One of the most prescribed medical treatments for osteoporosis are the oral bisphosphonates. These drugs are manufactured so as to have the same structure of pyrophosphate.
Pyrophosphate occurs naturally in the body and is an inhibitor of bone resorption in the bone remodelling system. The bisphosphonate drugs compounds include alendronate sodium, risedronate sodium, ibandronate sodium, Etidronate and clodronate.
As bisphosphonates are antiresorptive agents they act by decreasing osteoclasts that are responsible for bone resorption, but do not effect the function of the osteoblasts that create new bone. This leads to an increase in the rate of bone creation and in turn an increase in the density of bone.
The bisphosphonate is delivered to the surface of the bone by use of a pro-drug. Once at the bone surface bisphosphonates are able to bind to hydroxyapatite crystals of the bone and decrease the growth and activity of osteoclasts; this leads to the inhibition of bone reabsorption.
Following inhibition of the resorption process two things can happen to the pyrophosphate analogs.
1. They are removed by renal mechanisms
2. They remain in the bone matrix and act in further bone remodelling.
It is the latter case that gives bisphosphonate drugs such a long life span.
References
Mayes (2007) Review of post menopausal osteoporosis pharmacology. Nutr. Clin. Prac. 22:3: 276 to 285