Aqueous stability of human epidermal growth factor 1-48.

Human epidermal growth factor 1-48 (hEGF 1-48, Des(49-53)hEGF) is a single chain polypeptide (48 amino acids; 3 disulfide bonds; 5445 Da) possessing a broad spectrum of biologic activity including the stimulation of cell proliferation and tissue growth. In this study, three primary aqueous degradation products of hEGF 1-48 were isolated using isocratic, reverse phase/ion-pair HPLC. The degradation products were characterized using amino acid sequencing, electrospray ionization mass spectrometry, isoelectric focusing, and degradation kinetics. Results indicate that hEGF 1-48 degrades via oxidation (Met21), deamidation (Asn1), and succinimide formation (Asp11). The relative contribution of each degradation pathway to the overall stability of hEGF 1-48 changes as a function of solution pH and storage condition. Succinimide formation at Asp11 is favored at pH < 6 in which aspartic acid is present mostly in its protonated form. Deamidation of Asn1 is favored at pH > 6. The relative contribution of Met21 oxidation is increased with decreasing temperature, storage as a frozen solution (-20 degrees C), and exposure to fluorescent light.

The effects of bile salts and lipids on the physicochemical behavior of gemfibrozil.

Physicochemical effects caused by intestinal fluids on drugs in the gastrointestinal (GI) tract can be a contributing factor in food induced changes in bioavailability. To identify physicochemical properties of gemfibrozil that may be altered by endogenous and dietary lipids, in vitro studies were conducted in model systems approximating the conditions of the upper GI tract. Factors examined include pH, solubility in bile salt micellar and mixed micellar systems with monoolein and lecithin, effect of fatty acids, dissolution, wetting, and partitioning in triglyceride dispersions. Gemfibrozil was solubilized by glycocholate solutions in a manner typical of other lipids and a three-fold increase in solubility was observed over physiologic concentrations. Addition of increasing amounts of swelling amphiphiles (monoolein, lecithin) to glycocholate solutions resulted in a linear increase in solubility. Fatty acid salts had no effect on gemfibrozil solubilization by micellar solutions. The dissolution rate of gemfibrozil increased slightly in the presence of glycocholate relative to buffer, however, addition of monoolein increased the dissolution rate three-fold. In triglyceride dispersions of mixtures of lipids, monoolein increased the fraction of drug in the micellar subphase, whereas fatty acid reduced it. The results indicate that in the conditions of the fed state gemfibrozil solubility and dissolution could be substantially increased relative to the conditions in the fasted state.

Mechanism of drug release from an acrylic polymer-wax matrix tablet.

An acrylic polymer-wax matrix system was evaluated for oral sustained-release tablets of diphenhydramine HCl. A desirable release profile of diphenhydramine was achieved by incorporating Eudragit L in a carnauba wax matrix. In this polymer-wax system, carnauba wax maintained the integrity of the matrix, whereas Eudragit L slowly eroded in the matrix as the drug was released. Thus, the area-to-volume ratio of the tablet remained constant over the duration of the drug release. In vitro drug release studies were conducted at physiological pHs that exist in the gastrointestinal tract. Drug release rates decreased as the polymer:drug ratio increased from 1:2 to 2:1. The drug release rate was faster in pH 7.5 phosphate buffer than in 0.1 N HCl solution. The drug release from these polymer-wax matrices is described by a combination diffusion/erosion mechanism. Based on the typical pH encountered in intestinal fluids, complete dissolution of the drug and polymer at pH 7.5 in 8-10 h would ensure good bioavailability of the drug following oral administration.

The interconversion kinetics, equilibrium, and solubilities of the lactone and hydroxyacid forms of the HMG-CoA reductase inhibitor, CI-981.

The pH dependence of the interconversion kinetics, equilibrium, and solubilities of the lactone and hydroxyacid forms of the HMG-CoA reductase inhibitor, CI-981 ([R-(R*,R*)]-2-(4-fluorophenyl)- beta,delta-dihydroxy-5-(1-methylethyl)-3-phenyl-4-[(phenylamino)carbonyl ]- 1H-pyrrole-1-hepatonic acid), are important considerations when choosing and developing one of the forms of these compounds. Over a pH range of 2.1 to 6.0 and at 30 degrees C, the apparent solubility of the sodium salt of CI-981 (i.e., the hydroxyacid form) increases about 60-fold, from 20.4 micrograms/mL to 1.23 mg/mL, and the profile yields a pKa for the terminal carboxyl group of 4.46. In contrast, over a pH range of 2.3 to 7.7 and also at 30 degrees C, the apparent solubility of the lactone form of CI-981 varies little, and the mean solubility is 1.34 (+/- 0.53) micrograms/mL. The kinetics of interconversion and the equilibrium between the hydroxyacid and the lactone forms have been studied as a function of pH, buffer concentration, and temperature at a fixed ionic strength (0.5 M) using a stability-indicating HPLC assay. The acid-catalyzed reaction is reversible, whereas the base-catalyzed reaction can be treated as an irreversible reaction. More specifically, at pH < 6, an equilibrium favoring the hydroxyacid form is established, whereas at pH > 6, the equilibrium reaction is no longer detectable and greatly favors the hydroxyacid form.(ABSTRACT TRUNCATED AT 250 WORDS)

Determination of 2,2-dimethyl-N-(2,4,6-trimethoxyphenyl)-dodecanamide, a lipid regulator, in rat plasma and mesenteric lymph by reversed-phase high-performance liquid chromatography.

2,2-Dimethyl-N-(2,4,6-trimethoxyphenyl)dodecanamide (I, CI-976) has been determined in rat mesenteric lymph and plasma using a rapid and sensitive high-performance liquid chromatographic method. The samples prepared from plasma and lymph by liquid-liquid extraction were analysed on a reversed-phase C18 column isocratic conditions and ultraviolet detection. The method was applied to the determination of levels of I in Wistar rats after intraduodenal administration of 110 mg/kg of I as a lipid emulsion.

Aqueous stability and solubility of CI-988, a novel "dipeptoid" cholecystokinin-B receptor antagonist.

The aqueous solubility and solution stability of the N-methylglucamine and sodium salts of CI-988 (CI-988 NMG and CI-988 Na) were evaluated to aid in the development of a parenteral formulation for preclinical and clinical testing. CI-988 ([R-(R*,R*)]-4-[[2-[[3-(1H-indol-3-yl)-2-methyl-1-oxo-2- [[(tricyclo[3.3.1.1(3,7)]dec-2-yloxy)- carbonyl]amino]propyl]amino]-1-phenylethyl]amino]-4-oxobutanoic acid) is a selective "dipeptoid" cholecystokinin-B receptor antagonist. The shape of the pH-solubility profile, generated at 30 degrees C, is consistent with the ionization of the terminal carboxyl group (pKa of 4.34). The pH-rate profile is independent of the salt form and is well described by two reaction pathways: spontaneous or water-catalyzed degradation of the nonionized form and specific base-catalyzed catalyzed degradation of the ionized form. The primary mechanism of degradation from the former pathway is consistent with intramolecular, carboxyl-assisted, amide-bond cleavage, whereas the primary mechanism of degradation from the latter pathway appears to be intramolecular cyclization to a hydantoin product with expulsion of 2-adamantanol. The pH dependencies of the solubility and stability show that a simple aqueous buffered solution of CI-988 has a predicted t90 of 2.1 years and a solubility of 0.94 mg/ml at pH 6.5, the theoretical pH of maximum stability, and 30 degrees C.

Simultaneous determination of pseudoephedrine hydrochloride, chlorpheniramine maleate, and dextromethorphan hydrobromide by second-derivative photodiode array spectroscopy.

The simultaneous determination of the active ingredients in multicomponent pharmaceutical products normally requires the use of a separation technique, such as HPLC or GC, followed by quantitation. Presented here is a rapid, validated, analytical method that does not require prior separation for the simultaneous determination of three drugs, pseudoephedrine hydrochloride, chlorpheniramine maleate, and dextromethorphan hydrobromide, in a tablet formulation. A diode array spectrophotometer, capable of multicomponent analysis, was used for the quantitation. The utility of this method was demonstrated in two ways: the analysis of a chewable pediatric tablet (formulation CP) containing 7.5 mg of pseudoephedrine hydrochloride, 0.5 mg of chlorpheniramine maleate, and 2.5 mg of dextromethorphan hydrobromide, and the dissolution analysis of a hydroxypropyl methylcellulose-based sustained-release tablet (formulation SR) containing 120 mg of pseudoephedrine hydrochloride, 8 mg of chlorpheniramine maleate, and 60 mg of dextromethorphan hydrobromide. The sensitivity of this assay is 7.5 micrograms/mL for pseudoephedrine hydrochloride, 1.0 micrograms/mL for chlorpheniramine maleate, and 5.0 micrograms/mL for dextromethorphan hydrobromide, using the second-derivative spectra of the absorbance with respect to wavelength. Determinations were made in 0.1 M sodium acetate buffer at pH 5.0 using a 1-cm quartz cell. Absorbance spectra, and their first and second derivatives, from 240 to 300 nm were used for the determination. The results obtained by this method compared favorably with the results obtained by a validated HPLC method.

Relationship between powder surface characteristics and viscoelastic properties of powder-filled semisolids.

The viscoelastic properties of dispersions of powdered zinc oxide in anhydrous lanolin and colloidal sulfur in anhydrous lanolin were characterized by dynamic mechanical testing. The elastic shear modulus, G', viscous shear modulus, G", and loss tangent (damping), tan delta, were determined as a function of shear frequency, v, temperature, T, and volume fraction of powder, phi 2. A priori, it might be expected that zinc oxide and colloidal sulfur would elicit different viscoelastic properties due to their contrasting surface characteristics; zinc oxide has a hydrophilic surface and colloidal sulfur has a hydrophobic surface. Even though constitutive mathematical models, derived to predict the mechanical behavior of solid-filled polymeric materials, were not designed to account for differences in surface characteristics of the filler, the findings of these experiments show that these models are useful in explaining the differences in viscoelastic behavior of powder-filled semisolids due to surface characteristics of the filler. One model of particular value was the Kerner equation. With it, mechanisms were postulated for zinc oxide-zinc oxide interactions, sulfur-sulfur interactions, zinc oxide-anhydrous lanolin interactions, and sulfur-anhydrous lanolin interactions, within dispersions as a function of nu, T, and phi 2. In addition, damping was used to further identify the influence of temperature. Data obtained from three temperatures, where anhydrous lanolin exists in three different structural states, shows that the influence of the powder on damping is not only determined by the surface characteristics of the powder but also the structural state of anhydrous lanolin.

Application of dynamic mechanical testing to characterize the viscoelastic properties of powder-filled semisolids.

A nondestructive technique, dynamic mechanical testing, was used to characterize the viscoelastic properties of dispersions of powdered starch in anhydrous lanolin. The elastic shear modulus (G'), viscous shear modulus (G"), and loss tangent (damping; tan delta) were determined as a function of shear frequency, temperature, and the volume fraction of starch. The results of these studies show that constitutive mathematical models, derived to predict the mechanical behavior of solid-filled polymeric materials, can be applied to solid-filled semisolid pharmaceuticals. In particular, the Kerner equation was useful in describing the influence of starch on the G' of the dispersions. Even though the Kerner equation was unable to predict viscoelastic behavior at all shear frequencies, temperatures, and starch volume fractions, it proved beneficial in postulating mechanisms for starch-starch and starch-anhydrous lanolin interactions within the dispersions. In addition, damping was able to differentiate the influence of temperature. Data obtained from three temperature ranges, where anhydrous lanolin exists in three different structural states, shows that the influence of starch on damping is dictated by the structural state of anhydrous lanolin.

Phenomenological viscoelasticity of a heterogeneous pharmaceutical semisolid.

This study presents the results of an investigation of the viscoelastic properties of anhydrous lanolin USP, as determined by dynamic mechanical testing. The elastic shear modulus (G'), viscous shear modulus (G"), and loss tangent (tan delta) were determined as a function of shear frequency, nu, (0.01--10.0 Hz) and temperature, T, (0--30 degrees). These viscoelastic parameters were found to be temperature and shear frequency dependent. Up to 100-fold changes in shear moduli and tan delta values were observed with appropriate changes in T and nu. Many of the observed properties are also characteristic of high molecular weight polymers and can be attributed to a high degree of molecular structure. It was found that dynamic mechanical testing was a sensitive tool for measuring structural changes, and was especially useful in detecting a major structural transition well below the accepted melting temperature of anhydrous lanolin.

Temperature-frequency equivalence of the viscoelastic properties of anhydrous lanolin USP.

Methods of data analysis novel to pharmaceutical semisolids have been applied to the dynamic mechanical data obtained for anhydrous lanolin USP. It was found that the viscoelastic parameters determined over a wide range of temperatures and shear frequencies could be superposed. Elastic moduli (G') and viscous moduli (G") obtained at low temperatures (T) and frequencies (nu), were equivalent to moduli obtained at high T and nu. Empirical shifts of modulus versus shear frequency data obtained at different temperatures were used to produce G' and G" versus nu master curves (complete log modulus versus log frequency behavior at a constant temperature). A method of reduced variables, in conjunction with an Arrhenius-type relation, proved useful in calculating the energy of activation for the structural processes involved in a major mechanical transition.