Nitroglycerin diffusion rate

Matrix diffusion-controlled system in which the drug is homogeneously dispersed in a hydrophilic polymer diffusion from the matrix controls release rate Nitrodur (nitroglycerin key). 

The diffusion coefficients of nitroglycerin and triacetin in doublebase propellant have been measured at 77°-140°F. Activation energies for diffusion ranged from 10 to 13 kcal./mole. Thus, cure rates for a given propellant composition can be expected approximately to double in going from 120° to 140°F. 

To obtain ballistite with a more progressive rate of burning, attempts were made to produce laminated flakes, with the two outer layers made of attenuated ballistite and an inner one, sandwiched between, made of ordinary ballistite. In the attenuated ballistite DNT was substituted for part of the nitroglycerine. However a powder of this type retained its ballistic characteristics for only a few months, since, due to diffusion, the composition of all three layers gradually became equal. 

How does Deponit achieve the major share of the control of drug delivery The answer lies simply in the surface area of the different systems. The maximum rate that nitroglycerin can diffuse across intact human skin is on the order of 20 /rg/cm2/hr. Hence, if the target delivery rate is 0.4 mg/hr (i.e. 400 //g/hr), then a minimum surface area of about 20 cm2 is required. However, this does not leave much chance to build a... 

The microsealed delivery device is a variation of the matrix-type transdermal system in which the drug is dispersed in a reservoir phase which is then immobilized as discrete droplets in a cross-linked polymeric matrix. Release can be further controlled by inclusion of a polymeric microporous membrane. This system therefore combines the principles of both the liquid reservoir and matrix-type devices. Rate of release of a drug from a microsealed delivery system is dependent on the partition coefficient between the reservoir droplets and the polymeric matrix the diffusivity of the drug in the reservoir, the matrix and the controlling membrane and on the solubility of the drug in the various phases. There are, obviously, many ways to achieve the desired zero-order release rate, but only nitroglycerin has been commercially formulated into this type of delivery device (Karim 1983). 

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