Filgotinib: A Clinical Pharmacology Review.

Filgotinib (GS-6034, formerly GLPG0634; Jyseleca®) is an oral, preferential Janus kinase (JAK)-1 inhibitor. Preferential inhibition of JAK1 modulates a subset of proinflammatory cytokines within the JAK-signal transducer and activator of transcription pathway, which differ from those inhibited by JAK2 or JAK3. Filgotinib is absorbed extensively and rapidly after oral dosing and is metabolized by carboxylesterase isoform 2 to form its primary active metabolite, GS-829845. The primary metabolite has a similar JAK1 selectivity profile but reduced activity (by 10-fold) and increased systemic exposure (approximately 16- to 20-fold) compared with the parent compound. Both the parent and the metabolite demonstrate low binding to plasma proteins in humans (< 60%). Systemic exposures of filgotinib and its primary metabolite increase dose proportionally over a 50- to 200-mg once-daily dose range. Food does not affect the pharmacokinetics of filgotinib. Consistent with their terminal elimination half-lives (4.9-10.7 h for filgotinib and 19.6-27.3 h for the primary metabolite), steady state in plasma is reached by day 2 for filgotinib and day 4 for its metabolite. Filgotinib is mainly eliminated in the urine as the metabolite (> 80%). Intrinsic factors such as age, sex, race, mild renal impairment, and mild-to-moderate hepatic impairment have either no or minimal impact on the pharmacokinetics of filgotinib and its primary metabolite. Filgotinib has a low drug-drug interaction potential, without clinically significant interactions with commonly coadministered medications in patients with inflammatory diseases. Both filgotinib and its primary metabolite are substrates of P-glycoprotein (P-gp); however, coadministration with P-gp inhibitors and inducers does not affect filgotinib pharmacokinetics sufficiently to warrant dose adjustment. Neither filgotinib nor its primary metabolite affect the corrected QT interval (calculated using Fridericia's correction formula). Filgotinib is approved for the treatment of rheumatoid arthritis and ulcerative colitis in Europe, the UK, and Japan.

Exposure-response relationships for the efficacy and safety of filgotinib and its metabolite GS-829845 in subjects with rheumatoid arthritis based on phase 2 and phase 3 studies.

AIMS: Filgotinib is a potent, oral, JAK1-preferential inhibitor for the treatment of rheumatoid arthritis (RA). This report describes exposure-response (ER) analyses of filgotinib for dose confirmation based on three phase 3 and two phase 2 studies in moderate to severe RA patients. METHODS: The pharmacokinetic exposures used in ER analyses were derived from population pharmacokinetic analysis. The exposure-efficacy relationships were assessed for efficacy endpoints (ACR20/50/70 and DAS28) over effective area under curve (AUCeff ), the combined exposures of filgotinib and GS-829845 (major, active metabolite), with nonlinear logistic regression models developed. Also, a t-test was performed to compare the exposure between subjects who achieved response and those who did not. For the ER analyses of safety, exposures were examined between subjects who experienced and who did not experience the evaluated safety events, which was conducted separately for filgotinib and GS-829845. RESULTS: The nonlinear logistic regression showed increasing response with increasing exposure, with exposures at 200 mg dose primarily residing on the curve plateau. Also, AUCeff was significantly higher in the subjects who achieved responses compared to those who did not (10 900 vs 9900 h*ng/mL for ACR20, P value < .0001). For exposure-safety analyses, filgotinib and GS-829845 exposures were similar irrespective of the presence/absence of the evaluated safety endpoints, indicating no exposure-safety relationship for common treatment-emergent adverse events (TEAEs)/laboratory abnormalities and serious TEAEs/infections. CONCLUSIONS: ER analyses confirmed that filgotinib produced more robust therapeutic effects across the exposure range observed at 200 mg once daily compared to lower doses, and collectively with the lack of exposure-safety relationship, the 200 mg once daily dose was supported for commercialization.

Evaluation of the potential drug interactions mediated through P-gp, OCT2, and MATE1/2K with filgotinib in healthy subjects.

Filgotinib, a preferential Janus Kinase-1 inhibitor, is approved in Europe and Japan for treatment of rheumatoid arthritis and is being developed for treatment of other chronic inflammatory diseases. Three drug-drug interactions studies were conducted in healthy subjects to evaluate the effect of P-glycoprotein (P-gp) modulation (study 1: P-gp inhibition by itraconazole and study 2: P-gp induction by rifampin) on filgotinib pharmacokinetics and the potential of filgotinib to impact exposure of metformin, an organic cation transporter (OCT) 2 and multidrug and toxin extrusion (MATE) 1/2K substrate (study 3). Co-administration of filgotinib with itraconazole increased filgotinib exposure (maximum concentration [Cmax ] by 64% and area under the curve to infinity [AUCinf ] by 45%) but had no effect on the exposure of GS-829845, filgotinib's primary metabolite. Rifampin moderately reduced exposures of filgotinib and GS-829845 (Cmax by 26% and AUCinf by 27% for filgotinib; Cmax by 19% and AUCinf by 38% for GS-829845). The data confirmed that filgotinib is a P-gp substrate. However, the magnitude of change in filgotinib/GS-829845 exposure by P-gp modulators is not deemed to be clinically relevant based on filgotinib exposure-response analyses in subjects with rheumatoid arthritis. Filgotinib did not alter metformin exposures, indicating that filgotinib and GS-829845 do not inhibit OCT2 and MATE1/2K at the clinical doses. Filgotinib was generally well-tolerated when administered alone or with the co-administered drugs in the studies. Results from these studies were the basis to enable the use of P-gp modulators and substrates of OCT2, MATE1, and MATE2K with filgotinib without the need for dose modifications in the current approved rheumatoid arthritis population.

Assessment of the Effect of Filgotinib on the Pharmacokinetics of Atorvastatin, Pravastatin, and Rosuvastatin in Healthy Adult Participants.

Filgotinib, an oral Janus kinase-1 preferential inhibitor, is approved in Europe and Japan for adults with rheumatoid arthritis. Patients with rheumatoid arthritis are at higher risk of cardiovascular morbidity/mortality; thus, it is important to understand potential drug-drug interactions of filgotinib with lipid-lowering agents. This open-label, randomized, 2-way crossover study evaluated the pharmacokinetics of atorvastatin, pravastatin, and rosuvastatin with and without filgotinib coadministration. Healthy participants (N = 27) received single doses of atorvastatin (40 mg) and of a pravastatin (40 mg)/rosuvastatin (10 mg) cocktail-alone or with filgotinib (200 mg once daily for 11 days)-on 2 different occasions with washout in between. Serial pharmacokinetic blood samples were collected, and safety was assessed. Pharmacokinetic parameters were evaluated using 90% confidence intervals (CI) of the geometric least-squares mean (GLSM) ratio of the test treatment (statin coadministration with filgotinib) vs statin alone, with prespecified lack-of-interaction bounds of 0.70 to 1.43. Coadministration of filgotinib did not affect atorvastatin area under the plasma concentration-time curve extrapolated to infinity (AUCinf ; [GLSM ratios (90% CI): 0.91 (0.84-0.99)]), but maximum concentration [Cmax ] was slightly lower [0.82 (0.69-0.99)]. The exposure of 2-hydroxy-atorvastatin was unaffected (GLSM ratios [90% CI], 0.98 [0.81-1.19] for Cmax ; 1.11 [1.02-1.22] for AUCinf ). Pravastatin AUCinf was also unaffected (GLSM ratios, 1.22 [1.05-1.41], but Cmax was slightly higher 1.25 [1.01-1.54]). Rosuvastatin exposure was moderately higher with filgotinib coadministration-GLSM ratios (90% CI), 1.68 (1.43-1.97) for Cmax ; 1.42 (1.30-1.57) for AUCinf -but this was not considered clinically relevant. These results indicate that filgotinib has no clinically meaningful effect on exposure of atorvastatin, pravastatin, or rosuvastatin.

Lack of Drug-Drug Interaction Between Filgotinib, a Selective JAK1 Inhibitor, and Oral Hormonal Contraceptives Levonorgestrel/Ethinyl Estradiol in Healthy Volunteers.

Filgotinib (FIL) is a potent and selective JAK1 inhibitor in clinical development for treatment of severe inflammatory diseases. A drug-drug interaction study to evaluate the potential effect of FIL on the pharmacokinetics (PK) of the oral contraceptive levonorgestrel (LEVO)/ethinyl estradiol (EE) was conducted. This was a phase 1, open-label, randomized, crossover study in healthy female subjects (N = 24). Subjects received a single dose of LEVO (150 µg)/EE (30 µg) alone (reference), or in combination with multiple-dose FIL (200 mg once daily for 15 days; test). Intensive PK sampling was conducted, and safety was assessed throughout the study. PK interactions were evaluated using 90% confidence intervals of the geometric least squares mean ratios of the test versus reference treatments. All 24 subjects enrolled completed study treatments. Coadministration of FIL with the oral contraceptive did not alter the PK of LEVO and EE; the 90% confidence intervals of the geometric least squares mean ratios were contained within bioequivalence bounds (80%-125%). Exposures of FIL were consistent with observed clinical exposure data. Study treatments were generally well tolerated. All adverse events were mild. Coadministration with FIL did not alter the PK of LEVO/EE, and hormonal contraceptives can serve as an effective contraception method for subjects on FIL treatment.

Filgotinib, a JAK1 Inhibitor, Has No Effect on QT Interval in Healthy Subjects.

Filgotinib, a selective inhibitor of Janus kinase 1, is being developed for the treatment of chronic inflammatory diseases. Electrocardiograms evaluated the effect of filgotinib on the corrected QT (QTc) interval in 52 healthy subjects who received each of 4 treatments: filgotinib 200 mg (therapeutic dose), 450 mg (supratherapeutic dose), and placebo, each administered once daily for 7 days, and a single dose of moxifloxacin 400 mg (positive control). Plasma samples were collected for pharmacokinetic analysis. The QTc interval was calculated using Fridericia's correction factor (QTcF) or an individual correction factor (QTcI). The relationship between plasma concentrations of filgotinib and its major metabolite and time-matched, baseline-adjusted, placebo-corrected QTc (ΔΔQTc) was evaluated. Filgotinib did not prolong QTcF or QTcI and using an appropriate mixed-effect model, the upper limit of the 2-sided 90% confidence interval for ΔΔQTc for each filgotinib dose (200 and 450 mg) remained below 10 milliseconds at all postdose time points. There were no clinically relevant relationships between QTc interval and plasma concentrations of filgotinib or its major metabolite. Filgotinib, administered at 200 or 450 mg, was generally well tolerated. Results of this thorough QT study demonstrate that filgotinib and its major metabolite are not associated with QTc interval prolongation.

The Relative Bioavailability and Effects of Food and Acid-Reducing Agents on Filgotinib Tablets in Healthy Subjects.

Filgotinib is a potent, selective Janus kinase-1 inhibitor being developed to treat chronic inflammatory diseases. This phase 1 study in healthy subjects evaluated the relative bioavailability of filgotinib maleate tablets versus the reference tablet (filgotinib hydrochloride) and effects of food and acid-reducing agents (ARAs) on the pharmacokinetics of filgotinib and its major metabolite. Noncompartmental pharmacokinetic parameters of filgotinib and its major metabolite were compared between the 2 tablets at 100- and 200-mg doses and with or without food or ARAs. Filgotinib maleate tablets resulted in equivalent plasma exposures (area under concentration-time curve to infinity [AUC∞ ] and maximum concentration [Cmax ]) of filgotinib and its metabolite as the reference tablet (90%CIs of geometric least-squares mean ratios were within the prespecified no-effect boundary of 70% to 143%). Food intake had no effect on filgotinib AUC∞ , but a high-fat meal reduced Cmax by 20%. Coadministration of filgotinib with omeprazole or famotidine had no effect on filgotinib AUC∞ , but omeprazole decreased Cmax by 27%. Neither food nor ARAs affected metabolite exposure. Single-dose filgotinib 100 or 200 mg was well tolerated. This study supports evaluation of filgotinib maleate tablets, administered without regard to food or ARAs, in future clinical studies.

A rapid UPLC-MS/MS assay for eicosanoids in human plasma: Application to evaluate niacin responsivity.

A rapid and sensitive method using ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) was developed to simultaneously quantify hydroxyeicosatetraenoic (HETE), dihydroxyeicosatrienoic (DiHETrE), epoxyeicosatrienoic acid (EET), and prostaglandin metabolites of arachidonic acid in human plasma. Sample preparation consisted of solid phase extraction with Oasis HLB (30mg) cartridges for all metabolites. Separation of HETEs, EETs, and DiHETrEs was achieved on an Acquity UPLC BEH C18, 1.7µm (100×2.1mm) reversed-phase column (Waters Corp, Millford, MA) with negative electrospray ionization mass spectrometric detection. A second injection of the same extracted sample allowed for separation and assessment of prostaglandin metabolites under optimized UPLC-MS/MS conditions. Additionally, the endogenous levels of these metabolites in five different matrices were determined in order to select the optimal matrix for assay development. Human serum albumin was shown to have the least amount of endogenous metabolites, a recovery efficiency of 79-100% and a matrix effect of 71 - 100%. Linear calibration curves ranging from 0.416 to 66.67ng/ml were validated. Inter-assay and intra-assay variance was less than 15% at most concentrations. This method was successfully applied to quantify metabolite levels in plasma samples of healthy control subjects receiving niacin administration to evaluate the association between niacin administration and eicosanoid plasma level response.

Age predicts cytokine kinetics and innate immune cell activation following intranasal delivery of IFNγ and GM-CSF in a mouse model of RSV infection.

Respiratory syncytial virus (RSV) is the leading cause of lower respiratory tract infections in young children and is further associated with increased healthcare utilization and cost of care in the first years of life. Severe RSV disease during infancy has also been linked to the later development of allergic asthma, yet there remains no licensed RSV vaccine or effective treatment. Pre-clinical and clinical studies have shown that disease severity and development of allergic asthma are associated with differences in cytokine production. As a result, stimulation of the innate host immune response with immune potentiators is gaining attention for their prospective application in populations with limited immune responses to antigenic stimuli or against pathogens for which vaccines do not exist. Specifically, macrophage-activating cytokines such as interferon gamma (IFNγ) and granulocyte colony-stimulating factor (GM-CSF) are commercially available immune potentiators used to prevent infections in patients with chronic granulomatous disease and febrile neutropenia, respectively. Moreover, an increasing number of reports describe the protective function of IFNγ and GM-CSF as vaccine adjuvants. Although a positive correlation between cytokine production and age has previously been reported, little is known about age-dependent cytokine metabolism or immune activating responses in infant compared to adult lungs. Here we use a non-compartmental pharmacokinetic model in naïve and RSV-infected infant and adult BALB/c mice to determine the effect of age on IFNγ and GM-CSF elimination and innate cell activation following intranasal delivery.

Effect of Hypothermia and Targeted Temperature Management on Drug Disposition and Response Following Cardiac Arrest: A Comprehensive Review of Preclinical and Clinical Investigations.

Targeted temperature management (TTM) has been shown to reduce mortality and improve neurological outcomes in out-of-hospital cardiac arrest (CA) patients and in neonates with hypoxic-ischemic encephalopathy (HIE). TTM has also been associated with adverse drug events in the critically ill patient due to its effect on drug pharmacokinetics (PKs) and pharmacodynamics (PDs). We aim to evaluate the current literature on the effect of TTM on drug PKs and PDs following CA. MEDLINE/PubMed databases were searched for publications, which include the MeSH terms hypothermia, drug metabolism, drug transport, P450, critical care, cardiac arrest, hypoxic-ischemic encephalopathy, pharmacokinetics, and pharmacodynamics between July 2006 and October 2015. Twenty-three studies were included in this review. The studies demonstrate that hypothermia impacts PK parameters and increases concentrations of cytochrome-P450-metabolized drugs in the cooling and rewarming phase. Furthermore, the current data demonstrate a combined effect of CA and hypothermia on drug PK. Importantly, these effects can last greater than 4-5 days post-treatment. Limited evidence suggests hypothermia-mediated changes in the Phase II metabolism and the Phase III transport of drugs. Hypothermia also has been shown to potentially decrease the effect of specific drugs at the receptor level. Therapeutic hypothermia, as commonly deployed/applied during TTM, alters PK, and elevates concentrations of several commonly used medications. Hypothermia-mediated effects are an important factor when dosing and monitoring patients undergoing TTM treatment.

Advancing Pharmacogenomics Education in the Core PharmD Curriculum through Student Personal Genomic Testing.

OBJECTIVE: To develop, implement, and evaluate "Test2Learn" a program to enhance pharmacogenomics education through the use of personal genomic testing (PGT) and real genetic data. DESIGN: One hundred twenty-two second-year doctor of pharmacy (PharmD) students in a required course were offered PGT as part of a larger program approach to teach pharmacogenomics within a robust ethical framework. The program added novel learning objectives, lecture materials, analysis tools, and exercises using individual-level and population-level genetic data. Outcomes were assessed with objective measures and pre/post survey instruments. ASSESSMENT: One hundred students (82%) underwent PGT. Knowledge significantly improved on multiple assessments. Genotyped students reported a greater increase in confidence in understanding test results by the end of the course. Similarly, undergoing PGT improved student's self-perceived ability to empathize with patients compared to those not genotyped. Most students (71%) reported feeling PGT was an important part of the course, and 60% reported they had a better understanding of pharmacogenomics specifically because of the opportunity. CONCLUSION: Implementation of PGT in the core pharmacy curriculum was feasible, well-received, and enhanced student learning of pharmacogenomics.

Alveolar macrophages support interferon gamma-mediated viral clearance in RSV-infected neonatal mice.

BACKGROUND: Poor interferon gamma (IFNγ) production during respiratory syncytial virus (RSV) is associated with prolonged viral clearance and increased disease severity in neonatal mice and humans. We previously showed that intra-nasal delivery of IFNγ significantly enhances RSV clearance from neonatal lungs prior to observed T-lymphocyte recruitment or activation, suggesting an innate immune mechanism of viral clearance. We further showed that alveolar macrophages dominate the RSV-infected neonatal airways relative to adults, consistent with human neonatal autopsy data. Therefore, the goal of this work was to determine the role of neonatal alveolar macrophages in IFNγ-mediated RSV clearance. METHODS: Clodronate liposomes, flow cytometry, viral plaque assays, and histology were used to examine the role of alveolar macrophages (AMs) and the effects of intra-nasal IFNγ in RSV infected neonatal Balb/c mice. The functional outcomes of AM depletion were determined quantitatively by viral titers using plaque assay. Illness was assessed by measuring reduced weight gain. RESULTS: AM activation during RSV infection was age-dependent and correlated tightly with IFNγ exposure. Higher doses of IFNγ more efficiently stimulated AM activation and expedited RSV clearance without significantly affecting weight gain. The presence of AMs were independently associated with improved RSV clearance, whereas AM depletion but not IFNγ exposure, significantly impaired weight gain in RSV-infected neonates. CONCLUSION: We show here for the first time, that IFNγ is critical for neonatal RSV clearance and that it depends, in part, on alveolar macrophages (AMs) for efficient viral clearing effects. Early reductions in viral burden are likely to have profound short- and long-term immune effects in the vulnerable post-natally developing lung environment. Studies are ongoing to elucidate the pathologic effects associated with early versus delayed RSV clearance in developing neonatal airways.

Dexmedetomidine Reduces Shivering during Mild Hypothermia in Waking Subjects.

BACKGROUND AND PURPOSE: Reducing body temperature can prolong tolerance to ischemic injury such as stroke or myocardial infarction, but is difficult and uncomfortable in awake patients because of shivering. We tested the efficacy and safety of the alpha-2-adrenergic agonist dexmedetomidine for suppressing shivering induced by a rapid infusion of cold intravenous fluids. METHODS: Ten subjects received a rapid intravenous infusion of two liters of cold (4°C) isotonic saline on two separate test days, and we measured their core body temperature, shivering, hemodynamics and sedation for two hours. On one test day, fluid infusion was preceded by placebo infusion. On the other test day, fluid infusion was preceded by 1.0 µg/kg bolus of dexmedetomidine over 10 minutes. RESULTS: All ten subjects experienced shivering on placebo days, with shivering beginning at a mean (SD) temperature of 36.6 (0.3)°C. The mean lowest temperature after placebo was 36.0 (0.3)°C (range 35.7-36.5°C). Only 3/10 subjects shivered on dexmedetomidine days, and the mean lowest temperature was 35.7 (0.4)°C (range 35.0-36.3°C). Temperature remained below 36°C for the full two hours in 6/10 subjects. After dexmedetomidine, subjects had moderate sedation and a mean 26 (13) mmHg reduction in blood pressure that resolved within 90 minutes. Heart rate declined a mean 23 (11) bpm after both placebo and dexmedetomidine. Dexmedetomidine produced no respiratory depression. CONCLUSION: Dexmedetomidine decreases shivering in normal volunteers. This effect is associated with decreased systolic blood pressure and sedation, but no respiratory depression.

Evaluation in monkey of two candidate PET radioligands, [11 C]RX-1 and [18 F]RX-2, for imaging brain 5-HT4 receptors.

The serotonin subtype-4 (5-HT4 ) receptor, which is known to be involved physiologically in learning and memory, and pathologically in Alzheimer's disease, anxiety, and other neuropsychiatric disorders-has few radioligands readily available for imaging in vivo. We have previously reported two novel 5-HT4 receptor radioligands, namely [methoxy-11 C](1-butylpiperidin-4-yl)methyl 4-amino-3-methoxybenzoate; [11 C]RX-1), and the [18 F]3-fluoromethoxy analog ([18 F]RX-2), and in this study we evaluated them by PET in rhesus monkey. Brain scans were performed at baseline, receptor preblock or displacement conditions using SB 207710, a 5-HT4 receptor antagonist, on the same day for [11 C]RX-1 and on different days for [18 F]RX-2. Specific-to-nondisplaceable ratio (BPND ) was measured with the simplified reference tissue model from all baseline scans. To determine specific binding, total distribution volume (VT ) was also measured in some monkeys by radiometabolite-corrected arterial input function after ex vivo inhibition of esterases from baseline and blocked scans. Both radioligands showed moderate to high peak brain uptake of radioactivity (2-6 SUV). Regional BPND values were in the rank order of known 5-HT4 receptor distribution with a trend for higher BPND values from [18 F]RX-2. One-tissue compartmental model provided good fits with well identified VT values for both radioligands. In the highest 5-HT4 receptor density region, striatum, 50-60% of total binding was specific. The VT in receptor-poor cerebellum reached stable values by about 60 min for both radioligands indicating little influence of radiometabolites on brain signal. In conclusion, both [11 C]RX-1 and [18 F]RX-2 showed positive attributes for PET imaging of brain 5-HT4 receptors, validating the radioligand design strategy. Synapse 68:613-623, 2014. © 2014 Wiley Periodicals, Inc.

Therapeutic hypothermia decreases phenytoin elimination in children with traumatic brain injury.

OBJECTIVE: Preclinical and clinical studies have suggested that therapeutic hypothermia, while decreasing neurologic injury, may also lead to drug toxicity that may limit its benefit. Cooling decreases cytochrome P450 (CYP)-mediated drug metabolism, and limited clinical data suggest that drug levels are elevated. Fosphenytoin is metabolized by cytochrome P450 2C, has a narrow therapeutic range, and is a commonly used antiepileptic medication. The objective of this study was to evaluate the impact of therapeutic hypothermia on phenytoin levels and pharmacokinetics in children with severe traumatic brain injury. DESIGN: Pharmacokinetic analysis of subjects participating in a multicenter randomized phase III study of therapeutic hypothermia for severe traumatic brain injury. SETTING: ICU at the Children's Hospital of Pittsburgh. PATIENTS: Nineteen children with severe traumatic brain injury. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: A sum of 121 total and 114 free phenytoin levels were evaluated retrospectively in 10 hypothermia-treated and nine normothermia-treated children who were randomized to 48 hours of cooling to 32-33°C followed by slow rewarming or controlled normothermia. Drug dosing, body temperatures, and demographics were collected during cooling, rewarming, and posttreatment periods (8 d). A trend toward elevated free phenytoin levels in the hypothermia group (p=0.051) to a median of 2.2 mg/L during rewarming was observed and was not explained by dosing differences. Nonlinear mixed-effects modeling incorporating both free and total levels demonstrated that therapeutic hypothermia specifically decreased the time-variant component of the maximum velocity of phenytoin metabolism (Vmax) 4.6-fold (11.6-2.53 mg/hr) and reduced the overall Vmax by ~50%. Simulations showed that the increased risk for drug toxicity extends many days beyond the end of the cooling period. CONCLUSIONS: Therapeutic hypothermia significantly reduces phenytoin elimination in children with severe traumatic brain injury leading to increased drug levels for an extended period of time after cooling. Pharmacokinetic interactions between hypothermia and medications should be considered when caring for children receiving this therapy.

[¹¹C]Rhodamine-123: synthesis and biodistribution in rodents.

INTRODUCTION: Rhodamine-123 is a known substrate for the efflux transporter, P-glycoprotein (P-gp). We wished to assess whether rhodamine-123 might serve as a useful substrate for developing probes for imaging efflux transporters in vivo with positron emission tomography (PET). For this purpose, we aimed to label rhodamine-123 with carbon-11 (t(1/2)=20.4min) and to study its biodistribution in rodents. METHODS: [¹¹C]Rhodamine-123 was prepared by treating rhodamine-110 (desmethyl-rhodamine-123) with [¹¹C]methyl iodide. The biodistribution of this radiotracer was studied with PET in wild-type mice and rats, in efflux transporter knockout mice, in wild-type rats pretreated with DCPQ (an inhibitor of P-gp) or with cimetidine (an inhibitor of organic cation transporters; OCT), and in P-gp knockout mice pretreated with cimetidine. Unchanged radiotracer in forebrain, plasma and peripheral tissues was also measured ex vivo at 30min after radiotracer administration to wild-type and efflux transporter knockout rodents. RESULTS: [(¹¹C]Rhodamine-123 was obtained in 4.4% decay-corrected radiochemical yield from cyclotron-produced [¹¹C]carbon dioxide. After intravenous administration of [¹¹C]rhodamine-123 to wild-type rodents, PET and ex vivo measurements showed radioactivity uptake was very low in brain, but relatively high in some other organs such as heart, and especially liver and kidney. Inhibition of P-gp increased uptake in brain, heart, kidney and liver, but only by up to twofold. Secretion of radioactivity from kidney was markedly reduced by OCT knockout or pretreatment with cimetidine. CONCLUSIONS: [¹¹C]Rhodamine-123 was unpromising as a PET probe for P-gp function and appears to be a strong substrate of OCT in kidney. Cimetidine appears effective for blocking OCT in kidney in vivo.

Binding of a tritiated inverse agonist to cannabinoid CB1 receptors is increased in patients with schizophrenia.

This study sought to determine whether cannabinoid-1 (CB(1)) receptor binding was altered in the postmortem dorsolateral prefrontal cortex (DLPFC) of individuals with schizophrenia (schizophrenia; n=47) compared to controls (n=43). The CB(1) receptor inverse agonist radioligand [(3)H]MePPEP was used to measure specific binding to CB(1) receptors. The specific binding of [(3)H]MePPEP to CB(1) receptors was 20% higher in patients with schizophrenia than in controls. Power analyses suggested that 53 subjects per group would be needed to detect a similar difference in vivo with positron emission tomography (PET) and the structurally related inverse agonist radioligand [(18)F]FMPEP-d(2) (80% statistical power, p<0.05).

On quantitative relationships between drug-like compound lipophilicity and plasma free fraction in monkey and human.

Drug interactions with plasma proteins influence their pharmacokinetics and pharmacodynamics. We aimed to test whether a strong quantitative relationship exists between plasma free fraction (f(P) ) and lipophilicity for low molecular weight nonacidic drug-like compounds. We measured the n-octanol-buffer distribution coefficients at pH 7.4 ((m) logD) of 18 diverse radiotracers (<470 Da) used for brain imaging with positron emission tomography in vivo. Lipophilicities were also computed as (c) logD with two software packages. The f(P) values for monkeys and humans were determined by ultrafiltration and transformed into m logD(pr/pl) values representing the log(10) of the within phase partition of the radiotracers between plasma proteins and remaining plasma. (m) logD(pr/pl) correlated strongly with (m) logD for human ((m) logD(pr/pl) = 0.733(m) logD-0.780, r(2) = 0.74) and monkey ((m) logD(pr/pl) = 0.780(m) logD-1.15, r(2) = 0.83), but less strongly with (c) logD. These relationships were significantly different between species (P = 0.006). Removal of eight fluorinated compounds from the datasets raised r(2) to 0.81 and 0.91 for humans and monkeys, respectively. For the tested compounds, we conclude that n-octanol-buffer (pH 7.4) distribution strongly models that between plasma proteins and remaining plasma and moreover that (m) logD accounts for over 74% of compound (m) logD(pr/pl) and is a strong determinant of f(P).