In Vitro and Clinical Evaluations of the Drug-Drug Interaction Potential of a Metabotropic Glutamate 2/3 Receptor Agonist Prodrug with Intestinal Peptide Transporter 1.

Despite peptide transporter 1 (PEPT1) being responsible for the bioavailability for a variety of drugs, there has been little study of its potential involvement in drug-drug interactions. Pomaglumetad methionil, a metabotropic glutamate 2/3 receptor agonist prodrug, utilizes PEPT1 to enhance absorption and bioavailability. In vitro studies were conducted to guide the decision to conduct a clinical drug interaction study and to inform the clinical study design. In vitro investigations determined the prodrug (LY2140023 monohydrate) is a substrate of PEPT1 with Km value of approximately 30 µM, whereas the active moiety (LY404039) is not a PEPT1 substrate. In addition, among the eight known PEPT1 substrates evaluated in vitro, valacyclovir was the most potent inhibitor (IC50 = 0.46 mM) of PEPT1-mediated uptake of the prodrug. Therefore, a clinical drug interaction study was conducted to evaluate the potential interaction between the prodrug and valacyclovir in healthy subjects. No effect of coadministration was observed on the pharmacokinetics of the prodrug, valacyclovir, or either of their active moieties. Although in vitro studies showed potential for the prodrug and valacyclovir interaction via PEPT1, an in vivo study showed no interaction between these two drugs. PEPT1 does not appear to easily saturate because of its high capacity and expression in the intestine. Thus, a clinical interaction at PEPT1 is unlikely even with a compound with high affinity for the transporter.

Chronic Toxicology Studies of Basal Insulin Peglispro in Rats and Dogs: A Novel, PEGylated Insulin Lispro Analog with a Prolonged Duration of Action.

Basal insulin peglispro (BIL) consists of insulin lispro with a 20-kDa polyethylene glycol (PEG) moiety covalently attached to lysine B28. Because chronic parenteral administration of PEGylated proteins to animals has sometimes resulted in PEG vacuolation of tissue macrophages, renal tubular cells, and choroid plexus ependymal cells, we investigated whether chronic subcutaneous (sc) injection of BIL in rats (52 weeks) and dogs (39 weeks) was associated with systemic toxicities or other changes, including vacuolation of tissue macrophages, renal tubular cells, and ependymal cells. Rats and dogs received daily sc injections of BIL (rats: 0.17, 0.45, or 1.15 mg/kg/d and dogs: 0.025, 0.10, or 0.20 mg/kg/d) and the reference compound, HUMULIN N® (neutral protamine Hagedorn [NPH] human insulin; rats: 0.15 mg/kg/d and dogs: 0.02-0.03 mg/kg/d). Animals were evaluated for standard end points including mortality, clinical signs, body weights, toxicokinetics, glucodynamics, clinical pathology, and morphological pathology. Nonadverse injection site lipohypertrophy occurred for all BIL and NPH doses but more frequently with BIL. No BIL-related hyperplasia or neoplasia was observed. There was no vacuolation of tissue macrophages, renal tubular cells, or ependymal cells attributable to PEG. These studies demonstrate BIL is not associated with tissue vacuolation attributable to PEG at 4- to 6-fold multiple of the median clinical exposure in patients with diabetes.

Addition of 20-kDa PEG to Insulin Lispro Alters Absorption and Decreases Clearance in Animals.

PURPOSE: Determine the pharmacokinetics of insulin peglispro (BIL) in 5/6-nephrectomized rats and study the absorption in lymph duct cannulated (LDC) sheep. METHODS: BIL is insulin lispro modified with 20-kDa linear PEG at lysine B28 increasing the hydrodynamic size to 4-fold larger than insulin lispro. Pharmacokinetics of BIL and insulin lispro after IV administration were compared in 5/6-nephrectomized and sham rats. BIL was administered IV or SC into the interdigital space of the hind leg, and peripheral lymph and/or serum samples were collected from both LDC and non-LDC sheep to determine pharmacokinetics and absorption route of BIL. RESULTS: The clearance of BIL was similar in 5/6-nephrectomized and sham rats, while the clearance of insulin lispro was 3.3-fold slower in 5/6-nephrectomized rats than in the sham rats. In non-LDC sheep, the terminal half-life after SC was about twice as long vs IV suggesting flip-flop pharmacokinetics. In LDC sheep, bioavailability decreased to <2%; most of the dose was absorbed via the lymphatic system, with 88% ± 19% of the dose collected in the lymph after SC administration. CONCLUSION: This work demonstrates that increasing the hydrodynamic size of insulin lispro through PEGylation can impact both absorption and clearance to prolong drug action.

Disposition of Basal Insulin Peglispro Compared with 20-kDa Polyethylene Glycol in Rats Following a Single Intravenous or Subcutaneous Dose.

Basal insulin peglispro (BIL) comprises insulin lispro covalently bound to a 20-kDa polyethylene glycol (PEG) at lysine B28. The biologic fate of BIL and unconjugated PEG were examined in rats given a single 0.5-mg/kg i.v. or 2-mg/kg s.c. dose of BIL with (14)C label in 20-kDa PEG or (125)I label in lispro. Unconjugated (14)C-labeled 20-kDa PEG was dosed at 10 mg/kg i.v. or s.c. Blood, urine, and feces were collected up to 336 hours after dosing. Radioactivity was measured by scintillation spectrometry, and BIL was quantitated by enzyme-linked immunosorbent assay. Area under the curve and half-life for immunoreactive BIL were lower than those for both (14)C and (125)I after subcutaneous and intravenous administration. The half-lives of (14)C after BIL and PEG dosing were similar. The clearance of immunoreactive BIL was 2.4-fold faster than that of (14)C and 1.6-fold faster than (125)I. After a subcutaneous dose of BIL, immunoreactive BIL accounted for 31% of the circulating (125)I and 16% of the circulating (14)C, indicating extensive catabolism of BIL. Subcutaneous bioavailability of BIL was 23%-29%; bioavailability for unconjugated PEG was 78%. For unconjugated PEG, most of the (14)C dose was recovered in urine. For BIL, ≥86% of (125)I was eliminated in urine and (14)C was eliminated about equally in urine and feces. The major (14)C-labeled catabolism product of BIL in urine was 20-kDa PEG with lysine attached. The attachment of 20-kDa PEG to lispro in BIL led to a different elimination pathway for PEG compared with unconjugated 20-kDa PEG.

Effect of pomaglumetad methionil on the QT interval in subjects with schizophrenia.

OBJECTIVE: This thorough QT/QTc (TQT) study assessed the effects of a supratherapeutic dose of pomaglumetad methionil, a potential treatment for schizophrenia, compared to placebo on the QT interval in subjects with schizophrenia. METHODS: This double-blind, 3-period crossover study enrolled 86 subjects aged 22 - 63 years, who met Diagnostic and Statistical Manual, Fourth Edition, Test Revision (DSM-IV-TR) criteria for schizophrenia; 78 subjects completed the study. Subjects were randomly assigned to sequences of 3 treatment periods of single oral doses of pomaglumetad methionil 400 mg, moxifloxacin 400 mg, and placebo. Quadruplicate electrocardiograms (ECGs) were extracted from 2 hours predose to 12 hours postdose and were overread by a blinded central reader. Time-matched pharmacokinetic (PK) parameters were assessed. RESULTS: At all-time points, the upper bound of the 90% 2-sided confidence interval (CI) for the least squares (LS) mean difference in changes from baseline in Fridericia's corrected QT interval (ΔQTcF) between pomaglumetad methionil and placebo was < 10 milliseconds (msec). Sufficient assay sensitivity was not achieved, likely due to food effect; although the maximum observed drug concentration (Cmax) with moxifloxacin (1,410 ng/mL) was lower than expected, the slope of the regression line of moxifloxacin plasma concentrations versus placebo-subtracted ΔQTcF was similar to that reported in the literature. CONCLUSIONS: A single supratherapeutic dose of 400 mg pomaglumetad methionil did not prolong QTcF to a clinically significant degree and, importantly, did not result in any absolute QTcF > 450 msec or increase in QTcF from predose > 30 msec.

Effects of duloxetine on norepinephrine and serotonin transporter activity in healthy subjects.

Duloxetine selectively inhibits the serotonin (5-HT) and norepinephrine (NE) transporters (5-HTT and NET, respectively), as demonstrated in vitro and in preclinical studies; however, transporter inhibition has not been fully assessed in vivo at the approved dose of 60 mg/d. Here, the in vivo effects of dosing with duloxetine 60 mg once daily for 11 days in healthy subjects were assessed in 2 studies: (1) centrally (n = 11), by measuring concentrations of 5-hydroxyindoleacetic acid, 3,4-dihydroxyphenylglycol (DHPG), and NE in cerebrospinal fluid, and (2) versus escitalopram 20 mg/d (n = 32) in a 2-period crossover study by assessing the ΔDHPG/ΔNE ratio in plasma during orthostatic testing and by pharmacokinetic/pharmacodynamic modeling of reuptake inhibition using subjects' serum in cell lines expressing cloned human 5-HTT or NET. At steady state, duloxetine significantly reduced concentrations of DHPG and 5-hydroxyindoleacetic acid (P < 0.05), but not NE, in cerebrospinal fluid; DHPG was also decreased in plasma and urine. The ΔDHPG/ΔNE ratio in plasma decreased significantly more with duloxetine than escitalopram (65% and 21%, respectively; P < 0.0001). Ex vivo reuptake inhibition of 5-HTT was comparable (EC50 = 44.5 nM) for duloxetine and escitalopram, but duloxetine inhibited NET more potently (EC50 = 116 nM and 1044 nM, respectively). Maximal predicted reuptake inhibition for 5-HTT was 84% for duloxetine and 80% for escitalopram, and that for NET was 67% and 14%, respectively. In summary, duloxetine significantly affected 5-HT and NE turnover in the central nervous system and periphery; these effects presumably occurred via inhibition of reuptake by the 5-HTT and NET, as indicated by effects on functional reuptake inhibition ex vivo.

Nonclinical assessment of carcinogenic risk and tumor growth enhancement potential of prasugrel, a platelet-inhibiting therapeutic agent.

Prasugrel, a thienopyridine ADP receptor antagonist, is an orally administered prodrug requiring in vivo metabolism to form the active metabolite that irreversibly inhibits platelet activation and aggregation mediated by the P2Y12[sub 12] receptor. A comprehensive nonclinical safety assessment including genotoxicity and carcinogenicity studies supported the chronic use of prasugrel in patients with atherothrombotic disease. In addition, a special assessment of the potential for prasugrel to enhance tumor growth was undertaken to address regulatory concerns relating to increases in human cancers. Prasugrel demonstrated no evidence of genotoxicity and was not oncogenic in a 2-year rat carcinogenicity study. In the 2-year mouse study, an increase in hepatocellular adenomas was considered secondary to enzyme induction and not relevant to human safety. Further, the absence of any increase in common background tumors at any other organ site in either rodent study indicated a lack of tumor promoting activity (apart from the CYP450 induction-related increase in mouse liver tumors). Cell culture studies with 3 human tumor cell lines (lung, colon, prostate) demonstrated that exposure of serum-starved cells to prasugrel's active and major circulating human metabolites does not increase cell proliferation relative to starved cells stimulated to proliferate by addition of 10% FBS. Prasugrel also did not increase tumor growth relative to vehicle controls in nude mice implanted with 3 human tumor cell lines. Thus, traditional genotoxicity and 2-year bioassays as well as specially designed tumor growth enhancement studies in human tumor cell lines and mouse xenograft models clearly demonstrated prasugrel's lack of tumorigenic potential.

Population pharmacokinetics of orally administered duloxetine in patients: implications for dosing recommendation.

OBJECTIVES: The objectives of this analysis were to characterize the pharmacokinetics of duloxetine at steady state in patients, estimate the variability, identify significant covariates that may influence duloxetine pharmacokinetics and provide appropriate dosing recommendations for patients on duloxetine treatment. METHODS: The pharmacokinetic meta-analysis dataset was created from one open-label clinical study and four double-blind, placebo-controlled clinical studies. Duloxetine concentrations (N = 2002) were obtained from 594 patients diagnosed with major depressive disorder (n = 223), diabetic peripheral neuropathic pain (n = 112), stress urinary incontinence (n = 128) and fibromyalgia (n = 131). Patients were given 20-60 mg/day of oral duloxetine once or twice daily (the highest dose studied was 120 mg/day). A population pharmacokinetic model was developed using a nonlinear mixed-effects modelling method. Covariates including bodyweight, age, sex, ethnicity, smoking status, disease condition, dose, dosing regimen and creatinine clearance were tested for their influence on duloxetine pharmacokinetics. The final model was used to predict steady-state duloxetine concentration-time profiles in various patient subgroups. RESULTS: Duloxetine pharmacokinetics in patients were described by a one-compartmental pharmacokinetic model. The interpatient variability in apparent oral clearance (CL/F) was 59% and the interpatient variability in the apparent volume of distribution after oral administration (V(d)/F) was 97%. The residual error was 31%. Sex, smoking status, age and dose had a statistically significant effect on CL/F, whereas the V(d)/F was influenced by ethnicity. CL/F was 40% lower in females than in males and 30% lower in nonsmokers than in smokers. CL/F decreased with increasing dose and age. The V(d)/F in Hispanic patients was twice that of non-Hispanic patients. Simulations showed a considerable overlap in duloxetine exposure between the identified patient subgroups. CONCLUSION: Given the clinically insignificant change in the magnitude of duloxetine steady-state exposure and the considerable overlap in duloxetine exposure between the patient subgroups, specific dose recommendations based on sex, smoking status, age, dose and ethnicity are not warranted.

Predicting circulating human metabolites: how good are we?

The FDA issued a guidance on the safety testing of metabolites in February 2008, in which they stated that metabolites of concern are those that are detected at levels greater than 10% of the systemic exposure of the parent at steady state. This has presented many challenges in determining the circulating human metabolites at an early stage of development. The intention of this perspective is to address the question of how effective in vitro metabolism and early exploratory clinical data are in predicting the circulating metabolites from both a qualitative and a quantitative perspective. To this end, data were reviewed from 17 molecules in the Lilly portfolio for which there were in vitro data and a radiolabeled study in humans. Twelve example cases are presented in detail to demonstrate trends for when in vitro data adequately predicted in vivo (41%), when in vitro data underpredicted the circulating metabolites (35%), and when in vitro data overpredicted the circulating metabolites (24%). In addition, cases that present special challenges due to very low levels of the circulating parent or long half-lives of the parent and/or metabolites are presented. The trends indicate that the more complex the metabolism, the less likely the in vitro data were to predict the circulating metabolites. The in vitro data were also less predictive for N-glucuronidations and non-P450-mediated cleavage reactions. Although the in vitro data were better at predicting clearance pathways, the data set often failed to predict the quantity of metabolites, which is needed in consideration of whether or not a "disproportionate" metabolite may be circulating in human plasma.

Pharmacokinetics of duloxetine in breast milk and plasma of healthy postpartum women.

OBJECTIVE: The purpose of this study was to characterize duloxetine pharmacokinetics in the breast milk and plasma of lactating women and to estimate the duloxetine dose that an infant might consume if breastfed. METHODS: This open-label study included six healthy women aged 22-35 years who stopped nursing during and after the study. Duloxetine 40 mg was given orally every 12 hours for 3.5 days; seven plasma and milk samples over 12 hours were obtained after the seventh dose. Plasma and milk samples were analysed using validated liquid chromatography-tandem mass spectrometry methods. Safety measures included vital signs, ECGs, laboratory tests, adverse event monitoring and depression rating scales. RESULTS: The mean steady-state milk-to-plasma duloxetine exposure ratio was 0.25 (90% CI 0.18, 0.35). The amount of duloxetine in the breast milk was 7 microg/day (range 4-15 microg/day). The estimated infant dose was 2 microg/kg/day (range 0.6-3 microg/kg/day), which is 0.14% of the maternal dose. Dizziness, nausea and fatigue were commonly reported adverse events. No clinically important changes in safety measures occurred. CONCLUSION: Duloxetine is detected in breast milk, and steady-state concentrations in breast milk are about one-fourth of those in maternal plasma. As the safety of duloxetine in infants is unknown, prescribers should carefully assess, on an individual basis, the potential risks of duloxetine exposure to infants and the benefits of nursing an infant when the mother is on duloxetine therapy.

In vitro and in vivo evaluations of cytochrome P450 1A2 interactions with duloxetine.

OBJECTIVE: To determine whether duloxetine is a substrate, inhibitor or inducer of cytochrome P450 (CYP) 1A2 enzyme, using in vitro and in vivo studies in humans. METHODS: Human liver microsomes or cells with expressed CYP enzymes and specific CYP inhibitors were used to identify which CYP enzymes catalyse the initial oxidation steps in the metabolism of duloxetine. The potential of duloxetine to inhibit CYP1A2 activity was determined using incubations with human liver microsomes and phenacetin, the CYP1A2 substrate. The potential for duloxetine to induce CYP1A2 activity was determined using human primary hepatocytes treated with duloxetine for 72 hours. Studies in humans were conducted using fluvoxamine, a potent CYP1A2 inhibitor, and theophylline, a CYP1A2 substrate, as probes. The subjects were healthy men and women aged 18-65 years. Single-dose duloxetine was administered either intravenously as a 10-mg infusion over 30 minutes or orally as a 60-mg dose in the presence or absence of steady-state fluvoxamine (100 mg orally once daily). Single-dose theophylline was given as 30-minute intravenous infusions of aminophylline 250 mg in the presence or absence of steady-state duloxetine (60 mg orally twice daily). Plasma concentrations of duloxetine, its metabolites and theophylline were determined using liquid chromatography with tandem mass spectrometry. Pharmacokinetic parameters were estimated using noncompartmental methods and evaluated using mixed-effects ANOVA. Safety measurements included vital signs, clinical laboratory tests, a physical examination, ECG readings and adverse event reports. RESULTS: The in vitro results indicated that duloxetine is metabolized by CYP1A2; however, duloxetine was predicted not to be an inhibitor or inducer of CYP1A2 in humans. Following oral administration in the presence of fluvoxamine, the duloxetine area under the plasma concentration-time curve from time zero to infinity (AUC(infinity)) and the maximum plasma drug concentration (C(max)) significantly increased by 460% (90% CI 359, 584) and 141% (90% CI 93, 200), respectively. In the presence of fluvoxamine, the oral bioavailability of duloxetine increased from 42.8% to 81.9%. In the presence of duloxetine, the theophylline AUC(infinity) and C(max) increased by only 13% (90% CI 7, 18) and 7% (90% CI 2, 14), respectively. Coadministration of duloxetine with fluvoxamine or theophylline did not result in any clinically important safety concerns, and these combinations were generally well tolerated. CONCLUSION: Duloxetine is metabolized primarily by CYP1A2; therefore, coadministration of duloxetine with potent CYP1A2 inhibitors should be avoided. Duloxetine does not seem to be a clinically significant inhibitor or inducer of CYP1A2; therefore, dose adjustment of CYP1A2 substrates may not be necessary when they are coadministered with duloxetine.

Pharmacokinetics and tolerability of duloxetine following oral administration to healthy Chinese subjects.

OBJECTIVES: The objectives of the study were to characterise the pharmacokinetics and assess the tolerability of duloxetine in healthy Chinese subjects after single and multiple oral 60 mg dosing. METHODS: This was a single-centre, double-blind, randomised, placebo-controlled, single-period study in healthy native Chinese subjects. A total of 32 subjects, 19 men (14 on duloxetine, 5 on placebo) and 13 women (10 on duloxetine, 3 on placebo) between the ages of 20 and 39 years, participated in the study. Duloxetine 60 mg (enteric-coated pellets in a capsule) was given orally once on day 1 and once daily on days 4 to 9. Sequential blood samples were collected over 72 hours after the dose on days 1 and 9, and a predose sample was obtained on days 7 and 8. Duloxetine concentrations in plasma were determined by a validated liquid chromatography-tandem mass spectrometry method. The tolerability evaluation included a physical examination, vital signs, adverse event monitoring and clinical laboratory evaluations. RESULTS: Duloxetine disposition on oral administration is characterised by a one-compartment pharmacokinetic model. Duloxetine is well absorbed, with a median time of maximum plasma concentration at 6 and 4 hours following single and multiple dosing, respectively. At steady state, the mean apparent oral clearance (CL(ss)/F), mean apparent volume of distribution (V(ss)/F) and mean terminal elimination half-life (t((1/2))) were 86.8 L/h, 1570L and 11 hours, respectively. CL/F and V(ss)/F on single dosing were not statistically significantly different (p > 0.05) compared with multiple dosing. The linearity index, calculated as the ratio of the area under the plasma concentration-time curve (AUC) during the dosing interval tau at steady state (AUC(tau)(,ss)) to the AUC from time zero to infinity after single dosing (AUC(infinity,single dose)) was 1.15 (coefficient of variation 35.7%). The accumulation in duloxetine exposure was estimated to be 50% on multiple dosing compared with single dosing, consistent with the t((1/2)) and dosing interval (24 hours). The pharmacokinetic parameters of duloxetine in Chinese subjects were not statistically significantly different from those reported previously in Caucasian and Japanese subjects. There were no clinically significant adverse events, abnormal safety laboratory data or vital sign changes reported. CONCLUSION: Duloxetine pharmacokinetics in healthy Chinese subjects given a 60 mg once-daily dosing regimen were well characterised and consistent with known duloxetine pharmacokinetics in healthy Caucasian and Japanese subjects. Both single dosing and multiple once-daily dosing of duloxetine 60 mg were well tolerated by healthy Chinese subjects in this study.

Development and validation of a liquid chromatography-tandem mass spectrometric method for the determination of the major metabolites of duloxetine in human plasma.

A sensitive bioanalytical method for the measurement of two major circulating metabolites of duloxetine [4-hydroxy duloxetine glucuronide (LY550408) and 5-hydroxy-6-methoxy duloxetine sulfate (LY581920)] in plasma is reported. This method produced acceptable precision and accuracy over the validation range of 1-1000 ng/mL. Several issues had to be addressed in order to develop an LC/MS/MS assay for these metabolites. First, 4-hydroxy duloxetine glucuronide required chromatographic resolution from the 5-, and 6-hydroxy duloxetine glucuronide isomers. Second, the glucuronide conjugate is readily ionized under positive ESI conditions, while the sulfate conjugate required negative ESI conditions to obtain adequate sensitivity. Finally, the chromatographic conditions needed to separate the glucuronide isomers were not suitable for the analysis of the sulfate conjugate. The present method addressed these challenges, and was successfully applied to multiple human pharmacokinetic studies in which subjects received oral doses of duloxetine hydrochloride.

Quantification of Basal Insulin Peglispro and Human Insulin in Adipose Tissue Interstitial Fluid by Open-Flow Microperfusion.

BACKGROUND: Restoration of the physiologic hepatic-to-peripheral insulin gradient may be achieved by either portal vein administration or altering insulin structure to increase hepatic specificity or restrict peripheral access. Basal insulin peglispro (BIL) is a novel, PEGylated basal insulin with a flat pharmacokinetic and glucodynamic profile and altered hepatic-to-peripheral action gradient. We hypothesized reduced BIL exposure in peripheral tissues explains the latter, and in this study assessed the adipose tissue interstitial fluid (ISF) concentrations of BIL compared with human insulin (HI). METHODS: A euglycemic glucose clamp was performed in patients with type 1 diabetes during continuous intravenous (IV) infusion of BIL or HI, while the adipose ISF insulin concentrations were determined using open-flow microperfusion (OFM). The ratio of adipose ISF-to-serum concentrations and the absolute steady-state adipose ISF concentrations were assessed using a dynamic no-net-flux technique with subsequent regression analysis. RESULTS: Steady-state BIL concentrations in adipose tissue ISF were achieved by ∼16 h after IV infusion. Median time to reach steady-state glucose infusion rate across doses ranged between 8 and 22 h. The average serum concentrations (coefficient of variation %) of BIL and HI were 11,200 pmol/L (23%) and 425 pmol/L (15%), respectively. The ISF-to-serum concentration ratios were 10.2% for BIL and 22.9% for HI. CONCLUSIONS: This study indicates feasibility of OFM to measure BIL in ISF. The observed low ISF-to-serum concentration ratio of BIL is consistent with its previously demonstrated reduced peripheral action.

The dual transporter inhibitor duloxetine: a review of its preclinical pharmacology, pharmacokinetic profile, and clinical results in depression.

Major depressive disorder (MDD) poses a significant health problem and is estimated to be the third most costly and disabling disorder in the United States. Pharmacotherapy of depression has been successful, but improvements in response rates, remission rates, side effects, compliance and faster onset of therapeutic action have become prime objectives in drug development. There is considerable support for the hypothesis that dysfunctional serotonergic or noradrenergic neurotransmission may be etiological in depressed patients. Duloxetine is a balanced and potent reuptake inhibitor of serotonin (5-HT) and norepinephrine (NE) being studied as an antidepressant medication. In this review, we highlight the preclinical pharmacology, pharmacokinetic profile, and effects of duloxetine in the pharmacotherapy of depression. Evidence for 5-HT and NE reuptake inhibition by duloxetine comes from in vitro and in vivo transporter binding and functional uptake studies. Taken together with efficacy data from in vivo microdialysis, electrophysiological and behavioral studies, it is evident that duloxetine is balanced as a dual serotonin norepinephrine uptake inhibitor in vivo. The clinical efficacy and safety of duloxetine in the treatment of MDD has been studied in 6 multicenter, randomized, double-blind, placebo-controlled trials. In these studies, duloxetine was found to be effective in the treatment of emotional/psychological and painful physical symptoms associated with depression. More importantly, duloxetine appears to have better response rates and remission from depressive symptoms, perhaps due to its ability to treat a wider range of symptoms.

Relative contributions of presystemic and systemic peptidases to oral exposure of a novel metabotropic glutamate 2/3 receptor agonist (LY404039) after oral administration of prodrug pomaglumetad methionil (LY2140023).

Pomaglumetad methionil (LY2140023) is the prodrug of a novel metabotropic glutamate 2/3 receptor agonist (LY404039) being investigated for the treatment of schizophrenia. Using accelerator mass spectrometry (AMS) and an intravenous (i.v.) radiolabeled tracer approach, the absolute bioavailability of the prodrug and the extent of its conversion to active moiety (LY404039) were estimated at presystemic (intestinal/first pass) and systemic sites after simultaneous oral and i.v. dosing in healthy subjects. The mean absolute bioavailability of prodrug (80 mg oral) was 0.68. On the basis of these data and a previous radiolabeled mass balance study in which no prodrug was recovered in feces, we concluded that 0.32 of the dose is converted to active drug in the intestinal tract. The fraction of prodrug converted to active moiety was approximately 1, indicating complete conversion of the prodrug that reaches the systemic circulation to the active moiety. Prodrug (80 mg oral and 100 µg i.v.) and active moiety (100 µg i.v.) were well tolerated in healthy subjects. Thus, the absolute bioavailability of prodrug LY2140023 and the fraction converted presystemically and systemically to active moiety LY404039 were estimated simultaneously using radiolabeled tracer microdosing and AMS.

Duloxetine is both an inhibitor and a substrate of cytochrome P4502D6 in healthy volunteers.

BACKGROUND AND OBJECTIVES: Duloxetine, a potent dual reuptake inhibitor of serotonin and norepinephrine currently undergoing clinical investigation for treatment of depression and stress urinary incontinence, has the potential to act as both a substrate and an inhibitor of cytochrome P4502D6 (CYP2D6). Our objectives were to determine the effect of duloxetine on the pharmacokinetics of desipramine, a tricyclic antidepressant metabolized by CYP2D6 (study 1), and the effect of paroxetine, a potent CYP2D6 inhibitor, on duloxetine pharmacokinetics (study 2). METHODS: Subjects were healthy men and women between 21 and 63 years old. All subjects were genotypically CYP2D6 extensive metabolizers. In study 1, 50 mg of desipramine was administered as a single dose alone and in the presence of steady-state duloxetine 60 mg twice daily. In study 2, steady-state pharmacokinetics of duloxetine 40 mg once daily were determined in the presence and absence of steady-state paroxetine 20 mg once daily. RESULTS: Duloxetine increased the maximum plasma concentration of desipramine 1.7-fold and the area under the concentration-time curve 2.9-fold. Paroxetine increased the maximum plasma concentration of duloxetine and the area under the concentration-time curve at steady state 1.6-fold. Reports of adverse events were similar whether duloxetine was administered alone or in combination with desipramine or paroxetine. CONCLUSION: Duloxetine 60 mg twice daily is a moderately potent CYP2D6 inhibitor, intermediate between paroxetine and sertraline. The potent CYP2D6 inhibitor paroxetine has a moderate effect on duloxetine concentrations. The results of these 2 studies suggest that caution should be used when CYP2D6 substrates and inhibitors are coadministered with duloxetine.

Basal insulin peglispro demonstrates preferential hepatic versus peripheral action relative to insulin glargine in healthy subjects.

OBJECTIVE: We evaluated the endogenous glucose production (EGP) and glucose disposal rate (GDR) over a range of doses of basal insulin peglispro (BIL) and insulin glargine in healthy subjects. RESEARCH DESIGN AND METHODS: This was a single-center, randomized, open-label, four-period, incomplete-block, crossover study conducted in eight healthy male subjects. Subjects had 8-h euglycemic clamps performed with primed, continuous infusions of BIL (5.1 to 74.1 mU/min) in three dosing periods and insulin glargine (20 or 30 mU/m(2)/min) in a fourth period, targeted to achieve 50-100% suppression of EGP. D-[3-(3)H] glucose was infused to assess rates of glucose appearance and disappearance. RESULTS: Mean BIL and insulin glargine concentrations (targeted to reflect the differences in intrinsic affinities of the two basal insulins) ranged from 824 to 11,400 and 212 to 290 pmol/L, respectively, and increased accordingly with increases in dose. Suppression of EGP and stimulation of GDR were observed with increasing concentrations of both insulins. At insulin concentrations where EGP was significantly suppressed, insulin glargine resulted in increased GDR. In contrast, at comparable suppression of EGP, BIL had minimal effect on GDR at lower doses and had substantially less effect on GDR than insulin glargine at higher doses. CONCLUSIONS: The novel basal insulin analog BIL has relative hepatopreferential action and decreased peripheral action, compared with insulin glargine, in healthy subjects.

Effect of pitavastatin vs. rosuvastatin on international normalized ratio in healthy volunteers on steady-state warfarin.

OBJECTIVE: Statins have been shown to impact international normalized ratio (INR) when coadministered with warfarin. The aim of this study was to assess the effect of pitavastatin compared with rosuvastatin on steady-state pharmacodynamics (PD) of warfarin by measuring INR in healthy adult subjects. METHODS: Subjects received oral doses of warfarin 5 mg once daily on days 1 through 3. The dose was titrated on days 4 through 9 to reach a steady-state INR of 1.5 to 2.2. Warfarin was continued on days 10 through 21 and pitavastatin 4 mg or rosuvastatin 40 mg was administered once daily on days 14 through 22. After a 14-day washout period, the process was repeated with the alternate statin. STUDY NUMBER: NK-104-4.03US. RESULTS: For pitavastatin, mean INR changed from 1.73 ± 0.18 (n = 42) on day 14 before starting statin dosing, to 1.78 ± 0.29 (n = 42) on day 22 at treatment end; the difference in INR was not significant (p = 0.219). For rosuvastatin, mean INR increased significantly from 1.74 ± 0.20 (n = 43) at baseline to 1.90 ± 0.30 (n = 43) at treatment end (p < 0.001). Rosuvastatin caused a significantly greater increase in INR than pitavastatin (p < 0.001). CONCLUSION: Steady-state INR during warfarin treatment did not change significantly when pitavastatin 4 mg was added to the regimen, while a significant increase was observed when rosuvastatin 40 mg was added. The effect of rosuvastatin on INR was significantly larger than the effect of pitavastatin. This study is limited because it was done in healthy volunteers. Further studies in patient populations are needed to better understand the clinical significance of the results.

Duloxetine: clinical pharmacokinetics and drug interactions.

Duloxetine, a potent reuptake inhibitor of serotonin (5-HT) and norepinephrine, is effective for the treatment of major depressive disorder, diabetic neuropathic pain, stress urinary incontinence, generalized anxiety disorder and fibromyalgia. Duloxetine achieves a maximum plasma concentration (C(max)) of approximately 47 ng/mL (40 mg twice-daily dosing) to 110 ng/mL (80 mg twice-daily dosing) approximately 6 hours after dosing. The elimination half-life of duloxetine is approximately 10-12 hours and the volume of distribution is approximately 1640 L. The goal of this paper is to provide a review of the literature on intrinsic and extrinsic factors that may impact the pharmacokinetics of duloxetine with a focus on concomitant medications and their clinical implications. Patient demographic characteristics found to influence the pharmacokinetics of duloxetine include sex, smoking status, age, ethnicity, cytochrome P450 (CYP) 2D6 genotype, hepatic function and renal function. Of these, only impaired hepatic function or severely impaired renal function warrant specific warnings or dose recommendations. Pharmacokinetic results from drug interaction studies show that activated charcoal decreases duloxetine exposure, and that CYP1A2 inhibition increases duloxetine exposure to a clinically significant degree. Specifically, following oral administration in the presence of fluvoxamine, the area under the plasma concentration-time curve and C(max) of duloxetine significantly increased by 460% (90% CI 359, 584) and 141% (90% CI 93, 200), respectively. In addition, smoking is associated with a 30% decrease in duloxetine concentration. The exposure of duloxetine with CYP2D6 inhibitors or in CYP2D6 poor metabolizers is increased to a lesser extent than that observed with CYP1A2 inhibition and does not require a dose adjustment. In addition, duloxetine increases the exposure of drugs that are metabolized by CYP2D6, but not CYP1A2. Pharmacodynamic study results indicate that duloxetine may enhance the effects of benzodiazepines, but not alcohol or warfarin. An increase in gastric pH produced by histamine H(2)-receptor antagonists or antacids did not impact the absorption of duloxetine. While duloxetine is generally well tolerated, it is important to be knowledgeable about the potential for pharmacokinetic interactions between duloxetine and drugs that inhibit CYP1A2 or drugs that are metabolized by CYP2D6 enzymes.