Dalargin

What is Dalargin?

Dalargin is a synthetic hexapeptide, Tyr-D-Ala-Gly-Phe-Leu-Arg, built from leu-enkephalin by two deliberate changes: the natural glycine at position 2 is replaced with D-alanine, and an arginine is added at the C-terminus. Both modifications matter. The D-amino acid at position 2 confers resistance to the peptidases that destroy native enkephalins within minutes, and structure-activity work later showed it also determines how the molecule folds — the L-alanine version is nineteen times less potent and, unlike dalargin, remains peptidase-sensitive. The C-terminal arginine is not decorative either: in gastric mucosa studies, an arginine-free analogue had little effect on the endpoints dalargin acts on.\n\nThe peptide was developed in the Soviet Union in the 1980s and is registered in Russia as a prescription medicine under registration number ЛС-001548, supplied by Microgen as a 1 mg lyophilisate for intravenous and intramuscular injection. Its Russian INN is given as tyrosyl-D-alanyl-glycyl-phenylalanyl-leucyl-arginine diacetate. It has never been approved by the FDA, the EMA, or any other Western regulator, and it does not appear in the FDA drug label or Drugs@FDA databases at all.\n\nWhat makes dalargin pharmacologically interesting is not that it is an opioid agonist but where it is not one. Despite binding opioid receptors with reasonable potency in peripheral tissue, it is strikingly weak centrally: given intracisternally it was one to three orders of magnitude less active than the stable enkephalin analogue FK 33-824, and tens of times less active when given intravenously. The conclusion drawn in the original Soviet pharmacology — that dalargin is "an opioid-like peptide with the peripheral action" — is the key to both its intended clinical use and its unintended second career as a research tool.

What Dalargin Is Investigated For

Dalargin occupies an unusual position: it is a real registered medicine with a real clinical footprint, and almost none of that footprint is legible to a reader outside Russia. In Russian and post-Soviet practice it is given intravenously or intramuscularly for peptic ulcer disease, acute pancreatitis and exacerbations of chronic pancreatitis, on the rationale that peripheral opioid-receptor agonism is cytoprotective in gastrointestinal mucosa. The supporting literature is large by volume — PubMed indexes roughly 380 records mentioning dalargin — but heavily weighted toward Russian-language journals from the 1980s and 1990s, and many of the clinical papers, including the two most frequently cited for its gastroenterological use, have no abstract indexed in PubMed at all. That means their contents cannot be checked against the record, and this page does not assert what they found.\n\nThe mechanistic work is in better shape. Dalargin's peripheral restriction is well documented, its opioid-receptor activity profile has been characterised in bioassay across mu, delta and kappa preparations, and its effects on gastric mucosa have been tied to nitric oxide signalling — an NO synthase inhibitor abolished its stimulation of DNA synthesis in rat gastric epithelium.\n\nThe peptide also has a genuinely significant second life that has nothing to do with its indications. Because dalargin is potent at opioid receptors but cannot reach the brain on its own, it became the ideal reporter molecule for testing whether a drug-delivery system can cross the blood-brain barrier: if an animal shows central analgesia, the carrier worked. Alyautdin, Kreuter and colleagues used exactly this logic in the 1990s with polysorbate-80-coated polybutylcyanoacrylate nanoparticles, and the resulting line of work became one of the most cited in nanoparticle brain delivery. Dalargin's role there is as an instrument, not a therapy — a distinction the consumer-facing writing about it usually loses.\n\nTwo Phase 3 trials are registered and completed, both in Russia: a 200-patient randomized, double-blind, placebo-controlled study of dalargin for prevention of postoperative organ dysfunction in high-risk abdominal surgery, completed in September 2026, and a 320-patient open randomized study of dalargin combined with Leitragin for pulmonary complications of COVID-19, completed in November 2020. Neither has posted results, and neither has been published in a form this page could verify, so they establish that the drug is being formally studied — not what the studies showed.

History & Discovery

Dalargin came out of the Soviet peptide-chemistry programme of the late 1970s and early 1980s, in the period when enkephalins had just been identified and laboratories everywhere were trying to turn them into drugs. The central obstacle was universal: native enkephalins are destroyed by aminopeptidases and neprilysin almost as fast as they are released, so any therapeutic version needed either a peptidase shield or a redesign. The Soviet solution was the standard one of the era — substitute a D-amino acid at the vulnerable position — combined with a C-terminal arginine extension that turned out to matter for the gastrointestinal effects.\n\nWhat was less standard was the decision to treat poor brain penetration as a feature. By the mid-1980s the molecule was being described in the Soviet cardiology literature as "a peptide preparation with cytoprotective action" and as "a regulator of reparative tissue regeneration," and by 1988 Russian gastroenterology was calling it "the first enkephalin analogue used in gastroenterology." The pharmacology published that same year made the compartment argument explicit, showing that the peptide's activity was overwhelmingly peripheral. Clinical use settled on peptic ulcer disease and pancreatitis, and the drug was carried through the collapse of the Soviet Union into the Russian pharmaceutical register, where it remains, manufactured by Microgen under certificate ЛС-001548 with a registration date of 28 April 2006.\n\nIts international reputation, such as it is, was made elsewhere and for different reasons. In the mid-1990s Jörg Kreuter's group in Frankfurt, working with Renad Alyautdin in Moscow, needed a molecule to prove that polysorbate-80-coated nanoparticles could ferry a drug across the blood-brain barrier. Dalargin was close to ideal for the purpose — strongly active at opioid receptors, essentially unable to reach them from the bloodstream — and the resulting demonstration of naloxone-reversible central analgesia became a foundational result in nanomedicine. Dalargin has been the standard reporter molecule in that field ever since, which is why a peptide most Western clinicians have never heard of appears in hundreds of drug-delivery papers.\n\nThe modern chapter is thinner than the volume of literature suggests. Two Phase 3 trials have been registered and completed in Russia — a 320-patient open randomized study of dalargin with Leitragin in COVID-19 pulmonary complications, completed in November 2020, and a 200-patient randomized, double-blind, placebo-controlled study of perioperative organ protection in high-risk abdominal surgery, completed in September 2026. Neither has posted results.

How It Works

Your body makes its own opioid-like molecules called enkephalins, which are destroyed by enzymes within minutes of being released. Dalargin is a laboratory redesign of one of them, changed in two places so the enzymes cannot chew it up as quickly. The interesting part is what it does not do: it is very bad at getting into the brain. So instead of acting on the brain's opioid receptors the way morphine does, it acts almost entirely on opioid receptors out in the body — in the gut wall, the stomach lining, and blood vessels. That is the intention. Russian medicine uses it for stomach ulcers and pancreatitis on the theory that switching on those peripheral receptors protects the tissue. And because it is potent at opioid receptors but cannot reach the brain unaided, researchers adopted it as a test molecule: if you build a particle that carries dalargin into the brain, the animal shows pain relief, and that tells you the delivery system worked.

Dalargin is [D-Ala2,Leu5]-enkephalyl-Arg: leu-enkephalin (Tyr-Gly-Gly-Phe-Leu) with D-alanine substituted at position 2 and arginine appended at the C-terminus. Native enkephalins are cleaved rapidly by aminopeptidase N and neprilysin, which is why endogenous enkephalin signalling is so short-lived and why enkephalin-based drug design has centred on blocking that degradation or engineering around it. Dalargin takes the second route. Structure-activity work in isolated-organ bioassays established that the D-configuration at position 2 is doing more than blocking peptidase access: the L-alanine analogue is nineteen times less potent and remains peptidase-sensitive, implying the D-amino acid also determines the folded conformation the receptor sees.\n\nOn receptor profile, dalargin behaves broadly as an enkephalin does, with activity across preparations expressing mu, delta and kappa receptors and a delta-preferring character in assays designed to isolate that subtype. It has been compared directly against native leu- and met-enkephalin in the mouse vas deferens, a predominantly delta-opioid preparation, and against guinea-pig ileum for mu and kappa activity. What distinguishes it is not subtype selectivity but compartment selectivity.\n\nThat compartment restriction is the mechanistically important fact. Dalargin and its N-terminal fragments were profiled across guinea-pig ileum, mouse vas deferens and mouse large intestine, and produced analgesia in hot-plate and tail-flick testing — but when the route was changed to intracisternal administration, dalargin was one to three orders of magnitude weaker than the stable analogue FK 33-824, and tens of times weaker intravenously. The N-terminal tripeptide and the tyrosine-free fragment had no opioid activity at all, confirming that the intact N-terminal tyrosine is required, as it is throughout the opioid peptide family.\n\nIn the gastrointestinal tract, where the drug is actually used, the proposed mechanism runs partly outside classical opioid signalling. In rat gastric mucosa, dalargin stimulated epithelial DNA synthesis and increased the tissue's antiradical and antioxidant buffering capacity; an analogue lacking the C-terminal arginine had little effect, and pretreatment with the nitric oxide synthase inhibitor L-NAME abolished the DNA-synthesis effect entirely. That places nitric oxide downstream of, or parallel to, receptor engagement in the gastroprotective action — a mechanism the page's registered indications rest on, and one that has not been replicated outside this literature.\n\nThe blood-brain barrier work inverted dalargin's weakness into its utility. Adsorbed onto polybutylcyanoacrylate nanoparticles and coated with polysorbate 80, dalargin produced naloxone-reversible central analgesia at 5.0 and 7.5 mg/kg intravenously, where free dalargin produced none. Subsequent work established that the coating, not the particle, carries the effect: uncoated polybutylcyanoacrylate nanoparticles did not increase transport, while coatings with apolipoprotein B, apolipoprotein E or polysorbate 80 did — consistent with the particles acquiring a lipoprotein corona and entering via lipoprotein-receptor-mediated transcytosis. Later formulations extended this to oral administration with double-coated particle systems.

Evidence Snapshot

Research Gaps & Open Questions

What the current literature has not yet settled about Dalargin:

• 01Whether the Russian clinical evidence supports the registered indications at all, in the sense a reader outside Russia can check. The standard citations for dalargin in gastroenterology and pancreatitis are indexed in PubMed by title only, with no abstract, so their designs, sample sizes and results are not recoverable from the public record — and no Western replication exists.
• 02What the two completed Phase 3 trials found. A 200-patient randomized, double-blind, placebo-controlled study of perioperative organ protection and a 320-patient study in COVID-19 pulmonary complications have both finished, and neither has posted results. These are the most rigorous data ever generated on the molecule and they are currently inaccessible.
• 03Whether the nitric-oxide-dependent gastroprotective mechanism reproduces outside its originating literature. The finding that an NO synthase inhibitor abolishes dalargin's stimulation of gastric epithelial DNA synthesis is mechanistically specific and would be straightforward to test independently, but no independent replication has been published.
• 04Human pharmacokinetics. The published PK is in rats, described as a three-exponential curve after intravenous administration. No human PK study is available in the indexed English-language literature, which means there is no basis for reasoning about exposure, accumulation or dose scaling in people.
• 05Whether peripheral restriction is as complete as the pharmacology implies, across doses and in disease states that alter blood-brain-barrier permeability. The nanoparticle work demonstrates that the barrier is the only thing standing between dalargin and central opioid effects — which raises the untested question of what happens when that barrier is compromised by sepsis, inflammation or critical illness, precisely the settings the perioperative trial was conducted in.

Forms & Administration

In Russia, dalargin is supplied as a lyophilised powder for reconstitution, 1 mg per ampoule in packs of ten, for intravenous and intramuscular injection, manufactured by Microgen under registration number ЛС-001548. The active substance is listed as tyrosyl-D-alanyl-glycyl-phenylalanyl-leucyl-arginine diacetate. There is no oral formulation, which follows from the peptide's structure: a hexapeptide given by mouth faces the same gastrointestinal proteases that destroy dietary protein. There is no approved product in the United States, the European Union, the United Kingdom, Canada, Australia or Japan, and no English-language prescribing information. Dosing figures that circulate internationally are drawn from Russian package material for a product most buyers outside Russia do not have, and this page does not reproduce them, because a dose without a verified product behind it is not usable information. Research-grade dalargin sold through peptide marketplaces is unregulated, unverified for identity and purity, and not intended for human use.

Common Questions

Who Dalargin Is NOT For

Drug & Supplement Interactions

No formal interaction studies of dalargin have been published in a form this page could verify, so what follows is mechanistic inference rather than reported findings. As an opioid-receptor agonist, dalargin would be expected to produce additive effects with other opioid agonists on gastrointestinal motility, and its activity is blocked by naloxone — demonstrated directly in the nanoparticle experiments, where naloxone pretreatment abolished the central analgesia produced by nanoparticle-delivered dalargin. That makes opioid antagonists a pharmacological counterpart rather than an interaction risk in the usual sense.\n\nThe more interesting interaction is formulation-level rather than drug-level, and it is well documented. Dalargin's distribution depends heavily on what it is delivered with: uncoated polybutylcyanoacrylate nanoparticles did not increase its transport across the blood-brain barrier, while coating those particles with polysorbate 80, apolipoprotein B or apolipoprotein E did. In other words, excipients that would be inert for most drugs change this one's compartment of action. That is a research finding about carriers, not a clinical interaction, but it is the clearest evidence that dalargin's safety profile is contingent on its formulation in a way that most peptides' are not.\n\nBecause dalargin is a peptide cleared by peptidases rather than hepatic cytochrome metabolism, classical CYP-mediated interactions are not expected.

Safety Profile

Legal Status

Regulatory status changes over time. Verify current local rules with a qualified professional.

Myths & Misconceptions