Why does it carry a boxed warning?

Because it can cause anaphylaxis and serious infusion reactions, which is why it is given only in settings prepared to treat anaphylaxis, with pre-medication and monitoring. A serum uric acid level that stops falling is a warning sign of higher reaction risk.

Why must G6PD deficiency be ruled out first?

The uricase reaction generates hydrogen peroxide, which can cause haemolysis and methaemoglobinaemia in people with G6PD deficiency. It is contraindicated in these patients, so at-risk individuals are screened before the first dose.

Why is methotrexate given with it?

Many patients develop antibodies against pegloticase that cause loss of response and infusion reactions. Adding methotrexate suppresses these anti-drug antibodies, and randomized MIRROR data showed this substantially increases the number of durable responders.

Can pegloticase be used casually or for research or performance goals?

No. It is a hospital-administered enzyme with a boxed warning for anaphylaxis and a hard contraindication in G6PD deficiency, reserved for severe refractory gout. It has no legitimate self-administration or research-peptide use.

EMA-approvedaka Krystexxa

Pegloticase — Complete Research Guide (2026)

Last updated 2026-06-30

TL;DR

Pegloticase (also known as Krystexxa) is a peptide catalogued under Enzymes (PEG-urate oxidase). Neutral reference entry; EU status: EU-approved prescription medicine.

What is Pegloticase?

Pegloticase (brand name Krystexxa) is a pegylated recombinant uricase (urate oxidase) enzyme approved for chronic gout refractory to conventional urate-lowering therapy in adults. The US FDA approved it in 2010, and it is given as an intravenous infusion in a monitored clinical setting.

The evidence is human and pivotal: two replicate randomized controlled trials (Sundy 2011, JAMA) established efficacy, and later randomized work (the MIRROR programme) showed that co-administering methotrexate substantially increases sustained response by reducing anti-drug antibodies, supporting the 2022 FDA approval of the methotrexate co-therapy.

How does Pegloticase work?

Uricase converts poorly soluble uric acid into allantoin, a far more water-soluble metabolite that is readily excreted; humans lack a functional uricase gene, so the recombinant enzyme supplies this missing activity.

The PEG coating extends half-life and reduces immunogenicity, dramatically lowering serum urate and dissolving established tophi.

What does the research say about Pegloticase?

In two replicate phase 3 RCTs, pegloticase normalized serum uric acid in a substantial share of patients with chronic refractory gout who had failed conventional therapy. ^[1]
Adding methotrexate to pegloticase markedly increased the proportion of durable responders versus pegloticase alone in the randomized MIRROR trial. ^[2]
Over 12 months, methotrexate co-therapy sustained the improved response rate and reduced infusion reactions relative to pegloticase monotherapy. ^[4]

Clinical research & studies

The references below are the primary sources cited throughout this guide. Each links directly to PubMed or the regulator. Where evidence is preclinical (animal or in-vitro), that is stated rather than implied.

[1] Efficacy and tolerability of pegloticase for the treatment of chronic gout in patients refractory to conventional treatment: two randomized controlled trials — Sundy JS et al., JAMA 2011. (Two replicate phase 3 randomized controlled trials)
[2] A Randomized, Placebo-Controlled Study of Methotrexate to Increase Response Rates in Patients with Uncontrolled Gout Receiving Pegloticase: Primary Efficacy and Safety Findings — Botson JK et al., Arthritis and Rheumatology 2023. (Randomized controlled trial (MIRROR RCT))
[3] Pegloticase in Combination With Methotrexate in Patients With Uncontrolled Gout: A Multicenter, Open-label Study (MIRROR) — Botson JK et al., The Journal of Rheumatology 2021. (Multicenter open-label study)
[4] A Randomized, Double-Blind, Placebo-Controlled Multicenter Efficacy and Safety Study of Methotrexate to Increase Response Rates in Patients With Uncontrolled Gout Receiving Pegloticase: 12-Month Findings — Botson JK et al., ACR Open Rheumatology 2023. (Randomized controlled trial (12-month findings))
[5] Monosodium urate crystal depletion and bone erosion remodeling during pegloticase treatment in patients with uncontrolled gout: Exploratory dual-energy computed tomography findings from MIRROR RCT — Dalbeth N et al., Joint Bone Spine 2024. (Exploratory imaging sub-analysis of an RCT)

Dosing context

This is not medical advice or a usage recommendation. Dosing figures are reported research context only, cited from the published literature.

The approved regimen is 8 mg by intravenous infusion every two weeks, increasingly given together with methotrexate to curb immunogenicity and prolong response.

Administration is always in a supervised clinical setting with pre-infusion checks of serum uric acid; it is not an outpatient self-administered or research-use agent.

Side effects & safety profile

Pegloticase carries an FDA boxed warning for anaphylaxis and infusion reactions, which can occur at any time (most often within two hours of infusion); it must be given in a healthcare setting equipped to manage anaphylaxis, with pre-medication and monitoring, and a rising or non-falling serum uric acid predicts higher reaction risk.

It is CONTRAINDICATED in glucose-6-phosphate dehydrogenase (G6PD) deficiency because uricase-generated hydrogen peroxide can trigger haemolysis and methaemoglobinaemia; patients at risk (including those of African and Mediterranean ancestry) should be screened for G6PD deficiency before treatment.

Gout flares are common on initiation, so flare prophylaxis is advised.

Stacking & combinations

The only evidence-based combination is with an immunomodulator such as methotrexate to reduce anti-drug antibodies and prolong response, done under rheumatology supervision, not with recreational or research peptides.

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Frequently asked questions

It treats chronic gout in adults whose disease has not responded to conventional urate-lowering drugs such as allopurinol or febuxostat. It is a last-line intravenous therapy for refractory, often tophaceous, gout.

References

[1] Efficacy and tolerability of pegloticase for the treatment of chronic gout in patients refractory to conventional treatment: two randomized controlled trials — Sundy JS et al., JAMA 2011. PMID: 21846852. View sourceStudy: Two replicate phase 3 randomized controlled trialsPegloticase achieved sustained urate lowering in a significant fraction of patients with treatment-refractory chronic gout.
[2] A Randomized, Placebo-Controlled Study of Methotrexate to Increase Response Rates in Patients with Uncontrolled Gout Receiving Pegloticase: Primary Efficacy and Safety Findings — Botson JK et al., Arthritis and Rheumatology 2023. PMID: 36099211. View sourceStudy: Randomized controlled trial (MIRROR RCT)Co-administered methotrexate significantly raised durable response rates compared with pegloticase plus placebo.
[3] Pegloticase in Combination With Methotrexate in Patients With Uncontrolled Gout: A Multicenter, Open-label Study (MIRROR) — Botson JK et al., The Journal of Rheumatology 2021. PMID: 32934137. View sourceStudy: Multicenter open-label studyMethotrexate co-therapy improved pegloticase response rates and reduced infusion reactions in an open-label cohort.
[4] A Randomized, Double-Blind, Placebo-Controlled Multicenter Efficacy and Safety Study of Methotrexate to Increase Response Rates in Patients With Uncontrolled Gout Receiving Pegloticase: 12-Month Findings — Botson JK et al., ACR Open Rheumatology 2023. PMID: 37385296. View sourceStudy: Randomized controlled trial (12-month findings)The benefit of methotrexate co-therapy on response and tolerability was maintained through 12 months.
[5] Monosodium urate crystal depletion and bone erosion remodeling during pegloticase treatment in patients with uncontrolled gout: Exploratory dual-energy computed tomography findings from MIRROR RCT — Dalbeth N et al., Joint Bone Spine 2024. PMID: 38447697. View sourceStudy: Exploratory imaging sub-analysis of an RCTPegloticase treatment was associated with depletion of monosodium urate crystal deposits and remodeling of bone erosions on dual-energy CT.

This article is for educational and research purposes only. Peptides discussed here are not approved for human consumption by the FDA, EMA, or equivalent regulators outside of specific clinical contexts. Always consult a licensed medical professional before any therapeutic use.