Calcitonin (salmon)

Calcitonin is secreted by thyroid parafollicular C cells in response to high serum calcium. The salmon sequence is used clinically because it binds the human calcitonin receptor with roughly 40-fold greater affinity than human calcitonin and resists degradation longer. Receptor activation on osteoclasts causes rapid loss of the ruffled border, cytoplasmic retraction and cessation of resorption within minutes, alongside reduced renal tubular calcium and phosphate reabsorption. The osteoclast effect is potent but short-lived: receptors downregulate within days to weeks, which is why calcitonin is a poor long-term antiresorptive and why its BMD and fracture effects are far weaker than bisphosphonates. A separate central analgesic effect, probably mediated through endogenous opioid and serotonergic pathways, underlies its use for acute vertebral fracture pain.

Targets: Calcitonin receptor, Osteoclast ruffled border, Renal tubular calcium reabsorption

• · Dosed in international units: 200 IU (one spray) daily. This indication has fallen out of favour after the 2013 malignancy signal review.
• · 100 IU daily by subcutaneous or intramuscular injection. Bisphosphonates are now first line.
• · 4 IU per kg every 12 hours, escalating to 8 IU per kg every 6 to 12 hours. Tachyphylaxis makes it useless beyond about 48 hours.
• · 200 IU daily for 2 to 4 weeks. This is the one modern use with a reasonable evidence base.

Work out your exact syringe units →

• very commonRhinitis, nasal dryness and epistaxis— The dominant complaint with the nasal spray.
• commonNausea, flushing and vomiting— Mainly with injection; evening dosing helps.
• commonLoss of effect over time— Antibody formation and receptor downregulation both contribute.
• uncommonHypocalcaemia— Especially in vitamin D deficiency.
• rareIncreased malignancy rate in pooled trials— A meta-analysis found about 4.1 percent versus 2.9 percent cancer incidence; causality is unproven but it drove EMA withdrawal of the osteoporosis indication.
• rareHypersensitivity, including anaphylaxis— It is a fish-derived sequence; skin testing is available for high-risk patients.

• Known hypersensitivity to salmon calcitonin
• Pre-existing hypocalcaemia
• Long-term use for osteoporosis, which is no longer recommended in the EU

• conflictteriparatide — Opposing actions on bone turnover; combining wastes the anabolic signal.
• cautionetelcalcetide — Both lower serum calcium and can stack into symptomatic hypocalcaemia.

• · Serum calcium at baseline and during hypercalcaemia treatment
• · Nasal mucosa examination on long-term nasal therapy
• · Alkaline phosphatase in Paget's disease

Prescription drug in the US for Paget's disease, hypercalcaemia and postmenopausal osteoporosis; the osteoporosis nasal indication was withdrawn in the EU.

• Miacalcin FDA prescribing information (label)
• Chesnut et al. 2000 American Journal of Medicine, PROOF trial of nasal calcitonin in postmenopausal osteoporosis (trial)
• EMA 2012 review of calcitonin-containing medicines and malignancy risk (guideline)

The calcitonin receptor is a class B GPCR on the osteoclast, and what makes calcitonin unusual among antiresorptives is how fast and how mechanically it works. Within minutes of receptor engagement, Gs-cyclic AMP and Gq-PKC signalling cause the osteoclast to retract its cytoplasm and dismantle the ruffled border, which is the specialised membrane through which it secretes acid and cathepsin K into the resorption lacuna. No ruffled border means no resorption, immediately, without any change in osteoclast number. That is why serum calcium falls within two hours in hypercalcaemia, faster than any bisphosphonate. It is also why the effect does not last: the receptor is rapidly downregulated and the osteoclast escapes within days to weeks, a phenomenon so consistent it has its own name, the escape phenomenon. Add neutralising antibody formation against a foreign fish sequence and you have a drug that is potent for 48 hours and near-useless at 6 months, which is the whole story of its clinical decline. Renal tubular calcitonin receptors add a modest calciuric and phosphaturic effect. The analgesic action in acute vertebral fracture is genuinely separate and only partly understood, with evidence pointing at central calcitonin receptor populations, raised beta-endorphin, and serotonergic modulation of nociception; it is not explained by the antiresorptive effect and it occurs at doses and timescales that do not track bone turnover. Finally, the pooled-trial malignancy signal, roughly 4.1 percent versus 2.9 percent, has no established mechanism, was not the primary endpoint of any trial, and remains association rather than causation, but it was enough for the EMA to withdraw the osteoporosis indication.

Tachyphylaxis is not a rare complication, it is the expected course, and clinicians who plan a week of calcitonin for hypercalcaemia have misunderstood the drug. The escape happens within 48 hours through receptor downregulation and later through neutralising antibodies to a foreign fish sequence. Second, the nasal spray needs priming before first use and a lot of patients never do it, so early doses are air. Third, this is a fish-derived peptide and anaphylaxis has been reported; skin testing exists for high-risk atopic patients. Fourth, using it long-term for osteoporosis: the EMA withdrew that indication in 2012 to 2013 over the pooled malignancy signal, and even setting the cancer question aside the efficacy is poor compared with anything else available. Fifth, expecting the analgesic effect to be an antiresorptive effect; they are different mechanisms on different timescales and the analgesic use does not require or imply bone protection.

1. —Acute hypercalcaemia, hours 0-24 — Dosed in international units, not micrograms: 4 IU per kg subcutaneously or intramuscularly every 12 hours.
2. —Acute hypercalcaemia, if response is inadequate at 24-48 hours — Escalate to 8 IU per kg every 12 hours, and if still inadequate, 8 IU per kg every 6 hours. Beyond about 48 hours tachyphylaxis makes further dosing pointless; the bisphosphonate or denosumab you started on day one should be taking over.
3. —Paget's disease — 100 IU daily subcutaneously or intramuscularly, given in the evening to reduce nausea and flushing. Bisphosphonates are first-line and this is a fallback.
4. —Acute vertebral fracture pain, weeks 1-4 — 200 IU intranasally once daily, alternating nostrils, started within days of the fracture and continued for 2 to 4 weeks. This is the one modern indication with a defensible evidence base.

• Calcitonin receptor on osteoclasts — Salmon calcitonin binds the human receptor with roughly 40-fold greater affinity than human calcitonin. Numeric Kd not resolved this session.

  Gs and Gq signalling causing immediate cytoplasmic retraction and loss of the ruffled border. Resorption stops within minutes, but the receptor downregulates within days to weeks, producing tachyphylaxis.

• Renal tubular calcitonin receptor — Present

  Reduced tubular reabsorption of calcium and phosphate, adding a modest calciuric effect to the anti-resorptive one.

• Central calcitonin receptors and endogenous opioid pathways — Poorly characterised

  The probable basis of the analgesic effect in acute vertebral fracture, mediated at least in part through beta-endorphin and serotonergic pathways rather than through bone.

• PROOF (Prevent Recurrence Of Osteoporotic Fractures) Phase 3, randomised, double-blind, placebo-controlled · n=1255 · 260 weeks · 2000

  New vertebral fractures in postmenopausal women with established osteoporosis over 5 years. The 200 IU nasal dose reduced new vertebral fracture risk by 33 percent versus placebo (RR 0.67, p equals 0.03), and by 36 percent in women with existing vertebral fractures. Neither the 100 IU nor the 400 IU dose was significantly better than placebo, which is the reason this trial is generally regarded as weak: a dose-response that goes up and then down is hard to believe.

Serum calcium begins falling within 2 hours of injection in hypercalcaemia and the maximum effect is at 24 to 48 hours, after which escape begins. Analgesic benefit in acute vertebral fracture usually becomes apparent within one to two weeks. In Paget's disease, alkaline phosphatase falls over weeks to months. Antibody formation develops over months of continued use and correlates with loss of effect.

In acute hypercalcaemia of malignancy, calcitonin is explicitly a bridge and should never be the only thing you give: intravenous saline rehydration first, calcitonin for the first 24 to 48 hours because it works within hours, and a bisphosphonate or denosumab started at the same time to take over from day 2 to 4. Giving calcitonin alone is a plan that fails on day three. It should not be combined with teriparatide or abaloparatide, which it directly opposes. Combining it with etelcalcetide or any other calcium-lowering agent risks additive symptomatic hypocalcaemia. Calcium and vitamin D repletion belong alongside it in every non-hypercalcaemic use.

Against bisphosphonates and denosumab in hypercalcaemia: calcitonin is far faster, working in hours against 24 to 72 hours, and far weaker and shorter-lived. That combination makes it a bridge and nothing else. Against bisphosphonates in Paget's disease: zoledronate produces long remissions and calcitonin does not, so this is now a second-line agent for people who cannot take bisphosphonates. Against anything at all in osteoporosis: it is the weakest option on the shelf, its registration trial had a non-monotonic dose response, and it carries a malignancy signal that got the indication withdrawn in Europe. The only place it still earns a place on merit is short-course analgesia after an acute osteoporotic vertebral fracture.

$100–$400/month. Unverified estimate. Generic injectable calcitonin salmon is inexpensive; the nasal spray is more variable. Not sourced in this session.

• ?The salmon calcitonin sequence given is the standard published sequence, but the Miacalcin label renders it as a graphic and I could not confirm it character by character this session, so verified is false.
• ?Intranasal bioavailability is described qualitatively because I did not resolve a numeric figure from the nasal spray label.
• ?Volume of distribution is quoted by the label as 0.15 to 0.3 L/kg rather than in litres, so the litre field is null.
• ?Blood-brain barrier penetration is marked partial on the basis that a central analgesic effect exists, but the extent of central access and whether the analgesia requires it are genuinely unresolved.
• ?The malignancy signal is association only; no mechanism has been established and causality is unproven.
• ?Cost figures are unverified estimates.

• A randomized trial of nasal spray salmon calcitonin in postmenopausal women with established osteoporosis: the PROOF study Chesnut CH 3rd, et al., American Journal of Medicine, 2000 · PMID 10996576

  The osteoporosis registration trial, and the non-monotonic dose response is why almost nobody defends this indication now.

• MIACALCIN (calcitonin salmon) injection - FDA prescribing information Mylan Institutional, DailyMed

  Source of the 66 and 71 percent bioavailability figures, the 23 minute subcutaneous tmax, the 58 to 64 minute terminal half-life and the 0.15 to 0.3 L/kg volume of distribution.