The role of aggregation and ionization in the chemical instability of Amphotericin B in aqueous methanol.

Amphotericin B (AmB) is a potent antimicrobial agent used in clinical practice. Nevertheless, the mechanism of its aqueous instability remains not yet fully understood, especially the role that its aggregation state plays in this process. Therefore, the current study used an aqueous methanol media to evaluate the AmB instability as a function of pH-, organic solvent- and concentration-dependent ionization and aggregation.

Unveiling the Amphotericin B Degradation Pathway and Its Kinetics in Lipid-Based Solutions.

The purpose of this work was to determine the degradation pathway of Amphotericin B (AmB) and its kinetics in lipid-based solutions. Mixtures of AmB in lipophilic solvent media were stored under different conditions, such as surface area, temperature, light exposure, presence of antioxidants and other co-solutes. AmB was quantified by HPLC and UV-Vis spectrometry.

Using Manufacturing Design Space Concepts for Stability Risk Assessment-Gabapentin NIPTE/FDA Case Study.

A quantitative, model-based risk assessment process was evaluated using Bayesian parameter estimation to determine the posterior distribution of the probability of a model tablet formulation's (gabapentin) ability to meet end-of-expiry stability criteria-based manufacturing controls. Experimental data was obtained from an FDA-supported, multi-year project that involved researchers at nine universities working collaboratively with industrial and governmental scientists under the leadership of the National Institute for Pharmaceutical Technology and Education (NITPE). The risk assessment process involved the development of a design space manufacturing model and shelf life stability model that shared stability-related critical quality attributes (CQAs).

Particle Size Distribution Equivalency as Novel Predictors for Bioequivalence.

The use of particle size distribution (PSD) similarity metrics and the development and incorporation of drug release predictions based on PSD properties into PBPK models for various drug administration routes may provide a holistic approach for evaluating the effect of PSD differences on in vitro drug release and bioavailability of disperse systems. The objectives of this study were to provide a rational approach for evaluating the utility of in vitro PSD comparators for predicting bioequivalence for subcutaneously administered test and reference drug emulsions. Two types of in vitro comparators for test and reference emulsion products were evaluated: PSD characterization comparators (overlap metrics, median, and span ratios) and release profile comparators (f and various fractional time ratios).

Polymorphic and Covalent Transformations of Gabapentin in Binary Excipient Mixtures after Milling-Induced Stress.

Purpose: The purpose of the research described herein was to develop a kinetic model for quantifying the effects of conditional and compositional variations on non-covalent polymorphic and covalent chemical transformations of gabapentin.

Methods: Kinetic models that describe the relationship between polymorphs and degradation product in a series of sequential or parallel steps were devised based on analysis of the resultant concentration time profiles. Model parameters were estimated using non-linear regression and Bayesian methods and evaluated in terms of their quantitative relationship to compositional and conditional variations.

Quantification of gabapentin polymorphs in gabapentin/excipient mixtures using solid state C NMR spectroscopy and X-ray powder diffraction.

Gabapentin was used as a model pharmaceutical compound with susceptibility to polymorphic transformation as a function of environmental and mechanical stress. The utility of C CP/MAS NMR and XRPD as stability-indicating methods to quantify polymorphic transformation kinetics was investigated. Polymorphic Form II and III were distinguishable based on their chemical shift and distinct diffraction peak differences.

A Novel Method for Assessing Drug Degradation Product Safety Using Physiologically-Based Pharmacokinetic Models and Stochastic Risk Assessment.

Patient safety risk due to toxic degradation products is a potentially critical quality issue for a small group of useful drug substances. Although the pharmacokinetics of toxic drug degradation products may impact product safety, these data are frequently unavailable. The objective of this study is to incorporate the prediction capability of physiologically based pharmacokinetic (PBPK) models into a rational drug degradation product risk assessment procedure using a series of model drug degradants (substituted anilines).

The interaction mechanism between lipopeptide (daptomycin) and polyamidoamine (PAMAM) dendrimers.

The interaction mechanism of lipopeptide antibiotic daptomycin and polyamidoamine (PAMAM) dendrimers was studied using fluorescence spectroscopy. The fluorescence changes observed are associated with daptomycin-dendrimer interactions. The binding isotherms were constructed by plotting the fluorescence difference at 460 nm from kynurenine (Kyn-13) of daptomycin in the presence and absence of dendrimer.

Evaluation of lipopeptide (daptomycin) aggregation using fluorescence, light scattering, and nuclear magnetic resonance spectroscopy.

The aggregation behavior and critical aggregation concentration (CAC) values of daptomycin in aqueous solutions were evaluated under the external factors of pH, temperature, daptomycin concentration, and calcium ions concentration by using the complementary characterization techniques, fluorescence, dynamic and static light scattering, and nuclear magnetic resonance (NMR) spectroscopy. On the basis of the intrinsic fluorescence resonance energy transfer of daptomycin, the CAC values were identified by an upward inflection of the fluorescence emission from Kyn-13 at 460 nm. The pH-dependent CAC values were determined to be 0.

Studies on the instability of chlorhexidine, part I: kinetics and mechanisms.

The objectives of the studies presented herein were to determine the pH-dependent chlorhexidine (CHD) degradation scheme, to determine the rate laws, and to propose reasonable mechanisms for CHD hydrolysis in aqueous solutions. A series of degradation kinetic studies was conducted at 90.0 °C using reaction mixtures containing 0.

Kinetic model for solid-state degradation of gabapentin.

Gabapentin degrades directly to gabapentin-lactam (gaba-L) in the solid state. The objective of this study was to formulate a drug degradation model that accounted for the environmental storage conditions and mechanical stress (prior to storage) on lactamization kinetics. The effects of mechanical stress on drug degradation kinetics were determined by milling gabapentin in a FRITSCH Planetary Micro Mill for 0 and 60 min.

The stabilizing effect of moisture on the solid-state degradation of gabapentin.

Gabapentin is known to undergo intramolecular cyclization to form a lactam (gaba-L) with concomitant loss of water. Gabapentin was milled in a planetary mill for 15-60 min. Unmilled and milled gabapentin were stored at 50°C with relative humidity ranged between 5% and 90%.

Estimated pKa values for specific amino acid residues in daptomycin.

Daptomycin is a cyclic lipopeptide antibiotic. The ionization constants of daptomycin have not been individually elucidated. The objective of this research is to determine the sequence-specific ionization constants of daptomycin in the monomeric state.

Population pharmacokinetics of artesunate and dihydroartemisinin following single- and multiple-dosing of oral artesunate in healthy subjects.

Background: The population pharmacokinetics of artesunate (AS) and its active metabolite dihydroartemisinin (DHA) were studied in healthy subjects receiving single- or multiple-dosing of AS orally either in combination with pyronaridine (PYR) or as a monotherapy with or without food.

Methods: Data from 118 concentration-time profiles arising from 91 healthy Korean subjects were pooled from four Phase I clinical studies. Subjects received 2-5 mg/kg of single- and multiple-dosing of oral AS either in combination with PYR or as a monotherapy with or without food.

Glycosylation of aromatic amines III: Mechanistic implications of the pH-dependent glycosylation of various aromatic amines (kynurenine, 2'-aminoacetophenone, daptomycin, and sulfamethoxzaole).

Glycosylation reaction kinetics of a series of aromatic amines (kynurenine, 2'-aminoacetophenone, daptomycin, and sulfamethoxazole) was compared to propose a unifying reaction mechanism. Kinetic studies were conducted in aqueous solutions containing glucose in the pH range 1-6.5 with 2'-aminoacetophenone and daptomycin.

Glycosylation of aromatic amines II: Kinetics and mechanisms of the hydrolytic reaction between kynurenine and glucose.

The kinetics of the weakly basic aromatic amine, kynurenine, with glucose were studied as model reactants aimed at mechanistic understanding of pharmaceutically relevant amine-aldehyde reactions. The reaction kinetics of the forward and reverse processes (glycosylamine formation and hydrolysis) were studied under first-order conditions in aqueous solutions at 40 degrees C in the pH range 1-6.5 in the presence of various buffers.

Glycosylation of aromatic amines I: Characterization of reaction products and kinetic scheme.

The reactions of aliphatic and aromatic amines with reducing sugars are important in both drug stability and synthesis. The formation of glycosylamines in solution, the first step in the Maillard reaction, does not typically cause browning but results in decreased potency and is hence significant from the aspect of drug instability. The purpose of this research was to present (1) unreported ionic equilibria of model reactant (kynurenine), (2) the analytical methods used to characterize and measure reaction products, (3) the kinetic scheme used to measure reaction rates and (4) relevant properties of various reducing sugars that impact the reaction rate in solution.

Characterization of seed nuclei in glucagon aggregation using light scattering methods and field-flow fractionation.

Background: Glucagon is a peptide hormone with many uses as a therapeutic agent, including the emergency treatment of hypoglycemia. Physical instability of glucagon in solution leads to problems with the manufacture, formulation, and delivery of this pharmaceutical product. Glucagon has been shown to aggregate and form fibrils and gels in vitro.

The protein-binding and drug release properties of macromolecular conjugates containing daptomycin and dextran.

Prototype daptomycin-dextran macromolecular conjugates were prepared in an attempt to modify the biodistribution and protein-binding properties of daptomycin. Synthesis of daptomycin macromolecular conjugates involved dextran activation, daptomycin-dextran coupling, and purification. The reaction mixtures were separated on a Sephadex G-100 column using 10% acetronitrile in water as a mobile phase.

Studies on the mechanism of aspartic acid cleavage and glutamine deamidation in the acidic degradation of glucagon.

In this study, the polypeptide hormone glucagon was used as a model to investigate the mechanisms of aspartic acid cleavage and glutaminyl deamidation in acidic aqueous solutions. Kinetic studies have shown that cleavage at Asp-21 occurred at significantly slower rates than at Asp-9 and Asp-15 while deamidation rates were similar at the three Gln residues. The role of side-chain ionization in the cleavage mechanism was investigated by determining the pK(a) values of the three Asp residues using TOCSY and NOESY NMR methods.

Studies on the reactions between daptomycin and glyceraldehyde.

The objectives of this project were to determine the reaction pathways of daptomycin in the presence of glyceraldehyde in acidic solutions, and to quantitate the kinetics of the major pathways. In the presence of glyceraldehyde (pH range 1-7 at 25 to 60 degrees C), daptomycin formed two major products separable by RP-HPLC. The products were identified using UV spectroscopy, fluorimetry, mass spectrometry, and 2D-1H NMR.

Correlation of the thermal stability of phospholipid-based emulsions and the microviscosity measurements using fluorescence polarization.

The fluorescence polarization technique was used to measure the microviscosity of a series of phospholipid-based emulsions. Fourteen different oil-in-water emulsions containing 20% medium chain length triglycerides, various concentrations and types of phospholipids, and 2.2% glycerin were prepared by microfluidization and pH-adjusted to 4.

The estimation of glutaminyl deamidation and aspartyl cleavage rates in glucagon.

The major hydrolytic degradation pathways of glucagon under acidic conditions are cleavage at Asp-9, Asp-15, and Asp-21, and deamidation at Gln-3, Gln-20, Gln-24, and Asn-28. The rate constants for these pathways were determined in the pH range 1-2.4 at 60 degrees C by kinetic data analysis of substrate and degradation product concentration-time profiles.

Characterization methods for the physical stability of biopharmaceuticals.

The characterization of protein aggregation and gelation using various methods, including scanning and transmission electron microscopy, small angle X-ray scattering, static light scattering, dynamic light scattering. infrared spectroscopy, Raman spectroscopy, rheology, and size exclusion chromatography (coupled with on-line laser light scattering, refractive index, and ultraviolet absorbance detection), are described in terms of theory and applications.

An assessment of techniques for evaluating the physical stability of parenteral emulsions.

The physical stability of the parenteral emulsions is a key product quality issue. The purpose of this study is to develop, prepare and characterize model phospholipid emulsions and to critically evaluate various physical stability-indicating methods. Oil-in-water (O/W) emulsions were prepared using 20% (w/w) medium chain triglycerides (MCT) or soybean oil in 2.