Drugs loading

The earlier work of Miller (35), Outright (37), and Brady (5) on nonmedicated implants provided an excellent basis for further studies on specific controlled release formulations such as the determination of the biodegradation rates of lactide/glycolide drug-loaded microspheres (38). Those studies were done with l c-iabeled polymers produced from DL-lactic acid and glycolide. The final formulations tested in rats were microspheres loaded with H-labeled steroid and polymer as the matrix. The microspheres were administered intramuscularly and animals were serially sacrificed over a period of about a year. 

Two basic types of drug-loaded fibers have been reported. 

A method of the preparation of polylactic acid microcapsules of controlled particle size and drug loading, J. Microencapsul.,... 

The rate of release of levonorgestrel from films of block copolymers of e-caprolactone and dl-lactic acid (drug load 30%) was shown to be a function of the copolymer composition. The rate was unchanged for compositions of 100% and 88% e-capirolactone, but decreased thereafter as the e-caprolactone content decreased (42). 

FIGURE 10 In vitro rates of release of progesterone from PCL films, illustrating their dependence on the film thickness and drug load. The deviation from (time)l/2 kinetics reflects the contribution of an aqueous boundary layer. The solid lines were calculated assuming an aqueous boundary layer thickness of 19 ym. (From Ref. 68.)... 

Surface erosion not only leads to zero-order drug release from devices that maintain a constant surface area, but has other important consequences. Among these are the following (1) the rate of drug release is directly proportional to drug loading, (2) the lifetime... 

FIGURE 9 Effect of drug loading on cumulative drug release from polymer discs prepared from 3,9-bis(ethylidene-2,4,8,10-tetraoxaspiro-[5,5]undecane) and a 50 5Q mole ratio of trans-cyclohexane dimethanol and 1,6-hexanediol at pH 7.4 and 37 C. Drug loading 8 wt% (o),... 

E Allemann, JC Leroux, R Gurny, E Doelker. In vitro extended-release properties of drug loaded poly (dl-lactic acid) nanoparticles produced by a salting-out procedure. Pharm Res 10(12) 1732—1737, 1993. 

E Allemann, E Doelker, R Gurny. Drug loaded poly (lactic acid) nanoparticles produced by a reversible, salting-out process purification of an injectable dosage form. Eur J Pharm Biopharm 39 13-18, 1992. 

Crison et al. [52] presented an alternative derivation of Eq. (29) that included individualized transport of the solute and micelle while still maintaining the basic assumption of equilibrium. This was accomplished by rewriting Eq. (24) to include the magnitude of the individual diffiisional boundary layers for free drug and drug-loaded micelle according to Eq. (10), as follows ... 

The reaction plane model with heterogeneous reactions was discussed at length for acid-base reactions in the previous section. The same modeling technique, of confining the reactions to planes, can be applied to micelle-facilitated dissolution. As with the acid-base model, one starts with a one-dimensional steady-state equation for mass transfer that includes diffusion, convection, and reaction. This equation is then applied to the individual species i, i.e., the solute, s, the micelle, m, and the drug-loaded micelle, sm, to yield... 

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