Howard E. Greenberg

Single- and Multiple-Dose Pharmacokinetics of Caspofungin in Healthy Men

ABSTRACT Caspofungin, a glucan synthesis inhibitor, is being developed as a parenteral antifungal agent. The pharmacokinetics of caspofungin following 1-h intravenous infusions in healthy men was investigated in four phase I studies. In an alternating two-panel (six men each), rising-single-dose study, plasma drug concentrations increased proportionally with the dose following infusions of 5 to 100 mg. The β-phase half-life was 9 to 10 h. The plasma drug clearance rate averaged 10 to 12 ml/min. Renal clearance of unchanged drug was a minor pathway of elimination (∼2% of the dose). Multiple-dose pharmacokinetics were investigated in a 2-week, serial-panel (5 or 6 men per panel) study of doses of 15, 35, and 70 mg administered daily; a 3-week, single-panel (10 men) study of a dose of 70 mg administered daily; and a parallel panel study (8 men) of a dose of 50 mg administered daily with or without a 70-mg loading dose on day 1. Moderate accumulation was observed with daily dosing. The degree of drug accumulation and the time to steady state were somewhat dose dependent. Accumulation averaged 24% at 15 mg daily and ∼50% at 50 and 70 mg daily. Mean plasma drug concentrations were maintained above 1.0 μg/ml, a target selected to exceed the MIC at which 90% of the isolates of the most clinically relevant species of Candida were inhibited, throughout therapy with daily treatments of 70 or 50 mg plus the loading dose, while they fell below the target for the first 2 days of a daily treatment of 50 mg without the loading dose. Caspofungin infused intravenously as a single dose or as multiple doses was generally well tolerated. In conclusion, the pharmacokinetics of caspofungin supports the clinical evaluation of once-daily dosing regimens for efficacy against fungal infections.

Pharmacokinetics of Ertapenem in Healthy Young Volunteers

ABSTRACT Ertapenem (INVANZ) is a new once-a-day parenteral β-lactam antimicrobial shown to be effective as a single agent for treatment of various community-acquired and mixed infections. The single- and multiple-dose pharmacokinetics of ertapenem at doses up to 3 g were examined in healthy young men and women volunteers. Plasma and urine samples collected were analyzed using reversed-phase high-performance liquid chromatography with UV detection. Ertapenem is highly bound to plasma protein. The protein binding changes from ∼95% bound at concentrations of <50 μg/ml to ∼92% bound at concentrations of 150 μg/ml (concentration at the end of a 30-min infusion following the 1-g dose). The nonlinear protein binding of ertapenem resulted in a slightly less than dose proportional increase in the area under the curve from 0 h to infinity (AUC0-∞) of total ertapenem. The single-dose AUC0-∞ of unbound ertapenem was nearly dose proportional over the dose range of 0.5 to 2 g. The mean concentration of ertapenem in plasma ranged from ∼145 to 175 μg/ml at the end of a 30-min infusion, from ∼30 to 34 μg/ml at 6 h, and from ∼9 to 11 μg/ml at 12 h. The mean plasma t1/2 ranged from 3.8 to 4.4 h. About 45% of the plasma clearance (CLP) was via renal clearance. The remainder of the CLP was primarily via the formation of the β-lactam ring-opened metabolite that was excreted in urine. There were no clinically significant differences between the pharmacokinetics of ertapenem in men and women. Ertapenem does not accumulate after multiple once-daily dosing.

Exposure‐Dependent Inhibition of Intestinal and Hepatic CYP3A4 In Vivo by Grapefruit Juice

Consumption of typical quantities of grapefruit juice (GFJ) increases the oral bioavailability of several CYP3A4 substrates without affecting their elimination, consistent with selective inhibition of intestinal but not hepatic CYP3A4. However, increases in the AUCs of CYP3A4 substrates recently associated with the consumption of large amounts of GFJ were similar to those observed with potent inhibitors of hepatic CYP3A4. The current study compared the effects of consuming large quantities and more typical amounts of GFJ on the activity of hepatic and intestinal cytochrome P450 3A4 in vivo, employing the erythromycin breath test (EBT) and oral midazolam pharmacokinetics. This was a two‐phase, randomized, placebo‐controlled crossover study, with each phase conducted with a separate panel of subjects. In Phase I, 8 male volunteers were randomized to the order of receiving one glass (240 mL) of water (placebo) or double‐strength (DS) GFJ tid for 2 days and then 90, 60, and 30 minutes prior to administration of probe drugs on the 3rd day. In Phase II, 16 male volunteers were randomized to the order of receiving one glass of (1) single‐strength (SS) GFJ, (2) DS GFJ, and (3) water (placebo). All treatments were administered in a fasted state. There was at leasta a 7‐day washout period between treatments. Probe drugs, administered 30 minutes or 1 hour following each treatment in Phase I or II, respectively, consisted of oral midazolam (2 mg) coadministered with IV [14C N‐methyl] erythromycin (0.03 mg). The EBT was performed 20 minutes following erythromycin administration. Blood was collected during the 24 hours following probe drug administration for the analysis of midazolam pharmacokinetics. In Phase I, consumption of one glass of DS GFJ tid for 3 days increased the Cmax of midazolam 3‐fold, the AUC 6‐fold, and the t1/2 2‐fold and decreased the amount of exhaled 14CO2 in all 8 subjects, with a mean decrease in EBT of 18%. In Phase II, consumption of one glass of DS GFJ significantly increased the AUC and Cmax of midazolam ∼2‐fold without a significant effect on the t1/2 of midazolam or the EBT. The effects of consuming one glass of SS GFJ on midazolam pharmacokinetics and the EBT were not significantly different from those of one glass of DS GFJ. It was concluded that consumption of one glass of DS GFJ tid for 3 days significantly increased the AUC, Cmax, and t1/2 of midazolam and reduced EBT values, reflecting inhibition of both hepatic and intestinal CYP3A4. In contrast, consumption of one glass of SS or DS GFJ increased midazolam AUC and Cmax, with little effect on the midazolam t1/2 and EBT values, reflecting preferential inhibition of intestinal CYP3A4. Alterations of midazolam AUC and Cmax induced by nine glasses of DS GFJ were significantly greater than those produced by one glass of SS or DS GFJ. These data suggest that GFJ inhibits intestinal and hepatic CYP3A4 in an exposure‐dependent fashion and that patients taking medications that are CYP3A4 substrates are at risk for developing drug‐related adverse events if they consume large amounts of grapefruit juice.

Effects of aprepitant on the pharmacokinetics of ondansetron and granisetron in healthy subjects

BACKGROUND The neurokinin-1-receptor antagonist aprepitant, when given in combination with a corticosteroid and a 5-hydroxytryptamine type 3 (5-HT(3))-receptor antagonist, has been shown to be effective for the prevention of acute and delated chemotherapy-induced nausea and vomiting (CINV). OBJECTIVE Two studies were conducted to determine whether concomitant administration of aprepitant altered the pharmacokinetic profiles of ondansetron and granisetron, two 5-HT(3)-receptor antagonists commonly used as antiemetic therapy for CINV. METHODS The 2 studies were randomized, open-label, crossover trials conducted in healthy subjects aged between 18 and 46 years. Study 1 involved the following 2 treatment regimens: aprepitant 375 mg PO, dexamethasone 20 mg PO, and ondansetron 32 mg IV on day 1, followed by aprepitant 250 mg PO and dexamethasone 8 mg PO on days 2 through 5; and dexamethasone 20 mg PO and ondansetron 32 mg IV on day 1, followed by dexamethasone 8 mg PO on days 2 through 5. Study 2 involved the following 2 treatment regimens: aprepitant 125 mg PO with granisetron 2 mg PO on day 1, followed by aprepitant 80 mg PO on days 2 and 3; and granisetron 2 mg PO on day 1 only. Individual plasma samples were used to estimate area under the plasma concentration-time curve from time zero to infinity (AUC(0- infinity )), peak plasma concentration, and apparent terminal elimination half-life (t(12)) of both ondansetron and granisetron. RESULTS Study 1 included 19 subjects (10 women, 9 men), and study 2 included 18 subjects (11 men, 7 women). Coadministration of aprepitant 375 mg produced a small but statistically significant increase in the AUC(0- infinity ) for intravenous ondansetron (from 1268.3 to 1456.5 ng.h/mL; P = 0.019), with no significant effect on peak concentration at the end of the infusion (360.8 ng/mL with aprepitant vs 408.4 ng/mL without) or t(12) (5.0 vs 4.5 hours, respectively). Coadministration of aprepitant 125 mg/80 mg did not alter the mean pharmacokinetic characteristics of oral granisetron (AUC(0- infinity ), 101.4 ng.h/mL with aprepitant vs 92.2 ng.h/mL without; maximum plasma concentration, 9.0 ng/mL with and without aprepitant; time to maximum plasma concentration, both 3.0 hours; t(12), 6.5 vs 6.9 hours, respectively). CONCLUSION Concomitant administration of aprepitant had no clinically significant effect on the mean pharmacokinetic characteristics of either ondansetron or granisetron in these healthy subjects.

Potential for Interactions between Caspofungin and Nelfinavir or Rifampin

ABSTRACT The potential for interactions between caspofungin and nelfinavir or rifampin was evaluated in two parallel-panel studies. In study A, healthy subjects received a 14-day course of caspofungin alone (50 mg administered intravenously [IV] once daily) (n = 10) or with nelfinavir (1,250 mg administered orally twice daily) (n = 9) or rifampin (600 mg administered orally once daily) (n = 10). In study B, 14 subjects received a 28-day course of rifampin (600 mg administered orally once daily), with caspofungin (50 mg administered IV once daily) coadministered on the last 14 days, and 12 subjects received a 14-day course of caspofungin alone (50 mg administered IV once daily). The coadministration/administration alone geometric mean ratio for the caspofungin area under the time-concentration profile calculated for the 24-h period following dosing [AUC0-24] was as follows (values in parentheses are 90% confidence intervals [CIs]): 1.08 (0.93-1.26) for nelfinavir, 1.12 (0.97-1.30) for rifampin (study A), and 1.01 (0.91-1.11) for rifampin (study B). The shape of the caspofungin plasma profile was altered by rifampin, resulting in a 14 to 31% reduction in the trough concentration at 24 h after dosing (C24h), consistent with a net induction effect at steady state. Both the AUC and the C24h were elevated in the initial days of rifampin coadministration in study A (61 and 170% elevations, respectively, on day 1) but not in study B, consistent with transient net inhibition prior to full induction. The coadministration/administration alone geometric mean ratio for the rifampin AUC0-24 on day 14 was 1.07 (90% CI, 0.83-1.38). Nelfinavir does not meaningfully alter caspofungin pharmacokinetics. Rifampin both inhibits and induces caspofungin disposition, resulting in a reduced C24h at steady state. An increase in the caspofungin dose to 70 mg, administered daily, should be considered when the drug is coadministered with rifampin.

Characterization of Etoricoxib, a Novel, Selective COX‐2 Inhibitor

Etoricoxib is a potent selective COX‐2 inhibitor in man. Ex vivo whole‐blood assays assessed COX‐2 inhibition after oral administration of etoricoxib in single (5–500 mg) and multiple (25–150 mg) once‐daily doses to healthy human subjects. A separate study examined ex vivo gastric mucosal PGE2 synthesis after etoricoxib (120 mg qd), naproxen (500 mg bid), or placebo for 5 days. The effect of etoricoxib 120 mg qd on the COX‐1‐mediated antiplatelet effects of low‐dose aspirin (ASA) was also assessed. The mean (time)–weighted average inhibition (WAI) of lipopolysaccharide (LPS)–stimulated PGE2(COX‐2 assay) versus placebo was dose related after single (range: 3.1%–99.1%) and multiple doses (range: 52.5%–96.7%). PGE2 remained significantly inhibited 24 hours postdose at steady state. Inhibition of LPS‐stimulated PGE2 showed a strong relationship with etoricoxib plasma concentrations; ex vivo, IC50 was almost identical to in vitro. Multiple dosing of etoricoxib (up to 150 mg qd) showed no important effects on serum TXB2, bleeding time, or platelet aggregation (COX‐1‐mediated effects). The nonselective nonsteroidal anti‐inflammatory (NSAID) naproxen significantly inhibited (∼78%) ex vivo prostaglandin synthesis in gastric mucosa; etoricoxib had no effect. Etoricoxib did not interfere with the antiplatelet effects of low‐dose ASA, as assessed by serum TXB2 and platelet aggregation. Etoricoxib was generally well tolerated, even at doses above the clinical dose range. Based on these results, etoricoxib is a potent selective inhibitor of COX‐2 after single and multiple dosing regimens and does not inhibit prostaglandin synthesis in the gastric mucosa, even at doses above the clinical dose range of 60 to 120 mg.

A New Cyclooxygenase‐2 Inhibitor, Rofecoxib (VIOXX®), Did Not Alter the Antiplatelet Effects of Low‐Dose Aspirin in Healthy Volunteers

The present study examined whether rofecoxib (VIOXX®), a new specific inhibitor of cyclooxygenase‐2 (COX‐2), would interfere with the desired antiplatelet effects of aspirin. Thus, the effects of rofecoxib on inhibition of ex vivo serumgenerated thromboxane B2 (TXB2) and platelet aggregation by low doses (81 mg) of aspirin were examined in healthy volunteers. This was a double‐blind, randomized, placebo‐controlled, parallel study of two treatment groups (n = 12 per group) in which subjects received 50 mg of rofecoxib or placebo for 10 days in a blinded fashion. Subjects also received 81 mg aspirin once on each of days 4 through 10 in an open‐label fashion. Blood for measurement of serum TXB2 production and platelet aggregation studies was collected on day 1 (prior to rofecoxib/placebo), on day 4 (prior to aspirin), and on day 10 (before and 4 hours following the seventh dose of aspirin). Platelet‐derived serum TXB2 (COX‐1 assay) was measured in blood clotted for 1 hour at 37°C. Platelet aggregation was independently induced employing 1 mM arachidonic acid and 1 μg/mL collagen as agonists. Rofecoxib administered alone had no significant effect on serum TXB2 production or platelet aggregation (day 4). TXB2 production was inhibited 98.4% by aspirin coadministered with either rofecoxib or placebo (day 10). Similarly, platelet aggregation induced by arachidonic acid was inhibited 93.7% and 93.5% by aspirin coadministered with either rofecoxib or placebo, respectively (day 10). The comparable values for inhibition of collagen‐induced platelet aggregation were 86.8% and 90.8%, respectively. No important clinical or laboratory adverse experiences were observed. In conclusion, rofecoxib alone (50 mg QD for 4 days) did not inhibit serum TXB2 production or platelet aggregation. In addition, rofecoxib (50 mg QD for 10 days) did not alter the antiplatelet effects of low‐dose aspirin (inhibition of platelet aggregation and TXB2 production). Rofecoxib was generally well tolerated when administered alone or in combination with low‐dose aspirin.

Diurnal variation of the human adipose transcriptome and the link to metabolic disease

BackgroundCircadian (diurnal) rhythm is an integral part of the physiology of the body; specifically, sleep, feeding behavior and metabolism are tightly linked to the light-dark cycle dictated by earths rotation.MethodsThe present study examines the effect of diurnal rhythm on gene expression in the subcutaneous adipose tissue of overweight to mildly obese, healthy individuals. In this well-controlled clinical study, adipose biopsies were taken in the morning, afternoon and evening from individuals in three study arms: treatment with the weight loss drug sibutramine/fasted, placebo/fed and placebo/fasted.ResultsThe results indicated that diurnal rhythm was the most significant driver of gene expression variation in the human adipose tissue, with at least 25% of the genes having had significant changes in their expression levels during the course of the day. The mRNA expression levels of core clock genes at a specific time of day were consistent across multiple subjects on different days in all three arms, indicating robust diurnal regulation irrespective of potential confounding factors. The genes essential for energy metabolism and tissue physiology were part of the diurnal signature. We hypothesize that the diurnal transition of the expression of energy metabolism genes reflects the shift in the adipose tissue from an energy-expending state in the morning to an energy-storing state in the evening. Consistent with this hypothesis, the diurnal transition was delayed by fasting and treatment with sibutramine. Finally, an in silico comparison of the diurnal signature with data from the publicly-available Connectivity Map demonstrated a significant association with transcripts that were repressed by mTOR inhibitors, suggesting a possible link between mTOR signaling, diurnal gene expression and metabolic regulation.ConclusionDiurnal rhythm plays an important role in the physiology and regulation of energy metabolism in the adipose tissue and should be considered in the selection of novel targets for the treatment of obesity and other metabolic disorders.

Pharmacokinetics of Raltegravir in Individuals With UGT1A1 Polymorphisms

Raltegravir is a human immunodeficiency virus–1 (HIV‐1) integrase strand transfer inhibitor metabolized by glucuronidation via UDP‐glucuronosyltransferase 1A1 (UGT1A1). In this study, 30 subjects with a UGT1A1*28/*28 genotype (associated with decreased activity of UGT1A1) and 27 UGT1A1*1/*1 control subjects (matched by race, age, gender, and body mass index) received a single 400‐mg dose of raltegravir after fasting. No serious adverse experiences were reported, and there were no discontinuations due to adverse experiences. The geometric mean ratio (GMR) (UGT1A1*28/*28 to UGT1A1*1/*1) and 90% confidence interval (CI) were 1.41 (0.96, 2.09) for raltegravir area under the concentration–time curve (AUC0–∞), 1.40 (0.86, 2.28) for maximum plasma concentration (Cmax), and 1.91 (1.43, 2.55) for concentration at the 12‐h time point (C12 h). No clinically important differences in time to maximum concentration (Tmax) or half‐life were observed. Plasma concentrations of raltegravir are modestly higher in individuals with the UGT1A1*28/*28 genotype than in those with the UGT1A1*1/*1 genotype. This increase is not clinically significant, and therefore no dose adjustment of raltegravir is required for individuals with the UGT1A1*28/*28 genotype.

Pharmacokinetics of Aprepitant After Single and Multiple Oral Doses in Healthy Volunteers

Aprepitant is the first NK1 receptor antagonist approved for use with corticosteroids and 5HT3 receptor antagonists to prevent chemotherapy‐induced nausea and vomiting (CINV). The effective dose to prevent CINV is a 125‐mg capsule on day 1 followed by an 80‐mg capsule on days 2 and 3. Study 1 evaluated the bioavailability of the capsules and estimated the effect of food. The mean (95% confidence interval [CI]) bioavailabilities of 125‐mg and 80‐mg final market composition (FMC) capsules, as assessed by simultaneous administration of stable isotope‐labeled intravenous (IV) aprepitant (2 mg) and FMC capsules, were 0.59 (0.53, 0.65) and 0.67 (0.62, 0.73), respectively. The geometric mean (90% CI) area under the plasma concentration time curve (AUC) ratios (fed/fasted) were 1.2 (1.10, 1.30) and 1.09 (1.00, 1.18) for the 125‐mg and 80‐mg capsule, respectively, demonstrating that aprepitant can be administered independently of food. Study 2 defined the pharmacokinetics of aprepitant administered following the 3‐day regimen recommended to prevent CINV (125 mg/80 mg/80 mg). Consistent daily plasma exposures of aprepitant were obtained following this regimen, which was generally well tolerated.