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  • 1
    Electronic Resource
    Electronic Resource
    Diffusion in HPMC Gels. I. Determination of Drug and Water Diffusivity by Pulsed-Field-Gradient Spin-Echo NMR (1995)
    Springer
    Pharmaceutical research 12 (1995), S. 955-964 
    Details
    ISSN: 1573-904X
    Keywords: nuclear magnetic resonance spectroscopy ; pulsed-field-gradient spin-echo NMR ; hydroxypropyl methylcellulose ; HPMC ; extended release ; diffusion ; self-diffusion ; diffusion coefficient ; adinazolam mesylate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Purpose. This work describes diffusivity measurements of drug (adinazolam mesylate) and water in a variety of solutions including polymer gels. Methods. Pulsed-field-gradient spin-echo (PFGSE) NMR methods were employed to measure the diffusivity. Results. In binary component solutions, adinazolam diffusivity is generally found to exhibit an exponential dependence on the concentration of the viscosity-inducing agent (VIA), which is glucose, lactose, maltoheptaose, hydroxypropyl methylcellulose (HPMC) or drug itself. An increasing obstruction power to drug diffusion from glucose to HPMC is observed, which can be related to the polymerization degree of the VIA. In contrast, adinazolam diffusivity in HPMC gels shows little dependence upon the polymer viscosity grades examined (K100LV, K4M, and K15M). The temperature dependence of adinazolam diffusivity in dilute VIA solutions reveals that the diffusion barrier for the drug is similar to that for self-diffusion of water. Conclusions. The retarding effect from the VIA for drug diffusion is concluded to be primarily associated with a steric obstruction mechanism. In multicomponent gels with varied concentrations of drug, lactose and HPMC, the drug diffusivity can be approximately described as an exponential function of the summation of the products of the proportionality constant (Ki) and concentration for each VIA component. In contrast, water diffusion behavior shows an universal exponential dependence upon the VIA concentration and small dependence upon the nature of the VIA. The interpretation of the diffusivity data is discussed and compared to two existing diffusion models (Yasuda and Mackie-Meares models).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1016293911499
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    The 3′-Keto–Diol Equilibrium of Trospectomycin Sulfate Bulk Drug and Freeze-Dried Formulation: Solid-State Carbon-13 Cross-Polarization Magic Angle Spinning (CP/MAS) and High-Resolution Carbon-13 Nuclear Magnetic Resonance (NMR) Spectroscopy Studies (1993)
    Springer
    Pharmaceutical research 10 (1993), S. 75-79 
    Details
    ISSN: 1573-904X
    Keywords: nuclear magnetic resonance spectroscopy ; carbon-13 cross-polarization magic angle spinning spectroscopy ; water ; antibiotic
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Understanding how moisture interacts with a drug or formulation is a critical component of product development. This study demonstrates how water affects the 3′-gem-diol ↔ 3′-keto equilibrium in trospectomycin sulfate bulk drug and freeze-dried formulation, as probed by solid-state carbon-13 cross-polarization magic angle spinning (CP/MAS) and high-resolution nuclear magnetic resonance (NMR) spectroscopy. Drying the bulk drug or formulation to low water levels dehydrates trospectomycin sulfate from the diol to the keto form. Carbon-13 CP/MAS NMR spectroscopy measures the keto drug concentration in solid samples directly. The bulk drug, which contains approximately 16% water, is more than 90% in the 3′-diol form. Oven drying to 〈3% water converts approximately 75% of the drug to the 3′-keto form. The drug is formulated as a freeze-dried, sterile powder that can contain up to 12% water depending on the freeze-drying conditions. These studies show that the 3′-keto concentration rises uniformly (up to 75%) with decreasing residual water in the freeze-dried cake. The keto–diol equilibrium was also studied in solution by high-resolution carbon-13 NMR experiments, and it was found that raising the temperature or using dimethyl sulfoxide (DMSO) as a solvent also dehydrates the drug. For example, in aqueous solution at 25°C, nearly all (〉95%) of the drug is in the 3′-diol form. After equilibration at 60°C, however, the 3′-keto content increases to 7%, and in d 6-DMSO solvent at 25°C the drug is mostly (60%) in the 3′-keto form.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1018925113721
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    Paper (German National Licenses)
    Fulltext
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