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Biomedical subjects

L Van Campen

Publications and source records attributed to L Van Campen.

6 recordsLinked to original sources
PubMed1991

Issues surrounding MDI formulation development with non-CFC propellants.

Reformulation of metered-dose inhalers (MDIs) without the use of chlorofluorocarbon (CFC) propellants presents numerous obstacles because there are no alternative propellants that can serve as immediate replacements for pharmaceutical use. Hydrofluorocarbons (HFCs), hydrochlorofluorocarbons (HCFCs) and hydrocarbons (HCs) are all under consideration as possible alternatives for CFC propellants. However, no single propellant or combination of propellants has been identified with all of the physical-chemical properties of CFCs. Based on their zero ozone depletion potentials, relatively low global warming potentials, non-flammabilities, densities, and vapor pressures, HFA-134a and HFA-227 are the most attractive replacement propellants identified to date. Yet, their use in MDIs will still require: (1) identification of a metering valve with propellant and formulation-compatible gaskets, (2) use of current suspending agents at levels much lower than in present MDIs or identification (and characterization) of new suspending agents, and (3) modification of existing manufacturing technologies. Demonstration of acceptable final product stability, safety and efficacy will be necessary prior to submission to worldwide registration authorities.

Administration, Inhalation↗
PubMed1983

Moisture sorption kinetics for water-soluble substances. I: Theoretical considerations of heat transport control.

A model based on heat transport control was developed to describe the uptake of water on a deliquescent solid in an atmosphere of pure water vapor. The model assumes the presence of a saturated liquid film on the surface of the solid. The decrease in the vapor pressure of water over the surface, brought about by the colligative effect of solid dissolved in the liquid film, is effectively offset by the increase in temperature of the film (and the solid) caused by the heat released on condensation of the water vapor. The thermal transients die out quickly and a steady-state analysis is valid. At steady state the temperature of the liquid film (and solid) is that temperature at which the vapor pressure of water above the saturated solution is equal to the chamber pressure. Consequently, water uptake occurs at a rate that depends on the heat flux away from the surface. The water uptake rate, W'h, is constant at a given relative humidity and is described by an equation of the form W'h = (C + F) . ln (RHi/RHo), where C and F are conductive and radiative coefficients, RHi the chamber relative humidity, and RHo the relative humidity at and above which continuous water uptake (deliquescence) occurs. The model contains no adjustable parameters and can thus be directly tested against experimental results.

Absorption↗
PubMed1983

Moisture sorption kinetics for water-soluble substances. II: Experimental verification of heat transport control.

The rates of water sorption as a function of relative humidity for water-soluble substances exhibiting deliquescence have been measured in an atmosphere of pure water vapor. The substances studied included a series of alkali halides, choline halides, and sugars. The results were compared with a theoretical model, previously described, which relates the rate of water uptake to the transport of heat produced during the process away from the surface. Taking into account the heat of water vapor condensation, heat of solution, and heat of hydration, when hydration occurs, the model allows excellent a priori prediction of water uptake rates as a function of relative humidity.

Absorption↗
PubMed1983

Moisture sorption kinetics for water-soluble substances. III: Theoretical and experimental studies in air.

As an extension of the model of heat transport control developed for the kinetics of water sorption by water-soluble substances from an atmosphere of pure water vapor, equations have been developed to account for limitations of diffusion on mass transport of water vapor when air is present. Although the inability to determine the vapor diffusion layer thickness prevents using these equations to predict sorption behavior a priori, minimum water sorption rates can be calculated by assuming a diffusion layer thickness equal to the sample chamber radius. Combining heat transport and mass transport produces equations which describe very well the observed sorption by three water-soluble salts in one atmosphere of air. As in the absence of air, sorption rates are predicted and observed to be constant at a given atmospheric relative humidity.

Absorption↗