RESULTS: The Cmax of ceftriaxone total plasma concentration (297.42 ±â€Š21.0 mg/L) was approximately 5.5-fold higher than for free concentrations obtained with UF (52.83 ±â€Š5.07 mg/L), and only 3.5-fold higher than for free concentrations obtained with MD (81.37 ±â€Š26.93 mg/L). Non-linear, saturable PB binding was confirmed for both UF and MD. Significantly different dissociation constants (Kd) for the albumin/ceftriaxone complex were quantified: in UF it was 23.7 mg/L (95% CI 21.3-26.2) versus 15.9 mg/L (95% CI 13.6-18.6) in MD. Moreover, the estimated number of binding sites (95% CI) per albumin molecule was 0.916 (0.86-0.97) in UF versus 0.548 in MD (0.51-0.59). The PTA obtained with MD was at most 27% higher than with UF. CONCLUSIONS: In vitro UF versus in vivo intravasal MD revealed significantly different PB, especially during the distribution phase. The method of PB determination could have an impact on the breakpoint determination and dose optimisation of antibiotics.

Effect of the human endotoxin challenge on tedizolid tissue penetration.

The effects of the human endotoxin challenge on tissue pharmacokinetics are unknown. In the present study, we aimed to assess the effect of the endotoxin challenge on interstitial fluid pharmacokinetics of tedizolid in healthy volunteers using intramuscular microdialysis. Eight healthy male subjects were treated with 200 mg of tedizolid phosphate for 6 days. On Day 6, an intravenous bolus of lipopolysaccharide (LPS) (2 ng/kg body weight) was administered. LPS infusion did not affect plasma pharmacokinetics of tedizolid. In contrast, following LPS infusion, median muscle tissue fAUC (0.83 [0.75-1.15] vs. 1.14 [1.11-1.43] mg × h/L, P = .0078) and muscle tissue fCmax (0.15 [0.14-0.19] vs. 0.19 [0.18-0.24] mg/L, P = .0078) were significantly increased by 38% and 24%, respectively. The human endotoxin challenge was associated with increased tissue concentrations of tedizolid, without affecting its plasma concentration-time profile. The human endotoxin challenge combined with microdialysis may be used to investigate the influence of systemic inflammation on tissue pharmacokinetics.

Comparison of pharmacokinetics and stability of generics of cefepime, linezolid and piperacillin/tazobactam with their respective originator drugs: an intravenous bioequivalence study in healthy volunteers.

OBJECTIVES: The efficacy and quality of generic antibacterial drug formulations are often questioned by both healthcare specialists and patients. Therefore, the present study investigated the interchangeability of generic drugs with their originators by comparing bioequivalence parameters and stability data of generic cefepime, linezolid and piperacillin/tazobactam with their respective originator drugs. METHODS: In this open-label, randomized, crossover bioequivalence study, three groups of 12 healthy volunteers each received a single intravenous infusion of either 2 g of cefepime or 4.5 g of piperacillin/tazobactam and two generic formulations, or 600 mg of linezolid and one generic formulation. Plasma sampling was performed, with a 5 day washout period between study days. Stability was tested by storing reconstituted generic and originator products according to their own storage specifications and those of the comparator products. All concentrations were measured by LC-MS. RESULTS: Similar ratios of generic/originator (90% CI) Cmax were observed for Cefepime-MIP/Maxipime [93.7 (88.4-99.4)], Cefepime Sandoz/Maxipime [95.9 (89.1-103.2)], Linezolid Kabi/Zyvoxid [104.5 (91.1-119.9)], Piperacillin Kabi/Tazobac [95.9 (90.4-101.7)], Piperacillin Aurobindo/Tazobac [99.7 (84.9-104.7)], Tazobactam Kabi/Tazobac [93.4 (87.4-99.8)] and Tazobactam Aurobindo/Tazobac [97.4 (89.7-105.8)]. Accordingly, similar ratios of AUC0-t were observed for Cefepime-MIP/Maxipime [91.1 (87.6-94.8)], Cefepime Sandoz/Maxipime [97.9 (92.5-103.5)], Linezolid Kabi/Zyvoxid [99.7 (93.3-106.6)], Piperacillin Kabi/Tazobac [92.2 (88.3-96.3)], Piperacillin Aurobindo/Tazobac [99.9 (97.0-102.8)], Tazobactam Kabi/Tazobac [91.4 (86.4-96.7)] and Tazobactam Aurobindo/Tazobac [98.8 (94.3-103.6)]. Stable and similar concentrations were measured for all contiguous substances, regardless of storage conditions. CONCLUSIONS: Compared with their respective originator drugs, generic cefepime, linezolid and piperacillin/tazobactam met the predetermined bioequivalence criteria. All formulations were stable under the storage conditions of their respective comparators.

Influence of tedizolid on the cytokine response to the endotoxin challenge in healthy volunteers: a cross-over trial.

BACKGROUND: Preclinical data suggested anti-inflammatory properties of tedizolid. OBJECTIVES: To investigate the influence of tedizolid on the cytokine response to the human endotoxin challenge and the effect of endotoxaemia on the pharmacokinetics and protein binding of tedizolid. METHODS: In this cross-over trial, 14 male healthy volunteers underwent two treatment periods: (A) 200 mg of tedizolid phosphate once daily for 6 days (3 days orally and 3 days intravenously), followed by an intravenous bolus of 2 ng/kg body weight of LPS on the last treatment day; and (B) intravenous bolus of LPS (2 ng/kg body weight) without concomitant tedizolid treatment. Participants underwent first period A or B, separated by at least 6 weeks. Plasma was sampled to assess cytokines and the pharmacokinetics of tedizolid. RESULTS: Following the endotoxin challenge, the peak plasma concentration (median [IQR]; 280 [155-502] versus 287 [132-541]  pg/mL; P = 0.875) and AUC0-24 (979 [676-1319] versus 1000 [647-1632]  pg·h/mL; P = 0.638) of interleukin-6 remained unchanged with and without concomitant tedizolid treatment. The peak concentration and AUC0-24 of TNF-α remained also unchanged with and without tedizolid (47 [31-61] versus 54 [27-69]  pg/mL; P = 0.73 and 197 [163-268] versus 234 [146-280]  pg·h/mL; P = 0.875, respectively). The total maximum concentration (mean ± SD; 2.94 ± 0.69 versus 2.96 ± 0.62 mg/L), total AUC0-24 (22.3 ± 3.8 versus 21.1 ± 3.6 mg·h/L) and protein binding (21.4% ± 1.7% versus 21.6% ± 1.9%) of tedizolid were similar with and without the endotoxin challenge. CONCLUSIONS: Tedizolid did not attenuate the LPS-induced cytokine response in healthy volunteers. Furthermore, endotoxaemia did not influence the plasma pharmacokinetics of tedizolid.

Binding of temocillin to plasma proteins in vitro and in vivo: the importance of plasma protein levels in different populations and of co-medications.

BACKGROUND: Temocillin plasma protein binding (PPB) in healthy individuals is reported to be ∼85% but had not been studied in patients. OBJECTIVES: To obtain normative data on temocillin PPB in patients in relation to infection and impact of co-medications widely used in ICU. METHODS: Plasma was obtained from healthy individuals (Group #1), non-ICU patients with UTI (Group #2), ICU patients with suspected/confirmed ventriculitis (Group #3) or with sepsis/septic shock (Group #4). Total and unbound temocillin concentrations were measured in spiked samples from temocillin-naive donors (in vitro) or in plasma from temocillin-treated subjects (in vivo). The impact of diluting plasma, using pharmaceutical albumin, or adding drugs potentially competing for PPB was tested in spiked samples. Data were analysed using a modified Hill-Langmuir equation taking ligand depletion into account. RESULTS: Temocillin PPB was saturable in all groups, both in vitro and in vivo. Maximal binding capacity (Bmax) was 1.2-2-fold lower in patients. At 20 and 200 mg/L (total concentrations), the unbound fraction reached 12%-29%, 23%-42% and 32%-52% in Groups #2, #3, #4. The unbound fraction was inversely correlated with albumin and C-reactive protein concentrations. Binding to albumin was 2-3-fold lower than in plasma and non-saturable. Drugs with high PPB but active at lower molar concentrations than temocillin caused minimal displacement, while fluconazole (low PPB but similar plasma concentrations to temocillin) increased up to 2-fold its unbound fraction. CONCLUSIONS: Temocillin PPB is saturable, 2-4-fold lowered in infected patients in relation to disease severity (ICU admission, hypoalbuminaemia, inflammation) and only partially reproducible with albumin. Competition with other drugs must be considered for therapeutic concentrations to be meaningful.

Protein binding of clindamycin in vivo by means of intravascular microdialysis in healthy volunteers.

OBJECTIVES: The efficacy of an anti-infective drug is influenced by its protein binding (PB), since only the free fraction is active. We hypothesized that PB may vary in vitro and in vivo, and used clindamycin, a drug with high and concentration-dependent PB to investigate this hypothesis. METHODS: Six healthy volunteers received a single intravenous infusion of clindamycin 900 mg. Antibiotic plasma concentrations were obtained by blood sampling and unbound drug concentrations were determined by means of in vivo intravascular microdialysis (MD) or in vitro ultrafiltration (UF) for up to 8 h post dosing. Clindamycin was assayed in plasma and MD fluid using a validated HPLC-UV (ultraviolet) method. Non-linear mixed effects modelling in NONMEM® was used to quantify the PB in vivo and in vitro. RESULTS: C max was 14.95, 3.39 and 2.32 mg/L and AUC0-8h was 41.78, 5.80 and 6.14 mg·h/L for plasma, ultrafiltrate and microdialysate, respectively. Calculated ratio of AUCunbound/AUCtotal showed values of 13.9%±1.8% and 14.7%±3.1% for UF and microdialysate, respectively. Modelling confirmed non-linear, saturable PB for clindamycin with slightly different median (95% CI) dissociation constants (Kd) for the alpha-1 acid glycoprotein (AAG)-clindamycin complex of 1.16 mg/L (0.91-1.37) in vitro versus 0.85 mg/L (0.58-1.01) in vivo. Moreover, the estimated number of binding sites per AAG molecule was 2.07 (1.79-2.25) in vitro versus 1.66 in vivo (1.41-1.79). CONCLUSIONS: Concentration-dependent PB was observed for both investigated methods with slightly lower levels of unbound drug fractions in vitro as compared with in vivo.

Meropenem concentrations in brain tissue of neurointensive care patients exceed CSF levels.

BACKGROUND: Inadequate antibiotic exposure in cerebral infections might have detrimental effects on clinical outcome. Commonly, antibiotic concentrations within the CSF were used to estimate cerebral target levels. However, the actual pharmacological active unbound drug concentration beyond the blood-brain barrier is unknown. OBJECTIVES: To compare meropenem concentrations in blood, CSF and cerebral microdialysate of neurointensive care patients. PATIENTS AND METHODS: In 12 patients suffering subarachnoid haemorrhage, 2000 mg of meropenem was administered every 8 h due to an extracerebral infection. Meropenem concentrations were determined in blood, CSF and cerebral microdialysate at steady state (n = 11) and following single-dose administration (n = 5). RESULTS: At steady state, the free AUC0-8 was 233.2 ± 42.7 mg·h/L in plasma, 7.8 ± 1.9 mg·h/L in CSF and 26.6 ± 14.0 mg·h/L in brain tissue. The brain tissue penetration ratio (AUCbrain/AUCplasma) was 0.11 ± 0.06, which was more than 3 times higher than in CSF (0.03 ± 0.01), resulting in an AUCCSF/AUCbrain ratio of 0.41 ± 0.16 at steady state. After single-dose administration similar proportions were achieved (AUCbrain/AUCplasma = 0.09 ± 0.08; AUCCSF/AUCplasma = 0.02 ± 0.00). Brain tissue concentrations correlated well with CSF concentrations (R = 0.74, P < 0.001), but only moderately with plasma concentrations (R = 0.51, P < 0.001). Bactericidal thresholds were achieved in both plasma and brain tissue for MIC values ≤16 mg/L. In CSF, bactericidal effects were only reached for MIC values ≤1 mg/L. CONCLUSIONS: Meropenem achieves sufficient bactericidal concentrations for the most common bacterial strains of cerebral infections in both plasma and brain tissue, even in non-inflamed brain tissue. CSF concentrations would highly underestimate the target site activity of meropenem beyond the blood-brain barrier.

A phase I study assessing the safety, tolerability, immunogenicity, and low-density lipoprotein cholesterol-lowering activity of immunotherapeutics targeting PCSK9.

PURPOSE: AT04A and AT06A are two AFFITOPE® peptide vaccine candidates being developed for the treatment of hypercholesterolemia by inducing proprotein convertase subtilisin/kexin type 9 (PCSK9)-specific antibodies. This study aimed to investigate safety, tolerability, antibody development, and reduction of low-density lipoprotein cholesterol (LDLc) following four subcutaneous immunizations. METHODS: This phase I, single-blind, randomized, placebo-controlled study was conducted in a total of 72 healthy subjects with a mean fasting LDLc level at baseline of 117.1 mg/dL (range 77-196 mg/dL). Each cohort enrolled 24 subjects to receive three priming immunizations at weeks 0, 4, and 8 and to receive a single booster immunization at week 60 of either AT04A, AT06A, or placebo. In addition to safety (primary objective), the antigenic peptide- and PCSK9-specific antibody response and the impact on LDLc were evaluated over a period of 90 weeks. RESULTS: The most common systemic treatment-related adverse events (AEs) reported were fatigue, headache, and myalgia in 75% of subjects in the AT06A group and 58% and 46% of subjects in the placebo and AT04A groups, respectively. Injection site reactions (ISR) representing 63% of all treatment-emergent adverse events (TEAEs), were transient and mostly of mild or moderate intensity and rarely severe (3%). Both active treatments triggered a robust, long-lasting antibody response towards the antigenic peptides used for immunization that optimally cross-reacted with the target epitope on PCSK9. In the AT04A group, a reduction in serum LDLc was observed with a mean peak reduction of 11.2% and 13.3% from baseline compared to placebo at week 20 and 70 respectively, and over the whole study period, the mean LDLc reduction for the AT04A group vs. placebo was -7.2% (95% CI [-10.4 to -3.9], P < 0.0001). In this group, PCSK9 target epitope titers above 50 were associated with clinically relevant LDLc reductions with an individual maximal decrease of 39%. CONCLUSIONS: Although both AT04A and AT06 were safe and immunogenic, only AT04A demonstrated significant LDLc-lowering activity, justifying further development. TRIAL REGISTRATION: EudraCT: 2015-001719-11. ClinicalTrials.gov Identifier: NCT02508896.

Microdialysis as a potential tool for comparative assessment of tissue pharmacokinetics of two different patches containing lidocaine: A crossover pilot study.

OBJECTIVE: Lidocaine 5% patches are approved for the treatment of post-herpetic neuralgia in adults. Little information is available on the penetration of lidocaine into skin and skin-related soft tissue, which are thought to be closer to the site where lidocaine exerts its pharmacological action on neuronal structures. This pilot study investigated subcutaneous and systemic pharmacokinetics of lidocaine during topical application of two different lidocaine 5% patches. MATERIALS AND METHODS: This randomized two-way, two-period crossover study assessed lidocaine concentrations in subcutaneous tissue (by microdialysis) and plasma of n = 5 healthy subjects during 12-hour-long applications of a recently developed lidocaine 5% patch (Laboratorios Gebro Pharma, SA, Barcelona, Spain) and a marketed reference patch (Versatis 5% lidocaine patch, Grünenthal, Brunn am Gebirge, Austria), respectively. RESULTS: Lidocaine was detectable in subcutaneous tissue within 60 minutes from start of patch application, and in plasma only after a marked delay. The test formulation led to increased exposure to lidocaine in both subcutaneous tissue and plasma. CONCLUSION: This study has underscored the potential of microdialysis to comparatively assess the pharmacokinetics of two different drug formulations and encourages its further use in this area.

Clinical Pharmacokinetics of Fosfomycin after Continuous Infusion Compared with Intermittent Infusion: a Randomized Crossover Study in Healthy Volunteers.

Continuous infusion (CON) of fosfomycin has been proposed as potentially advantageous in certain clinical scenarios. However, no clinical data on the pharmacokinetics (PK) of fosfomycin after CON are available to date. This study aimed to investigate the PK of fosfomycin after CON and compare it with intermittent infusion (INT) of fosfomycin. A randomized two-way crossover study including 8 healthy male volunteers was performed. Each subject received fosfomycin as INT of 8 g over 30 min every 8 h and, separated by a washout period, as CON of 1 g/h preceded by a loading dose of 8 g over 30 min. PK sampling was performed for 18 and 24 h in the CON and INT groups, respectively. Fosfomycin was generally well tolerated. However, 2 out of 8 subjects (25%) developed thrombophlebitis at the infusion site following CON, which was prevented in the following subjects with a simultaneous coinfusion of Ringer's lactate. The steady-state maximum concentration of drug in serum (Cmax) and area under the concentration-time curve from 0 to 24 h at steady state (AUCSS,0-24) of fosfomycin after INT were 551.5 ± 67.8 mg/liter and 3,678.5 ± 601.9 h · mg/liter, respectively. CON led to an average steady-state concentration of 183.8 ± 35.9 mg/liter, resulting in a calculated AUCSS,0-24 of 4,411.2 ± 862.4 h · mg/liter, which was 1.2-fold higher than that with INT. CON resulted in a 100% T>MIC (time during which the drug concentration exceeds the MIC) for MICs of ≤128 mg/liter, whereas the %T>MIC for INT was only 44% for an MIC of 128 mg/liter. CON of fosfomycin led to improved PK and PK/pharmacodynamic (PD) determinants in plasma of healthy volunteers. The clinical relevance of these findings remains to be investigated in patients.

Single-dose pharmacokinetics of temocillin in plasma and soft tissues of healthy volunteers after intravenous and subcutaneous administration: a randomized crossover microdialysis trial.

BACKGROUND: The antibiotic temocillin has recently been rediscovered as a promising therapeutic option against MDR Gram-negative bacteria. However, some aspects of the pharmacokinetic (PK) profile of the drug are still to be elucidated: subcutaneous administration of temocillin might be of interest as an alternative to the intravenous route in selected patients. Similarly, information on the penetration of temocillin into human soft tissues is lacking. OBJECTIVES: To investigate the feasibility and plasma PK of subcutaneous dosing as well as soft tissue PK of temocillin after intravenous administration to healthy volunteers. METHODS: Eight healthy volunteers received 2 g of temocillin both as intravenous and subcutaneous infusion in a randomized two-period crossover study. Concentration-time profiles of total temocillin in plasma (after both routes) and of unbound temocillin in plasma, muscle and subcutis (only after intravenous dosing) were determined up to 12 h post-dose. RESULTS: Subcutaneous dosing caused some infusion site discomfort but resulted in sustained drug concentrations over time with only slightly decreased overall exposure compared with intravenous dosing. Plasma protein binding of temocillin showed concentration-dependent behaviour and was higher than previously reported. Still, unbound drug concentrations in muscle and subcutis determined by microdialysis markedly exceeded those in plasma, suggesting good tissue penetration of temocillin. CONCLUSIONS: The subcutaneous administration of temocillin is a valid and feasible alternative to intravenous dosing. With the description of plasma protein binding and soft tissue PK of temocillin in healthy volunteers, this study provides important information that adds to the ongoing characterization of the PK profile of temocillin and might serve as input for PK/PD considerations.

Measurement of Hepatic ABCB1 and ABCG2 Transport Activity with [11C]Tariquidar and PET in Humans and Mice.

P-Glycoprotein (ABCB1) and breast cancer resistance protein (ABCG2) in the canalicular membrane of hepatocytes mediate the biliary excretion of drugs and drug metabolites. To measure hepatic ABCB1 and ABCG2 activity, we performed positron emission tomography (PET) scans with the ABCB1/ABCG2 substrate [11C]tariquidar in healthy volunteers and wild-type, Abcb1a/b(-/-), Abcg2(-/-), and Abcb1a/b(-/-)Abcg2(-/-) mice without and with coadministration of unlabeled tariquidar. PET data were analyzed with a three-compartment pharmacokinetic model. [11C]Tariquidar underwent hepatobiliary excretion in both humans and mice, and tariquidar coadministration caused a significant reduction in the rate constant for the transfer of radioactivity from the liver into bile (by -74% in humans and by -62% in wild-type mice), suggesting inhibition of canalicular efflux transporter activity. Radio-thin-layer chromatography analysis revealed that the majority of radioactivity (>87%) in the mouse liver and bile was composed of unmetabolized [11C]tariquidar. PET data in transporter knockout mice revealed that both ABCB1 and ABCG2 mediated biliary excretion of [11C]tariquidar. In vitro experiments indicated that tariquidar is not a substrate of major hepatic basolateral uptake transporters (SLCO1B1, SLCO1B3, SLCO2B1, SLC22A1, and SLC22A3). Our data suggest that [11C]tariquidar can be used to measure hepatic canalicular ABCB1/ABCG2 transport activity without a confounding effect of uptake transporters.

Determination of free clindamycin, flucloxacillin or tedizolid in plasma: Pay attention to physiological conditions when using ultrafiltration.

Pharmacokinetic/pharmacodynamic indices of anti-infective drugs should be referenced to free drug concentrations. In the present study, clindamycin, flucloxacillin and tedizolid have been determined in human plasma by HPLC-UV. The drugs were separated isocratically within 3-6 min on a C18 column using mixtures of phosphate buffer-acetonitrile of pH 7.1-7.2. Sample treatment for the determination of total drug concentrations in plasma included extraction/back-extraction (clindamycin) or protein precipitation (flucloxacillin, tedizolid). The free drug concentrations were determined after ultrafiltration. An ultrafiltration device with a membrane consisting of regenerated cellulose proved to be suitable for all drugs. Maintaining a physiological pH was crucial for clindamycin, whereas maintaining body temperature was essential for tedizolid. The methods were applied to the analysis of total and free drug concentrations in clinical samples and were sufficiently sensitive for pharmacokinetic studies and therapeutic drug monitoring.

Effect of Rifampicin on the Distribution of [11C]Erlotinib to the Liver, a Translational PET Study in Humans and in Mice.

Organic anion-transporting polypeptides (OATPs) mediate the uptake of various drugs from blood into the liver in the basolateral membrane of hepatocytes. Positron emission tomography (PET) is a potentially powerful tool to assess the activity of hepatic OATPs in vivo, but its utility critically depends on the availability of transporter-selective probe substrates. We have shown before that among the three OATPs expressed in hepatocytes (OATP1B1, OATP1B3, and OATP2B1), [11C]erlotinib is selectively transported by OATP2B1. In contrast to OATP1B1 and OATP1B3, OATP2B1 has not been thoroughly explored yet, and no specific probe substrates are currently available. To assess if the prototypical OATP inhibitor rifampicin can inhibit liver uptake of [11C]erlotinib in vivo, we performed [11C]erlotinib PET scans in six healthy volunteers without and with intravenous pretreatment with rifampicin (600 mg). In addition, FVB mice underwent [11C]erlotinib PET scans without and with concurrent intravenous infusion of high-dose rifampicin (100 mg/kg). Rifampicin caused a moderate reduction in the liver distribution of [11C]erlotinib in humans, while a more pronounced effect of rifampicin was observed in mice, in which rifampicin plasma concentrations were higher than in humans. In vitro uptake experiments in an OATP2B1-overexpressing cell line indicated that rifampicin inhibited OATP2B1 transport of [11C]erlotinib in a concentration-dependent manner with a half-maximum inhibitory concentration of 72.0 ± 1.4 µM. Our results suggest that rifampicin-inhibitable uptake transporter(s) contributed to the liver distribution of [11C]erlotinib in humans and mice and that [11C]erlotinib PET in combination with rifampicin may be used to measure the activity of this/these uptake transporter(s) in vivo. Furthermore, our data suggest that a standard clinical dose of rifampicin may exert in vivo a moderate inhibitory effect on hepatic OATP2B1.

Target site pharmacokinetics of doxycycline for rosacea in healthy volunteers is independent of the food effect.

AIMS: Doxycycline (DFD-09) oral capsules 40 mg are approved for the treatment of inflammatory lesions of rosacea. Unlike the food-induced lowering of doxycycline's peak plasma concentration (Cmax ), its exposure under fed conditions in the skin, the drug's target site for rosacea, is unknown. The present study explored the effect of food on the dermal pharmacokinetics of doxycycline. METHODS: The pharmacokinetics of doxycycline in the dermal interstitial fluid (d-ISF) and plasma of healthy volunteers were assessed in parallel groups under fed (n = 6) and fasting (n = 6) conditions during a 14-day once-daily treatment course with doxycycline oral capsules 40 mg (DFD-09). Sampling of d-ISF and plasma was performed on days 1, 10 (fasting group d-ISF only) and 14. RESULTS: Twelve subjects were randomized, and 11 analysed. No causally drug-related adverse events occurred. Dermal doxycycline exposures (Cmax and area under the curve) under the fed state were about 30% lower than under the fasting state at day 1 but were similar at steady state. In analogy to skin, plasma exposure showed no between-group difference at steady state. Accumulation ratios were higher in the skin than in plasma. Correcting for plasma protein binding (~90%), dermal doxycycline exposure was approximately threefold higher than unbound plasma exposure. CONCLUSIONS: At steady state, doxycycline concentrations in the skin of fed and fasting healthy volunteers were comparable. Doxycycline's efficacy in rosacea is possibly due to considerable dermal accumulation of unbound doxycycline and is independent of the effect of food.

Human Bile Reduces Antimicrobial Activity of Selected Antibiotics against Enterococcus faecalis and Escherichia coli In Vitro.

It has been known from previous studies that body fluids, such as cerebrospinal fluid, lung surfactant, and urine, have a strong impact on the bacterial killing of many anti-infective agents. However, the influence of human bile on the antimicrobial activity of antibiotics is widely unknown. Human bile was obtained and pooled from 11 patients undergoing cholecystectomy. After sterilization of the bile fluid by gamma irradiation, its effect on bacterial killing was investigated for linezolid (LZD) and tigecycline (TGC) against Enterococcus faecalis ATCC 29212. Further, ciprofloxacin (CIP), meropenem (MEM), and TGC were tested against Escherichia coli ATCC 25922. Time-kill curves were performed in pooled human bile and Mueller-Hinton broth (MHB) over 24 h. Bacterial counts (in CFU per milliliter after 24 h) of bile growth controls were approximately equal to MHB growth controls for E. coli and approximately 2-fold greater for E. faecalis, indicating a promotion of bacterial growth by bile for the latter strain. Bile reduced the antimicrobial activity of CIP, MEM, and TGC against E. coli as well as the activity of LZD and TGC against E. faecalis This effect was strongest for TGC against the two strains. Degradation of TGC in bile was identified as the most likely explanation. These findings may have important implications for the treatment of bacterial infections of the gallbladder and biliary tract and should be explored in more detail.

Effect of P-glycoprotein inhibition at the blood-brain barrier on brain distribution of (R)-[11 C]verapamil in elderly vs. young subjects.

AIMS: The efflux transporter P-glycoprotein (ABCB1) acts at the blood-brain barrier (BBB) to restrict the distribution of many different drugs from blood to the brain. Previous data suggest an age-associated decrease in the expression and function of ABCB1 at the BBB. In the present study, we investigated the influence of age on the magnitude of an ABCB1-mediated drug-drug interaction (DDI) at the BBB. METHODS: We performed positron emission tomography scans using the model ABCB1 substrate (R)-[11 C]verapamil in five young [26 ± 1 years, (mean ± standard deviation)] and five elderly (68 ± 6 years) healthy male volunteers before and after intravenous administration of a low dose of the ABCB1 inhibitor tariquidar (3 mg kg-1 ). RESULTS: In baseline scans, the total distribution volume (VT ) of (R)-[11 C]verapamil in whole-brain grey matter was not significantly different between the elderly (VT  = 0.78 ± 0.15) and young (VT  = 0.79 ± 0.10) group. After partial (incomplete) ABCB1 inhibition, VT values were significantly higher (P = 0.040) in the elderly (VT  = 1.08 ± 0.15) than in the young (VT  = 0.80 ± 0.18) group. The percentage increase in (R)-[11 C]verapamil VT following partial ABCB1 inhibition was significantly greater (P = 0.032) in elderly (+40 ± 17%) than in young (+2 ± 17%) volunteers. Tariquidar plasma concentrations were not significantly different between the young (786 ± 178 nmol l-1 ) and elderly (1116 ± 347 nmol l-1 ) group. CONCLUSIONS: Our results provide the first direct evidence of an increased risk for ABCB1-mediated DDIs at the BBB in elderly persons, which may have important consequences for pharmacotherapy of the elderly.

Single- and Repeated-Dose Pharmacokinetics of Ceftaroline in Plasma and Soft Tissues of Healthy Volunteers for Two Different Dosing Regimens of Ceftaroline Fosamil.

Ceftaroline fosamil (CPT-F) is currently approved for use for the treatment of complicated skin and soft tissue infections and community-acquired pneumonia at 600 mg twice daily (q12h), but other dosing regimens are under evaluation. To date, very limited data on the soft tissue pharmacokinetics (PK) of the active compound, ceftaroline (CPT), are available. CPT concentrations in the plasma, muscle, and subcutis of 12 male healthy volunteers were measured by microdialysis after single and repeated intravenous administration of 600 mg CPT-F q12h or three times daily (q8h) in two groups of 6 subjects each. Relevant PK and PK/pharmacodynamic (PD) parameters were calculated and compared between groups. In plasma, the area under the concentration-time curve (AUC) from 0 to 24 h for total CPT and the cumulative percentage of the dosing interval during which the free drug concentrations exceeded the MIC (fTMIC) for unbound CPT for the currently established threshold of 1 mg/liter were significantly higher in the group receiving CPT-F q8h. Exposure to free drug in soft tissues was higher in the group receiving CPT-F q8h, but high interindividual variability in relevant PK parameters was observed. The mean ratios of the AUC from time zero to the end of the dosing interval (AUC0-τ) for free CPT in soft tissues and the AUC0-τ for the calculated free fraction in plasma at steady state ranged from 0.66 to 0.75. Administration of CPT-F q8h led to higher levels of drug exposure in all investigated compartments. When MIC values above 1 mg/liter were assumed, the calculated fTMIC after dosing q12h was markedly lower than that after dosing q8h. The clinical implications of these differences are discussed in light of recently completed clinical phase III and PK/PD studies.

Signal transducer and activator of transcription-6 (STAT6) inhibition suppresses renal cyst growth in polycystic kidney disease.

Autosomal-dominant (AD) polycystic kidney disease (PKD) is a leading cause of renal failure in the United States, and currently lacks available treatment options to slow disease progression. Mutations in the gene coding for polycystin-1 (PC1) underlie the majority of cases but the function of PC1 has remained poorly understood. We have previously shown that PC1 regulates the transcriptional activity of signal transducer and activator of transcription-6 (STAT6). Here we show that STAT6 is aberrantly activated in cyst-lining cells in PKD mouse models. Activation of the STAT6 pathway leads to a positive feedback loop involving auto/paracrine signaling by IL13 and the IL4/13 receptor. The presence of IL13 in cyst fluid and the overexpression of IL4/13 receptor chains suggests a mechanism of sustained STAT6 activation in cysts. Genetic inactivation of STAT6 in a PKD mouse model leads to significant inhibition of proliferation and cyst growth and preservation of renal function. We show that the active metabolite of leflunomide, a drug approved for treatment of arthritis, inhibits STAT6 in renal epithelial cells. Treatment of PKD mice with this drug leads to amelioration of the renal cystic disease similar to genetic STAT6 inactivation. These results suggest STAT6 as a promising drug target for treatment of ADPKD.