Drug diffusion coefficient

In these materials, the drug diffusion coefficients and release rates will vary greatly with environmental pH. 

To examine the effect of time-dependent diffusion coefficient on the release behavior from a swellable polymer system containing dissolved or dispersed drug, we consider a polymer sheet with half thickness i, an initial drug loading A, a drug solubility in the polymer matrix C, and a time-dependent drug diffusion coefficient of the following form ... 

A drug diffusion experiment has been carried out over a long period of time to reach a steady-state condition. The data shown in Figure 6.10 have been collected. Calculate the partition coefficient and the drug solubility. The drug diffusion coefficient of 2 x Kb6 cm2/sec was independently determined by a time-lag experiment. The surface area, volume, and thickness of the membrane reservoir are 1.2 cm2, 32.4 cm3, and 50 pm, respectively. The total amount of drug in the membrane reservoir is 25 mg. 

To describe various anomalous release behaviors from glassy hydrogels, the following time-dependent drug diffusion coefficient is defined ... 

Gao et al. [71, 72] developed a mathematical model to describe the effect of formulation composition on the drug release rate for hydroxypropyl methylcellulose-based tablets. An effective drug diffusion coefficient T>, was found to control the rate of release as derived from a steady-state approximation of Fick s law in one dimension ... 

A comparison of Equations (3) and (4) shows that, in both equations, the amounts of released drug are directly dependent on the area of the device, the square root of the time t, the drug-loading concentration C0, the respective saturated drug concentrations, and the drug diffusion coefficients. In addition, the release rate (the time derivate of the amount of released material) depends on the square root of time and can be stated as... 

Membranes Useful Device for Drug Diffusion Coefficient Measurement.438... 

MEMBRANES USEFUL DEVICE FOR DRUG DIFFUSION COEFFICIENT MEASUREMENT... 

Interestingly, if the drug concentration profile inside the two stagnant layers and the membrane has always a linear trend, is time independent and the drug diffusion coefficient is concentration independent (these conditions are usually met for thin membranes and well stirred donor and receiver compartments), the proposed numerical model has the following analytical solution ... 

Colombo I, Grassi M, Lapasin R, and Pricl S. Determination of the drug diffusion coefficient in swollen hydrogel polymeric matrices by means of the inverse sectioning method. J. Control. Rel. 1997 47 305-314. 

Harland RS and Peppas NA. On the accurate experimental determination of drug diffusion coefficients in polymers. S.T.P. Pharm. Sci. 1993 3(5) 357-361. 

This equation is more appropriate for determining drug diffusion coefficients of high-molecular-weight drugs. ° ... 

The kinetic profile was thus interpreted by a burst effect coupled with a drug diffusion process through the particle modelled as a homogeneous sphere. The drug diffusion coefficient was considerably reduced when entrapped in the carrier DVE = 1.1 10-20 cm2 s 1 compare to DVE = 10 9 m2 s-1 in solution. The encapsulation of different drugs into nanospheres showed that carriers had... 

A number of assumptions were made and then verified to develop a model (i) The rate-limiting step for transport is drug diffusion through pores (other steps such as water penetration into the matrix and drug dissolution occur in less than 40 hours), (ii) The effect of concentration dependence on the drug diffusion coefficient is not significant. This was verified by an analysis of diffusion effects at the concentrations in the... 

Polymeric network topology heavily reflects on drug diffusion as it concurs in determining the drug diffusion coefficient as later on discussed. Additionally, polymeric network can also be responsible for a non-Fickian diffusion. Indeed, in the presence of a very complex topology. 

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