What it is
Ziconotide is a 25-amino-acid peptide from snail venom, turned into a painkiller. The cone snail Conus magus hunts fish with a venom made of many small peptides; one of them, omega-conotoxin MVIIA, is the template. Ziconotide is a synthetic copy, sold as Prialt and approved in the US on 28 December 2004.
The Prialt label gives 25 amino acids, three disulfide bridges and a molecular weight of 2,639 daltons. The snail's own sequence, in UniProt's record for the toxin (P05484), is CKGKGAKCSRLMYDCCTGSCRSGKC, ending in an amide. Six of the 25 are cysteines — nearly a quarter — and they pair up into the three bridges that fold the chain into a tight, stable knot. That knot is what lets a venom peptide survive long enough to act.
How it works
Pain signals travel from the body into the dorsal horn of the spinal cord, where the incoming nerve endings release transmitters to pass the message on. That release depends on calcium flowing in through N-type calcium channels. Ziconotide plugs those channels on the pain-carrying A-delta and C fibres, so the signal is not handed on. The label is candid that this mechanism is established in animals and "has not been established in humans".
It is not an opioid — the reason it exists as an option when intrathecal morphine has failed or is not tolerated.
The evidence
The label describes three double-blind, placebo-controlled trials with 457 patients (268 on ziconotide, 189 on placebo), using two titration speeds.
| Trial design (Prialt label) | Result |
|---|---|
| Slow titration to ≤19.2 mcg/day over 21 days, pain resistant to intrathecal morphine, bupivacaine or clonidine | Pain scores improved 12% vs 5% at week 3; 95% CI for the difference 0.4% to 13% |
| Fast titration to 57.6 mcg/day in 5–6 days | Worse tolerated, with substantially more adverse events |
The average benefit is small, and the confidence interval nearly touches zero; the trials were short. The label's safety pool is larger — 1,254 adults, 662 patient-years, 173 treated for at least a year. Only 3 of the 329 MEDLINE records naming ziconotide are tagged as randomised controlled trials (Europe PMC, 2026-09-28).
Doses on the label
Reported as the Prialt label states them, not as guidance: a start of no more than 2.4 mcg per day (0.1 mcg per hour), raised by up to 2.4 mcg per day no more than two to three times a week, to a maximum of 19.2 mcg per day (0.8 mcg per hour). By arithmetic, that ceiling is eight times the starting rate; in the label's slow-titration trial, the final mean dose at day 21 was 6.9 mcg per day. Delivery is by a programmable implanted pump or an external pump and catheter, prescribed by a physician experienced in intrathecal therapy.
Safety
Prialt carries a boxed warning for neuropsychiatric adverse reactions: severe psychiatric symptoms and neurological impairment can occur. It is contraindicated in anyone with a history of psychosis, and the label calls for frequent monitoring for cognitive impairment, hallucinations and changes in mood or consciousness, with the infusion stopped for serious signs. The most frequent reactions in trials — 25% or more — were dizziness, nausea, confusion and nystagmus (involuntary eye movement). Infection risks come with the pump and catheter as well as the drug.
Where it stands
FDA application data list three vial presentations as current prescription products and a fourth, the 200 mcg/2 mL vial, as discontinued, with no generic (2026-09-28). The label was last revised on 31 July 2026. ClinicalTrials.gov holds 14 records with ziconotide as an intervention.
Related reading
Another approved drug in the library that began as an animal venom is exenatide, from the Gila monster. For how three disulfide bridges hold a short chain in shape, compare linaclotide, a 14-amino-acid gut peptide with the same number of bridges.