ziconotide
Meaning of ziconotide: A cone snail venom peptide turned painkiller, which works only when delivered straight into the fluid around the spinal cord.
Definition of ziconotide
Ziconotide is a synthetic copy of a peptide from the venom of a marine cone snail, used for severe pain that has not answered other treatments. It blocks a calcium channel on nerve endings in the spinal cord, preventing release of the chemicals that pass pain signals upward. It is effective only when infused directly into the fluid around the cord.
How does it work?
Nerve endings release their chemical messengers only when calcium floods in through channels in the membrane. Ziconotide plugs one particular type, the N type channel, concentrated on the endings of pain carrying fibers where they meet the spinal cord. With the channel blocked the signal reaches the ending but is not handed across. The mechanism is entirely unlike that of an opioid, which acts at separate receptors, so the drug can still work where opioids no longer do.
Why must it go into the spinal fluid?
The molecule is a peptide, a short chain of amino acids. Swallowed, it would be digested like any protein. Injected into a vein, it would not reach the nervous system in useful amounts, and blocking the same channels throughout the body would disturb blood pressure control. Delivery is therefore by a pump, usually implanted under the skin of the abdomen, feeding a fine catheter into the fluid filled space around the cord. Doses are measured in micrograms per day and raised slowly.
How does it compare with opioids?
| Feature | Ziconotide | Opioids |
|---|---|---|
| Target | N type calcium channels | Opioid receptors |
| Route for this use | Into the spinal fluid only | Mouth, patch, injection or spinal |
| Tolerance over time | Not described | Develops, so doses climb |
| Dependence | Not described | A recognized problem |
| Limiting effects | Confusion, hallucination, mood change, dizziness | Sedation, constipation, slowed breathing |
The absence of tolerance and dependence is the reason the drug exists, and the psychiatric and neurological effects are the reason it is not used more widely. Those effects build gradually and ease when the infusion is reduced or stopped, but they set the ceiling on the dose that can be given.
Where did it come from?
From a cone snail that hunts fish by firing a harpoon loaded with paralyzing peptides. One component of that venom blocks the N type channel with unusual precision. Isolating it and making it synthetically produced the drug marketed as Prialt. Its place is narrow: severe chronic pain in people for whom a spinal pump is already suitable and other approaches have failed.
Also known as
Used in a sentence
Intrathecal ziconotide was started after opioid therapy failed to control the pain.
Good to know
The drug is inactive by mouth and unsuitable for intravenous use, so it is delivered into the cerebrospinal fluid by pump, and unlike opioids it produces neither tolerance nor dependence.