Labedipinedilol‐A: A vanilloid‐based α/β‐adrenoceptor blocker with calcium entry blocking and long‐acting antihypertensive properties

The combination of β‐adrenoceptor blockade and vasodilator action have proved highly useful in antihypertensive therapy. Studies of the mechanisms of action of labedipinedilol‐A that combine these effects within a single molecule are described in this report. Intravenous labedipinedilol‐A (0.1–1.0 mg/kg) produced dose‐dependent hypotensive and bradycardia responses for above 1.0 h, significantly different from nifedipine (0.5 mg/kg, i.v.)‐induced hypotensive and reflex tachycardia activities in pentobarbital‐anesthetized Wistar rats. Pretreatment with labedipinedilol‐A also inhibited phenylephrine (20 μg/kg, i.v.)‐induced hypertensive and (‐)isoprenaline (0.5 μg/kg, i.v.)‐induced tachycardia effects. Oral administration of labedipinedilol‐A (5–50 mg/kg) in spontaneously hypertensive rats (SHR) reduced the blood pressure and heart rate for 24 h but did not increase heart rate. Labedipinedilol‐A (10^–7–10^–5 M) competitively antagonized (‐)isoprenaline (10^–10–10^–4M)‐induced positive chronotropic and inotropic effects of the isolated rat atria and tracheal relaxation responses of the isolated guinea pig tissues. Labedipinedilol‐A also prevented the rate‐increasing effects of increased extracellular Ca²⁺ (3.0–9.0 mM) in a concentration‐dependent manner. In the isolated rat aorta, labedipinedilol‐A competitively antagonized CaCl₂ and norepinephrine‐induced contractions with pKCa^–1 and pA₂ values of 8.46 ± 0.05 and 8.28 ± 0.03 and had a potent effect of inhibiting high K⁺‐induced vasocontraction. Furthermore, labedipinedilol‐A, in an equal antagonist activity, inhibited norepinephrine‐induced phasic and tonic contraction. In the cultured blood vessel smooth muscle cell (A7r5 cell line), KCl, norepinephrine, and Bay K 8644‐induced intracellular calcium changes were decreased after application of labedipinedilol‐A (10^–9–10^–6 M). The binding characteristics of labedipinedilol‐A were evaluated in [³H]CGP‐12177 binding to ventricle and lung and [³H]nitrendipine and [³H]prazosin binding to brain membranes in rats. The ‐logIC₅₀ values of labedipinedilol‐A for β₁‐, β₂‐, and α₁‐adrenoceptor and calcium channel, were 8.17 × 10^–7 M, 8.20 × 10^–7 M, 2.20 × 10^–8 M, and 2.46 × 10^–8 M, respectively. Labedipinedilol‐A‐induced sustained depressor effect was mainly attributed to its calcium entry and α‐adrenoceptor blocking activities in the blood vessel. Sustained bradycardia effect resulted from β‐adrenoceptor and calcium entry blocking, which deleted the sympathetic activation‐associated reflex tachycardia in the heart. Drug Dev. Res. 49:94–108, 2000. © 2000 Wiley‐Liss, Inc.     

Metabolism,oral bioavailability and pharmacokinetics of chemopreventive kaempferol in rats

The purpose of this study was to compare the hepatic and small intestinal metabolism, and to examine bioavailability and gastro‐intestinal first‐pass effects, of kaempferol in rats. Liver and small intestinal microsomes fortified with either NADPH or UDPGA were incubated with varying concentrations of kaempferol for up to 120 min. Based on the values of the kinetic constants (K_m and V_max), the propensity for UDPGA‐dependent conjugation compared with NADPH‐dependent oxidative metabolism was higher for both hepatic and small intestinal microsomes. Male Sprague‐Dawley rats were administered kaempferol intravenously (i.v.) (10, 25 mg/kg) or orally (100, 250 mg/kg). Gastro‐intestinal first‐pass effects were observed by collecting portal blood after oral administration of 100 mg/kg kaempferol. Pharmacokinetic parameters were obtained by non‐compartmental analysis using WinNonlin. After i.v. administration, the plasma concentration–time profiles for 10 and 25 mg/kg were consistent with high clearance (～3 L/hr/kg) and large volumes of distribution (8–12 L/hr/kg). The disposition was characterized by a terminal half‐life value of 3–4 h. After oral administration the plasma concentration–time profiles demonstrated fairly rapid absorption (t_max～1–2 h). The area under the curve (AUC) values after i.v. and oral doses increased approximately proportional to the dose. The bioavailability (F) was poor at ～2%. Analysis of portal plasma after oral administration revealed low to moderate absorption. Taken together, the low F of kaempferol is attributed in part to extensive first‐pass metabolism by glucuronidation and other metabolic pathways in the gut and in the liver. Copyright © 2009 John Wiley & Sons, Ltd.     

Pharmacokinetics of dietary cancer chemopreventive compound dibenzoylmethane in rats and the impact of nanoemulsion and genetic knockout of Nrf2 on its disposition

The pharmacokinetic disposition of a dietary cancer chemopreventive compound dibenzoylmethane (DBM) was studied in male Sprague‐Dawley rats after intravenous (i.v.) and oral (p.o.) administrations. Following a single i.v. bolus dose, the mean plasma clearance (CL) of DBM was low compared with the hepatic blood flow. DBM displayed a high volume of distribution (Vss). The elimination terminal t_1/2 was long. The mean CL, Vss and AUC_0?∞/dose were similar between the i.v. 10 and 10 mg/kg doses. After single oral doses (10, 50 and 250 mg/kg), the absolute oral bioavailability (F^*) of DBM was 7.4%–13.6%. The increase in AUC was not proportional to the oral doses, suggesting non‐linearity. In silico prediction of oral absorption also demonstrated low DBM absorption in vivo. An oil‐in‐water nanoemulsion containing DBM was formulated to potentially overcome the low F^* due to poor water solubility of DBM, with enhanced oral absorption. Finally, to examine the role of Nrf2 on the pharmacokinetics of DBM, since DBM activates the Nrf2‐dependent detoxification pathways, Nrf2 wild‐type (+/+) mice and Nrf2 knockout (?/?) mice were utilized. There was an increased systemic plasma exposure of DBM in Nrf2 (?/?) mice, suggesting that the Nrf2 genotype could also play a role in the pharmacokinetic disposition of DBM. Taken together, the results show that DBM has low oral bioavailability which could be due in part to poor water solubility and this could be overcome by a nanotechnology‐based drug delivery system and furthermore the Nrf2 genotype could also play a role in the pharmacokinetics of DBM. Copyright © 2010 John Wiley & Sons, Ltd.     

Isoeugenodilol: A vasorelaxant α/β‐adrenoceptor blocker with antioxidant activity

Isoeugenodilol, derived from isoeugenol, was investigated under in vivo and in vitro conditions. Isoeugenodilol (0.1, 0.5, 1.0, and 3.0 mg kg^–1, i.v.) produced dose‐dependent hypotensive and bradycardia responses in pentobarbital‐anesthetized Wistar rats. Isoeugenodilol (0.5 mg kg^–1, i.v.) also markedly inhibited both the tachycardia effects induced by (‐) isoproterenol and arterial pressor responses induced by phenylephrine. A single oral administration of isoeugenodilol at doses of 10, 30, and 100 mg kg^–1 dose‐dependently reduced blood pressure, with a decrease in heart rate in conscious spontaneously hypertensive rats (SHRs). In the isolated Wistar rat right atria, left atria, and guinea pig tracheal strips, isoeugenodilol competitively antagonized the (‐) isoproterenol‐induced positive chronotropic effects, inotropic effects, and tracheal relaxation effects in a concentration‐dependent manner. The parallel shift to the right of the concentration–response curve of (‐) isoproterenol suggested that isoeugenodilol was a β₁/β₂‐adrenoceptor competitive antagonist. The apparent pA₂ values were 7.33 ± 0.12 in the right atria, 7.80 ± 0.09 in the left atria, and 7.26 ± 0.11 in the trachea, indicating that isoeugenodilol was a nonselective β‐adrenoceptor blocker. In thoracic aorta experiments, isoeugenodilol also produced a competitive antagonism of norepinephrine‐induced contraction with a pA₂ value of 7.47 ± 0.45. In isolated atria of reserpinized rats, cumulative additions of isoeugenodilol and propranolol produced significantly cardiodepressant responses at high concentrations (10^–5 M) and were without intrinsic sympathomimetic activity (ISA). In isolated rat thoracic aorta, isoeugenodilol more potently relaxed the contractions induced by norepinephrine (3 × 10^–6 M) than those by high K⁺ (75 mM). The vasorelaxant effects of isoeugenodilol on norepinephrine‐induced contractions were attenuated by pretreatment with tetraethylammonium (TEA) and glibenclamide, implying the involvement of K⁺ channel opening. In addition, isoeugenodilol inhibited norepinephrine‐induced biphasic contraction; it affected the fast phase significantly more than the slow phase. Furthermore, the binding characteristics of isoeugenodilol and various β‐adrenoceptor antagonists were evaluated in [³H]CGP‐12177 binding to rat ventricle and lung tissues and [³H]prazosin binding to brain membranes. The ranking order of inhibition for [³H]CGP‐12177 binding on β‐adrenoceptor was propranolol > labetalol > isoeugenodilol, and that for [³H]prazosin binding to α‐adrenoceptors was isoeugenodilol > labetalol. Furthermore, isoeugenodilol inhibited lipid peroxidation induced by Fe²⁺ and ascorbic acid with IC₅₀ of 0.74 ± 0.03 mM, indicating that it possesses the antioxidant activity inherent in isoeugenol. In conclusion, isoeugenodilol was found to be a new generation α/β‐adrenoceptor antagonist with vasorelaxant activity by inhibiting Ca²⁺ channel, receptor‐mediated Ca²⁺ mobilization and by K⁺ channel opening, and to have additional potentially antioxidant effects. Drug Dev. Res. 51:29–42, 2000. © 2000 Wiley‐Liss, Inc.     

Stereoselective pharmacokinetics of desbutylhalofantrine, a metabolite of halofantrine, in the rat after administration of the racemic metabolite or parent drug

The main objective of this study was to determine the pharmacokinetics of the enantiomers of desbutylhalofantrine (DHF), a metabolite of halofantrine (HF), in the rat. Rats received either intravenous (2 mg/kg) or oral (7 mg/kg) (+/-)-DHF HCl, or (+/-)-HF HCl intravenously (3 mg/kg). Enantiomer concentrations in plasma were determined by a stereospecific assay. In all rats, the plasma concentrations of (+)-DHF exceeded those of (-)-DHF. After (+/-)-DHF, the mean (+):(-) ratios of AUC(0-infinity) after oral and intravenous dosing were 3.7 and 2.8, respectively. After intravenous doses of DHF, the (-):(+) enantiomeric ratios of Cl and V(dss) were approximately 2.8. There were no significant differences between the enantiomers in t(1/2) (mean 14-23 h) or t(max) (mean 10-12 h) after intravenous or oral administration of DHF. Oral bioavailability estimates of DHF enantiomers (>59%) were higher than those previously estimated for HF in the rat. The stereoselectivity in HF kinetics was not as pronounced as for DHF. It was estimated that over 44% of the dose of HF is metabolized to DHF enantiomers. It was concluded that DHF possesses a pharmacokinetic profile similar to that of HF, each possessing low values of clearance and high volume of distribution. DHF differed from HF in its degree of stereoselectivity in pharmacokinetics, and in its extent of oral bioavailability.     

Factors Responsible for the Variability of Saquinavir Absorption: Studies Using an Instrumented Dog Model

PURPOSE: To study the effect of dose and food on the bioavailability of saquinavir in dogs. METHODS: A Youden Square block design was used for six female mongrel dogs (20-24 kg) who received six saquinavir treatments. The six randomized treatments were 1 mg/kg intravenous infusion over 30 min; 200, 400, 600, and 800 mg of saquinavir in the form of 200-mg capsules given orally with food; and 400 mg of saquinavir given orally after an overnight fast. A 200-mg 14C-saquinavir capsule was used to replace one of the 200-mg unlabeled saquinavir capsules in the 200- and 800-mg oral study. RESULTS: Absorption of saquinavir from the gut was variable. (F(A): 49-95%). The 14C-saquinavir study shows that the total radioactivity absorbed from the gut was insignificantly different from that of unlabeled saquinavir, suggesting first-pass gut metabolism was unimportant. The bioavailability of saquinavir under fasting condition was significantly lower (8.41 +/- 4.7% vs. 20.3 +/- 2.6%, p < 0.05). Saquinavir underwent significant first-pass liver metabolism because hepatic clearance values (22 to 30 ml min(-1) kg(-1)) approached that of liver blood flow. CONCLUSIONS: Incomplete gut absorption and extensive first-pass liver metabolism are the causes for low bioavailability of saquinavir in dogs. Absorption was further reduced under fasted conditions.     

Estimation of absorption rate of α‐human atrial natriuretic peptide from the plasma profile and diuretic effect after intranasal administration to rats

The absorption rate of α‐human atrial natriuretic peptide (α‐hANP) after intranasal (i.n.) administration to rats was estimated from the plasma profile and pharmacological effect (diuretic effect) using a pharmacokinetic (PK) model and a PK–pharmacodynamic (PD) model involving data obtained after intravenous (i.v.) bolus injection. The plasma concentrations of α‐hANP after i.v. administration at different doses were fitted to a two‐compartment PK model with zero‐order excretion and input of endogenous α‐rat atrial natriuretic peptide (α‐rANP) and two elimination processes represented by Michaelis–Menten and first‐order kinetics. However, the saturable process was ignored at low doses. The plasma concentrations after low doses via the i.n. route could also be expressed by this model, but with first‐order absorption, so that an absorption rate constant was calculated using a deconvolution method. In addition, the diuretic effect plotted against the i.v. dose was represented by the Hill equation and showed an anti‐clockwise hysteresis loop versus the plasma concentration. These results suggest that the diuretic effect could be estimated by a PK–PD model having an ‘effect’ compartment or a homeostatic system. Such a PK–PD model accurately expressed the diuretic effect of α‐hANP at all doses after i.v. and i.n. administrations. The resulting absorption rate constant calculated using the PK–PD model agreed closely with that obtained by the PK model alone. The absorption rate and simulated diuretic effect suggest that, for i.n. administration of α‐hANP, a higher absorption rate constant causes a more potent diuretic effect (a dramatic effect over the early period), whereas greater bioavailability is associated with a better hypotensive effect (sustained effect). Copyright © 2001 John Wiley & Sons, Ltd.     

Preclinical Pharmacokinetic Evaluation of β-Lapachone: Characteristics of Oral Bioavailability and First-Pass Metabolism in Rats

β-Lapachone has drawn increasing attention as an anti-inflammatory and anti-cancer drug. However, its oral bioavailability has not been yet assessed, which might be useful to develop efficient dosage forms possibly required for non-clinical and clinical studies and future market. The aim of the present study was thus to investigate pharmacokinetic properties of β-lapachone as well as its first-pass metabolism in the liver, and small and large intestines after oral administration to measure the absolute bioavailability in rats. A sensitive HPLC method was developed to evaluate levels of β-lapachone in plasma and organ homogenates. The drug degradation profiles were examined in plasma to assess the stability of the drug and in liver and intestinal homogenates to evaluate first-pass metabolism. Pharmacokinetic profiles were obtained after oral and intravenous administration of β-lapachone at doses of 40 mg/kg and 1.5 mg/kg, respectively. The measured oral bioavailability of β-lapachone was 15.5%. The considerable degradation of β-lapachone was seen in the organ homogenates but the drug was quite stable in plasma. In conclusion, we suggest that the fairly low oral bioavailability of β-lapachone may be resulted from the first-pass metabolic degradation of β-lapachone in the liver, small and large intestinal tracts and its low aqueous solubility.     

Characterization of Intestinal and Hepatic CYP3A-Mediated Metabolism of Midazolam in Children Using a Physiological Population Pharmacokinetic Modelling Approach

Purpose

Changes in drug absorption and first-pass metabolism have been reported throughout the pediatric age range. Our aim is to characterize both intestinal and hepatic CYP3A-mediated metabolism of midazolam in children in order to predict first-pass and systemic metabolism of CYP3A substrates.

Methods

Pharmacokinetic (PK) data of midazolam and 1-OH-midazolam from 264 post-operative children 1–18 years of age after oral administration were analyzed using a physiological population PK modelling approach. In the model, consisting of physiological compartments representing the gastro-intestinal tract and liver,intrinsic intestinal and hepatic clearances were estimated to derive values for bioavailability and plasma clearance.

Results

The whole-organ intrinsic clearance in the gut wall and liver were found to increase with body weight, with a 105 (95% confidence interval (CI): 5–405) times lower intrinsic gut wall clearance than the intrinsic hepatic clearance (i.e. 5.08 L/h (relative standard error (RSE) 10%) versus 527 L/h (RSE 7%) for a 16 kg individual, respectively). When expressed per gram of organ, intrinsic clearance increases with increasing body weight in the gut wall, but decreases in the liver, indicating that CYP3A-mediated intrinsic clearance and local bioavailability in the gut wall and liver do not change with age in parallel. The resulting total bioavailability was found to be age-independent with a median of 20.8% in children (95%CI: 3.8–50.0%).

Conclusion

In conclusion, the intrinsic CYP3A-mediated gut wall clearance is substantially lower than the intrinsic hepatic CYP3A-mediated clearance in children from 1 to 18 years of age, and contributes less to the overall first-pass metabolism compared to adults.

     

First-Pass Effect of cis-3,4-Dichloro-N-methyl-N-(2-(l-pyrrolidinyl)-cyclohexyl)-benzamide (U-54494) in Rats— A Model with Multiple Cannulas for Investigation of Gastrointestinal and Hepatic Metabolism

A multiple cannulated rat model was utilized to investigate the relative contribution of the gut and liver as sites of first-pass metabolism of orally administered U-54494 A, an anticonvulsant drug candidate. Each rat received a dose of U-54494 A by oral, intraportal, and intravenous routes on three separate occasions. Intraportal and intravenous doses were administered through chronic cannulas surgically implanted in the portal vein and superior vena cava, respectively. Blood samples were collected over a 6-hr period from the superior vena cava cannula. The mean (n = 3) bioavailability of orally dosed U-54494A was 4.5 ± 1.1%, while that dosed intraportally was 19.1 ± 3.0%. The relative contribution of the gut and liver as sites of first-pass extraction and/or metabolism of orally administered drug was 69.9 ± 14.0% and 24.5 ± 12.2%, respectively. Approximately 35 to 40% of the total plasma clearance was attributed to the liver. The plasma concentrations of the four known metabolites of U-54494A were apparently higher for the oral and intraportal routes compared to that after intravenous administration. This investigation confirms that the low oral bioavailability of U-54494A in the rat can be primarily attributed to both extensive intestinal and hepatic first-pass metabolism.     

Oral absorption and presystemic first-pass effect of chlorpheniramine in rabbits

The oral absolute bioavailabilities of chloropheniramine (CPM) in four rabbits (New Zealand White, male, mean wt. 3.71 kg), averaged 0.06±0.03, 0.11±0.08, and 0.09±0.01 following a 3, 10.5, and 21 mg/kg dose, respectively. The individual bioavailability data and the AUCof one of the demethylated metabolites, desdimethyl CPM (DDCPM) obtained following different doses suggested the existence of saturable presystemic elimination. Two rabbits received an additional 10.5 mg/kg dose of CPM through portal vein infusion. Based on the oral, intraportal vein and i.v. studies, the mean extraction ratios of gut and the liver calculated for these two rabbits averaged 0.58 and 0.76, respectively. The latter value agreed well with the estimated hepatic extraction ratio from the in vitro liver homogenate study (0.89) or from the i.v. studies (0.83). The extensive prehepatic first-pass effect observed in the present study was consistent with similar findings in humans and dogs.     

Use of Freund's Complete Adjuvant (FCA) in inflammatory pain models: consequences on the metabolism and pharmacokinetics of the non-peptidic delta receptor agonist SNC80 in the rat

This study was initiated to characterize the metabolism and pharmacokinetics of SNC80 in rats and to evaluate the impact of Freund's complete adjuvant (FCA)-induced inflammation on its body disposition. In vitro, the disappearance and intrinsic clearance (CL(int)) of SNC80 were measured following incubations in recombinant rat CYPs and in phenotyped liver microsomes from naive and 24-h FCA-treated rats. The unbound fraction (f(u)) was assessed by ultrafiltration. Based on the Clint values, in vivo blood clearance of 3.35 and 2.48 L/h/kg were predicted in naive and FCA-treated rats. In vivo, SNC80 was administered to naive and 24-h FCA-treated rats at 10 micromol/kg i.v. and 50 micromol/kg p.o. The naive animals showed high plasma clearance (3.1 L/h/kg), low renal clearance (<0.02 L/h/kg) and poor bioavailability (<4%). Following i.v. administration, plasma clearance was lower (22%) in FCA-treated vs. untreated rats. Despite the decreases in f(u) (approximately 30%) and CL(int) (approximately 40%) in vitro, in vivo the apparent bioavailability and oral clearance were not significantly different between FCA-treated and naive rats. Hepatic and possibly intestinal losses contribute to the low bioavailability of SNC80. Non-hepatic mechanisms may compensate for the decrease in plasma clearance found in FCA-treated rats, preventing an increase in the oral bioavailability of SNC80.     

Paclitaxel in self-micro emulsifying formulations: oral bioavailability study in mice

The anticancer drug paclitaxel is formulated for i.v. administration in a mixture of Cremophor EL and ethanol. Its oral bioavailability is very low due to the action of P-glycoprotein in the gut wall and CYP450 in gut wall and liver. However, proof-of-concept studies using the i.v. formulation diluted in drinking water have demonstrated the feasibility of the oral route as an alternative when given in combination with inhibitors of P-glycoprotein and CYP450. Because of the unacceptable pharmaceutical properties of the drinking solution, a better formulation for oral application is needed. We have evaluated the suitability of various self-micro emulsifying oily formulations (SMEOF’s) of paclitaxel for oral application using wild-type and P-glycoprotein knockout mice and cyclosporin A (CsA) as P-glycoprotein and CYP450 inhibitor. The oral bioavailability of paclitaxel in all SMEOF’s without concomitant CsA was low in wild-type mice, showing that this vehicle does not enhance intestinal uptake by itself. Paclitaxel (10 mg/kg) in SMEOF#3 given with CsA resulted in plasma levels that were comparable to the Cremophor EL-ethanol containing drinking solution plus CsA. Whereas the AUC increased linearly with the oral paclitaxel dose in P-glycoprotein knockout mice, it increased less than proportional in wild-type mice given with CsA. In both strains more unchanged paclitaxel was recovered in the feces at higher doses. This observation most likely reflects more profound precipitation of paclitaxel within the gastro-intestinal tract at higher doses. The resulting absolute reduction in absorption of paclitaxel from the gut was possibly concealed by partial saturation of first-pass metabolism when P-glycoprotein was absent. In conclusion, SMEOF’s maybe a useful vehicle for oral delivery of paclitaxel in combination with CsA, although the physical stability within the gastro-intestinal tract remains a critical issue, especially when applied at higher dose levels.     

Preclinical pharmacokinetics of a novel HIV-1 attachment inhibitor BMS-378806 and prediction of its human pharmacokinetics

BMS-378806 is a prototype of novel HIV attachment inhibitors that block the gp120 and CD4 interaction, the first step of HIV-1 entry into cells. The present work investigated the pharmacokinetics of BMS-378806 in rats, dogs and monkeys and assessed its in vitro permeability and metabolism. BMS-378806 exhibited species-dependent oral bioavailability which was 19%-24% in rats and monkeys and 77% in dogs. In rats and monkeys, absorption was prolonged, with an apparent terminal half-life of 2.1 and 6.5 h, respectively. In rats, linear pharmacokinetics was observed between i.v. doses of 1 and 5 mg/kg and between p.o. doses of 5 and 25 mg/kg. The total body clearance was intermediate in rats and low in dogs and monkeys. The steady-state volume of distribution was moderate (0.4-0.6 l/kg), contributing to a short half-life (0.3-1.2 h) after i.v. dosing. Studies in bile-duct cannulated rats together with intraportal infusion studies revealed that the renal and hepatic clearance each accounted for 30% and 70% of the total elimination in rats, with the hepatic clearance largely being oxidative metabolism. In vitro, BMS-378806 was not highly protein bound (44%-73%). The Caco-2 permeability was modest (51 nm/s) and confounded by P-glycoprotein mediated efflux transport. Both of these may contribute to the low brain penetration observed in rats (brain/plasma AUC ratio=0.06). In human liver microsomes BMS-378806 was equally metabolized by cytochrome P450 1A2, 2D6 and 3A4 and did not inhibit major drug-metabolizing enzymes to a significant extent. Based on in vitro and animal data, a mechanistic approach that factors in absorption and first-pass metabolism was employed to predict the human oral bioavailability of BMS-378806 (ca 20%). This, together with the complex Dedrick plot method, was used to simulate human oral profiles and to project an efficacious dose. These study results offer a comprehensive assessment of the developability of BMS-378806 and provide important guidance to improving absorption and half-life of future compounds in the series. The current studies also demonstrate the value and approaches of understanding pharmacokinetic properties in the early stage of drug discovery.     

Ferulidilol: A vasodilatory and antioxidant adrenoceptor and calcium entry blocker,with ancillary β2‐agonist activity

Intravenous injection of ferulidilol (0.5, 1.0, 1.5 mg kg⁻¹) produced dose‐dependent hypotensive and bradycardia responses in pentobarbital‐anesthetized Wistar rats. Ferulidilol competitively antagonized (‐)isoprenaline‐induced positive inotropic and chronotropic effects of the atria and tracheal relaxation responses on isolated guinea pig tissues. The parallel shift to the right of the concentration–response curve of (‐)isoprenaline suggested that ferulidilol was a β‐adrenoceptor antagonist. The apparent pA₂ values were 8.04 ± 0.09 for the right atria, 8.03 ± 0.15 for the left atria, and 7.51 ± 0.06 for the trachea, respectively. Ferulidilol was more potent than labetalol. In thoracic aorta experiments, ferulidilol also produced a competitive antagonism of norepinephrine‐ and CaCl₂‐induced contraction with pA₂ and pKCa⁻¹ values of 7.05 ± 0.03 and 6.04 ± 0.05, respectively. Ferulidilol produced cumulative relaxation responses on isolated tracheal strips from reserpine‐treated guinea pigs. The effects were competitively antagonized by ICI 118,551 (10⁻⁸–10⁻⁶ M), a relatively selective β₂‐adrenoceptor antagonist. The results implied that ferulidilol had partial β₂‐agonist activity. In the radioligand binding assay, ferulidilol produced dose‐dependent inhibition of [³H]CGP‐12177 binding to rat ventricle and lung membranes with K_i values of 3.40 and 17.94 nM, respectively. In addition, ferulidilol also antagonized [³H]prazosin and [³H]nitrendipine binding to rat brain membrane with K_i values of 32.48 and 305.01 nM, respectively. These results further confirmed the α/β and calcium entry blocking activities of ferulidilol described in functional studies. Furthermore, ferulidilol (10⁻⁸–10⁻⁵ M] inhibited lipid peroxidation induced by Fe²⁺ and ascorbic acid, indicating that it possesses the antioxidant activity inherent in ferulic acid. Our results demonstrate that ferulidilol is a new generation α/β‐adrenoceptor blocker with ancillary calcium entry blockade, partial β₂‐agonist activities and additional antioxidant effects. Drug Dev. Res. 47:77–89, 1999. © 1999 Wiley‐Liss, Inc.     

Contribution of a significant first‐pass effect of dimethyl‐4,4′‐dimethoxy‐5,6,5′,6′‐dimethylene dioxybiphenyl‐2,2′‐dicarboxylate in the liver to its poor bioavailability in rats

Objectives The objective of this study was to investigate the mechanism responsible for the poor oral bioavailability of dimethyl-4′,4′-dimethoxy-5,6,5′,6′-dimethylene dioxy-biphenyl-2,2′-dicarboxylate (DDB), a hepatoprotective agent, in rats. Methods DDB was intravenously administered to rats at doses of 0.2-1 mg/kg. To determine the hepatic first-pass effect in rats, DDB (1 mg/kg) was administered via the pyloric vein and the femoral vein. Direct measurement of intestinal permeability was attempted using Caco-2 cell monolayers and rat intestinal epithelium. Key findings A moment analysis indicated that the volume of distribution and clearance remained unchanged with the magnitude of the dose, indicating that DDB exhibited linear pharmacokinetics. When the area under the curve for DDB after administration to the pyloric vein was compared with that after femoral vein administration, the ratio (F_H) was found to be 0.294, indicating a significant first-pass effect for DDB. The permeability of DDB was high in the rat intestine (1.78 ± 0.229 × 10⁻⁵ cm/s) and in Caco-2 cell monolayers (6.8 ± 0.70 × 10⁻⁵ cm/s), suggesting that DDB, in soluble form, was readily permeable across the intestinal epithelium. Conclusions These observations indicated that despite the fact that DDB was readily permeable to the intestinal epithelium, a significant first-pass metabolism was associated with its pharmacokinetics in rats.     

Use of Freund's Complete Adjuvant (FCA) in inflammatory pain models: Consequences on the metabolism and pharmacokinetics of the non-peptidic delta receptor agonist SNC80 in the rat

This study was initiated to characterize the metabolism and pharmacokinetics of SNC80 in rats and to evaluate the impact of Freund's complete adjuvant (FCA)-induced inflammation on its body disposition. In vitro, the disappearance and intrinsic clearance (CL_int) of SNC80 were measured following incubations in recombinant rat CYPs and in phenotyped liver microsomes from naive and 24-h FCA-treated rats. The unbound fraction (f_u) was assessed by ultrafiltration. Based on the Clint values, in vivo blood clearance of 3.35 and 2.48 L/h/kg were predicted in naive and FCA-treated rats. In vivo, SNC80 was administered to naive and 24-h FCA-treated rats at 10?µmol/kg i.v. and 50?µmol/kg p.o. The naive animals showed high plasma clearance (3.1 L/h/kg), low renal clearance (<0.02 L/h/kg) and poor bioavailability (<4%). Following i.v. administration, plasma clearance was lower (22%) in FCA-treated vs. untreated rats. Despite the decreases in f_u (～30%) and CL_int (～40%) in vitro, in vivo the apparent bioavailability and oral clearance were not significantly different between FCA-treated and naive rats. Hepatic and possibly intestinal losses contribute to the low bioavailability of SNC80. Non-hepatic mechanisms may compensate for the decrease in plasma clearance found in FCA-treated rats, preventing an increase in the oral bioavailability of SNC80.     

Influence of dose and route of administration on disposition of metronidazole and its major metabolites

Summary The influence of dose and route of administration on the kinetics of metronidazole and its major metabolites has been investigated in 8 healthy volunteers given 0.5 and 2.0 g i.v. and p.o. Metronidazole elimination kinetics from plasma could be described by an open two-compartment model. The systemic oral bioavailability of both doses was approximately 1. The total systemic clearance of the intravenous 2.0 g dose was 9% lower than that of the 0.5 g dose (p<0.05). There were no significant dose-related differences in volume or rate of distribution. The elimination half-life was similar after the four treatments with metronidazole. The major elimination pathways, renal excretion and hepatic oxidation and glucuronidation, accounted for more than 2/3 of the total systemic clearance. Clearance both by hepatic oxidative metabolism and renal excretion was significantly lower after 2.0 than after 0.5 g i.v., whereas there was no significant difference after the oral doses. The results indicate that a high therapeutic dose of metronidazole may be eliminated at a reduced rate, but this is probably not of clinical importance. No single saturable elimination pathway was identified.     

The Proteolytic Stability and Cytotoxicity Studies of l‐Aspartic Acid and l‐Diaminopropionic Acid derived β‐Peptides and a Mixed α/β‐Peptide

The use of peptides as drugs in pharmaceutical applications is hindered by their susceptibility to proteolysis and therefore low bioavailability. β‐Peptides that contain an additional methylene group in the backbone, are gaining recognition from a pharmaceutical stand point as they are considerably more resilient to proteolysis and metabolism. Recently, we reported two new classes of β ‐peptides, β ³‐ and β²‐peptides derived from l ‐aspartic acid and l ‐diaminopropionic acid, respectively. Here, we report the proteolytic stability of these β‐peptidic compounds and a mixed α /β‐peptide against three enzymes (pronase, trypsin and elastase), as well as, human serum. The stability of these peptides was compared to an α‐peptide. Peptides containing β‐linkages were resistant to all conditions. The mixed α /β‐peptide, however, exhibited proteolysis in the presence of trypsin and pronase but not elastase. The rate of degradation of the mixed α /β‐peptide was slower than that would be expected for an α‐peptide. In addition, these β‐peptides were not toxic to HeLa and COS‐1 cell lines as observed by MTT cytotoxicity assay. These results expand the scope of mixed α /β‐peptides containing β‐amino acids or small β‐peptide fragments as therapeutic peptides.     

Comparative tacrolimus pharmacokinetics: normal versus mildly hepatically impaired subjects

Tacrolimus (FK506, Prograf), marketed for the prophylaxis of organ rejection following allogenic liver or kidney transplantation, is virtually completely metabolized. The major metabolic pathways are P450 3A4-mediated hydroxylation and demethylation. Since P450 hepatic drug-metabolizing enzymes may be impaired in hepatic dysfunction, a study was conducted to characterize oral and intravenous tacrolimus pharmacokinetics in 6 patients with mild hepatic dysfunction and compared with parameters to those from normal subjects obtained in a separate study. Patients received two treatments: a single 0.020 mg/kg ideal body weight (IBW) i.v. dose infused over 4 hours and approximately 0.12 mg/kg IBW orally; normal subjects were dosed at 0.02 mg/kg 4-hour i.v. and 5 mg (0.065 mg/kg) p.o. Mean blood pharmacokinetic parameters with mild hepatic dysfunction were as follows: clearance = 0.035 L/h/kg, terminal exponential volume of distribution = 2.59 L/kg, terminal exponential half-life = 60.6 hours (i.v.), p.o. maximum blood concentration = 48.2 ng/mL, time of p.o. maximum blood concentration = 1.5 hours, and absolute bioavailability = 22.3%. The respective parameters in normal subjects were as follows: 0.040 L/h/kg, 1.91 L/kg, 34.2 hours (i.v.), 29.7 ng/mL, 1.6 hours, and 17.8%. Inasmuch as clearance and bioavailability were not substantially different from that in normal subjects, patients with mild hepatic impairment may initially be treated with conventional tacrolimus doses, with subsequent dosage adjustments based on response, toxicity, and therapeutic drug monitoring.