Pharmacodynamics and pharmacokinetics of oral salmon calcitonin in the treatment of osteoporosis.

INTRODUCTION: Salmon calcitonin (sCT) has been used for the treatment of postmenopausal osteoporosis for over 30 years. It is available in injectable and intranasal formulations. Two oral formulations have recently been developed. AREAS COVERED: The basis for oral sCT's bioavailability rests with a carrier molecule (8-(N-2-hydroxy-5-chloro-benzoyl)-amino-caprylic acid) or an acid-resistant enteric coating (Eudragit® polymer containing citric acid). With these formulations, sCT is resistant to gastric acid, and thus becomes available for absorption at the higher pH of the small intestine. Even though the changes in bone mineral density and bone turnover markers are greater with oral compared to nasal sCT, it shows only minor effects on these surrogate markers. EXPERT OPINION: Oral sCT is attractive in concept as it is would be more convenient to patients than other routes of administration. While there may be other advantages to the oral formulation such as improving bone mineral density to a greater extent than nasal CT, anti-fracture efficacy has not been shown in a recent major clinical trial. Together with the possibility of an association between the drug and cancer and the availability of antiresorptive drug classes that are clearly more efficacious than sCT, successful development of oral sCT as a treatment for postmenopausal osteoporosis is uncertain.