One of the unsung heroes in Amgen's product portfolio is Sensipar/Mimpara for secondary hyperparathyroidism (HPT), which has grown fairly steadily since its launch more than a decade ago to top $1bn in sales last year.
Now, Amgen is edging close to bringing a successor to Sensipar (cinacalcet) to market after follow-up AMG 416 (formerly known as velcalcetide) met its objectives in a phase III trial involving patients on dialysis for chronic kidney disease.
AMG 416 was significantly more effective than placebo in improving parathyroid hormone (PTH) levels by 30 per cent or more in the six-month study, achieving that objective in 75 per cent of patients, compared to less than 10 per cent of the placebo arm.
Amgen's drug was also significantly more effective than placebo on various secondary measures, including reducing serum phosphorus and calcium which are elevated in the disease as a result of the elevated levels of PTH in patients and can cause serious complications, including cardiovascular disease.
There are important differences between AMG 416 and Sensipar. Most importantly, the new drug is administered intravenously, rather than orally, and has been specifically designed for delivery during the haemodialysis procedure. There are around 2 million people worldwide who are on dialysis as a result of kidney failure.
"Secondary HPT can be a challenging disease to manage and control," said Sean Harper, Amgen's executive vice president of R&D. "There is an important role for an effective calcimimetic that can be administered intravenously with haemodialysis to help treat this disease."
Specifically, Amgen believes that an intravenous formulation of this type of drug - known as a calcimimetic - could help overcome compliance issues with oral therapies that mean a sizeable proportion of patients do not adhere to treatment fully over a 12-month period.
AMG 416 was also well tolerated in the phase III trial, which coupled with its compliance-boosting delivery could also be a significant finding.
Amgen tried and failed to show that Sensipar could reduce the risk of death and cardiovascular events in patients with chronic kidney disease (CKD) receiving dialysis in the large-scale EVOLVE trial. The company acknowledged at the time that the study had been something of a clinical long shot, but the potential for even tighter control of PTH, calcium and phosphorus levels using the new drug could - at least hypothetically - put reduction in cardiovascular risk back in the frame.
Amgen is now waiting for the results of a second placebo-controlled phase III trial - due later this year - as well as a head-to-head comparison with Sensipar that should generate data in 2015. The company acquired AMG 416 as part of its $315m purchase of Kai Pharmaceuticals in 2012.
Analysts have suggested that AMG 416 could match Sensipar's sales at peak, although much will depend on the eventual clinical profile as well as the impact of generic versions of its older sibling, which could reach the market in 2016.