Elcatonin
(Asu1,7)-eel calcitonin, carbocalcitonin, ECT, elcatonin acetate, aminosuberic eel calcitonin
Elcatonin is a chemically stabilised analogue of eel calcitonin in which the disulfide bridge between the first and seventh residues is replaced by a non-reducible ethylene bridge. That single change makes it far more resistant to degradation than natural calcitonins. It has been licensed in Japan since the early 1980s, mainly for the pain of osteoporosis rather than for fracture prevention, and is not approved in the US, UK or EU.
Mechanism
Elcatonin binds and activates the same class B G-protein-coupled calcitonin receptor as salmon and human calcitonin. Receptor occupancy on the osteoclast raises cyclic AMP and intracellular calcium, causing rapid disassembly of the ruffled border and actin sealing ring and retraction of the cell, so resorption stops within minutes without any change in osteoclast number. In the kidney it reduces tubular reabsorption of calcium and phosphate, promoting their excretion and contributing to a fall in serum calcium.
The distinguishing feature is chemical rather than pharmacological. Natural calcitonins carry a Cys1-Cys7 disulfide that closes an N-terminal ring essential for receptor activation, but disulfides are reducible and are a common point of degradation. In elcatonin, alpha-aminosuberic acid at position 1 supplies a carbon chain that forms an ethylene bridge to position 7, replacing the sulfur-sulfur linkage with a stable carbon-based arrangement. The ring geometry (and therefore receptor activation) is preserved, but the molecule resists reduction and proteolysis, allowing higher purity in manufacture and greater stability in vitro and in vivo. Elcatonin also shows the central antinociceptive activity attributed to the calcitonin class. Animal work in ovariectomised rats, a model of oestrogen-deficient hyperalgesia, showed that repeated peripheral administration raised nociceptive thresholds. The pathways proposed include central calcitonin receptor signalling with downstream beta-endorphin and serotonergic involvement, but this remains considerably less well characterised than the skeletal mechanism.
What the research shows
Elcatonin's therapeutic evidence is dominated by Japanese trials with pain and bone density endpoints rather than fractures. The best single controlled study is a multiclinic randomised trial in 228 Japanese women with acute lumbar pain from osteoporotic vertebral fracture, comparing weekly intramuscular elcatonin 20 units against oral non-steroidal anti-inflammatory drugs. Elcatonin gave greater pain relief and better recovery of mobility over the treatment period. A smaller randomised trial in postmenopausal women with back pain reported a similar direction of effect. A systematic review with network meta-analysis pooling sixteen randomised trials in 2,754 postmenopausal women found that elcatonin, alone or combined with other agents, produced significantly lower pain scores than non-elcatonin comparators, and reported comparable safety.
The same network meta-analysis contains the important negative finding: fracture rates and bone mineral density change with elcatonin were comparable to, not better than, the non-elcatonin medications it was compared against. In other words, more than four decades after licensing, elcatonin has no adequately powered placebo-controlled trial demonstrating that it prevents fractures, and the pooled evidence does not suggest it outperforms established antiresorptives on skeletal endpoints. At least one head-to-head trial found alendronate superior to elcatonin for pain and quality of life in postmenopausal osteoporosis, which sits awkwardly against the pooled analgesic claim. Bone density gains reported in involutional osteoporosis are small. The trial literature is also geographically narrow, mostly conducted in Japan in Japanese populations, frequently small, and often open-label, which limits how far it generalises. A further consideration that the elcatonin literature has largely not addressed is whether the malignancy signal that led European regulators to restrict salmon calcitonin in 2012 applies to the calcitonin class as a whole; elcatonin was not part of that European review because it has never been authorised in the EU, so the question is simply unexamined rather than answered.
Evidence assessment
Mixed evidence
Elcatonin has genuine randomised human evidence (including a 228-patient multicentre trial, a smaller randomised trial and a network meta-analysis of sixteen randomised studies, all now verified) and long-standing approved labelling in Japan. But the trials are small, largely single-country, often open-label, and concentrated on pain rather than fracture; the pooled analysis found no advantage on fracture or bone density; and no placebo-controlled fracture trial exists. Mixed is the honest description. It is not preclinical: three of the four surviving citations are human randomised evidence.
Tiers are applied consistently across the library and re-checked when new trials read out. Read the grading method.
Key studies
Effect of elcatonin versus nonsteroidal anti-inflammatory medications for acute back pain in patients with osteoporotic vertebral fracture: a multiclinic randomized controlled trial Preclinical only
Weekly elcatonin was more effective than oral NSAIDs for relief of acute lumbar pain and for improvement in mobility. The comparator was an active analgesic rather than placebo, and the trial was conducted in a single national population.
Anti-nociceptive effects of elcatonin injection for postmenopausal women with back pain: a randomized controlled trial Preclinical only
Elcatonin injection reduced back pain scores relative to control in postmenopausal women with osteoporosis. The study was small and conducted in a single country, and the pain endpoint is subjective, so the result is supportive rather than definitive.
Ovariectomy-induced hyperalgesia and antinociceptive effect of elcatonin, a synthetic eel calcitonin Preclinical only
Ovariectomy produced hyperalgesia, and repeated elcatonin administration increased withdrawal latency relative to vehicle. Provides the animal basis for the analgesic claim in oestrogen-deficient states, but is an animal model and does not establish clinical benefit.
Safety
The reported adverse effect profile mirrors that of other calcitonins: nausea, vomiting, flushing of the face and upper body, dizziness, and injection-site reactions. Hypersensitivity reactions including rash and, rarely, anaphylaxis have been described, and because the peptide is of non-human origin, prior sensitivity testing has been part of some prescribing practice. Hypocalcaemia can occur, more relevantly when the drug is used for hypercalcaemia. Antibody formation is a recognised issue with calcitonins generally; elcatonin's chemical stability does not exempt it from immunogenicity, since the antigenic determinants are sequence-based rather than dependent on the disulfide. Two broader points deserve stating plainly. First, elcatonin has no adequately powered placebo-controlled fracture trial, so it should not be assumed to reduce fracture risk. Second, the malignancy signal that caused European regulators to withdraw nasal salmon calcitonin and to cap the duration of injectable calcitonin in 2012 has never been formally evaluated for elcatonin, because elcatonin held no European authorisation to review. Whether that class signal extends to elcatonin is unknown, not disproven. This entry is educational and contains no dosing or administration guidance.
Regulatory status
| Jurisdiction | Status |
|---|---|
| United Kingdom | Not authorised by the MHRA and not available as a licensed medicine in the UK, nor in the EU. It is licensed and marketed principally in Japan, where it has been used since the early 1980s, and in several other Asian territories. Note that the 2012 EMA restriction on calcitonin-containing medicines did not consider elcatonin, because it held no European authorisation to review. |
| United States | Not approved by the FDA. Elcatonin has never held a US marketing authorisation and is not available as a prescription medicine in the United States. Any material offered for sale in the US is unapproved. |
| WADA (sport) | Not named on the WADA Prohibited List. Calcitonins are calcium-regulating antiresorptive hormones and do not fall within the S2 growth factor provisions, which concern agents acting on muscle, tendon or ligament. Athletes should verify against the current list. |
Questions
Asu is alpha-aminosuberic acid, an eight-carbon amino acid placed at position 1. Its long side chain reaches across to position 7 and forms a stable ethylene bridge, replacing the sulfur-sulfur disulfide that closes the N-terminal ring in natural calcitonins. The ring shape needed for receptor activation is retained, but the bond can no longer be reduced or cleaved as easily.
It is chemically more stable, which improves manufacturing purity and resistance to degradation. Whether that translates into a clinically meaningful advantage has never been established in a well-powered head-to-head trial. On the endpoints that matter most in osteoporosis (fracture and bone density), neither agent has a convincing record.
Because that is where its evidence lies. Japanese trials and a network meta-analysis of sixteen randomised studies consistently show a pain benefit, particularly in acute osteoporotic vertebral fracture, while the same pooled analysis found fracture rates and bone density changes no better than comparators. Its licensed positioning in Japan reflects that pattern. Even the analgesic claim is not uncontested: at least one randomised comparison found alendronate better than elcatonin for pain and quality of life.
No. Elcatonin has never been authorised by the MHRA, the EMA or the FDA. It is licensed principally in Japan and some other Asian markets. Any product offered in the UK or US is unlicensed.
Nobody knows, and that is the honest answer. The 2012 European review that found a small excess of cancers with long-term calcitonin use assessed salmon and human calcitonin products holding EU authorisations. Elcatonin was not included because it had none. The absence of a finding is not the same as a finding of absence.