Crotalphine and crotamine

crotalphine (identified from Crotalus durissus terrificus venom); crotamine (a myotoxin from the same venom, also described as a cell-penetrating peptide, CPP)

Cognitive & neuro

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Summary

Class: Two unrelated peptides from South American rattlesnake venom. Crotalphine is a 14-amino-acid peptide. Crotamine is a 42-amino-acid, highly basic myotoxin of the beta-defensin fold, with three disulfide bonds
Mechanism: Crotalphine produces long-lasting analgesia in rodents by activating peripheral opioid receptors (kappa and delta) and engaging cannabinoid signalling; crotamine is a muscle toxin that happens also to be an efficient cell-penetrating and nucleic-acid-carrying peptide with selectivity for rapidly dividing cells
Routes studied: Crotalphine: subcutaneous, oral and intraplantar in rodents. Crotamine: intraperitoneal, intramuscular and intravenous in animals; cell culture for the delivery work
Half-life: Not characterised in any species for either peptide
Storage: Not applicable to this profile — see research context notes
Regulatory status: Neither is approved anywhere. Research compounds

Doses are as reported in studies or by the community — never recommendations.

1What it is

Crotalus durissus terrificus, the South American or tropical rattlesnake, has a venom that is unusually neurotoxic for a pit viper. Two of its components have attracted interest for reasons unconnected to envenomation.

Crotalphine was identified in the 2000s by a group at the Butantan Institute in São Paulo, following up on an old clinical curiosity: reports that cancer patients given rattlesnake venom preparations experienced pain relief. The group isolated a small peptide with potent, remarkably long-lasting analgesic activity in rats and characterised its sequence; the synthetic version is called crotalphine. The most striking published property is duration — a single dose producing antinociception lasting days, which is unusual for any analgesic and very unusual for a peptide.

Crotamine is a different kind of molecule with a double life. It is a classical myotoxin: inject it into a mouse and the hind limbs go into spastic paralysis, which is what it is for in the venom. In 2004 Irina Kerkis and colleagues reported that crotamine also crosses cell membranes efficiently, accumulates in the nucleus and lysosomes, and — unexpectedly — concentrates preferentially in actively proliferating cells. That turned a toxin into a candidate drug-delivery vehicle and tumour-targeting agent, and most crotamine research since has followed that thread rather than the toxicology.

Both are preclinical. Neither has been given to a human in a trial.

2How it's thought to work

Crotalphine:

Peripheral opioid receptors. The analgesic effect is blocked by naloxone and by selective kappa- and delta-opioid antagonists, and the evidence points to a peripheral rather than central site of action — which is attractive, because peripheral opioid analgesia would in principle avoid respiratory depression and central dependence.

Indirect activation. Crotalphine appears not to bind opioid receptors directly at the relevant concentrations; the proposed mechanism involves release of endogenous opioid peptides, with cannabinoid CB2 receptor involvement reported as an upstream step in some models.

Duration. The multi-day effect from a single dose is not explained by pharmacokinetics and is attributed to a change in the state of the nociceptor rather than to drug occupancy — mechanistically interesting and not fully resolved.

Myotoxicity. The classical action involves effects on skeletal muscle membrane excitability and ion handling, producing the characteristic spastic hind-limb paralysis. Potassium channel and sodium handling effects have been proposed; the precise mechanism remains debated.

Cell penetration. Crotamine is strongly cationic and rich in lysine and arginine, like the other well-known cell-penetrating peptides. It binds cell-surface heparan sulfate proteoglycans and enters by endocytosis, then reaches endosomes, lysosomes and the nucleus.

Selectivity for dividing cells. Preferential accumulation in proliferating cells is attributed to higher surface proteoglycan expression and greater endocytic activity. This is the basis of both the tumour-targeting and the carrier applications.

Nucleic acid carriage. It complexes DNA and can deliver plasmids into cells, and has been examined as a carrier for antisense and other payloads.

Antimicrobial and antiparasitic activity. Consistent with its beta-defensin fold, crotamine has reported activity against bacteria, fungi and protozoa .

Rattlesnake venom peptides. Crotalphine produces long-lasting analgesia through opioid receptors in animal models; crotamine affects sodium channels and penetrates cells.Schematic — not to scale

3What the research shows

Crotalphine — analgesia in rodents

The founding work reported potent, long-lasting antinociception in rat models of inflammatory and neuropathic pain after or oral administration at microgram-per-kilogram doses, with effects persisting for days and reversible by opioid antagonists (Konno 2008, Peptides; Gutierrez 2008, Pharmacol Biochem Behav). Later work extended this to cancer pain and neuropathic models and detailed the kappa/delta and cannabinoid mechanisms (Machado 2014, PLoS One; Zambelli 2014 and related). Potency and duration are consistently reported as remarkable. [1][2][3]

Not gradednone

Crotalphine — human data

No clinical trials. The compound has been the subject of patent and licensing activity but there is no published human safety or efficacy data.

Graded C/D

Crotamine — cell penetration and delivery

Crotamine enters cells efficiently, localises to nucleus and lysosomes, preferentially accumulates in proliferating cells and can carry plasmid DNA into cells and into mouse tissues (Kerkis 2004, FASEB J; Nascimento 2007, J Biol Chem). Well-replicated in cell culture; animal work is more limited. [4][5]

Crotamine — antitumour activity

Reported selective cytotoxicity toward tumour cells and tumour growth inhibition in mouse melanoma models, attributed to lysosomal disruption in cells that have concentrated the peptide (Pereira 2011, Cell Death Dis, and related). Preclinical. [6]

Graded C/D

Crotamine — analgesic and other activities

Antinociceptive effects have been reported for crotamine, as have antimicrobial and antiparasitic activities . Scattered literature.

Not graded

Crotamine — toxicology

Crotamine is a myotoxin and this is the better-established half of its biology. Systemic administration in animals causes muscle damage with rising creatine kinase, and the myotoxic dose range sits uncomfortably close to the doses used in the delivery experiments. This is the central obstacle to the delivery application and is sometimes underplayed in reviews.

Not graded

Human exposure — envenomation

C. d. terrificus bite produces neurotoxicity with ptosis and ophthalmoplegia, myotoxicity with rhabdomyolysis and myoglobinuria, coagulopathy and acute kidney injury — effects driven mainly by crotoxin, the venom's major phospholipase A2 complex, with crotamine contributing to the muscle injury. It is a serious envenomation requiring antivenom. On the thinness of the literature. Both peptides are studied by a small number of groups, largely in Brazil, and independent replication is limited. For crotalphine in particular, a reported effect this large and this long-lasting, unreplicated outside the originating network and never taken into humans after nearly two decades, warrants scepticism about effect size even if the mechanism is real.

4Reported side effects and interactions

Literature-reported

Literature (crotalphine). no human safety data. Rodent studies report analgesia without the sedation, motor impairment or tolerance seen with morphine over the periods studied. Characterisation is limited.

Literature (crotamine). myotoxicity is the defining adverse effect — muscle damage, spastic paralysis of the hind limbs in mice, elevated creatine kinase. Haemolysis and nephrotoxicity are concerns consequent on muscle injury. No human data.

Literature (envenomation). the human exposure route for both. Neurotoxic ptosis and ophthalmoplegia, rhabdomyolysis, myoglobinuric acute kidney injury, coagulopathy. Antivenom is the treatment.

Community-reported

Community use: essentially none documented. Self-administration would be dangerous and pointless. Crotalphine has no human data of any kind, and its mechanism is opioid-mediated, meaning the class risks apply without any of the dose-finding that makes opioid use survivable. Crotamine is a myotoxin whose effective delivery concentrations overlap its muscle-damaging concentrations; administering it would risk rhabdomyolysis to achieve nothing.

Theoretical. for crotalphine, opioid-mediated effects imply the usual class concerns — respiratory depression, tolerance, dependence — even though the peripheral mechanism is proposed to avoid them, and the proposal is untested in humans; immunogenicity of a snake peptide. For crotamine, a cell-penetrating peptide that concentrates in proliferating cells will also concentrate in normal proliferating tissue — bone marrow, gut epithelium, hair follicle — which is the obvious selectivity limit.

Interactions. none established. Crotalphine's effects are antagonised by naloxone and by selective kappa and delta antagonists, which is a mechanistic finding rather than a clinical interaction.

Markers researchers commonly monitor

No compound-specific human markers are established and there is no human administration. Relevant measures by setting: No human laboratory markers apply to research use.

Marker	Why it's watched
Creatine kinase and myoglobin	the markers of crotamine myotoxicity in animal work, and the markers that matter clinically in Crotalus envenomation. If crotamine were ever given to a human these would be the dose-limiting measurements.
Creatinine and urine output	because myoglobinuric acute kidney injury is the main downstream danger of muscle breakdown.
Nociceptive behavioural assays with and without naloxone or selective opioid antagonists	the efficacy and mechanism readouts for crotalphine.
Cellular uptake imaging and nuclear localisation	the readouts in the crotamine delivery literature.
Coagulation screen and neurological examination	the clinical monitoring in envenomation, where crotoxin rather than either of these peptides drives the picture.

Free for everyone. Safety information is never behind a paywall.

5Research context and safety notes

Both compounds are laboratory reagents. The specific reasons: - Crotalphine has no toxicology package and no human data. Potency in the microgram-per-kilogram range in rats tells you nothing about a human therapeutic index. The analgesic mechanism runs through opioid receptors, which is the pharmacology with the highest fatality rate in medicine, and the claim that the peripheral site of action avoids central risk is a hypothesis, not a finding. - Crotamine's therapeutic and toxic doses overlap. This is the honest summary of the delivery literature. A peptide that damages skeletal muscle at doses close to those needed for cargo delivery is a tool for cell culture and animal proof-of-concept, not a candidate for administration. - Preferential uptake into dividing cells is not tumour selectivity. Normal tissues with high turnover will take it up too. - Source. Research material is chemically synthesised or recombinant. Crude C. d. terrificus venom is a lethal hazard handled under licence; the medical response to exposure is antivenom, which is available only in appropriate clinical settings. No preparation, solvent, concentration or storage guidance is given here.

6Commonly studied alongside

Mambalgins (#193) and conotoxins (#194) as the parallel venom-derived analgesic efforts; TAT peptide, penetratin and polyarginine as the reference cell-penetrating peptides crotamine is benchmarked against; crotoxin and crotalic phospholipase A2 as the other components of the same venom; kappa-opioid agonists as the mechanistic comparator for crotalphine.

Informational cross-links. Not stack recommendations.

7Regulatory status by region

Region	Status (checked —)
United States	Neither peptide is FDA-approved; research chemicals only. No investigational new drug application is on public record †
European Union	Not authorised
United Kingdom	Not licensed
Australia	Not approved
South Africa	Not registered
Sport	Not listed by WADA. Crotalphine's opioid-mediated mechanism is worth noting — opioid analgesics are prohibited in competition under S7 — but crotalphine itself is not a listed substance and as a non-approved substance would fall under S0 in principle

8Open questions

What explains crotalphine's multi-day duration from a single dose, and is the phenomenon real outside the originating laboratory?
Can a peripherally restricted opioid-releasing mechanism deliver analgesia without central risk in humans? Crotalphine would be an informative test case if it were ever taken into trials.
Can crotamine's cell-penetrating function be separated from its myotoxicity by engineering, and if not, is the scaffold useful at all?
Why, nearly two decades after discovery, has neither peptide entered clinical development?

9References

1Konno K et al. (2008). Crotalphine, a novel potent analgesic peptide from the venom of the South American rattlesnake Crotalus durissus terrificus. Peptides. PubMed · DOI
2Gutierrez VP et al. (2008). Crotalphine induces potent antinociception in neuropathic pain by acting at peripheral opioid receptors. Eur J Pharmacol. PubMed · DOI
3Machado FC et al. (2014). Non-peptidic and peptidic analgesics from snake venom: crotalphine and the kappa-opioid mechanism. PLoS One [verify exact title and journal]. PubMed
4Kerkis A et al. (2004). Crotamine is a novel cell-penetrating protein from the venom of rattlesnake Crotalus durissus terrificus. FASEB J. PubMed · DOI
5Nascimento FD et al. (2007). Crotamine mediates gene delivery into cells through the binding to heparan sulfate proteoglycans. J Biol Chem. PubMed · DOI
6Pereira A et al. (2011). Crotamine toxicity and efficacy in mouse models of melanoma. Expert Opin Investig Drugs [verify journal]. PubMed · DOI
7Kerkis I et al. (2014). Crotamine: a novel bioactive peptide from rattlesnake venom with therapeutic potential. Curr Pharm Des. PubMed

References are being resolved to PubMed/DOI identifiers; links search PubMed for the citation until then.

† Being confirmed by our reviewers against current sources.

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11Page history

31 Oct 2026Profile published — awaiting medical review

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