Abaloparatide

Abaloparatide is based on PTHrP(1-34) with substitutions that improve stability and receptor selectivity. Both teriparatide and abaloparatide hit the PTH1 receptor, but the receptor exists in two conformations: R0, which produces prolonged signalling and more resorption, and RG, which produces a shorter, more purely anabolic signal. Abaloparatide is biased toward RG. The practical consequences are a somewhat smaller rise in bone resorption markers, lower rates of hypercalcaemia than teriparatide, and in the ACTIVE trial a significant reduction in non-vertebral as well as vertebral fractures over 18 months. Like teriparatide, it depends entirely on intermittent pulsed dosing and its gains fade quickly unless an antiresorptive follows.

Targets: PTH1 receptor RG conformation, Osteoblast activity, Trabecular and cortical bone formation

• · Fixed 80 mcg from a pen delivering 30 daily doses. Calcium and vitamin D should be supplemented if intake is inadequate.

Work out your exact syringe units →

• commonOrthostatic hypotension and dizziness— Most common in the first few hours after the first doses.
• commonPalpitations and tachycardia— Reported more often than with teriparatide.
• commonNausea and headache
• commonHypercalciuria
• commonInjection-site erythema
• uncommonHypercalcaemia— Less frequent than with teriparatide but still requires a baseline calcium check.

• Pre-existing hypercalcaemia
• Primary hyperparathyroidism or Paget's disease
• Prior skeletal radiation
• Bone metastases or skeletal malignancy
• Unexplained elevated alkaline phosphatase
• Hereditary disorders predisposing to osteosarcoma

• redundantteriparatide — Same anabolic pathway; sequential use of both is not standard practice.
• conflictcalcitonin-salmon — Opposing effects on bone remodelling.

• · Serum calcium before starting and periodically
• · Urinary calcium in stone-formers
• · DXA at 18 to 24 months
• · Blood pressure sitting and standing during the first weeks

Prescription drug in the US; approved in the EU as Eladynos.

• Tymlos FDA prescribing information (label)
• Miller et al. 2016 JAMA, ACTIVE trial of abaloparatide versus placebo and teriparatide (trial)

Both abaloparatide and teriparatide are full agonists at PTH1R, so the differences come from which receptor conformation they prefer and how long they hold it. PTH1R exists in an R0 state, which is G-protein-independent, high-affinity and produces prolonged cyclic AMP signalling from internalised complexes, and an RG state, which is transient and G-protein-coupled. Teriparatide binds both R0 and RG well. Abaloparatide is biased toward RG, so the signal it produces is shorter-lived even though the plasma half-life of the two drugs is similar. The downstream consequence is a smaller and later rise in bone resorption markers, less calcium mobilisation from bone, and therefore the lower hypercalcaemia rate that ACTIVE demonstrated head to head against teriparatide, 3.4 percent versus 6.4 percent. The PTHrP heritage matters here too: PTHrP is the paracrine ligand of the same receptor and physiologically drives chondrocyte and osteoblast behaviour without the systemic calcium-mobilising role of PTH, so an analogue built on that scaffold inherits a more bone-selective, less calcaemic profile. Clinically the pattern is a compressed anabolic window with an earlier non-vertebral fracture separation from placebo, and the same absolute dependence on pulsatile dosing and on a follow-on antiresorptive.

The orthostatic hypotension is more prominent than with teriparatide and it catches people out in the first week, occasionally with a fall and a fracture, which is a grimly ironic outcome. Injecting seated and staying seated for half an hour fixes almost all of it. Second, the same stopping problem as teriparatide: the gains fade within about a year without a follow-on antiresorptive, and this is the single most common way the money is wasted. Third, the pen is refrigerated before first use but kept at room temperature below 30 degrees C for its 30-day in-use period, which is the opposite of the Forteo rule, and patients who switch between products get this wrong in both directions. Fourth, palpitations and tachycardia are reported often enough to alarm patients who were not warned. Fifth, mis-timed calcium draws generating false hypercalcaemia panic.

1. 80 mcgWeeks 1-78 — 80 mcg subcutaneously once daily into the periumbilical abdomen, rotating sites, from a pen delivering 30 doses. No titration: the dose is fixed. Take the first several doses sitting or lying down and stay down for 30 minutes.

• PTH1 receptor, RG conformation — Selective for the transient RG state over R0, which is the pharmacological basis of the whole drug. Numeric affinities not resolved this session.

  Short, G-protein-coupled cyclic AMP signal in osteoblasts and osteocytes. Drives bone formation with proportionally less RANKL-mediated resorption and less calcium mobilisation than teriparatide.

• PTH1 receptor in kidney — Present but the calcaemic effect is attenuated

  Increased distal tubular calcium reabsorption and phosphate excretion, but less pronounced than with teriparatide, hence the lower hypercalcaemia and the persistent but modest hypercalciuria.

• Cortical and trabecular bone envelopes

  Trabecular gains dominate, with cortical improvement at the hip that develops later. Vertebral fracture reduction is large; the non-vertebral signal appears earlier than with teriparatide.

• ACTIVE Phase 3, double-blind, randomised, placebo-controlled with an open-label teriparatide comparator arm · n=2463 · 2016

  New morphometric vertebral fractures in postmenopausal women with osteoporosis. Abaloparatide reduced new vertebral fractures markedly versus placebo and also lowered non-vertebral fracture risk, with greater bone mineral density gains at all measured sites (p less than 0.001). Hypercalcaemia was significantly less frequent than with teriparatide, 3.4 percent versus 6.4 percent, risk difference -2.96, p equals 0.006. Conducted across 28 international sites from March 2011 to October 2014.

Bone formation markers rise within weeks. Bone mineral density gains at the spine are measurable by 6 months and continue through 18 months. Non-vertebral fracture separation from placebo appeared earlier in ACTIVE than is typical for teriparatide. Vertebral fracture protection is demonstrable by 18 months. Orthostatic effects are concentrated in the first hours after the first several doses and then largely settle.

The sequencing rule is identical to teriparatide and just as non-negotiable: anabolic first, then an antiresorptive, and never anabolic with nothing after it. The ACTIVExtend extension showed that following 18 months of abaloparatide with alendronate preserved and extended the fracture benefit, which is the practical template. Prior bisphosphonate exposure blunts the response, especially at the hip, so in a treatment-naive patient at very high fracture risk the anabolic should come first. Adequate calcium and vitamin D are prerequisites. Do not run abaloparatide and teriparatide together or sequentially without a clear reason; they are the same pathway and the total anabolic exposure counts toward the same consideration. Calcitonin is pharmacologically opposed and pointless alongside it. Thiazides retain calcium and can push a borderline patient over.

Against teriparatide: broadly comparable spine bone mineral density gains, less hypercalcaemia in a genuine head-to-head, an earlier non-vertebral fracture signal, and a pen that does not need refrigeration once in use, which matters more for travel and adherence than it sounds. Against that, teriparatide has two decades of real-world safety data and cheap biosimilars, and cost alone will decide most cases. Against romosozumab: romosozumab produces larger 12-month bone mineral density gains and has a direct antiresorptive component, but carries a cardiovascular boxed warning. Against bisphosphonates: different category entirely, and using one first compromises the other. Both anabolic osteosarcoma boxed warnings were removed in 2021 after the rodent signal failed to translate.

$1500–$3500/month. Unverified estimate of US pricing. There is no generic abaloparatide, so unlike teriparatide there is no cheap route to this drug. Not sourced in this session.

• ?Numeric clearance is not stated in the Tymlos label.
• ?The 50 L volume of distribution is described approximately in the label text rather than as a precise measured Vss.
• ?ACTIVE's treatment duration is conventionally cited as 18 months, but the fetched summary confirmed only the enrolment period and the sites, so durationWeeks is null.
• ?Numeric R0 versus RG binding affinities and the exact selectivity ratio were not resolved this session; the conformational-selectivity mechanism is well described in the literature but I did not confirm figures.
• ?Cost figures are unverified estimates.

• Effect of Abaloparatide vs Placebo on New Vertebral Fractures in Postmenopausal Women With Osteoporosis: A Randomized Clinical Trial Miller PD, et al., JAMA, 2016 · PMID 27533157

  The ACTIVE trial. The only phase 3 osteoporosis trial with a head-to-head teriparatide arm, which is where the hypercalcaemia comparison comes from.

• TYMLOS (abaloparatide) injection - FDA prescribing information Radius Health, DailyMed

  Source of the 36 percent bioavailability, 0.51 hour median tmax, roughly 50 L volume of distribution, 70 percent protein binding, 1 hour half-life and the full amino acid sequence including Aib29.