Both clinical and laboratory studies have shown that the chemotherapy drug, Methotrexate (MTX), has adverse shortterm effects on bone, There are no studies that demonstrate the long-term response of bone to MTX, The purpose of this study was to determine the short- and long-term effects of MTX on bone volume, turnover, mineralization and strength, Three-month-old Sprague-Dawley rats were randomly assigned to a control (CTL) or MTX group and were given either daily MTX or saline injections for two separate 5-day courses (5 on/9 off/5 on), Fluorochrome compounds were injected prior to killing to label actively mineralizing bone surfaces, One CTL and MTX group were killed at 30, 80 and 170 days after treatment, Both femurs and tibiae were harvested for cancellous and cortical bone histomorphometry and biomechanical testing (torsion), Standard cancellous and cortical histomorphometric parameters were measured from undecalcified, methyl-methacrylate-embedded sections from the right proximal tibia and tibial and femoral diaphyses. The contralateral femur and tibia were torsionally loaded to failure and standard mechanical parameters were measured, All bone responses were statistically analyzed using a two-way ANOVA followed by Duncan's multiple comparison procedure (significance: p = 0.05), Cancellous bone volume was significantly lower in the MTX-treated group at 80 and 170 days. Cancellous mineralizing surface and longitudinal bone growth were significantly depressed at all time points yet mineral apposition rate was only depressed at the l70-day point, Cancellous osteoclast surface was increased at all time points for the MTX-treated animals, Cortical cross-sectional area and periosteal mineral apposition rate were significantly lower for both the femur and tibia in the MTX groups at all time points, However, periosteal mineralizing surface was significantly depressed in the MTX group only for the femur. MTX had minimal effects on the bone's biomechanical response. Methotrexate decreased bone volume, bone formation, and osteoblast activity and increased osteoclast activity. The results indicate that MTX had negative effects on both cortical and cancellous bone long after cessation of treatment.
