Bisphosphonate drug holidays--when, why and for how long?

Bisphosphonates are first-line agents used for the treatment of osteoporosis in postmenopausal women and men. Although their efficacy in the reduction of vertebral, non-vertebral and hip fracture risk has been established, some concerns have arisen associated with their long-term use. These include osteonecrosis of the jaw and atypical (subtrochanteric and femoral shaft) fractures. The latter may result from accumulation of fatigue damage due to oversuppression of bone turnover in susceptible individuals. In this respect, the concept of a 'drug holiday' after completion of a reasonable period of bisphosphonate therapy has emerged. Theoretically, this allows bone turnover to increase and permits normal skeletal maintenance and repair, although there is as yet no good evidence that bisphosphonate discontinuation will reduce the risk of these adverse events. Current data derive from studies in postmenopausal women and support a beneficial effect of alendronate or zolendronate continuation in high-risk groups, such as those with T-score < -2.5 or prevalent vertebral fractures after completion of 5 or 3 years, respectively. The optimal length of a 'drug holiday' has not been established but existing data suggest up to 5 years with alendronate, 3 years with zoledronate and 1 year with risedronate. A decision to recommence therapy should then probably be based on regular reassessment of bone mineral density and fracture risk.