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PeptideAI
Approved drugimmuneinflammation

Zilucoplan

A once-daily self-injected macrocyclic peptide that blocks complement C5, giving myasthenia gravis patients an alternative to monthly infusion antibodies.

Also known as Zilbrysq, RA101495, macrocyclic C5 inhibitor, Zilbrysq, RA101495, UCB7665

Approved drug — Licensed by a major regulator for human use, with phase-3 trial data behind it.

FDA-approved in October 2023 on the RAISE phase 3 trial, which showed a statistically significant 2.09-point placebo-adjusted improvement in MG-ADL at week 12 in AChR-antibody-positive generalised myasthenia gravis. The open-label RAISE-XT extension supports durability. The effect size is real but modest, and the practical draw is daily self-injection instead of infusions.

How it works

In acetylcholine-receptor-antibody-positive generalised myasthenia gravis, autoantibodies fix complement on the postsynaptic membrane and the resulting C5b-9 membrane attack complex physically destroys the folds where acetylcholine receptors sit. Zilucoplan is a 15-amino-acid macrocyclic peptide that binds C5 with sub-nanomolar affinity at a site distinct from where eculizumab binds, sterically blocking C5 convertase cleavage. It additionally binds C5b and prevents it from associating with C6, giving a second layer of blockade that also stops the pathway in patients carrying the C5 R885H polymorphism that renders eculizumab ineffective. A polyethylene glycol spacer and a lipid moiety confer albumin binding and a half-life long enough for once-daily subcutaneous dosing.

Targets: Complement component C5, C5b-C6 association, Membrane attack complex (C5b-9)

Dosing

ProtocolDoseFrequencyRoute
Generalised myasthenia gravis (label protocol)Same time each day, rotating between abdomen, thigh and upper arm.16.6 mg – 32.4 mgonce dailysubcutaneous
  • · 0.3 mg/kg once daily, dispensed as three fixed weight-band syringes: 16.6 mg for under 56 kg, 23 mg for 56 to under 77 kg, and 32.4 mg for 77 kg and above. Meningococcal vaccination must be completed at least 2 weeks before the first dose, or antibiotic prophylaxis started if treatment cannot wait.

Titration

No titration. The dose is set by weight band and recalculated if the patient's weight crosses a band boundary.

Cycling

Continuous daily therapy for as long as it is working. There is no cycling; stopping restores complement function over roughly 2-4 weeks and MG symptoms typically return.

Work out your exact syringe units →

Pharmacology

Half-life
Roughly 172 hours, which is about 7 days - the long tail means complement suppression persists for weeks after stopping.
Onset
Complement inhibition is near-complete within hours of the first dose; clinical MG-ADL improvement is measurable by week 1 and continues through week 12.
Routes
subcutaneous
Molecule
Synthetic macrocyclic peptide, 15 residues, with a PEG and lipid tail for albumin binding
Sequence length
15 amino acids
Molecular weight
3562.2 Da

Handling

Diluent
Not applicable - supplied as a ready-to-use prefilled syringe
Lyophilised
Not supplied lyophilised.
Reconstituted
Refrigerate at 2-8 C in the original carton. May be kept at up to 30 C for a single period of no more than 3 months, after which it must be used or discarded.
Light sensitive
Yes — keep it out of the light

Mixing

Prefilled single-dose syringes at 16.6 mg/0.416 mL, 23 mg/0.574 mL and 32.4 mg/0.81 mL. Let the syringe reach room temperature for about 30 minutes before injecting to reduce sting.

Side effects

  • very commonInjection-site reaction - bruising, pain, erythema— Reported by roughly a third of patients; largely manageable with site rotation.
  • commonUpper respiratory tract infection
  • commonDiarrhoea
  • commonHeadache
  • uncommonElevated lipase and amylase— Usually asymptomatic but pancreatitis has been reported.
  • rareMeningococcal infection— Boxed warning. C5 blockade removes the terminal complement defence against encapsulated organisms; infection can be fulminant and fatal.

Do not use if

  • Unresolved Neisseria meningitidis infection - starting C5 blockade here is dangerous.
  • Patients not vaccinated against meningococcus, unless antibiotic prophylaxis is running and the delay in treatment would be more harmful.
  • Known hypersensitivity to zilucoplan.

Combining it

  • redundanteculizumab — Both are terminal complement C5 inhibitors; combining them adds infection risk with no additional benefit.
  • redundantravulizumab — Same target, same problem. A washout is needed when switching.
  • cautionlive attenuated vaccines — Complement suppression means live vaccines need careful timing, ideally before starting therapy.
  • cautionimmunosuppressants — Commonly co-prescribed in MG, but stacked immune suppression compounds infection risk.

What to monitor

  • · Documented meningococcal vaccination, boosted per national schedule, and a patient safety card carried at all times.
  • · Immediate evaluation of any fever, headache with stiff neck, or photophobia as possible meningococcal disease.
  • · MG-ADL and QMG scores to confirm the drug is earning its place.
  • · Serum lipase and amylase if abdominal pain develops.

Legal status

FDA- and EMA-approved prescription drug for anti-AChR-antibody-positive generalised myasthenia gravis, dispensed through a REMS-style safety programme in the US.

References

  • Zilbrysq (zilucoplan) FDA prescribing information with boxed meningococcal warning (label)
  • Howard et al. 2023, RAISE phase 3 trial of zilucoplan in generalised myasthenia gravis, Lancet Neurology (trial)

Mechanism in depth

Zilucoplan binds complement C5 and prevents its cleavage by C5 convertase into C5a and C5b. No C5b means no assembly of C5b-9, the membrane attack complex. In acetylcholine receptor antibody-positive generalised myasthenia gravis, the autoantibodies are predominantly IgG1 and IgG3, which are potent complement activators; they bind the postsynaptic acetylcholine receptor, fix complement, and the resulting membrane attack complex physically destroys the junctional folds of the postsynaptic membrane. That structural damage, not simple receptor blockade, is what makes the disease severe. Inhibiting C5 stops the destruction and allows the endplate to recover, which is why the clinical benefit builds over weeks rather than appearing immediately. Zilucoplan has a second, mechanistically distinct action that antibody C5 inhibitors lack: it also binds C5b and sterically blocks its interaction with C6, so even C5 that does get cleaved cannot proceed to form the membrane attack complex. That dual block is the argument for a macrocyclic peptide over an antibody. Complement inhibition is near-complete and fast, 97.5 percent by the end of the first week in RAISE, but the MG-ADL improvement was a placebo-adjusted 2.09 points at week 12, which is real, statistically robust, and modest. The lipid-PEG tail is what makes daily subcutaneous self-injection possible at all: it drives albumin binding, raises protein binding above 99 percent, and stretches the terminal half-life to about 172 hours. That long tail cuts both ways, because complement suppression and therefore meningococcal susceptibility persists for weeks after the last dose.

What usually goes wrong

Meningococcal disease is the catastrophic risk and it is what the boxed warning and the REMS programme exist for. It has occurred in vaccinated patients, so vaccination reduces but does not remove the risk, and the practical harm-reduction step is that every patient carries a safety card and treats fever plus headache as an emergency rather than a virus. Pancreatitis is the surprising one, and the reason baseline lipase and amylase are required. The 172-hour half-life means complement stays suppressed for weeks after stopping, so someone who quits the drug is still immunosuppressed and still needs to treat fever as an emergency. Beyond safety, the commonest disappointment is expectation: a 2.09-point MG-ADL improvement is a genuine benefit but it is not a cure, and the real-world draw is a daily self-injection instead of a monthly infusion chair.

Titration ladder

  1. 16.6 mgFrom day 1, body weight under 56 kg — 16.6 mg once daily subcutaneously (rubine red plunger rod). Weight-banded, not titrated: the dose is set on day one and does not escalate.
  2. 23 mgFrom day 1, body weight 56 kg to under 77 kg — 23 mg once daily subcutaneously (orange plunger rod).
  3. 32.4 mgFrom day 1, body weight 77 kg and above — 32.4 mg once daily subcutaneously (dark blue plunger rod). Recheck the band if body weight changes materially.

Bloodwork worth running

MarkerWhenWhy it matters
Meningococcal vaccination status (A, C, W, Y and B)At least 2 weeks before the first dose, with revaccination per ACIP schedules for patients on complement inhibitors, which differ from the standard vaccine schedules.Complement inhibition removes the only effective defence against Neisseria meningitidis. Life-threatening and fatal meningococcal infection has occurred in vaccinated as well as unvaccinated patients on complement inhibitors. This is the single most important item on the list and it is a documentation check, not a blood test.Act if: If treatment cannot wait 2 weeks, start antibacterial prophylaxis and vaccinate immediately. Any fever, headache with neck stiffness or petechial rash on zilucoplan is meningococcal disease until proven otherwise.
Serum lipase and amylaseBaseline before the first dose, then whenever abdominal pain appears.Pancreatitis and pancreatic cysts have been reported on zilucoplan and the label requires baseline values before initiation. This is unusual for a complement inhibitor and is easy to miss.Act if: Suspected pancreatitis means stop zilucoplan and investigate before restarting.
Complement activity (CH50 or sheep red blood cell lysis assay)If clinical response is poor despite adherence.The pharmacodynamic readout of whether the drug is doing its job. Not required for routine care, but useful when response is inadequate or adherence is in question.Act if: Incomplete complement suppression on a correct weight-band dose is a reason to look for a C5 polymorphism or an alternative diagnosis.
MG-ADL and QMG scoresBaseline, week 4, week 12, then quarterly.Not blood, but the actual efficacy measure. The trial effect size was 2.09 points on MG-ADL at week 12, so a patient needs a structured score rather than an impression to know whether it is working.Act if: No improvement in MG-ADL by week 12 on full dose with confirmed complement suppression means this drug is not going to work for this patient.

Pharmacokinetics

Tmax
4.5 h
Volume of distribution
3.51 L
Protein binding
99%
Time to steady state
28 days
Crosses blood-brain barrier
no
Accumulates
Yes — doses stack before steady state
Metabolism
Catabolised into small peptides and amino acids. Two plasma metabolites matter mechanistically: RA103488, formed mainly by CYP4F2, which has pharmacological activity similar to the parent, and RA102758, formed by protease-mediated degradation, which is inactive. Each is present at roughly 10 percent of parent AUC, so the active metabolite contributes little.
Elimination
Catabolic. Renal and faecal excretion together account for under 1 percent. Severe renal impairment lowers exposure by only 13 percent and moderate hepatic impairment by 24 percent, neither of which requires dose adjustment.

Receptor targets

  • Complement component C5

    Binds C5 and blocks cleavage by C5 convertase, preventing generation of the C5a anaphylatoxin and of C5b. Complement inhibition reached 97.5 percent by the end of week one at the approved dose.

  • Complement component C5b (C6 interaction interface)

    Sterically prevents C5b from binding C6, blocking membrane attack complex assembly even downstream of any C5 that is cleaved. This is the mechanistic feature that distinguishes it from anti-C5 antibodies.

Trials

  • RAISE Phase 3 · n=174 · 12 weeks · 2023

    Change from baseline to week 12 in MG-ADL score in AChR-antibody-positive generalised myasthenia gravis. Least squares mean change -4.39 with zilucoplan versus -2.30 with placebo, a placebo-adjusted difference of -2.09 points (p=0.0004). Injection site bruising was the commonest adverse event.

  • RAISE-XT Phase 3 open-label extension · 2024

    Long-term safety and durability of zilucoplan. Interim analysis supports sustained MG-ADL improvement beyond the 12-week controlled period.

What to expect, and when

Complement inhibition is 89 percent within 3 hours of the first dose and 97.5 percent by the end of week one. Clinical improvement in MG-ADL begins within the first one to two weeks and continues to build through week 12. Steady-state trough concentrations are reached by about four weeks. After stopping, complement suppression persists for several weeks given the 7 to 8 day half-life.

Stacking and comparisons

Zilucoplan is used on a background of pyridostigmine, corticosteroids and steroid-sparing immunosuppressants, and the realistic goal is steroid reduction over time rather than immediate withdrawal. Do not combine it with another complement inhibitor: eculizumab, ravulizumab and zilucoplan all block C5 and stacking them multiplies infection risk without adding efficacy. If switching from an antibody C5 inhibitor, the long half-lives on both sides need planning. Intravenous immunoglobulin and plasma exchange both remove or dilute circulating drug; plasma exchange in particular will strip zilucoplan out and supplemental dosing considerations apply. Live vaccines are a problem while complement is suppressed.

Against eculizumab and ravulizumab: same target, similar effect size in generalised myasthenia gravis, but those are intravenous infusions every two weeks or every eight weeks while zilucoplan is a daily subcutaneous injection the patient gives themselves. Zilucoplan additionally blocks the C5b-C6 interaction, which the antibodies do not. Against efgartigimod and rozanolixizumab, the FcRn blockers: entirely different mechanism, stripping pathogenic IgG rather than blocking its effector arm, cyclical rather than continuous dosing, and no meningococcal risk. For an AChR-positive patient the choice is largely about route, schedule and infection tolerance rather than efficacy.

Rough cost

A specialty complement inhibitor dispensed through a REMS-restricted programme; list prices for this class run in the tens of thousands of dollars per month in the US. I did not verify a current figure and will not invent one.

Genuinely uncertain

  • A numeric systemic clearance value is not published in the label; only the volume of distribution, protein binding and half-life are given.
  • RAISE-XT enrolment and follow-up duration were not resolved to specific numbers and are left null.
  • The relative contribution of the active metabolite RA103488 to overall effect is stated by the label as expected to be low, based on a roughly 10 percent AUC ratio, rather than measured directly.

Papers