No abstract

Biodegradable ion-exchange microspheres, prepared from a prefabricated conjugate of albumin and heparin were investigated as carriers for adriamycin. The ion-exchange microspheres could be loaded with adriamycin giving payloads up to 33% w/w, depending on the heparin content of the conjugate. In vitro adriamycin release depended on the ionic strength of the release medium. In ion containing media, for instance saline, 90% of the drug was released within 45 min, whereas in non-ionic media, such as distilled water, only 30% was released. Drug release profiles could be modelled by combining ion-exchange kinetics and diffusion controlled drug release models.

Albumin-heparin microspheres were prepared by a two-step process which involved the preparation of a soluble albumin-heparin conjugate, followed by formation of microspheres from this conjugate or by a double cross-linking technique involving both coupling of soluble albumin and heparin and microsphere stabilization in one step. The first technique was superior since it allowed better control over the composition and the homogeneity of the microspheres. Microspheres could be prepared with a diameter of 5-35 microns. The size could be controlled by adjusting the emulsification conditions. The degree of swelling of the microspheres was sensitive to external stimuli, and increased with increasing pH and decreasing ionic strength of the medium.

Albumin-heparin and albumin microspheres were prepared as ion exchange gels for the controlled release of uositivelv charaed wlvoeotides and oroteins. The adsorotion isotherms of chicken eaa and egg lys&ymd on ~lbmnin-heparin &rospher& was linear until saturation was abruptly reached.The adsorption isotherms of human lysozyme at low and high ionic strength were typical of adsorption isotherms of proteins on ion exchange gels. The adsorption of human lysozyme on albumin-heparin and albumin microspheres tit the Freundlich equation suggesting heterogeneous binding sites. This was consistent with the proposed multivalent, electrostatic interactions between human lysozyme and negatively charged microspheres. Scatchard plots of the adsorption processes of human lysozyme on albumin-heparin and albumin microspheres suggested negative cooperativity, while positive cooperativity was observed for chicken egg lysozyme adsorption on albumin-heparin microspheres.Human lysoayme loading of albumin-heparin microspheres was 3 times higher than with albumin micmspheres, with long term release occurring via an ion exchange mechanism. Apparent diffusion coefficients of 2.1 x 1O-'2 and 3.9~ IO-" cm*& were obtained for the release of human lysozyme from albumin-heparin and albumin microspheres, respectively. The release was found to be independent of diffusion, since the rate determining step was likely an adsorption/desorption processes. An apparent diffusion coefficient of 4.1 x lo-'* cm2/sec was determinr..: &r lhe reiease of ch cke,t egg lysozyme from albumin-heparin microspheres.Low release of the lysozymes from albumin-heparin microspheres was observed in deionized water, consistent with the proposed ion exchange release mechanism. Overall, albumin-heparin microspheres demonstrated enhanced ion exchange characteristics gver albumin microspheres.

Adriamycin (ADR) was formulated in albumin-heparin conjugate microspheres (AHCMS) to improve site-specific delivery and to reduce the toxicity of the drug. The effect of formulating ADR in AHCMS was investigated upon intrahepatic administration to male Wag/Rij rats. After intraveno-portal (i.v.p.) administration of ADR-AHCMS, ADR peak plasma concentrations were reduced 10-fold and ADR tissue levels of non-target tissues were significantly reduced, as compared to i.v.p, administration of the free drug. At an i.v.p, administered drug dose of 7.5 mg/kg, free ADR showed distinct signs of acute toxicity. At the same dose of ADR-AHCMS, signs of toxicity were absent. Cardiac function parameters which were determined using an isolated working heart model did not change as a result of i.v.p, administration of free ADR or ADR-AHCMS at a dose of 7.5 mg/kg. Heart weights of animals in the ADR-AHCMS or the free ADR groups, however, were significantly lower than controls. Dose tolerance studies after intrahepatic-arterial (i.h.a.) administration of free ADR, empty AHCMS and ADR-AHCMS in rats demonstrated that empty AHCMS are tolerated at a dose of 45 mg/kg. Free ADR was tolerated at a dose of 4 mg/kg, whereas ADR-AHCMS were tolerated up to a dose of 10 mg ADR/kg, as indicated by the survival.