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Development and characterization of methotrexate loaded poly(L-lactic acid) microspheres for the treatment of rheumatoid arthritis Liang, Sanching Linda

Abstract

Methotrexate (MTX) has shown anti-inflammatory effects in the treatment of rheumatoid arthritis. Attempts by other groups have been made to improve the efficacy and reduce toxicity by administering the drug intra-articularly, but the outcomes were not successful due to rapid clearance of the drug from the joint cavity. MTX loaded polymeric microspheres may provide a controlled release drug delivery system to maintain an effective concentration of MTX in the joint cavity. The goals were to develop MTX loaded microspheres and to determine the in vivo biodistribution and efficacy following intra-articular injection in rabbit joints. MTX loaded poly(L-lactic acid) microspheres (size range 33-110 μm) manufactured from poly(L-lactic acid) with an average molecular weight of 2000 g/mole (PLLA2k) showed good tolerability in rabbit joints. The in vitro drug release profiles of MTX loaded PLLA2k microspheres demonstrated a rapid burst phase with more than 50% of drug being released within 5 days followed by a slow release phase. Pharmacokinetics of MTX following intra-articular injection of both 1.5 mg and 10 mg doses of either MTX solution or MTX loaded microspheres (33-110 μm) were investigated in healthy rabbits. Plasma concentration peaked at 15 min (t[sub max]) following intra-articular injection, and the maximum plasma concentration (C[sub max]) for rabbits injected with MTX solution was 5 fold higher than for rabbits injected with MTX microspheres. Approximately 70% of injected MTX dose was excreted in the urine of the rabbits injected with MTX solution while only 12% of the dose was excreted in the urine of the rabbits injected with MTX microspheres 24 h following intra-articular injection. In vivo efficacy of intra-articular MTX loaded PLLA2k microspheres (33-110 μm) or MTX solution was evaluated using an antigen-induced arthritis rabbit model. Arthritis was successfully induced in the joints of rabbits with the observation of histopathological features resembling rheumatoid arthritis. Based on the degree of swelling of the knee joints and a system of scoring the pathological features of the disease, there was no significant difference between MTX solution and microspheres treated groups compared to phosphate buffered saline (control) animals. The lack of therapeutic responses to MTX loaded microspheres treatment was likely due to the severity of the disease induced and insufficient length of the observation period. MTX loaded PLLA2k microspheres were shown to be well tolerated in the rabbit knee joints and provide a controlled, localized delivery of MTX into the joint cavity following intra-articular injection.

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