Biodegradable polyanhydride devices of cefazolin sodium, bupivacaine, and taxol for local drug delivery: preparation, and kinetics and mechanism of in vitro release

Abstract

The overall objective was to design and evaluate biodegradable implants for local drug delivery in clinical conditions and/or diseases described below, which are currently treated with systemic administration of drugs. Local delivery of cefazolin is desired in conditions such as osteomyelitis, soft-tissue infection and for prevention of post-surgical infections. Similarly, implanting a biodegradable device loaded with taxol in the cavity created by tumor resection will provide high local concentrations of taxol killing the malignant cells which may have survived the surgery, thus preventing metastasis and regrowth of the tumor and also prevent the systemic side effects of taxol. Prolonged reversible nerve blockade required in a number of clinical situations involving acute or chronic pain such as post-surgical pain following herniorrhaphy and thoracotomy can be achieved with local delivery of bupivacaine. Therefore, disk-shaped implants of polyanhydride, P(FAD-SA, 50:50 w/w), loaded with 10% w/w of cefazolin sodium, taxol and bupivacaine were prepared and evaluated for content uniformity and in vitro release characteristics for the above mentioned local drug delivery applications. All of cefazolin sodium was released in 14 days while 90% bupivacaine was released in 35 days. In striking contrast, taxol was released very slowly, and only 15% taxol was released in 77 days. The overall release appeared to be following first order kinetics, and the initial linear profile was fitted to zero order kinetics to obtain release parameters. Since cefazolin is highly water soluble and bupivacaine is moderately water soluble, compared to taxol which is extremely lipophilic, the aqueous solubility of the incorporated drug appeared to influence its release characteristics. Very good correlation was observed between release parameters ( A 0, k 0) and the solubility and intrinsic dissolution rate (IDR) of drugs suggesting that the hydrophilic/hydrophobic nature of the drug influences its release from polyanhydride devices. Since polyanhydrides are believed to undergo pure surface erosion, release of the incorporated drug should be independent of its physicochemical properties, however the results presented in this study suggest otherwise. Therefore, P(FAD-SA, 50:50 w/w) may not be undergoing surface erosion, and that diffusion and dissolution properties of the drug in addition to erosion characteristics of the polyanhydride appear to play a role in drug release. Implants prepared and evaluated in this study released cefazolin, bupivacaine and taxol for a prolonged duration of time; however, depending upon the desired duration of release, an appropriate polyanhydride will have to be selected. For example, taxol was released so slowly that a more hydrophilic polyanhydride may have to be selected to release all the drug in a shorter period of time to be of any therapeutic use. Cefazolin implants released the drug for a sufficient duration for osteomyelitis and soft-tissue infection but the release was more prolonged than required for prevention of post-surgical wound infection.