PN-881_Dosage, benefits & legal status
A peptide taken by mouth that blocks all three forms of IL-17A and IL-17F, the pathway targeted by injected psoriasis antibodies such as bimekizumab. Phase 1 is complete; a psoriasis phase 2b is planned for early 2027.
Common vial size is what vendors typically sell, not a recommendation. Enter your own vial in the calculator.
What is PN-881?
Plain language first. The technical label stays, but it never stands alone.Overview
The IL-17 blockers used for psoriasis, such as secukinumab, ixekizumab and bimekizumab, are antibodies given by injection, and PN-881 is meant to block the same pathway as a once-daily pill. So far the evidence is lab and animal work: in human skin cells it blocked IL-17AA at 0.15 nanomolar in one company assay, and in rats it reduced ear swelling at oral doses as low as 1 mg/kg twice daily. Its phase 1 in 146 healthy volunteers reported no serious side effects, but the doses, side-effect rates and half-life have not been made public, and no one with psoriasis has taken it yet.
PN-881 is an oral peptide, described by BioWorld as macrocyclic, that binds the cytokines IL-17A and IL-17F and blocks all three dimers (IL-17AA, IL-17AF and IL-17FF), the same triple coverage as the antibody bimekizumab. In company assays on human dermal fibroblasts its IC50 against IL-17AA was 0.15 nanomolar, against 0.12 for bimekizumab and 10 for secukinumab; secukinumab does not block IL-17FF at all. Protagonist Therapeutics owns it outright, and it comes from the same oral peptide platform as icotrokinra (Icotyde), a separate drug that blocks the IL-23 receptor upstream and is licensed to Janssen Biotech.
What it's used for
Nothing outside clinical trials. Protagonist plans a phase 2b dose-finding trial of the daily pill in plaque psoriasis from early 2027.
How does PN-881 work?
What it does in the body, and where.PN-881 is a peptide pill that catches IL-17, a signaling protein that immune cells release in psoriatic skin, before it reaches its receptor.
- 01Surviving the gutIt was selected for stability in simulated stomach and intestinal fluid, and taken by mouth it reached the blood in mice, rats, dogs and monkeys. In people, once-daily dosing kept 24-hour trough levels above the company's target, though no numbers have been published.
- 02Catching IL-17It binds IL-17A and IL-17F themselves rather than their receptor, blocking all three paired forms (AA, AF and FF), the same coverage as the antibody bimekizumab. Secukinumab does not block the FF form.
- 03Quieting the skinBound IL-17 cannot switch on skin cells such as keratinocytes and fibroblasts, so inflammatory signals like CXCL1 should fall; in mice they did, in blood and skin. Icotrokinra, from the same company, acts upstream at the IL-23 receptor; PN-881 acts downstream on IL-17 itself.
What else is it used for?
Each group carries its own evidence level.Approved means regulators have cleared it for that purpose. Investigational means it is in trials. Early research means it is being studied and is not established.
Lab potency (2025)
Early research- Lab studyHuman dermal fibroblasts: IC50 0.15 nanomolar against IL-17AA, 29 against IL-17AF and 15 against IL-17FF; bimekizumab 0.12, 18 and 14; secukinumab 10 and 175, and inactive on IL-17FF.
- Lab studyOn IL-17AA it measured about 70-fold more potent than secukinumab.
Animal models
Early research- Animal studyMice challenged with human IL-17AA: once-daily oral dosing lowered CXCL1 in blood and skin (p<0.001 and p<0.0001); the doses were not given.
- Animal studyRats with an IL-23 ear challenge for 4 days: twice-daily oral dosing reduced ear thickness (p<0.05 to p<0.0001); the company's 2026 slides add that doses as low as 1 mg/kg worked.
Phase 1 in healthy volunteers
Investigational- human-earlyGenerally well tolerated, with no serious adverse events; no rates or side-effect table released.
- human-earlyOnce-daily dosing kept 24-hour trough levels several-fold above the target IC90 values (0.031, 0.124 and 0.098 nanomolar for IL-17AA, IL-17FF and both together), with accumulation to higher steady-state levels; no exposure numbers released.
- No dataDoses, half-life and full results are not public; the company says the data will be presented at a future medical meeting.
Against bimekizumab (2026 assay)
Early research- Lab studyWith IL-17A and IL-17F at a 1:30 ratio, bimekizumab's IC90 was about 10-fold lower on IL-17AA (0.003 against 0.031 nanomolar), about 3-fold lower on IL-17FF (0.037 against 0.124) and similar on both together (0.071 against 0.098).
The August 5, 2026, update is often quoted as if it reported doses or a half-life; it gave neither, only that once-daily trough levels stayed above target IC90 values and that there were no serious adverse events, so any dose or half-life quoted for PN-881 is unsupported. The phase 1 is often given as about 142 healthy volunteers, the figure in the company's slides; the registry lists 146 enrolled. Potency claims shift with the source: about 100-fold greater than secukinumab in the 2024 nomination, about 70-fold in the 2025 EADV data, and an IL-17AA IC50 of 0.15 nanomolar in 2025 against 0.0026 in a 2026 assay with a different ratio of IL-17A to IL-17F. 'Comparable to bimekizumab' is loose: the company's own 2026 table puts bimekizumab about 10-fold ahead on IL-17AA and about 3-fold on IL-17FF, and level only on the combined form. The next trial is described both as a phase 2 psoriasis program and as a phase 2b dose-range-finding study, due to start in early Q1 2027. It is not a Johnson & Johnson drug: icotrokinra is licensed to Janssen, but PN-881 is wholly owned by Protagonist. A Protagonist patent lists 720 IL-17-binding peptide sequences, and none is identified as PN-881.
The published record
Papers and trials about PN-881
1 papers tagged human · 0 not reviews or lab · 0 clinical trial publications
1 registered trials · none with posted results
Furthest stage reached: Phase 1, completed, no results posted
Counted from Europe PMC indexing, not read by a person; a human tag can land on reviews, commentary or lab papers; clinical trial publications is the narrower count.
At a glance
Four things to know about PN-881
Evidence
Investigational
Category
Immune support
Common vial
Varies
Half-life
Not established
How much, and do you cycle it?
The range, and whether you take breaks.No dose disclosed (phase 1 trial), once daily (intended). No established pattern No range
Only a phase 1 has been run, testing single and repeated doses and once against twice daily. The company intends a daily pill; no long-term schedule has been tested.
How long does it stay in the body?
The half-life, and where the figure comes from.Not establishedNo figure
No human half-life, peak level or bioavailability has been published. The company says only that once-daily dosing kept 24-hour trough levels several-fold above its target IC90 values and that levels built up to a higher steady state. One of its candidate selection criteria was lab stability in serum, with a half-life above 24 hours, and the company says it met that criterion. That is a test-tube stability measure, not a half-life in the body.
Source: Protagonist corporate slides, August 5, 2026 (no figure given)
You can compare this against the whole library to see where it sits.
What does it cost?
Typical dose and cost, in plain numbers.PN-881 is not injected
It is taken by mouth (oral). The phase 1 tested an oral solution in single and repeated doses, a tablet, the tablet fed against fasted, and once against twice daily, but its dose levels have not been made public in the registry, the releases or the company slides. Protagonist intends once-daily dosing. Rats responded at 1 mg/kg twice daily and monkeys reached blood levels above 100 ng/mL at 2.5 mg/kg by mouth; neither translates to a human dose. It is not sold, and with no published human dose the calculator starts with an empty dose field; as a pill, it would not need a vial calculation.
How do you store it?
Before mixing, and after.Room temperature. Cool, dry, out of light.
PN-881 is taken as a pill or capsule. Keep it in its original container at room temperature, away from heat, humidity, and direct sun. No fridge or mixing needed. Check the expiration date on the bottle.
What are the side effects and cautions?
Known cautions and warnings for this compound.Who should avoid it
- Not studied in anyone who could become pregnant: the phase 1 enrolled only people of non-childbearing potential, and no reproductive data exist
- Not studied in people with psoriasis or any other disease: only healthy volunteers have taken it
- Use outside a clinical trial: it is not sold or approved anywhere
Stop and get help
- Fever, chills, a cough that will not go away or other signs of a serious infection: tell the trial team, since the injected IL-17 blockers carry infection warnings and PN-881 hits the same target; whether it shares them is not yet known
- New or worse belly pain, diarrhea or blood in the stool: injected IL-17 blockers can trigger or worsen Crohn's disease and ulcerative colitis, and PN-881 has not been tested long enough to rule this out
Common effects
- No side-effect rates have been released from the phase 1 in 146 healthy volunteers
- No serious adverse events were reported, and the company describes it as generally well tolerated
- Individual side effects, lab results and vital signs have not been disclosed, and no results are posted on ClinicalTrials.gov
- 7-day and 3-month toxicology studies were under way in November 2024; their results are not public
Where this page says nothing is established, that means nobody has studied it, not that a compound is safe.
Is PN-881 approved?
And where the numbers on this page come from.No. PN-881 is not approved anywhere and is currently in company-run clinical trials. There is no legal route to obtain it outside a trial.
- Approval statusInvestigational
- RouteBy mouth (oral)
- Checked18 October 2026
- DoseFrom published clinical trials. Not approved by a regulator for this dose.
- Vial sizeFrom what vendors typically list; not a recommendation.
- SourcesClinicalTrials.gov, NCT07153146Protagonist, second quarter 2026 results (August 5, 2026)Protagonist corporate slides, Form 8-K Exhibit 99.2 (August 5, 2026)Protagonist Form 10-Q, quarter ended June 30, 2026Protagonist, PN-881 nomination (BioSpace, November 21, 2024)Protagonist, EADV 2025 presentations (September 17, 2025)Manrique M, EADV 2025 oral presentation slidesProtagonist, third quarter 2025 results (November 6, 2025)Patent application IL328609A0, human IL-17 cytokine binding peptides (Protagonist)BioWorld, PN-881 unveiled (May 14, 2025)Society for Investigative Dermatology 2025 poster listingFDA GSRS, exact-name search for PN-881
What has happened recently
Not approved anywhere, and no designations have been announced. Protagonist Therapeutics of Newark, California, nominated PN-881 as a development candidate on November 21, 2024, showed it first in a poster at the Society for Investigative Dermatology meeting on May 7 to 10, 2025, and presented it at EADV in September 2025; it owns the drug outright, with no partner. The phase 1 (NCT07153146) ran at one site in Melbourne, Australia, where no IND was needed: it started on October 7, 2025, the first person dosed was announced on November 6, 2025, and it was completed on July 29, 2026, with 146 enrolled. On August 5, 2026, Protagonist said once-daily dosing kept 24-hour trough levels well above its target IC90 values and that a phase 2b dose-range-finding trial in plaque psoriasis would start in early Q1 2027; that trial is not yet registered, and a US IND has not been announced. A possible phase 2 in hidradenitis suppurativa is listed in company slides without a date.
You can compare this against the whole library, or read how to check a seller.
What else is like PN-881?
Others in Immune support, side by side.If you're weighing PN-881, it's worth reading Splenopentin, Thymopentin (TP-5), and Tuftsin in the same class.
A peptide taken by mouth that blocks all three forms of IL-17A and IL-17F, the pathway targeted by injected psoriasis antibodies such as bimekizumab. Phase 1 is complete; a psoriasis phase 2b is planned for early 2027.
- Dose
- No dose disclosed (phase 1 trial)
- How often
- Once daily (intended)
A five-amino-acid spleen peptide, sold on an evidence base almost nobody has read.
- Dose
- Research only
- How often
- Not established
Five amino acids that carry the whole activity of a thymus hormone.
- Dose
- 50 mg per dose
- How often
- 3x per week
A four-amino-acid immune peptide from the 1970s, and the parent of Selank.
- Dose
- Research only
- How often
- Not established
Guides for this compound
- mcg vs mg: The Peptide Dosing Mistake to Avoid
Your vial says mg and your protocol says mcg. Here is the conversion and how to check it.
- How to Read a Peptide COA
What the purity number does and does not tell you, and how to spot an edited report.
- How to Vet a Peptide Vendor
Independent COAs, HPLC purity, and the red flags that mean walk away.
Sources
- ClinicalTrials.gov, NCT07153146(2026)Phase 1 in healthy volunteers in five parts; 146 enrolled; October 7, 2025, to July 29, 2026, at Nucleus Network, Melbourne; no results posted.
- Protagonist, second quarter 2026 results (August 5, 2026)(2026)Once-daily 24-hour trough levels well above target IC90 values; phase 2 psoriasis program from early Q1 2027; wholly owned.
- Protagonist corporate slides, Form 8-K Exhibit 99.2 (August 5, 2026)(2026)IC50 and IC90 table against bimekizumab; about 142 volunteers; no serious adverse events; phase 2b dose-range-finding planned.
- Protagonist Form 10-Q, quarter ended June 30, 2026(2026)PN-881 listed as a company program; Icotyde approval in March 2026 and the Janssen license terms.
- Protagonist, PN-881 nomination (BioSpace, November 21, 2024)(2024)Development candidate named; blocks IL-17AA, AF and FF; about 100-fold more potent than secukinumab; 7-day and 3-month toxicology under way.
- Protagonist, EADV 2025 presentations (September 17, 2025)(2025)Presented at EADV, abstract #2155; about 70-fold more potent than secukinumab; phase 1 to start in Q4 2025.
- Manrique M, EADV 2025 oral presentation slides(2025)IC50 0.15, 29 and 15 nanomolar for IL-17AA, AF and FF against 0.12, 18 and 14 for bimekizumab; mouse and rat results.
- Protagonist, third quarter 2025 results (November 6, 2025)(2025)First human subject dosed in the phase 1.
- Patent application IL328609A0, human IL-17 cytokine binding peptides (Protagonist)(2026)Priority November 20, 2024; 720 sequences of IL-17-binding peptides; none is identified as PN-881.
- BioWorld, PN-881 unveiled (May 14, 2025)(2025)Describes PN-881 as an oral macrocyclic peptide.
- Society for Investigative Dermatology 2025 poster listing(2025)First poster, at SID 2025 (May 7 to 10, 2025), presented by Jason Halladay.
- FDA GSRS, exact-name search for PN-881(2026)No substance record: no UNII, formula or molecular weight.
Beyond these, 1 records are indexed. Browse the records