Relaxin-2 (Serelaxin) Dosing, Need to Know Information, Safety, Stacks, Dosing Calculator and more!

How much do I take?

Is this right for me?

How do I use it?

Is it safe?

How do I know it's working?

Compound Profile

Scientific & Efficacy Data

C256H408N74O74S8

Molecular Formula

5,963 Da (Daltons)

Molecular Weight

Varies by route of administration

Half-Life

Bioavailability

See PubChem for identifiers

CAS #

71300755

PubChem ID ↗

Developed By · Research ongoing

Academic research consortium

Multiple research institutions

Primary Benefits

Supports improved cardiovascular function and hemodynamics

May improve symptoms and exercise capacity in acute heart failure patients

Potential to improve quality of life in heart failure management

Amino Acid Sequence

Dosing

How muchdo I take?

Intravenous: Delivered straight into a vein through a drip (IV), done by a clinician.

Bioavailability Complete (about 100%) — delivered straight into the bloodstream.

Standard Dose

30 mcg/kg/day

Frequency

Continuous IV infusion

Duration

48 hours

Weight-adjusted continuous IV infusion used across the RELAX-AHF programme for acute heart failure; improved dyspnea but did not reduce mortality in RELAX-AHF-2 [3][5]. Hospital administration only.

Timing

Best time to take

Administer at a consistent time each day. Consistency matters more than the specific time of day.

With food?

Food timing does not significantly affect absorption for injectable peptides.

If stacking

If combining Relaxin-2 (Serelaxin) with other peptides, space administrations by 15-30 minutes. Consult your healthcare provider before combining with prescription medications.

Adjusting Your Dose

Increase if

+Current dose is well-tolerated for 2+ weeks

+Desired effects not yet noticeable

+Healthcare provider recommends dose increase

Decrease if

-Side effects become bothersome or persistent

-Desired effects achieved at lower dose

-Healthcare provider recommends reduction

Signs of right dose

✓Noticeable improvement in target symptoms

✓Good tolerance with minimal side effects

✓Consistent positive response between doses

Dosing Calculator

Calculate Your Exact Dose

Step 1: Peptide Weight

Find the weight printed on your peptide vial label

Look here!

The peptide weight is printed on the label

The weight is on the label

Select Weight

Look for a number followed by 'mg' on the vial label (e.g., 5mg, 10mg)

Suitability

Is thisright for me?

Best For

Acute heart failure symptom management

Relaxin-2 (Serelaxin) is particularly effective for individuals focused on acute heart failure symptom management. Research supports its use in this area.

Cardiovascular recovery and support

Relaxin-2 (Serelaxin) is particularly effective for individuals focused on cardiovascular recovery and support. Research supports its use in this area.

Hospital-based therapeutic interventions

Relaxin-2 (Serelaxin) is particularly effective for individuals focused on hospital-based therapeutic interventions. Research supports its use in this area.

Consider Alternatives If

Goal: Alternative healing & recovery peptides

Consider: BPC-157, TB-500, GHK-Cu

Goal: Non-peptide alternatives

Consider: Consult healthcare provider for alternatives, Lifestyle modifications, Conventional pharmaceutical options

Who Should Avoid

Do not use if

×Severe hypotension or hemodynamic instability

×Pregnancy (despite relaxin's natural role)

×Acute kidney injury or severe renal dysfunction

×Recent myocardial infarction (within 7 days)

×Uncontrolled arrhythmias

Use with caution if

!You have any chronic medical conditions

!You are taking prescription medications

!You have a history of allergic reactions to peptides

Not Sure?

Compare Relaxin-2 (Serelaxin) with similar peptides to find the best fit for your goals.

Administration

How do Iuse it?

Reconstitution

What you need

•Bacteriostatic water

•Insulin syringes

•Alcohol swabs

Example

Follow standard reconstitution procedures for peptide preparations.

Calculate dose based on reconstitution volume and desired dose.

Injection

Route

Topical application (no injection required)

Best sites

•Apply to clean, dry skin on target area

Technique

1.Apply thin layer to clean skin

2.Follow product-specific instructions

Storage

Before reconstitution

Refrigerate at 36-46°F (2-8°C).

After reconstitution

Refrigerate and use within 30 days.

Signs of degradation

Cloudy solution

Discoloration

Particles visible

Sample Daily Schedule

Morning (or as directed)

1-10 mcg injection

Site: As directed

Administer once daily. Maintain consistency for optimal results.

Safety

Is itsafe?

Safety Profile

Serelaxin (recombinant relaxin-2) completed Phase III heart failure trials with favorable safety profile and cardiovascular benefit signals. Hypotension occurs in 20-25% of subjects requiring hemodynamic monitoring; no serious adverse events directly attributable to serelaxin beyond expected vasodilatory effects. Flushing and headaches mild and transient. No serious immunogenicity despite being recombinant human peptide; repeat dosing shows consistent response.

RELAX-AHF Phase III trial (n=1200) demonstrates serelaxin mechanism through vasodilation measured via invasive hemodynamics with pulmonary capillary wedge pressure reductions (20-30% decreases). Cardiac remodeling prevention shown via echocardiographic left ventricular diameter measurements. Safety data from >1200 patients shows 1-day mortality reduction of 37% in intention-to-treat analysis; no serious immunological reactions despite recombinant origin.

Common Side Effects

Experienced by some users

Hypotension (low blood pressure) - most common

Vasodilation induced by relaxin-2 activation of RXFP1/RXFP2 receptors on vascular endothelium predictably reduces systemic vascular resistance and blood pressure. This is dose-dependent and most pronounced in the first 24 hours of IV infusion, with systolic BP typically dropping 10-20 mmHg.

Management: Establish baseline blood pressure before infusion. Monitor BP every 2-4 hours during the 48-hour infusion and for 2 hours post-infusion. Position patient semi-recumbent or upright to promote venous return. If systolic BP falls below 90 mmHg, reduce infusion rate by 50% or pause infusion and notify physician. Ensure adequate hydration. Have vasopressor agents (norepinephrine, dopamine) immediately available in ICU setting.

Tachycardia (increased heart rate)

Compensatory tachycardia occurs as the heart responds to vasodilation and reduced peripheral resistance. Heart rate typically increases 5-15 bpm and reflects normal baroreceptor reflex activation, though some patients experience reflex tachycardia exceeding 100 bpm.

Management: Monitor heart rate continuously during infusion. Document baseline and post-infusion rates. Tachycardia typically resolves as blood pressure stabilizes. If heart rate exceeds 120 bpm or patient reports palpitations, notify physician—may indicate arrhythmia or inadequate pain control. Ensure adequate hydration and avoid sudden position changes.

Headache

Cerebral vasodilation from relaxin's endothelial effects combined with hemodynamic changes can trigger or exacerbate headaches. Occurs in approximately 5-10% of infusion recipients, typically mild to moderate severity.

Management: Administer acetaminophen (500-1000mg) or NSAIDs if not contraindicated for AHF patients. Ensure dark, quiet environment. Apply cool compresses to temples. Assess BP—hypotension-induced headaches resolve when BP normalizes. Maintain hydration. If severe or accompanied by neurological signs, notify physician immediately.

Nausea

Nausea can result from acute hemodynamic changes, IV administration discomfort, or medication interactions. Generally mild and transient, occurring during initial hours of infusion.

Management: Premedicate with ondansetron (4-8mg IV) or metoclopramide (10mg IV) if nausea anticipated. Avoid food 1-2 hours before and during infusion. Maintain NPO status per institutional protocol. Monitor hydration status. Most nausea resolves within first 12 hours. If severe or associated with vomiting, notify physician and consider alternative antiemetics.

Dizziness

Dizziness or lightheadedness results from acute blood pressure reduction and changes in cerebral perfusion. Risk increases with rapid infusion rate or inadequate hydration. More common in elderly or volume-depleted patients.

Management: Maintain semi-recumbent position to enhance cerebral perfusion. Move slowly when changing positions. Ensure adequate hydration per heart failure protocol. Monitor orthostatic vital signs (supine, sitting, standing if applicable). Reduce infusion rate if dizziness severe. Assess for concurrent medication effects (narcotics, sedatives). Notify physician if accompanied by syncope risk.

Peripheral edema (swelling)

Relaxin-mediated vascular permeability increases and sodium/fluid retention in acute HF can cause or exacerbate peripheral edema, particularly in dependent areas (ankles, sacrum in bed-bound patients). May reflect improved hemodynamics allowing better renal perfusion and fluid redistribution.

Management: Monitor daily weights pre- and post-infusion. Assess pedal edema severity and location. Elevate lower extremities above heart when resting. Apply compression stockings if ordered. Diuretic regimen continuation per cardiology. Check for signs of cellulitis or skin breakdown from chronic edema. Notify physician if edema worsens despite appropriate diuresis.

Increased creatinine levels

Serum creatinine may transiently rise during infusion due to reduced renal perfusion pressure from hypotension or intrinsic glomerular effects. Typically reversible post-infusion as hemodynamics normalize. Can reflect acute tubular necrosis risk in pre-existing renal disease.

Management: Draw baseline creatinine and BUN before infusion start. Repeat every 12-24 hours during 48-hour infusion and at 24-48 hours post-infusion. Calculate eGFR to assess glomerular filtration rate trend. If creatinine increases >0.5 mg/dL or doubling from baseline, reduce infusion rate or pause and notify physician. Ensure adequate hydration. Monitor urine output for oliguria. Hold ACE-I/ARB per institutional protocol during infusion.

Hyperkalemia (high potassium)

Acute kidney injury risk and potential aldosterone suppression from improved renal hemodynamics can elevate serum potassium. Risk increases in patients with baseline renal impairment (eGFR <30) or on ACE-I/ARB therapy.

Management: Draw baseline potassium before infusion. Repeat every 12-24 hours during infusion and post-infusion per protocol. If K+ exceeds 5.5 mEq/L, notify physician immediately. Restrict potassium intake during hospitalization. Hold potassium supplements and potassium-sparing agents. Have calcium gluconate, insulin/glucose, and emergency kayexalate available. Perform EKG if K+ elevated to assess for peaked T-waves or other cardiac changes.

Syncope (fainting)

Profound hypotension combined with positive chronotropic effects can precipitate vasovagal syncope or hypotensive episodes, particularly with sudden position changes or straining. Risk highest in first 24 hours of infusion.

Management: Maintain patient on continuous cardiac telemetry. Institute fall precautions—bed in low position, side rails up, call bell within reach. Assist with all position changes and ambulation. If syncope occurs, immediately lay patient flat, elevate legs, reduce/pause infusion, and notify physician. Assess for injuries from fall. May require vasopressor support or infusion rate reduction. Hold patient in ICU setting post-syncope.

Atrial fibrillation

Acute hemodynamic changes, atrial dilation from HF, or catecholamine surges can trigger atrial fibrillation de novo or exacerbate pre-existing AF. Occurs in 2-5% of infusion recipients, particularly those with structural heart disease or elevated filling pressures.

Management: Maintain continuous cardiac telemetry throughout infusion. Obtain baseline 12-lead EKG before infusion. If AF develops, notify physician immediately. Do not delay intervention. Prepare for possible rate control (beta-blockers, calcium channel blockers) or rhythm control strategies per cardiology. Ensure adequate anticoagulation if not already on anticoagulant. Monitor for hemodynamic deterioration with rapid ventricular response. Have emergency equipment available.

Blood pressure checks every 2-4 hours during infusion

Continuous hemodynamic monitoring is essential to assess the critical vasodilatory effects of relaxin-2 and catch hypotension early. Invasive (arterial line) or non-invasive BP monitoring every 1-4 hours captures BP trend and infusion tolerance.

Management: Establish continuous non-invasive BP monitoring (automatic cuff every 2-4 hours minimum) or invasive arterial line for closer monitoring. Position BP cuff at heart level for accuracy. Document systolic, diastolic, and mean arterial pressures. Plot trend on chart to visualize hemodynamic response. If MAP drops below 65 mmHg or SBP below 90 mmHg, reduce infusion rate by 50%, notify physician, and reassess in 15-30 minutes before restarting.

Kidney function (creatinine and eGFR)

Acute kidney function assessment is critical because hypotension and intrinsic renal effects from relaxin can precipitate acute kidney injury. Baseline renal function predicts risk—patients with eGFR <30 are at higher risk for worsening function.

Management: Draw baseline serum creatinine, BUN, and calculate eGFR before infusion. Repeat creatinine every 12-24 hours during 48-hour infusion. Monitor 24-hour urine creatinine and urine electrolytes per protocol. Assess urine output hourly (target >0.5 mL/kg/hr). If creatinine rises >0.5 mg/dL acutely, reduce infusion rate and ensure adequate hydration. Hold nephrotoxic agents. Consider contrast avoidance for any imaging during treatment window.

Electrolytes, particularly potassium

Acute shifts in serum electrolytes (sodium, potassium, magnesium) occur from hemodynamic changes, diuretic therapy, and altered renal handling. Hyponatremia and hyperkalemia represent the primary electrolyte concerns during relaxin infusion.

Management: Draw baseline comprehensive metabolic panel (CMP) before infusion including Na+, K+, Mg2+, Cl-. Repeat CMP every 12-24 hours during infusion per institutional protocol. Monitor and restrict sodium intake during HF hospitalization (typically <2g daily). Supplement potassium only if serum K+ <3.5 mEq/L. Monitor for hyponatremia symptoms (confusion, altered mental status, seizures). If electrolyte abnormality detected, notify physician and adjust supplementation accordingly.

Heart rate and cardiac rhythm

Continuous cardiac monitoring captures the heart rate response to hemodynamic changes and detects arrhythmias. Telemetry surveillance is mandatory during 48-hour infusion given the potent hemodynamic effects of relaxin.

Management: Initiate continuous cardiac telemetry before infusion starts. Monitor QRS rate, rhythm, PR interval, and QT interval. Obtain baseline 12-lead EKG before infusion. Watch for new arrhythmias including AF, PACs, PVCs, or conduction abnormalities. If significant arrhythmia develops (sustained VT, bradycardia <50, AF with RVR >120), immediately notify physician and be prepared for intervention. Continue telemetry for 2+ hours post-infusion.

Urine output

Diuresis or oliguria responses to relaxin infusion depend on baseline renal function and hemodynamics. Expected response is improved urine output (>1-1.5 L/24hr in most) as renal perfusion improves. Oliguria (<400-500 mL/24hr) signals acute kidney injury.

Management: Insert Foley catheter and monitor urine output hourly during infusion. Document color, clarity, and specific gravity. Target urine output >0.5 mL/kg/hr (approximately 30-40 mL/hr for average adult). If output <0.3 mL/kg/hr, assess fluid status, reduce infusion rate if hypotensive, and notify physician—may indicate acute kidney injury. Maintain accurate I/O records. Send urine for urinalysis and electrolytes if oliguria develops.

Stop and Seek Help If

×Severe allergic reaction—difficulty breathing, significant swelling, or anaphylaxis

×Persistent or worsening side effects that don't resolve with dose adjustment

×Your healthcare provider recommends discontinuation

×Pregnancy or planned pregnancy

×Achievement of treatment goals (discuss maintenance protocol with provider)

Relaxin-2 (Serelaxin) should only be used under the guidance of a qualified healthcare provider. This information is for educational purposes only and does not constitute medical advice. Always consult your healthcare provider before starting, adjusting, or stopping any peptide protocol.

Interactions

With other peptides

✓Standard heart failure therapies (ACE inhibitors, beta-blockers)

✓Diuretics for fluid management

✓Vasodilators for hemodynamic support

With medications

!Other IV vasodilators - Other IV vasodilators (may cause excessive hypotension)

!Strong ACE inhibitors without dose adjustment - Strong ACE inhibitors without dose adjustment

With supplements

✓Vitamin D3 - Generally safe and may support overall health

✓Magnesium - Generally safe and may enhance peptide absorption

Effectiveness

Does itwork?

Evidence Level

Limited human trials

What to Expect

Discovery & Development (Early 2000s)

What you might notice

•Novartis and Corthera develop recombinant serelaxin based on understanding of relaxin's natural cardiovascular benefits during pregnancy

•Preclinical studies demonstrate vasodilatory and cardioprotective properties

•Mechanism of action established

What's normal

•Full integration of Relaxin-2 (Serelaxin) into physiological systems is established

•Long-term Relaxin-2 (Serelaxin) response remains personalized to your physiology

•Relaxin-2 (Serelaxin) tolerance is well-maintained with consistent dosing

What's next

→Maintain your established Relaxin-2 (Serelaxin) protocol for sustained benefits

→Continue periodic monitoring to confirm Relaxin-2 (Serelaxin) efficacy

→Review comprehensive Relaxin-2 (Serelaxin) response with your provider

Early Clinical Trials (2005-2014)

•Phase 1 and 2 studies in various populations including pregnant women and heart failure patients

•Safety profile established with hypotension as main side effect

•Vascular effects study (NCT01979614) completed in 2016 with 58 patients

•FDA Breakthrough Therapy Designation - June 2013

•Relaxin-2 (Serelaxin) has achieved stable, long-term homeostatic integration

•Sustained efficacy of Relaxin-2 (Serelaxin) remains consistent

•Chronic Relaxin-2 (Serelaxin) effects remain stable and predictable

Phase 3 - RELAX-AHF (2012-2013)

•Large randomized controlled trial in acute heart failure patients

•Study showed 37% reduction in mortality at 180 days and was well-tolerated

•Results published in The Lancet January 2013

•Positive efficacy signals and safety data

Phase 3 - RELAX-AHF-2 (2018-2023)

•Follow-up trial designed to confirm RELAX-AHF results

•Approximately 3.5-year study enrolling additional patients

•Failed to meet primary endpoints of reducing cardiovascular death or worsening heart failure by day 180

•Trial terminated early - June 2023

Current Status (2024-Present)

•Serelaxin remains a research compound without FDA approval for acute heart failure

•No ongoing pivotal trials

•Continued investigation in research settings for mechanism of action and potential applications

•Research interest continues in cardiovascular biology

•Full therapeutic effects of Relaxin-2 (Serelaxin) are well-characterized at this point

•Maintenance of Relaxin-2 (Serelaxin)'s therapeutic effects is typical

•Tolerance patterns with Relaxin-2 (Serelaxin) are generally stable over months

→Comprehensive assessment of Relaxin-2 (Serelaxin) efficacy should be conducted

→Discuss long-term continuation, cycling, or protocol modifications

→Continue regular monitoring of relevant biomarkers or symptoms

Signs It's Working

Treatment Response

✓Progressive benefits over time with consistent use

✓Reduced severity of condition being treated

General Well-being

✓Improved energy and vitality

✓Better overall sense of wellness

✓Positive feedback from healthcare provider on progress

Not Seeing Results?

Common reasons

•Not allowing enough time—most peptides require consistent use for weeks to months before full effects are apparent

•Inconsistent dosing schedule—maintaining regular administration is critical for optimal results

•Improper storage or handling leading to degraded product

•Individual variation in response—genetics, health status, and other factors affect how you respond

•Dose may need adjustment—consult with your healthcare provider about optimizing your protocol

Key Research

[1]"End-organ protective effect of serelaxin in patients hospitalized for heart failure: Results of the biomarker substudy of Relaxin in Acute Heart Failure-2 (RELAX-AHF-2)"

Voors AA, et al., 2025

Finding: This study investigated Relaxin-2 (Serelaxin), contributing to our understanding of its mechanism and therapeutic potential.

[2]"Relaxin and the Cardiovascular System: from Basic Science to Clinical Practice"

Martins RC, et al., 2020

[3]"Effects of Serelaxin in Patients with Acute Heart Failure"

Metra M, et al., 2019

[4]"Efficacy and safety of serelaxin when added to standard of care in patients with acute heart failure: results from a PROBE study, RELAX-AHF-EU"

Maggioni AP, et al., 2019

[5]"Serelaxin, recombinant human relaxin-2, for treatment of acute heart failure (RELAX-AHF): a randomised, placebo-controlled trial"

Teerlink JR, Cotter G, Davison BA, et al., 2013

The Science

Stacking & Combinations

Frequently Asked Questions

Why did serelaxin not get FDA approved?

Is serelaxin the same as relaxin?

How is serelaxin administered?

What are the main side effects?

What makes serelaxin interesting from a research perspective?

Technical Specifications