[Relationship of pharmacokinetics, changes of bone turnover markers and BMD/fractures efficacy during treatment with anabolic agents;Teriparatide daily and once weekly subcutaneous injections.]

Teriparatide(recombinant human PTH1-34, 20 μg daily subcutaneous injection)has been approved for osteoporosis patients at high risk of fracture in many countries including Japan. Teriparatide daily injection therapy has been reported to increase BMD, improve microarchitecture of bone, and reduce the risk of new vertebral fractures and that of non-vertebral fractures. Pharmakokinetic(PK)study after a single Teriparatide injection of the daily dose in healthy Japanese postmenopausal women(n=18)revealed very rapid achievement of peak blood level(median of tmax=0.25 hr)followed by fast disappearance from the blood(mean t1/2=0.708 hr, n=17). Consistent with these PK characteristics, a rapid increase in bone formation marker and later increase in bone resorption marker has previously been observed, which was described as a bone anabolic window. More recently, once weekly subcutaneous injection of teriparatide acetate(56.5 μg)has been reported to reduce the risk of new vertebral fractures compared with placebo and has been approved in Japan. PK study after injection of the higher weekly dose in healthy Japanese postmenopausal women(n=10)revealed a relatively slow achievement of the peak blood level(mean tmax=0.875 hr)compared to daily injections, followed by relatively slow disappearance from the blood(mean t1/2=1.295 hr). Consistent with these PK characteristics, an initial(<24 hr)transient decrease of bone formation markers(serum osteocalcin and P1NP)and transient increase of bone resorption markers(serum NTX and urinary CTX)were observed. However, afterword, the bone formation and resorption markers were increased and decreased, respectively, for longer than 1 week from the baseline levels. The relationship of pharmacokinetics, changes of bone turnover markers and BMD/fractures efficacy during daily versus weekly teriparatide treatment needs to be clarified.