Diketopiperazine Formation,Hydrolysis, and Epimerization of the New Dipeptide Angiotensin-Converting Enzyme Inhibitor RS-10085

The degradation kinetics, products, and mechanisms of RS-10085(1), 2-[2-(l-ethoxycarbonyl)-3-phenylpropyl]amino-l-oxopropyl]-6,7-dimethoxy-l,2,3,4-tetrahydroisoquinoline-3-carboxylic acid(S,S,S), in aqueous solution were investigated at 40, 60, and 80°C from pH 1 to pH 13. Pseudo-first-order kinetics were observed throughout the pH range studied and the log(rate)–pH profiles reflected four kinetic processes (k _o, k_o, k_o, and k _OH) as well as the two pKa's of 1. Excellent (>98%) mass balance was obtained through products 2–5. At pH 4 or below, intramolecular cyclization leading to diketopiperazine 5 accounted for greater than 93% of the observed neutral- or water-catalyzed processes (k _o and k_o). At pH levels greater than 5, hydrolysis giving 2 predominated and was responsible for the observed neutral- or water-catalyzed (k_o) and specific base-catalyzed (k _OH) kinetic processes. Some epimerization leading to the S,S,R drug isomer (4) was also observed at pH levels greater than 7. The relative acidity of the protons at the three chiral centers of 1 was qualitatively compared and was used to explain the observed specificity in epimerization.     

Immobilized Artificial Membrane (lAM)-HPLC for Partition Studies of Neutral and Ionized Acids and Bases in Comparison with the Liposomal Partition System

Purpose. To study the partitioning of model acids ((RS)-warfarin and salicylic acid), and bases (lidocaine, (RS)-propranolol and diazepam), with immobilized artificial membrane (lAM)-HPLC, as compared to partitioning in the standardized phosphatidylcholine liposome/buffer system. Methods. The pH-dependent apparent partition coefficients D were calculated from capacity factors (k_IAM) obtained by IAM-HPLC, using a 11-carboxylundecylphosphocholine column. For lipophilic compounds k_IAM, values were determined with organic modifiers and extrapolation to 100% water phase (k_IAMw) was optimized. Temperature dependence was explored (23 to 45° C), and Gibbs free energy (G), partial molar enthalpy (H) and change in entropy (S) were calculated. Equilibrium dialysis was used for the partitioning studies with the liposome/buffer system. Results. For extrapolation of k_IAMw, linear plots were obtained both with the respective dielectric constants and the mole fractions of the organic modifier. All tested compounds showed a similar pH-D diagram in both systems; however, significant differences were reproducibly found in the pH range of 5 to 8. In all cases, G and H were negative, whereas S values were negative for acids and positive for bases. Conclusions. In both partitioning systems, D values decreased significantly with the change from the neutral to the charged ionization state of the solute. The differences found under physiological conditions, i.e. around pH 7.4, were attributed to nonspecific interactions of the drug with the silica surface of the IAM column.     

Complexation of Nifedipine with Substituted Phenolic Ligands

The bioavailability of nifedipine in man is highly variable. This may be partly due to its poor aqueous solubility (5–6 µg/ml over pH 2.2–10.0, as determined in this laboratory). We initiated this study to examine the enhancement of aqueous nifedipine solubility via complexation. A series of substituted aromatic ligands was studied to identify those structural features important for complexation with nifedipine. The studies were performed at 25°C employing the solubility technique, using pH 2.2 or 7.0 buffers at an ionic strength of 0.25 M. The apparent equilibrium complexation constants for the 1:1 and/or 1:2 complexes were determined, where appropriate. A linear free-energy approach was used to relate K _1:1 with Hammett's sigma () and fractional partition coefficient () parameters. The following correlation was obtained: log (K _l:l/K _o = 0.31 + 0.l0 + 0.36 (r ² = 0.86, P < 0.003, N = 9), where K _o is the complexation constant for phenol. Statistical analyses showed that was more important than in affecting nifedipine complexation. The exact location of this interaction on the nifedipine molecule is undefined at present.     

Stability of Lidocaine in Aqueous Solution: Effect of Temperature,pH, Buffer,and Metal Ions on Amide Hydrolysis

The degradation of lidocaine in aqueous solution obeys the expression k _obs = (k _H+[H ⁺] + k _o ) [H⁺]/([H ⁺ ] + K _a + k_o K _a([H ⁺ ] + K _a) where k _H+ is the rate constant for hydronium ion catalysis, and k _o and k_o are the rate constants for the spontaneous (or water-catalyzed) reactions of protonated and free-base lidocaine. At 80°C, the rate constants for these processes are 1.31 × 10^–7 M ^–l sec^–1, 1.37 × 10^–9 sec^–1, and 7.02 × 10^–9sec^–1; the corresponding activation energies are 30.5, 33.8, and 26.3 kcal mol^–1, respectively. It was found that the room temperature pH of maximum stability is 3–6 and that lidocaine is more reactive in the presence of metal ions such as Fe²⁺ and Cu²⁺. The dissociation constant, K _a, for lidocaine at 25–80°C was also measured at 0.1 M ionic strength and a plot of pK _a versus 1/T gave a slope of (1.88 ± 0.05) × 10³ K^–1 and intercept 1.56 ± 0.16.     

Stabilizing and Solubilizing Effects of Sulfobutyl Ether β-Cyclodextrin on Prostaglandin E1 Analogue

Purpose. Parent cyclodextrins are known to accelerate the degradations such as dehydration and isomerization of E-type prostaglandins in neutral and alkaline solutions. The objective of this study was to attempt the stabilization and solubilization of E₁-type prostaglandin analogue in aqueous solution by biocompatible cyclodextrin derivatives. Methods. The interaction of an E₁-type prostaglandin, methyl 7-[(1R,2R,3R)-3-hydroxy-2-[(E)-(3S)-3-hydroxy-4-(m-methoxymethylphenyl)1-butenyl]-5-oxocyclopentyl]-5-thiaheptanoate (MEester) with cyclodextrins (CyDs) was studied by spectroscopies and the solubility method. The degradation of MEester was monitored by high-performance liquid chromatography. Results. ¹H-nuclear magnetic resonance spectroscopic studies indicated that MEester forms 1:1 inclusion complexes with -, -, and -CyDs in solutions, where -CyD interacts with the -side chain containing methyl ester moiety of the drug, whereas - and -CyDs preferentially include around the five-membered ring and both side chains of the drug. Parent -CyD and hydrophilic derivatives, such as 2-hydoxypropyl-- and --CyDs, sulfobutyl ether -CyD (SBE--CyD) and maltosyl -CyD showed higher solubilizing abilities against MEester over parent - and -CyDs. SBE--CyD and 2,6-dimethyl--CyD (DM--CyD) significantly decelerated the degradation of MEester, particularly the base-catalyzed dehydration, in neutral and alkaline solutions, whereas other CyDs accelerated the degradation. The acid-catalyzed degradation of MEester (pH < 3) was decelerated by the addition of CyDs, especially -CyD. Conclusions. SBE--CyD with low hemolytic activity and low toxicity is useful as a pharmaceutical carrier for the preparation of injectable MEester, because of its higher stabilizing and solubilizing effects on MEester. Furthermore, SBE--CyD can be useful as a stabilizing agent for drugs, that are subject to base-catalyzed degradations, probably because of the electric repulsion between anionic charges of the sulfobutyl moiety and catalytic anionic species such as hydroxide ion.     

A Simple Rheological Method for the in Vitro Assessment of Mucin-Polymer Bioadhesive Bond Strength

A simple viscometric method was used to quantify mucin-polymer bioadhesive bond strength. Viscosities of 15% (w/v) porcine gastric mucin dispersions in 0.1 N HC1 (pH 1) or 0.1 N acetate buffer (pH 5.5) were measured with a Brookfield viscometer in the absence (_m) or presence (_t) of selected neutral, anionic, and cationic polymers (0.1–2.5%, w/v). Viscosity components of bioadhesion (1%) were calculated from the equation, _t = _m + _p + _b, where _p is the viscosity of corresponding pure polymer solution as measured by an Ostwald viscometer. The forces of bioadhesion (F) were calculated from the equation, F = _b, where is the rate of shear/sec. _b's and F's for polyelectrolytes, e.g., polyacrylic acid, cationic gelatin, and chitosan were always higher in acetate buffer than in HC1. Validity of the technique and the effect of ionic charge, polymer conformation, and rate of shear on _b and F are discussed, as is a comparison of this method to other methods for evaluating bioadhesive materials.     

Limits for the Scaled Average Bioequivalence of Highly Variable Drugs and Drug Products

Purpose. To provide a rational procedure for establishing regulatory bioequivalence (BE) limits that can be applied in determinations of scaled average BE for highly-variable (HV) drugs and drug products. Methods. Two-period crossover BE investigations with either 24 or 36 subjects were simulated with assumptions of a coefficient of variation of 10, 20, 30, or 40%. The decline in the fraction of accepted studies was recorded as the ratio of geometric means (GMR) for the two formulations was raised from 1.00 to 1.45. Acceptance of BE was evaluated by scaled average BE, assuming various BE limits, and, for comparison, by unscaled average BE. A procedure for calculating exact confidence limits in two-period studies is presented, and an approximate method, based on the linearization of the regulatory model, is applied. Results. A mixed model is proposed for average BE. Accordingly, at low variabilities, the BE limit is constant, ±BEL_o, generally log(1.25). Beyond a logarithmic, limiting, switching variability (_o), in the region of HV drugs, the approach of scaled average BE is applied with limits of ±(BEL_o /_o). It is demonstrated that the performance of the mixed model corresponds to these expectations. The effect of _o and of the resulting BE limits is also demonstrated. Scaled average BE, with all reasonable limits for HV drugs, requires fewer subjects than an unscaled average BE. In two-period studies, the exact and approximate methods calculating confidence limits yield very comparable inferences. Conclusions. Scaled average BE can be effectively applied, with the recommended limits, for determining the BE of HV drugs and drug products. The limiting, switching variability (_o) will have to be established by regulatory authorities.     

Analysis of the Compression Mechanics of Pharmaceutical Agglomerates of Different Porosity and Composition Using the Adams and Kawakita Equations

Purpose. To analyze the mechanics of some pharmaceuticalagglomerates during uniaxial confined compression by using compressionparameters derived from the Heckel, Kawakita and Adams equations, and tostudy the influence of these compression parameters on the tablet-formingability of agglomerates. Methods. Force and displacement data sampled during in-diecompression of agglomerates was used to calculate compression parametersaccording to the Heckel ( _y ), Kawakita(1/b and a), and Adams (₀)equations. Mechanical strength of single agglomerates as well as the airpermeability and tensile strength of tablets prepared from them were alsodetermined. Results. _y from the Heckelequation did not differ between agglomerates of different porosity. Both1/b and ₀ varied with agglomerate porosityand composition. These two compression parameters were linearly related toeach other. No general correlation was found between 1/b and₀ and the strength of single agglomerates. The twoparameters were related to the intergranular pore structure and tensilestrength of tablets formed from the agglomerates. Conclusions. 1/b and ₀ maybe interpreted as measures of the agglomerate shear strength during uniaxialconfined compression, and as such they may be used as indicators of thetabletting performance of the agglomerates.     

Synthesis and Cytotoxic Evaluation of a Series of γ-Substituted γ-Aryloxymethyl-α-methylene-γ-butyrolactones Against Cancer Cells

Purpose. The main objective of this investigation was to explore thecytotoxic structure-activity relationships of -substituted -aryloxymethyl--methylene--butyrolactones against cancer cells. Methods. The target compounds were synthesized in two stepscommencing with aryl-OH which was treated with a bromomethyl ketonefollowed by the Reformatsky-type condensation. Results. Seven types of -methylene--butyrolactones were evaluatedin vitro against 60 human cancer cell lines derived from nine cancercell types. The average values of log G₅₀ indicated that for thearylportion, potencies of these -methylene--butyrolactones are in adecreasing order of quinolin-2(1H)-one (or 2-hydroxyquinoline, 21,–5.89) > quinoline (19, –5.79) > 2-methylquinoline (20, –5.69)> 8-hydroxyquinoline (17, –5.64) > 2-naphthalene (16, –5.59)> benzene (15, –4.90). The same order was obtained for both log TGIand log LC₅₀. However, for the -substituent, the potencies are in adecreasing order of biphenyl (16f–21f) > phenyl and4-substituted phenyl (16b-e–21b-e) > methyl (16a–21a). Conclusions. Unlike cardiovascular activities of -methylene--butyrolactones in which a -methyl substituent is necessary for vasorelaxingeffect while a phenyl or a halogen-substituted phenyl is prefer for theantiplatelet activities, a -biphenyl substituent proved to be the bestfor their cytotoxicities against various cancer cell lines tested.     

β2-Adrenergic Receptor Genotype-Related Changes in cAMP Levels in Peripheral Blood Mononuclear Cells After Multiple-Dose Oral Procaterol

Purpose. To evaluate the ₂-adrenergic receptor (₂AR) genotype frequency in the Japanese population and the relationship between ₂AR genotype at amino acid position 16 (₂AR-16) and desensitization to ₂-agonist ex vivo. Methods. The ₂AR genotypes at amino acid positions 16, 27, and 164 of 92 healthy Japanese subjects were determined by polymerase chain reaction-restriction fragment-length polymorphism. The relationship between the ₂AR-16 genotype and the desensitization to ₂-agonist was examined in 10 male subjects ex vivo. Procaterol tablet (HCl salt, 50g, Meptin®) was given orally for 5 days, and peripheral blood was obtained before and after 5 days of consecutive medications followed by the assessment of the intracellular cAMP levels in peripheral blood mononuclear cells after incubation with or without procaterol hydrochloride (0-1000 ng/mL). Results. Allele frequency was Arg16:Gly16 = 46%:54%, Gln27:Glu27 = 92%:8%, and Thr164:Ile164 = 100%:0%, respectively. The cAMP levels were increased by incubation with procaterol hydrochloride, and the increase was suppressed after 5 days of consecutive medications. The suppression was more significant in the homozygote for Gly16 than the homozygote for Arg16. Conclusions. The desensitization to ₂-agonist was associated more frequently with the mutation at ₂AR-16 (Gly16).     

Hydroxypropyl-β-Cyclodextrin Increases the Aqueous Solubility and Stability of Pilocarpine Prodrugs

Purpose. The effects of 2-hydroxypropyl--cyclodextrin (HP--CD) on the aqueous solubility and stability of two lipophilic bispilocarpine prodrugs were investigated at pH 7.4. Methods. The solubility of prodrugs was studied by phase-solubility method (0–72.5 mM HP--CD). The stability of one of the prodrugs was investigated as a function of temperature (40°C–70°C) and HP--CD concentration (0–72.5 mM). The apparent rate constants (k ₁, k ₂) for degradation of prodrug in 1:1 and 1:2 inclusion complexes and apparent stability constants (K _1:1, K _l:2) were calculated by the curve-fitting method. Results. The phase-solubility diagrams were classified as A_p-type and the apparent stability constants (K _l:l, K _l:2) for 1:1- and 1:2-inclusion complexes were calculated to be 143–815 M^–l and 29–825 M^–1, respectively. The stability of prodrug increased as a function of HP--CD concentration over the studied temperature range. The shelf-life (t _90%, calculated by the Arrhenius equation) of the prodrug in 72.5 mM HP--CD solution increased 5.1-fold and 6.1-fold at 25°C and 4°C, respectively. Conclusions. The solubility of the prodrugs was shown to increase markedly in phase-solubility studies. The degradation rate of prodrug in stability studies was shown to be slower in the l:2-complex than in the l:l-complex and the relative amounts of complex species were found to be dependent on CD concentration.     

Simple model to explain effects of plasma protein binding and tissue binding on calculated volumes of distribution,apparent elimination rate constants and clearances

Summary A simple pharmacokinetic model, incorporating linear plasma protein binding, linear tissue binding, and first order elimination of free (unbound) drug, was studied. If Cl_p is the plasma clearance, V_f is the true volume of distribution of free drug, is the apparent elimination rate constant, is the fraction of the drug which is free in plasma, f is the fraction of the drug which is free in the entire body, k_f is the intrinsic elimination rate constant for free drug, and A _TB ^o is the initial amount of drug which is bound to tissues, then the model indicates that the following relationships hold: (1) Cl_p = V_f k_f; (2) = f k_f; and V_dext = (/f) V_f. Only , and not f, can be measuredexperimentally. Dividing Cl_p by provides an estimate of the intrinsic clearance of free drug, V_fk_f. A plot of V_dext versus has an intercept equal to V_f, and the ratio of the slope/intercept is an estimate of A _TB ^o /A _f ^o , where A _f ^o is the initial amount of free drug (equal to V_f times initial concentration of free drug in plasma). Thus, an estimate of A _TB ^o may be obtained. Dividing the intrinsic clearance by V_f provides an estimate of k_f. Thus, theoretically, estimates of V_f, k_f, A _TB ^o and f may be obtained. The variables are not separated when is plottedversus , and curvature of such plots is expected; no useful information is obtained from such plots.Partly supported by Public Health Service Grant 5-P-11-GM 1559 and partly by Grant 1RO1AAOO683-O1A1 from the National Institute on Alcohol Abuse and Alcoholism, Rockville, Maryland.     

Snake F(ab′)2 Antivenom from Hyperimmunized Horse: Pharmacokinetics Following Intravenous and Intramuscular Administrations in Rabbits

Purpose. The pharmacokinetics of a currently available horse F(ab)₂ antivenoms to Vipera aspis, V. ammodytes, and V. berus (Ipser Europe) and a new more purified and pasteurized preparation (SAV) was investigated in the rabbit. Methods. An immunoradiometric assay using an affinity-purified goat IgG horse F(ab)₂ specific and the same IgG labelled with iodine 125 as a tracer was developed. The limit of quantification in plasma was 0.032 µg/ml. Specificity study showed that mouse F(ab)₂ and Fab did not cross-react. Results. Pharmacokinetic analysis showed that the plasma F(ab)₂ concentration followed a biexponential decline after intravenous bolus administration with distribution and elimination half-lives of 2.66 ± 0.18 hrs and 49.69 ± 4.13 hrs, respectively. The total volume of distribution (Vdss or Vd) was between 209 and 265 ml.kg^–1 and was similar to the volume of the extracellular fluid in the rabbit (300 ml.kg^–1). Total body clearance ranged from 3.33 to 3.96 ml. h^–1 · kg^–1. After intramuscular administration which was only investigated with SAV, Tmax was 48 hrs and the absolute bioavailability was 42%. Conclusions. No difference in pharmacokinetics was observed between the two antivenom preparations following the intravenous administration. In contrast, a reduced rate and extent of absorption was shown following intramuscular administration.     

The Anomalous Hydrolytic Behavior of 1-Phenylvinyl Phosphate

The kinetics of hydrolysis of 1-phenylvinyl phosphate, 1, were studied over a pH range of 1 to 8.3 and over a pD range of 1 to 5.6 at 25°C and µ = 0.5 M with sodium chloride. The hydrolytic behavior of 1 was found to differ, in many respects, from that of alkyl and aryl phosphomonoesters. First, the rates of hydrolysis of 1 were extremely rapid and, in the hydronium ion-catalyzed region, gave a solvent deuterium isotope effect (k _H/k _D) of 3.20. Also, the ¹H-NMR spectrum of acetophenone formed upon complete hydrolysis of 1 in D₂O (pD 1.2) revealed that only one deuterium atom was incorporated into the methyl group. Hence, the evidence was consistent with a rate-limiting and nonreversible proton transfer from the solvent to 1. In addition, using an H₂ ¹⁸O labeling study in conjunction with ³¹P-NMR analysis, the hydrolytic mechanism appeared to involve nucleophilic attack by water at both the -carbon and the phosphorus atom with concurrent C–O and P–O bond fission. Second, in the pH region where the monoanionic species of 1 predominated, buffers had a pronounced catalytic effect on the hydrolysis rate; there appeared to be a normal solvent deuterium isotope effect; and the rate constant, k_o, showed a positive deviation from the established Brønsted relationship. The dissimilarities between 1 and alkyl and aryl phosphomonoesters supported the involvement of an alternate dephosphorylation pathway. One potential mechanism for the hydrolysis of 1, consistent with the experimental findings, might be rate-limiting and nonreversible protonation of the -carbon of the olefmic bond, resulting in the formation of a rapidly hydrated carbonium ion intermediate, a mechanism similar to that proposed for the more acidic pH region. Alternatively, a concerted mechanism involving proton transfer with expulsion of a monomeric metaphos-phate anion might be operating.     

Investigation of solid-state reactions using variable temperature X-ray powder diffractometry. II. Aminophylline monohydrate

Purpose. The object of this investigation was to demonstrate the utility of X-ray powder diffractometry (XRD) to study the kinetics of a complex pharmaceutical solid-state reaction wherein the reactant, product and intermediate phases were all simultaneously quantified. Methods. Aminophylline monohydrate (I) decomposed to anhydrous theophylline (III) either directly or through an intermediate (anhydrous aminophylline, II). The reaction kinetics were studied isothermally at several temperatures ranging from 65 to 100°C. By measuring the intensities of the XRD peaks unique to I, II and III, it was possible to simultaneously quantify the 3 phases during the entire reaction. Results. Assuming that all the reaction steps follow first-order kinetics, the three equations describing the concentrations of I, II and III as a function of time, were derived. By fitting the experimental data to these equations, it was possible to obtain the rate constants for the three reaction steps. The rate constants were obtained at different temperatures and were used to draw Arrhenius type plots from which the activation energies were determined. At lower temperatures (<80°C), the concentration of the intermediate phase, i.e., II, was low throughout the reaction while at higher temperatures (>90°C), there was rapid formation and accumulation of II during the early stages of the reaction. These differences could be attributed to the fact that k₁ (I II) had a more pronounced temperature dependence than k₂ (I III) and k₃ (II II). The XRD results were confirmed with isothermal thermogravimetry. Conclusions. Variable temperature XRD is a powerful tool to probe reaction kinetics in crystalline pharmaceuticals since it permits simultaneous quantification of multiple solid phases.     

Design and Evaluation of an Osmotic Pump Tablet (OPT) for Chlorpromazine Using (SBE)7m-β-CD

Purpose. The purpose of this study was to develop a controlled-porosity osmotic pump tablet (OPT) which exhibits pH-independent release profiles for a basic drug using a sulfobutyl ether--cyclodextrin, (SBE)_7m--CD, which acts as both a solubilizer and as an osmotic agent. Methods. Chlorpromazine free base (CLP) was chosen as a model drug for this study. The release of CLP from osmotic pump tablets was studied in vitro. In vivo absorption of CLP from the OPT was evaluated in male beagle dogs. Results. The CLP release profile from an OPT prepared from a core tablet composed of a 1:10 molar ratio of CLP to (SBE)_7m--CD was pH-independent, and was controlled by modulating the membrane thickness of the OPT. Another cyclodextrin, hydroxypropyl--cyclodextrin (HP--CD), and a sugar mixture of lactose and fructose resulted in pH-dependent release at the same molar ratio. An in vivo absorption study in dogs with an OPT containing (SBE)_7m--CD correlated very well with the in vitro release profiles using the Japanese Pharmacopoeia dissolution method. Conclusions. In addition to serving as a solubilizer and osmotic agent, (SBE)_7m--CD can also serve as the controlling agent for pH independent release of CLP from OPTs. This system successfully modified the in vivo input rate of CLP without compromising oral bioavailability.     

The Relationship of Diastereomer Hydrolysis Kinetics to Shelf-Life Predictions for Cefuroxime Axetil

Cefuroxime axetil, an ester prodrug of cefuroxime, is comprised of a 50:50 mixture of diastereomers A and B. The first-order hydrolysis kinetics of cefuroxime axetil were investigated as a function of pH, temperature, buffers, and ionic strength. Chromatographically identified hydrolysis products were cefuroxime, ²-cefuroxime axetil, and ,-sulfoxides. Buffer catalysis was observed in acetate and phosphate buffers. No significant kinetic effect was observed for ionic strength in the range µ = 0.1-1.0. The pH–rate profiles for hydrolysis of cefuroxime axetil isomeric mixture were obtained at 45, 35, and 25°C. The equation defining the cefuroxime axetil hydrolysis rate constant as a function of pH was k _obs = k _H(a _H) + k _s + k _OH(K _w/a _H), exhibiting maximal stability in the pH range 3.5 to 5.5. The predicted profile at 5°C was in excellent agreement with experimental data in the pH range 3.6 to 5.5. In the pH range 1 to 9, the maximum difference observed for individual hydrolysis constants of isomers was 27%. Shelf-life estimates based on the hydrolysis rate constants for cefuroxime axetil as an isomeric mixture were shown to be equivalent to those based on individual hydrolysis rate constants for isomers A and B.     

Further studies on (±)-YM-12617, a potent and selective α1-adrenoceptor antagonist and its individual optical enantiomers

Summary YM-12617, 5-[2-[[2-(o-ethoxyphenoxy)ethyl]amino]propyl]-2-methoxybenzenesulfonamide HCl is structurally novel, an extremely potent and highly selective ₁-adrenoceptor antagonist. An asymmetric center exists at the -carbon atom in the phenethylamine portion of YM-12617, therefore two optical enantiomers exist. -Adrenoceptor blocking properties and hypotensive activities of YM-12617 and its enantiomers have been compared in vitro and in vivo. 1. In the isolated rabbit aorta, R(–)- and S(+)-YM-12617 competitively antagonized phenylephrine-induced contraction with pA₂ values of 9.95 and 7.69, respectively. Although R(–)- and S(+)-YM-12617 were also competitive antagonists toward UK-14,304 at prejunctional ₂-adrenoceptors in the isolated guinea-pig ileum, the affinities of R(–)-YM-12617 (pA₂ = 6.18) and S(+)-YM-12617 (pA₂ = 5.64) for these receptors were 5,900 and 110 times lower than those displayed for postjunctional ₁-adrenoceptors in the isolated rabbit aorta. 2. R(–)- and S(+)-YM-12617 displaced both ³H-prazosin and ³H-idazoxan binding to rat brain membranes; however, the affinities of the R(–)- and S(+)-enantiomers for ₁-adrenoceptors (pK_i = 9.95 and 7.83, respectively) were 21,000 and 72 times higher than those for ₂-adrenoceptors (pK _i = 5.62 and 5.97), respectively. 3. Based on pA₂ values obtained in the isolated tissues and pK _i values in the binding assays, R(–)-YM-12617 was 132–182 times more potent than S(+)-YM-12617 as an antagonist at ₁-adrenoceptors. In contrast, the R(–)- and S(+)-enantiomers were similar in potency at blocking ₂-adrenoceptors. 4. In normotensive pithed rats, R(–)- and S(+)-YM-12617 preferentially antagonized the ₁-adrenoceptor mediated pressor effect of phenylephrine with DR₁₀ values of 1.38 and 705 g/kg i. v., respectively, although a high dose (3,000 g/kg i.v.) also inhibited the effect of UK-14,304 at postjunctional ₂-adrenoceptors. R(–)-YM-12617 exhibited an over 2,000-fold selectivity for postjunctional ₁-adrenoceptors, and R(–)-YM-12617 was over 500 times more potent than S(+)-YM-12617 in antagonizing postjunctional ₁-adrenoceptors based on DR₁₀ values. 5. In anesthetized rats, R(–)- and S(+)-YM-12617 dose-dependently produced hypotension with ED₂₀ values, doses required decreased mean blood pressure by 20%, of 0.64 and 61 g/kg i. v., respectively. R(–)-YM-12617 exerted a 95 times more potent hypotensive activity than S(+)-YM-12617, and its isomeric activity ratio was consistent with that for ₁-adrenoceptors but not ₂-adrenoceptors. 6. The present results suggest that the high stereoselectivity of the optical enantiomers of YM-12617 is in the ₁-adrenoceptor, but not in the ₂-adrenoceptor, and their antagonist potency for ₁-adrenoceptors is likely to contribute to the hypotensive effect. Send offprint requests to K. Honda     

Co-Administration of a Water-Soluble Polymer Increases the Usefulness of Cyclodextrins in Solid Oral Dosage Forms

Purpose. The aim of this study was to investigate the effect of cyclodextrins (-CD, HP--CD and (SBE)_7m--CD), and co-administration of a water-soluble polymer (HPMC) and cyclodextrins, on the oral bioavailability of glibenclamide in dogs. Methods. Effects of cyclodextrins on the aqueous solubility of glibenclamide, with and without hydroxypropylmethylcellulose (HPMC), were determined by a phase-solubility method. Solid inclusion complexes were prepared by freeze-drying. Glibenclamide was administered orally and intravenously to beagle dogs. Results. Aqueous solubility of glibenclamide increased as a function of cyclodextrin concentration, showing an A_L-type diagram for -CD and an A_p-type diagrams for both of the -CD derivatives studied. HPMC enhanced the solubilising effect of cyclodextrins, but did not affect the type of phase-solubility diagram. Orally administered glibenclamide and its physical mixture with HP--CD showed poor absolute bioavailability, while orally administered glibenclamide/cyclodextrin-complexes significantly enhanced the absolute bioavailability of glibenclamide. Orally administered glibenclamide/-CD/HPMC and glibenclamide/(SBE)_7m--CD/HPMC complexes showed similar absolute bioavailability compared to formulations not containing HPMC, even though 80% (in the case of (SBE)_7m--CD) or 40% (in the case of -CD) less cyclodextrin was used. Conclusions. The oral bioavailability of glibenclamide was significantly increased by cyclodextrin complexation. HPMC increased the solubilising effect of cyclodextrins and, therefore, the amount of cyclodextrin needed in the solid dosage form was significantly reduced by their co-administration. In conclusion, the pharmaceutical usefulness of cyclodextrins in oral administration may be substantially improved by co-administration of a water-soluble polymer.