Serelaxin (RLX030)_Dosage, benefits & legal status
Also known as RLX-030, Reasanz, recombinant human relaxin-2
Recombinant human relaxin-2, a two-chain hormone that relaxes arteries, given as a 48-hour drip in acute heart failure. In RELAX-AHF-2 cardiovascular deaths were 8.7% against 8.9% on placebo, and Novartis ended development in 2017.
Common vial size is what vendors typically sell, not a recommendation. Enter your own vial in the calculator.
What is Serelaxin (RLX030)?
Plain language first. The technical label stays, but it never stands alone.Overview
Acute heart failure brings sudden breathlessness and fluid congestion, and serelaxin, a copy of the body's own hormone relaxin-2, was given as a 48-hour drip to relax blood vessels and ease the strain on the heart. The first phase 3 (1,161 patients) improved one of its two breathlessness measures and hinted at fewer deaths, but the 6,600-patient RELAX-AHF-2 trial found cardiovascular deaths of 8.7% against 8.9% on placebo by day 180 and no significant drop in worsening heart failure (6.9% against 7.7%). It was never approved anywhere, and Novartis ended development in 2017.
Serelaxin is recombinant human relaxin-2, described as identical to the natural hormone: a 24-residue A chain beginning with pyroglutamate and a 29-residue B chain, joined by two interchain disulfides (A11 to B11 and A24 to B23) with a third inside the A chain (A10 to A15). It activates RXFP1, a leucine-rich-repeat G protein-coupled receptor on blood vessels, kidney and heart (pKi 8.96 and cAMP pEC50 10.49 at the human receptor), raising cAMP and nitric oxide signaling so that arteries relax and kidney blood flow rises. Corthera ran the phase 2 dose-finding trial and started RELAX-AHF in October 2009, shortly before Novartis agreed to buy the company in December 2009; after an FDA complete response letter and an EU refusal in 2014, Novartis ended development in 2017 when RELAX-AHF-2 missed both co-primary endpoints.
What it's used for
Nothing today. It was tested as a 48-hour hospital drip for acute heart failure and was never approved.
How does Serelaxin (RLX030) work?
What it does in the body, and where.Serelaxin is the body's own relaxin-2 hormone, made by recombinant methods and given by drip to relax blood vessels.
- 01The hormone and its receptorRelaxin-2 is a two-chain peptide: a 24-residue A chain and a 29-residue B chain held together by disulfide bonds. It acts on RXFP1, a G protein-coupled receptor with leucine-rich repeats found on blood vessels, the kidney and the heart, and its effects depend on that receptor being present.
- 02Relaxing the vesselsBinding RXFP1 raises cAMP and nitric oxide signaling. Arteries relax and become more compliant, and kidney blood flow rises: by 65% at 2 hours in a cirrhosis trial. An increase in endothelin B receptors has been proposed as one route, but that is speculative, and anti-scarring effects have been seen in animals.
- 03What happened in peopleIn acute heart failure the 48-hour drip gave modest signals on breathlessness and congestion but no survival benefit in RELAX-AHF-2, the same pattern as nesiritide, another vessel-relaxing hormone drip. B7-33 is a 27-residue single chain built from serelaxin's B chain; it binds RXFP1 far more weakly (pKi 5.54 against 8.96 for relaxin-2) and has no human data.
A schematic of the compound's mechanism, not a diagnostic image.
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.
Acute heart failure, first phase 3 (RELAX-AHF)
Investigational- Human trial1,161 patients (581 against 580): breathlessness on a visual analog scale improved by 448 mm×h to day 5 (95% CI 120 to 775; P=0.007), but moderate or marked improvement on a Likert scale in the first 24 hours was 27% against 26% (P=0.70).
- Human trialCardiovascular death or readmission for heart or kidney failure to day 60: HR 1.02 (P=0.89); days alive out of hospital 48.3 against 47.7.
- No dataDeaths by day 180, an exploratory outcome: 42 against 65 (HR 0.63, 95% CI 0.42 to 0.93; P=0.019), the basis of a 37% figure that RELAX-AHF-2 did not confirm.
Acute heart failure, confirmatory phase 3 (RELAX-AHF-2)
tested-and-failed- Human trial6,600 randomized, 6,545 analyzed: cardiovascular death through day 180, 285 of 3,274 (8.7%) against 290 of 3,271 (8.9%); HR 0.98 (95% CI 0.83 to 1.15; P=0.77).
- Human trialWorsening heart failure through day 5: 227 (6.9%) against 252 (7.7%); HR 0.89 (95% CI 0.75 to 1.07; P=0.19). No secondary outcome was significant.
- RegulatoryNovartis announced the result on March 22, 2017, and its first-quarter 2017 report recorded a charge for ending development.
Open-label European trial (RELAX-AHF-EU)
Investigational- Human trial2,666 randomized 2 to 1 to serelaxin with standard care or standard care alone: adjudicated worsening heart failure or death through day 5, 5.0% against 6.9% (HR 0.71, 95% CI 0.51 to 0.98; P=0.0172).
- Human trialThe day-14 composite and length of stay were not significant, and the trial stopped early, short of its 3,183 target, after RELAX-AHF-2.
- No dataOpen-label treatment with blinded endpoint review; the authors cautioned that the design limits interpretation.
Systemic sclerosis (earlier relaxin program)
tested-and-failed- Human trialPhase 3, 231 patients given 0, 10 or 25 mcg/kg per day by continuous infusion under the skin for 24 weeks: no improvement in the modified Rodnan skin score.
- No dataSerious kidney events (doubled creatinine, renal crisis or grade 3 or 4 high blood pressure) in 7 relaxin-treated patients against 0 on placebo, mostly after the infusion stopped; creatinine clearance fell after stopping at both doses, and lung capacity (FVC) fell in the relaxin groups.
Kidney blood flow in cirrhosis
Early research- Human trialOpen-label randomized phase 2 against terlipressin, 40 randomized: kidney artery blood flow rose 65% at 120 minutes on serelaxin (95% CI 40% to 95%; P<0.001) against 14% on terlipressin (P=0.25).
- Human trialAt least one adverse event in 15% on serelaxin against 55% on terlipressin, with no low blood pressure events.
A 2013 Novartis announcement cited a 37% reduction in mortality at 6 months; that came from an exploratory outcome in RELAX-AHF (42 against 65 deaths, HR 0.63) and was not confirmed, since cardiovascular death in RELAX-AHF-2 was 8.7% against 8.9% (HR 0.98) and all-cause death did not differ significantly. RELAX-AHF-2 is often reported as enrolling 6,545 patients; 6,600 were randomized and 6,545 were analyzed. RELAX-AHF is often said to have improved breathlessness, but only the visual analog scale endpoint was met; the 24-hour Likert endpoint was 27% against 26%, the first reason the EMA gave for its refusal. RELAX-AHF-EU is sometimes cited as a positive trial; its primary endpoint was met (HR 0.71), but it was open-label and stopped early, and its authors said to weigh it against the blinded trials. It is sometimes called a synthetic relaxin; it is recombinant and identical in sequence to the natural relaxin-2, including the pyroglutamate at the start of the A chain. Plain 'relaxin' also names the natural hormone family and unrelated supplements, none of them serelaxin.
The published record
Papers and trials about Serelaxin (RLX030)
241 papers tagged human · 147 not reviews or lab · 52 clinical trial publications
17 registered trials · 10 with posted results
Furthest stage reached: Phase 3, 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 Serelaxin (RLX030)
Evidence
Investigational
Category
Healing and recovery
Common vial
Varies
Half-life
7 to 16 hours
How much, and do you cycle it?
The range, and whether you take breaks.30 mcg/kg per day by continuous infusion for 48 hours (phase 3 trials), once, as a single 48-hour infusion. Single 48-hour infusion; development ended in 2017 Trial dose
The heart failure trials gave one 48-hour infusion during the hospital admission, on top of standard care. RELAX-REPEAT gave three infusions 4 weeks apart in chronic heart failure and found repeat dosing safe. No product exists, so there is no schedule to plan around.
7 to 16 hoursHuman study
Terminal half-life after intravenous infusion, as given in a 2017 review; the kidney impairment study it cites reported mean values of 6.5 to 8.8 hours after a single 4-hour infusion. Exposure rises in proportion to dose over 10 to 100 mcg/kg per day, and steady state is reached within 4 hours of starting the drip. In the cirrhosis trial, median blood levels were 14.6 ng/mL after the first infusion step, 12.2 ng/mL after the second and 6.1 ng/mL in recovery, and were undetectable at week 4. Serelaxin was given only into a vein. In RELAX-REPEAT, 1 of 200 patients given three infusions developed transient, non-neutralizing antibodies.
Source: Unemori E, British Journal of Pharmacology 2017, citing a Novartis kidney impairment study (Dahlke 2015)
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How is it given?
Dosing context and source notes.Given in hospital from a prepared product, so there is nothing to mix.
Trial dose: 30 mcg/kg per day. Metra M et al., NEJM 2019 (RELAX-AHF-2)
Given into a vein as a continuous infusion of 30 micrograms per kg per day for 48 hours, started within 16 hours of presentation and added to standard heart failure care, in RELAX-AHF, RELAX-AHF-2, RELAX-AHF-EU and RELAX-AHF-ASIA. RELAX-AHF-2 and RELAX-AHF-EU enrolled only people with a systolic blood pressure of at least 125 mm Hg and mild to moderate kidney impairment. The phase 2 dose-finding study (234 patients) compared 48-hour infusions of 10, 30, 100 and 250 mcg/kg per day with placebo, and 30 was carried into phase 3. Other trials used 80 then 30 mcg/kg per day for an hour each in cirrhosis and 15 mcg/kg per day for 72 hours in preeclampsia. It was supplied as a concentrate diluted for infusion. It was never approved, and it was a weight-based hospital drip in a program that ended in 2017, so the calculator starts with an empty dose field.
How do you store it?
Before mixing, and after.Given in a hospital or trial clinic, so the pharmacy stores it.
Serelaxin (RLX030) goes into a vein and is prepared by hospital, clinic or trial pharmacy staff, following the product label or the trial protocol. Some products like this are ready-made solutions and others are powders mixed just before use, often with hours rather than weeks of shelf life once prepared. It is not a medicine people store at home.
What are the side effects and cautions?
Known cautions and warnings for this compound.Solubility, computed: 31% charged residues, 52% hydrophobic. Water usually sufficient.
A first-pass rule from peptide manufacturers' guidance. It does not account for disulfide bridges, salt form or how the powder was dried, and it predicts what should be easy rather than what will happen in your vial.
Who should avoid it
- Not studied in people with a systolic blood pressure below 125 mm Hg: RELAX-AHF-2 and RELAX-AHF-EU enrolled only people at or above it
- Not studied when started more than 16 hours after arrival: the heart failure trials began the infusion within 16 hours of presentation
- Not studied in pregnancy: both preeclampsia trials were stopped early, one after only 3 patients were enrolled
- Use outside a trial: it was never approved, and no medical product exists
Stop and get help
- Dizziness, fainting or a sharp fall in blood pressure during the infusion: low blood pressure was more frequent with serelaxin in RELAX-AHF-EU
- Swelling of the face or throat, a rash or trouble breathing during the infusion
Common effects
- Adverse events in 219 of 437 on serelaxin against 253 of 433 on placebo, serious adverse events in 37 against 50 and deaths in 34 against 41, in RELAX-AHF-ASIA
- Adverse event rates were similar in both arms of RELAX-AHF-2, with 6,545 patients analyzed
- Low blood pressure and falls in hemoglobin and hematocrit were more frequent with serelaxin in the open-label RELAX-AHF-EU (2,666 randomized)
- In a 24-week systemic sclerosis trial of recombinant relaxin, serious kidney events (doubled creatinine, renal crisis or grade 3 or 4 high blood pressure) in 7 treated patients against 0 on placebo, mostly after the infusion stopped
Where this page says nothing is established, that means nobody has studied it, not that a compound is safe.
Is Serelaxin (RLX030) approved?
And where the numbers on this page come from.No. Serelaxin (RLX030) was never approved, and its development has ended. There is no legal route to obtain it as a medicine.
- Approval statusInvestigational
- RouteInto a vein (48-hour infusion)
- Checked21 October 2026
- DoseFrom published clinical trials. Not approved by a regulator for this dose.
- Vial sizeFrom what vendors typically list; not a recommendation.
- SourcesFDA GSRS substance record, serelaxin (UNII W0122B976Y)Teerlink JR et al., Lancet 2013;381:29-39 (RELAX-AHF)Metra M et al., New England Journal of Medicine 2019;381:716-726 (RELAX-AHF-2)ClinicalTrials.gov, RELAX-AHF-2 (NCT01870778)Maggioni AP et al., European Journal of Heart Failure 2019;21:322-333 (RELAX-AHF-EU)ClinicalTrials.gov, RELAX-AHF-ASIA posted results (NCT02007720)EMA, Reasanz (refused)Novartis, Form 6-K on Breakthrough Therapy designation (2013)GEN, FDA rejects Novartis' serelaxin (May 2014)Novartis, Form 6-K on RELAX-AHF-2 topline results (March 22, 2017)Novartis, first-quarter 2017 report (Form 6-K)Unemori E, British Journal of Pharmacology 2017;174:921-932Khanna D et al., Arthritis and Rheumatism 2009;60:1102-1111Hossain MA et al., Chemical Science 2016 (B7-33)
What has happened recently
Never approved anywhere. Corthera, formerly BAS Medical, sponsored a phase 1 preeclampsia trial in 2006 and RELAX-AHF, registered in August 2007, and Novartis announced on December 23, 2009, that it would buy Corthera for $120 million upfront plus up to $500 million in milestones, gaining worldwide rights except in Australia and Canada. Novartis announced on June 21, 2013, that the FDA had granted Breakthrough Therapy designation for acute heart failure. Its Cardiovascular and Renal Drugs Advisory Committee voted 11 to 0 against approval on March 27, 2014, and the FDA issued a complete response letter, reported on May 16, 2014, saying further evidence of efficacy was required. In the EU, Novartis applied for approval as Reasanz: the EMA's committee for human medicines (CHMP) gave a negative opinion on January 23, 2014, and confirmed it on re-examination on May 22, 2014, and the refusal was dated August 5, 2014. The stated reasons were that the main study did not show relief of breathlessness in the first 24 hours, the clinical relevance of the 5-day benefit was unclear, the handling of patients who died or worsened raised concerns, background treatment may have been unbalanced, and there was only one main study. Novartis announced on March 22, 2017, that RELAX-AHF-2 had missed its primary endpoints, and its first-quarter 2017 report recorded a net charge of $0.2 billion for discontinuing RLX030 development; RELAX-AHF-EU and RELAX-AHF-ASIA were terminated early. An FDA orphan designation for progressive systemic sclerosis, from the earlier recombinant relaxin program, is listed as withdrawn.
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What else is like Serelaxin (RLX030)?
Others in Healing and recovery, side by side.If you're weighing Serelaxin (RLX030), it's worth reading BPC-157, TB-500 / Thymosin Beta-4, and PDA (Pentadeca Arginate) in the same class.
Recombinant human relaxin-2, a two-chain hormone that relaxes arteries, given as a 48-hour drip in acute heart failure. In RELAX-AHF-2 cardiovascular deaths were 8.7% against 8.9% on placebo, and Novartis ended development in 2017.
- Dose
- 30 mcg/kg per day by continuous infusion for 48 hours (phase 3 trials)
- How often
- Once, as a single 48-hour infusion
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- Dose
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- How often
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A recovery peptide for healing muscle and tendon, often paired with BPC-157.
- Dose
- 2 up to 2.5 mg per injection (start low, increase slowly)
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- Dose
- 0.25 up to 0.5 mg per day (start low, increase slowly)
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Guides for this compound
- How to Reconstitute a Peptide
Mix peptide powder with bacteriostatic water, step by step.
- How to Read an Insulin Syringe
Read the units, convert to millilitres, and draw the exact dose.
- 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
- FDA GSRS substance record, serelaxin (UNII W0122B976Y)(2026)A chain of 24 and B chain of 29 residues, three disulfides and an A1 pyroglutamate; CAS 99489-94-8; names RLX030 and RLX-030; sequence-calculated MW 5969.0.
- Teerlink JR et al., Lancet 2013;381:29-39 (RELAX-AHF)(2013)Published online November 7, 2012. 1,161 patients: breathlessness by visual analog scale improved (P=0.007), the 24-hour Likert endpoint did not (27% against 26%); exploratory day-180 deaths 42 against 65 (HR 0.63).
- Metra M et al., New England Journal of Medicine 2019;381:716-726 (RELAX-AHF-2)(2019)6,545 analyzed: cardiovascular death through day 180, 8.7% against 8.9% (HR 0.98, P=0.77); worsening heart failure through day 5, 6.9% against 7.7% (HR 0.89, P=0.19).
- ClinicalTrials.gov, RELAX-AHF-2 (NCT01870778)(2018)Phase 3, 6,600 randomized; ran October 2, 2013, to February 1, 2017; results posted March 30, 2018.
- Maggioni AP et al., European Journal of Heart Failure 2019;21:322-333 (RELAX-AHF-EU)(2019)2,666 randomized, open-label with blinded endpoint review, stopped early: worsening heart failure or death through day 5, 5.0% against 6.9% (HR 0.71, P=0.0172).
- ClinicalTrials.gov, RELAX-AHF-ASIA posted results (NCT02007720)(2019)876 enrolled at 132 sites in 11 countries, terminated early; adverse events 219 of 437 against 253 of 433; deaths 34 against 41.
- EMA, Reasanz (refused)(2014)Negative CHMP opinion January 23, 2014, confirmed on re-examination May 22, 2014; refusal dated August 5, 2014; no relief of breathlessness shown to 24 hours and only one main study.
- Novartis, Form 6-K on Breakthrough Therapy designation (2013)(2013)Breakthrough designation for acute heart failure announced June 21, 2013; cited a 37% reduction in mortality at 6 months.
- GEN, FDA rejects Novartis' serelaxin (May 2014)(2014)Complete response letter asking for further evidence of efficacy; the advisory committee voted 11 to 0 against approval on March 27, 2014.
- Novartis, Form 6-K on RELAX-AHF-2 topline results (March 22, 2017)(2017)RELAX-AHF-2 did not meet its primary endpoints.
- Novartis, first-quarter 2017 report (Form 6-K)(2017)Net charge of $0.2 billion related to discontinuing RLX030 development and $499 million in impairment charges, mainly RLX030.
- Unemori E, British Journal of Pharmacology 2017;174:921-932(2017)Half-life 7 to 16 hours, dose-proportional exposure and steady state by 4 hours; systemic sclerosis, preeclampsia and cirrhosis trials; 1 of 200 with transient antibodies after repeat dosing.
- Khanna D et al., Arthritis and Rheumatism 2009;60:1102-1111(2009)Systemic sclerosis phase 3, 231 patients for 24 weeks: no improvement in skin score; serious kidney events in 7 relaxin-treated patients against 0 on placebo.
- Hossain MA et al., Chemical Science 2016 (B7-33)(2016)Relaxin-2 binds human RXFP1 with pKi 8.96 and cAMP pEC50 10.49; B7-33, built from the B chain, binds with much lower affinity (pKi 5.54 against 8.96).
Beyond these, 340 records are indexed. Browse the records