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R A Kenley

Publications and source records attributed to R A Kenley.

At least 19 recordsLinked to original sources
PubMed2000

Orthogonal HPLC methods for quantitating related substances and degradation products of pramlintide.

Pramlintide is a 37-amino acid peptide that is being evaluated as a drug candidate for treating people with type 1 and insulin-using type 2 diabetes. Two high-performance liquid chromatography (HPLC) methods were developed for quantitating related substance impurities in pramlintide drug substance as well as degradation products of pramlintide formulated for parenteral administration. The methods differ with respect to separation mode and therefore provide orthogonal information concerning related substances and degradation products. One method uses a reverse phase (RP) separation mode, and the other involves a strong cation exchange (SCX) separation. Method performance testing showed that the RP- and SCX-HPLC methods both afford a high degree of selectivity, accuracy, precision, and sensitivity. The limit of quantitation for determining spiked authentic samples of degradation products was shown to be approximately 0.1% (relative to intact pramlintide) for both methods. Relative retention times for known pramlintide degradation products were determined for both the RP- and SCX-HPLC methods, demonstrating the selectivities of the 2 methods as well as the orthogonality of the information. The methods were also shown to be diastereospecific with respect to separating pramlintide from authentic samples of D-isomers at Ala5, Ala8, Ala5-Ala8, and Leu12. The methods did not resolve pramlintide, however, from diastereomers with D-isomers near the C- and N-termini, namely Lys1,Cys2, and Tyr37.

Amyloid↗
PubMed2000

Kinetics of pramlintide degradation in aqueous solution as a function of temperature and pH.

The stability of the 37-amino acid peptide pramlintide, in aqueous solution, was studied as a function of pH and temperature. Samples of pramlintide formulated as a parenteral product were exposed to elevated temperatures and to realistic storage conditions for as long as 30 months. Pramlintide degradation was monitored by three high-performance liquid chromatography (HPLC) methods: a reversed-phase (RP-HPLC) and a strong-cation exchange (SCX-HPLC) method for percentage purity determination by area normalization, plus a second RP-HPLC method for potency determination versus external standards. The pH-rate profile for pramlintide shows increasing degradation rate constants with increasing pH over the range pH = 3.5 to 5.0. The Arrhenius expression for pramlintide degradation at pH = 4.0 over the temperature range 5 degrees C to 50 degrees C is ln(k(0))= 37.39-21.900/RT, where k(0) is the zero-order rate constant (in %/mo) for pramlintide degradation. The pramlintide parenteral product formulated at pH = 4.0 is extremely stable, with percentage purity and percentage potency loss of only approximately 2% over 30 months at 5 degrees C. The formulated pramlintide drug product has acceptable shelf life for long-term storage at 5 degrees C and up to a 30-day patient use when stored at ambient temperature.

Amino Acid Sequence↗
PubMed2000

Pramlintide injection drug product robustness studies.

The article examines the effects of temperature excursions and actual dose withdrawal on the quality of pramlintide injection, a multidose liquid parenteral formulation. Studies were designed to demonstrate product robustness under conditions that may occur during patient use. Pramlintide %Purity was determined by two high-performance liquid chromatography (HPLC) methods, a reversed-phase (RP-HPLC) and a strong-cation exchange (SCX-HPLC) method. A second RP-HPLC method was used to determine pramlintide potency and the concentration of the m-cresol preservative. Antimicrobial preservative effectiveness testing was per USP and European Pharmacopeia (Ph. Eur.). Short-term stability studies were undertaken to probe the effects of the following conditions: 5 degrees C to 40 degrees C and 5 degrees C to -20 degrees C temperature cycling over 10 days; once daily or four-times daily dose withdrawal over 12 or 42 days; and combined 30 degrees C storage and four-times daily dose withdrawal over 42 days. In all cases, pramlintide %Purity and potency values remained essentially unchanged or unchanged relative to controls. Similarly, product appearance, and m-cresol concentration and preservative effectiveness were not significantly affected by the stress conditions used in the 5 studies. Pramlintide injection drug product is extremely robust to challenging stress conditions that may occur during patient use of this multidose product for chronic administration.

Amyloid↗
PubMed1995

Gamma irradiation effects on molecular weight and in vitro degradation of poly(D,L-lactide-CO-glycolide) microparticles.

PURPOSE: The objective of the reported work was to quantitatively establish gamma-irradiation dose effects on initial molecular weight distributions and in vitro degradation rates of a candidate erodible biopolymeric delivery system. METHODS: Poly(D,L-lactide-coglycolide) (PLGA) porous microparticles were prepared by a phase-separation technique using a 50:50 copolymer with 30,000 nominal molecular weight. The microparticles were subjected to 0, 1.5, 2.5, 3.5, 4.5, and 5.5 Mrad doses of gamma-irradiation and examined by size exclusion chromatography (SEC) to determine molecular weight distributions. The samples were subsequently incubated in vitro at 37 degrees C in pH 7.4 PBS and removed at timed intervals for gravimetric determinations of mass loss and SEC determinations of molecular weight reduction. RESULTS: Irradiation reduced initial molecular weight distributions as follows (Mn values shown parenthetically for irradiation doses): 0 Mrad (Mn = 25200 Da), 1.5 Mrad (18700 Da), 2.5 Mrad (17800 Da), 3.5 Mrad (13800 Da), 4.5 Mrad (12900 Da), 5.5 Mrad (11300 Da). In vitro degradation showed a lag period prior to zero-order loss of polymer mass. Onset times for mass loss decreased with increasing irradiation dose: 0 Mrad (onset = 3.4 weeks), 1.5 Mrad (2.0 w), 2.5 Mrad (1.5 w), 3.5 Mrad (1.3 w), 4.5 Mrad (1.0 w), 5.5 Mrad (0.8 w). The zero-order mass loss rate was 12%/week, independent of irradiation dose. Onset of erosion corresponded to Mn = 5200 Da, the point where the copolymer becomes appreciably soluble. CONCLUSIONS: The data demonstrated a substantial effect of gamma-irradiation on initial molecular weight distribution and onset of mass loss for PLGA, but no effect on rate of mass loss.

Biocompatible Materials↗
PubMed1994

Acid-catalyzed peptide bond hydrolysis of recombinant human interleukin 11.

Recombinant human interleukin 11 (rhIL-11) is a multispectrum cytokine that plays an important role in megakaryocytopoiesis and platelet production. Probing rhIL-11 chemical reactivity in aqueous solution is an important initial step in developing a dosage form for rhIL-11 clinical trials. This report documents rhIL-11 degradation kinetics at 50 degrees C in solutions adjusted to pH 3.0 to 9.5. Stressed samples were analyzed by reverse-phase HPLC and degradation product peaks were isolated for structural characterization. The results show maximal stability in the region pH 6.5 to 7.0. Degradation product identification shows that the major reaction pathway in acidic solution involves peptide cleavage at aspartate133-proline134. In alkaline solution, protein disappearance proceeds via nonspecific loss to container surfaces. Degradation products at alkaline pH have not been identified.

Acids↗
PubMed1993

Biotechnology and bone graft substitutes.

Trauma, disease, developmental deformities, and tumor resection frequently cause bone defects that seriously challenge the skills of orthopedic and maxillofacial surgeons. Currently, repairing osseous deficiencies involves various medical surgical techniques, including autogenous grafts, allografts, internal and external fixation devices, electrical stimulation, and alloplastic implants. The existing technology, though effective in many cases, still is beset with numerous difficulties and disadvantages. A critical need for improved treatment methods exists today. Biotechnology now provides access to new bone repair concepts via administration of protein growth and morphogenic factors. Implantable device and drug delivery system technologies also have advanced. The converging biopharmaceutical, device, and delivery technologies represent an opportunity to improve the quality of health care for individuals with orthopedic and maxillofacial deficiencies. This report reviews current concepts in fracture healing and bone repair and examines existing treatment modalities. It also addresses novel protein drugs that stimulate osseous regeneration and delivery systems for these drugs.

Amino Acid Sequence↗
PubMed1993

Degradation pathways for recombinant human macrophage colony-stimulating factor in aqueous solution.

Recombinant human macrophage colony-stimulating factor (rhM-CSF) promotes macrophage proliferation and activity. rhM-CSF clinical trials are currently in progress and require a stable, pharmaceutically acceptable dosage form. This report documents pH effects on rhM-CSF degradation profiles in aqueous solution, with an emphasis on identifying degradation products. Thus, highly purified rhM-CSF was maintained at 30 to 50 degrees C in solutions adjusted to pH 2 to 10. Stressed samples were analyzed by SDS-PAGE, reverse-phase HPLC, size exclusion HPLC, scanning microcalorimetry, and murine bone marrow activity. The results show maximal protein stability in the region pH 7 to 8. Degradation product chromatographic and electrophoretic analyses show distinctly different degradation product profiles in acidic versus alkaline solution. For samples stressed in acidic solution, degradation products were isolated chromatographically and electrophoretically. These degradation products were characterized by N-terminal amino acid sequencing, fast-atom bombardment mass spectrometry, and peptide mapping. The results show that the major degradation pathway in acidic solution involves peptide cleavage at two sites: aspartate169-proline170 and aspartate213-proline214. A third potential cleavage site (aspartate45-proline46) remains intact under conditions that cleave Asp169-Pro170 and Asp213-Pro214. In alkaline solution, degradation proceeds via parallel cleavage and intramolecular cross-linking reactions. A beta-elimination mechanism is proposed to account for the degradation in alkaline solution. Consistent with literature observations, the rhM-CSF N-terminal cleavage products retain biological activity.

Alcaligenes↗
PubMed1990

Influence of solute degradation on the accumulation of solutes migrating into solution from polymeric parenteral containers.

Solute stability in solution, in addition to solute-polymer interaction properties and the total solute available pool, impacts the interaction between a polymeric container and a parenteral product, specifically in terms of the migration of trace polymer components into the contained solution. A specific solute/polymer system has been studied with respect to properties impacting the magnitude and rate of solute migration from the polymer into solution. The solute, an alkyl ester, originates in a polyolefin composite packaging material. Solute degradation kinetics were studied as a function of solution temperature and pH. Solute-polymer interaction properties including the equilibrium binding constant and diffusion coefficient were obtained. An accumulation rate model is developed for the determination of the solution phase concentration of the liberated solute as a function of storage time and conditions. Coupling the model with the properties of the polymer-solute system studied provides a tool that accurately predicts solute accumulation behavior in a representative parenteral product configuration.

Drug Packaging↗
PubMed1990

Determination of solute-polymer interaction properties and their application to parenteral product container compatibility evaluations.

Kinetic and thermodynamic interaction properties between dialkyl phthalate test compounds and a polyolefin polymer were examined via a permeation-cell experimental design. Disappearance and appearance rates of solute in the receptor and donor solutions, as well as the equilibrium composition of the test system, are used to determine sorption and diffusion coefficients and the solute/polymer equilibrium binding constant. Sorption rate constants and diffusion coefficients exhibit Arrenhius-type behavior. The binding constants obtained correlate well with the solute's octanol-water partition coefficient. The kinetic and thermodynamic data generated combine with proposed interaction models to identify solute/polymer interactions (binding and leaching) pertinent to evaluating container/solution compatibility for parenteral products.

Diffusion↗
PubMed1987

Temperature and pH dependence of fluocinolone acetonide degradation in a topical cream formulation.

We investigated the degradation of fluocinolone acetonide (FA) incorporated into an oil-in-water cream base. The study examined the influence of temperature (23 to 80 degrees C) and cream pH (pH 2.3 to 6) on FA degradation rates. FA degradation followed pseudo-first-order kinetics and adhered to the Arrhenius expression over the entire temperature range investigated. At all temperatures, the pH strongly influenced the observed degradation rate constant (kobs) values, with rate minima observed near pH 4. The FA log(degradation rate)-pH profiles were consistent with a reaction mechanism requiring drug hydrolysis catalyzed by hydroxide and hydrogen ions. Taking into account both the temperature and the pH dependence of FA degradation permits calculating kobs values from the following equation: kobs = exp[22.5 - (17,200/RT)] + exp[38.7 - (22,200/RT)] x [H+] + exp[49.5 - (21,100/RT)] x [OH-] where the three bracketed terms represent Arrhenius expressions for neutral, acid-catalyzed, and base-catalyzed hydrolysis reactions. FA degradation in the cream base parallels the degradation of a related steroid (triamcinolone acetonide) in an aqueous alcohol solution. The equivalence between FA and triamcinolone acetonide kinetics in the different reaction media suggests that in the cream base, FA degradation is limited to an aqueous phase largely unperturbed by the presence of nonaqueous constituents that comprise the cream formulation.

Acids↗
PubMed1987

Electrochemical evaluation of the interaction between ascorbic acid and the cardiotonic drug RS-82856.

The solution phase interaction between ascorbic acid and the cardiotonic drug N-cyclohexyl-N-methyl-4(7-oxy 1,2,3,5-tetrahydroimidazol[2,1-b] quinazolin-2-one butyramide (RS-82856) was evaluated using a differential pulse voltammetric technique. Shifts in the peak potential of ascorbic acid to higher energy as well as decreases in peak current values were monitored as a function of RS-82856 concentration. The electrochemical data were obtained under conditions where both the drug and the ascorbic acid concentrations exhibited linear relationships with peak current values. The methodology was extended to the study of two other structurally related phosphodiesterase inhibitors cilostamide and anagrelide. The complexation of these drugs with ascorbic acid were also characterized by decreases in the diffusion currents of ascorbic acid as well as by anodic shifts in the peak potential. The significance of these observations may be related to the inhibition of cyclic nucleotide phosphodiesterase activity by both the drugs tested and the ascorbic acid.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1986

Water soluble complexes of the antiviral drugs, 9-[(1,3-dihydroxy-2-propoxy)methyl]guanine and acyclovir: the role of hydrophobicity in complex formation.

We investigated water-soluble complexes of various ligands with the antiviral drugs, 9-[(2-hydroxyethoxy)methyl]guanine (acyclovir) and 9-[(1,3-dihydroxy-2-propoxy)methyl]guanine (DHPG). For comparison, we also examined the "parent" compounds, guanine and guanosine, as substrates for complex formation. Using the phase-solubility technique, we measured formation constant (K1) values at 23 degrees C in pH 7 buffer. For a single substrate, formation constants with different ligands varied in the order: caffeine greater than pyridoxine approximately cytidine greater than nicotinamide greater than sucrose. With caffeine as the ligand, formation constants with different substrates varied in the order: guanine greater than guanosine approximately acyclovir greater than DHPG. The largest formation constant observed was 58 M-1 (for guanine-caffeine), and the smallest formation constant was 0.29 M-1 (for DHPG-sucrose). Examining the literature for formation constant data on compounds related to DHPG, and comparing literature data with our own, reveals a significant correlation between formation constants and ligand hydrophobicity. For 41 substrate-ligand pairs, least squares linear regression analysis of log K1 values versus various parameters reflecting donor-acceptor abilities (e.g., substrate and ligand HOMO and LUMO values, or substrate oxidation potentials) failed to significantly correlate. We conclude that ligand hydrophobicity is a general determinant of water soluble complex formation, but not necessarily the exclusive or dominant controlling factor for all complexes. Charge-transfer interactions are not important determinants of complex formation for the substrate-ligand combinations that we have considered.

Acyclovir↗
PubMed1986

Reactivity of enprostil stereoisomers in soft elastic gelatin capsules.

Enprostil (methyl 7-[(1R*,2R*,3R*)-3-hydroxy-2-[(E)-(3R*)-3-hydroxy-4-phenoxy-1-butenyl]- 5-oxocyclopentyl]-4,5-heptadienoate), a gastric acid secretion inhibitor and potent anti-ulcer drug, is formulated as a propylene carbonate solution which is filled into soft elastic gelatin capsules. The drug molecule features two unresolved asymmetric carbon atoms, and synthesis yields an equimolar mixture of four different optical isomers (two diastereomeric pairs of enantiomers). The objective of this study was to establish the degree to which enprostil does or does not degrade stereoselectively in the soft elastic gelatin capsule formulation. Accordingly, we developed an HPLC method capable of resolving enprostil diastereoisomers and applied the method to determining reaction rates of enprostil in soft elastic gelatin capsules maintained at 40 degrees C. The study included three soft elastic gelatin capsule lots: the first two contained an equimolar mixture of all four enprostil enantiomers; and the third contained an equimolar mixture of two individual diastereoisomers of known optical purity. Comparing enprostil degradation rates in the three capsule lots showed that reactivity ratios in all cases were (within the limits of experimental uncertainty) equal to unity. This observation conclusively excludes the possibility of significant enantioselectivity for enprostil degradation in the soft elastic gelatin capsule formulation. We also report kinetic equations for the general case of relating stereospecific reactivity ratios to drug product shelf life when drug concentrations are monitored with nonstereoselective analytical techniques.

Capsules↗
PubMed1986

Multidimensional column-switching liquid chromatographic method for dissolution testing of enprostil soft elastic gelatin capsules.

Enprostil (methyl 7-[(1 R,2R,3R)-3-hydroxy-2-[(E)-(3R)-3-hydroxy-4- phenoxy-1-butenyl]-5-oxocyclopentyl]-4,5-heptadienoate), an E-type prostaglandin exhibiting anti-ulcer activity, is formulated as a propylene carbonate solution filled into soft elastic gelatin (SEG) capsules. Enprostil SEG capsules were maintained for timed intervals at 50 degrees C, 30 degrees C, and room temperature, and the quantity of drug released upon complete capsule dissolution was determined as a function of storage condition. The dissolution test adhered to USP XXI guidelines (paddle method) and used a multidimensional HPLC technique to provide a sensitive and selective enprostil assay. Parallel HPLC assays determined the enprostil concentration in the propylene carbonate fill that was physically expressed from initially manufactured and from aged capsules. This corrected for any enprostil loss via chemical degradation on storage. The study included six different aged samples (six replicates each), and for all six samples, the enprostil recovered from dissolved capsules averaged 104 +/- 1.4% of the enprostil physically expressed from the capsules. Similarly, the enprostil recovered from dissolved, aged capsules averaged 103 +/- 5% of the enprostil physically expressed from capsules at the initial time point. These findings exclude the possibility that interactions with the SEG capsule wall reduce drug availability during storage under normal conditions. The multidimensional HPLC technique should generally extend to analysis of other noncationic drugs formulated into soft gelatin capsules.

Capsules↗
PubMed1986

Nonquaternary cholinesterase reactivators. 3. 3(5)-Substituted 1,2,4-oxadiazol-5(3)-aldoximes and 1,2,4-oxadiazole-5(3)-thiocarbohydroximates as reactivators of organophosphonate-inhibited eel and human acetylcholinesterase in vitro.

As an extension of an earlier investigation (J. Med. Chem. 1984, 27, 1431), we prepared a series of 3-substituted 5-[(hydroxyimino)methyl]-1,2,4-oxadiazoles and the corresponding 5-thiocarbohydroximic acid 2-(N,N-dialkylamino)ethyl S-esters. The compounds were evaluated in vitro as reactivators of phosphonylated electric eel and human erythrocyte (RBC) acetylcholinesterases (AChE). The compounds were characterized with respect to (hydroxyimino)methyl acid dissociation constant, nucleophilicity, octanol/buffer partition coefficient, reversible AChE inhibition, and kinetics of reactivating ethyl methylphosphonylated AChE. One compound was also tested for effectiveness in preventing AChE phosphonylation. All of the tested compounds significantly reactivate ethyl methylphosphonylated AChE: the 3-n-octyl- and 3-(1-naphthyl)-substituted aldoximes are as reactive (within a factor of 5-10) toward the inhibited enzymes as the benchmark pyridinium reactivators, 2-PAM and HI-6. All of the substituted thiocarbohydroximic acid S-esters are powerful reversible inhibitors of AChE's: the 3-n-octyl- and 3-(1-naphthyl)-substituted thiocarbohydroximates inhibit eel AChE to 50% initial activity at concentrations less than 5 microM. When added to an eel AChE solution at concentrations between 5 and 50 microM, the 3-phenyl-substituted thiocarbohydroximate effectively antagonizes AChE inhibition by ethyl p-nitrophenyl methylphosphonate (EPMP), suggesting the potential utility of this compound for preventing anti-AChE-agent poisoning.

Acetylcholinesterase↗
PubMed1986

Stability of ganciclovir sodium (DHPG sodium) in 5% dextrose or 0.9% sodium chloride injections.

The stability of 9-[(1,3-dihydroxy-2-propoxymethyl]) guanine sodium (ganciclovir sodium, also known as DHPG sodium) in two infusion solutions was studied. Lyophilized ganciclovir sodium 500 mg was reconstituted with sterile water 10 mL to give a theoretical concentration of 50 mg/mL. After reconstitution, 6-mL aliquots of the solution were added to 100 mL of 0.9% sodium chloride injection or 5% dextrose injection in polyvinyl chloride i.v. bags. One sample was withdrawn from each of 10 bags of each solution and analyzed by high-performance liquid chromatography (HPLC). Thirty bags of each solution were then stored under each of the following conditions: at room temperature under laboratory light, at room temperature in the dark, and under refrigeration for up to five days. Single potency assays were performed by HPLC on each of three bags of solution at three and five days after initial dilution of the solutions. The solutions were visually inspected, and the pH of the solutions was measured. All solutions of ganciclovir were stable for at least five days under all storage conditions; mean ganciclovir concentrations did not drop below 98% of initial theoretical values throughout the storage period. No important changes in the pH of the solutions occurred during the study period. Under the conditions of this study, ganciclovir sodium is stable for up to five days when prepared in 5% dextrose injection or 0.9% sodium chloride injection.

Acyclovir↗