Pharmacokinetic profile of bisphosphonates in the treatment of metabolic bone disorders.

The pharmacokinetic profile of bisphosphonates is complex and depends on their potency in inhibiting bone resorption through their cellular effects and on the physicochemical action related to the interaction of these compounds with bone matrix. Amino-substituted bisphosphonates exert a more potent cellular effect on osteoclast via the inhibition of the mevalonate pathway, whereas non-nitrogen containing compounds exert a weaker effect deriving from the induction of intracellular metabolites in osteoclasts. For nitrogen-containing bisphosphonates there is a correlation between in vitro potency of inhibition of a specific enzyme, farnesyl pyrophosphate synthase, and their antiresorptive potency in vivo. Besides these effects on osteoclasts, bisphosphonates may in part mediate indirectly their antiresoprtive activity through several effects on osteoblasts and osteocytes. Different binding affinities of bisphopshonates to hydroxyapatite depend on both side chains structures and may explain how these drugs reach bone cells and exert their prolonged action in terms of adsorption and desorption processes. Clinical and animal-models derived data indicate that agents with high anti-resorptive potency, favourable bone binding characteristics and good tolerability can be used with long between-dose intervals to optimize therapeutic outcomes.