Effects of the Antiepileptic Drugs Phenytoin, Gabapentin, and Levetiracetam on Bone Strength, Bone Mass, and Bone Turnover in Rats

Abstract

Long-term treatment with antiepileptic drugs (AEDs) is accompanied by reduced bone mass that is associated with an increased risk of bone fractures. Although phenytoin has been reported to adversely influence bone metabolism, little is known pertaining to more recent AEDs. The aim of this study was to evaluate the effects of gabapentin or levetiracetam on bone strength, bone mass, and bone turnover in rats. Male Sprague-Dawley rats were orally administered phenytoin (20 mg/kg), gabapentin (30 or 150 mg/kg), or levetiracetam (50 or 200 mg/kg) daily for 12 weeks. Bone histomorphometric analysis of the tibia was performed and femoral bone strength was evaluated using a three-point bending method. Bone mineral density (BMD) of the femur and tibia was measured using quantitative computed tomography. Administration of phenytoin significantly decreased bone strength and BMD, which was associated with enhanced bone resorption. In contrast, treatment with gabapentin (150 mg/kg) significantly decreased bone volume and increased trabecular separation, as shown by bone histomorphometric analysis. Moreover, the bone formation parameters, osteoid volume and mineralizing surface, decreased after gabapentin treatment, whereas the bone resorption parameters, osteoclast surface and number, increased. Levetiracetam treatment did not affect bone strength, bone mass, and bone turnover. Our data suggested that gabapentin induced the rarefaction of cancellous bone, which was associated with decreased bone formation and enhanced bone resorption, and may affect bone strength and BMD after chronic exposure. To prevent the risk of bone fractures, patients prescribed a longterm administration of gabapentin should be regularly monitored for changes in bone mass.Key words gabapentin; levetiracetam; osteoblast; osteoclast; rat Epilepsy is a chronic neurological disorder characterized by recurrent seizures. 1) Pharmacotherapy with antiepileptic drugs (AEDs) is the mainstay of treatment for epilepsy and is effective in the prevention of seizures. Patients with epilepsy usually require long-term treatment with AEDs; thus, the prevention of side effects is important in the continuation of medication.The bone is a metabolically active organ that undergoes continuous remodeling from bone resorption by osteoclasts and bone formation by osteoblasts.2) Under healthy conditions, the balance between bone formation and bone resorption is always uniform; thus, bone strength and bone mass are maintained. Certain pathological states and drugs affect normal bone remodeling, which can induce skeletal disorders, such as osteopenia or osteoporosis.3) A serious side effect associated with long-term administration of AEDs is the elevated risk of bone fracture owing to a decrease in bone mass.4-7) Patients taking AEDs are approximately 2-6 times more at risk of bone fracture than healthy individuals are. 8,9) Previous studies have demonstrated that treatment with phenytoin decreased bone mineral density (BMD) owing to enhanced bone resorption.10,11) Currently, new...

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