Infusion at constant rate in vivo

Interspecies differences in systemic drug availability following subcutaneous pulsatile administration in cattle, sheep, dogs, and rats

Rats, dogs, sheep, and cattle were implanted subcutaneously with stainless-steel tissue cages. Bolus injections of cefoxitin and ivermectin were administered to the interiors of the tissue cages 11, 32, and 60 days after implantation to simulate pulsatile drug release from an implanted device. Plasma drug levels were determined for 6 h for cefoxitin and up to 8 days for ivermectin. Tissue cages were retrieved 3 and 6 months after implantation for macroscopic and microscopic examination. In dogs and rats, plasma levels of both drugs following administrations to the tissue cages were significantly lower than those following subcutaneous injection, suggesting that the tissue growth around and in the cages posed a barrier to systemic drug availability in those species. In cattle and sheep, the tissue cages and associated tissue did not inhibit systemic availability of either drug as compared with routine subcutaneous administration.

Subcutaneous tissue cages for examination of slow release of materials from long-term implants

A subcutaneous tissue cage implant system was examined for its utility in evaluating the subcutaneous response to slow release of potentially irritating materials from implanted devices. The degree of the inflammatory response was measured by the total number of polymorphonuclear leucocytes per microliter in the tissue exudate. Bolus injection of kappa carrageenan resulted in a 100-fold increase in polymorphonuclear leucocytes within 2 d with a return to basal levels within the next 3 d. Slow infusion of the same solution over 7 d also resulted in a statistically significant increase in polymorphonuclear leucocytes response 4 d following expected termination of infusion, which did not return to basal levels before study termination 3 d later. The peak response obtained from slow infusion of carrageenan did not differ significantly from that observed following bolus injection of the same solution.