Microspheres drug release rate

Spenlehauer (59) reported that in the case of cisplatin-loaded microspheres, irradiation only changes the processing considerations and does not influence drug release. This observation is in conflict with other literature reports showing increases in drug release rates (60,61). 

Because PCL hydrolyzes slowly compared to PLA and PLGA, it is most suitable for long-term drug delivery. Capronor , a 1-year contraceptive represents such a system [106]. The release of drugs is diffusion controlled rather than erosion controlled [106]. Nitrofurantoin, an antibacterial agent used in the treatment of urinary tract infections, has been incorporated into PCL microspheres [ 105]. The drug release rate was proportional to the square-root of time, i.e., fol-... 

Berkland, C. King, M. Cox, A. Kim, K. Pack, D.W. Precise control of PLG microsphere size provides enhanced control of drug release rate. J. Controlled Release 2002, 82, 137-147. 

Changes in Drug Release Rate from Polymeric Matrix Dosage Forms, Including Microspheres... 

S. Izumikawa, S. Yoshioka, Y. Aso, and Y. Takeda, Preparation of poly(Z-lactide) microspheres of different crystalline morphology and effect of crystalline morphology on drug release rate, J. Controll. Release 15, 133-140 (1991). 

Drug release rate from cellulose esters microspheres is dependent on the porosity of the matrix, and on the solubility of the drug in the matrix material or in the dissolution medium. Hydrophobic drugs exhibit prolonged release rates that can be modified using hydrophilic polymers such as PEG4000 and HPC. Cellulose acetate phthalate (CAPh) is a pH dependent cellulose ester, frequently employed alone, or in combination with other polymers to obtain microspheres with enteric properties. ... 

Microspheres demonstrate similar drug release rates in phosphate buffer solution (pH 7.0) and simulated gastric fluid. A significant increase in drug release (83.2%) is observed in the medium containing 4% rat caecal content which corresponds to in vivo analysis. 

C. Berkland, K.K. Kim, D.W. Pack, PLG microsphere size control drug release rate through several competing factors. Pharm Res 20,1055-1062,2003. 

Mladenovska, K. et al., BSA-loaded gelatin microspheres preparation and drug release rate in the presence of coUagenase, Acta Pharm. (Zagreb, Croatia), 52,91,2002. 

The investigators studied various blends of the three polymers in order to control the rate of chain scission and thus influence the induction period and onset of drug release. None of the blends provided the desired 1-week zero-order kinetics. However, blends of different microsphere types did show promise in vitro (88). 

Lactic acid oligomer microspheres containing aclarubicin have been studied for selective lymphatic delivery. Low (less than 10,000 molecular weight oligomers were used to produce microspheres designed to release drug over a 30-day period (99). Additives have been used to alter the release rate of aclarubicin-loaded poly(lactide) microspheres (100). Mitomycin C was incorporated into poly(lactic... 

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