In a patient with psoriatic arthritis and mildly elevated liver enzymes, should bimekizumab be administered every 4 weeks (standard dosing) or can it be given every 8 weeks?

Bimekizumab Dosing in Psoriatic Arthritis with Elevated Liver Enzymes

Continue bimekizumab at the standard 160 mg every 4 weeks dosing for psoriatic arthritis, even with mildly elevated liver enzymes, as the FDA-approved label requires baseline liver enzyme testing but does not mandate dose reduction or interval extension for mild elevations. 1

FDA-Approved Dosing for Psoriatic Arthritis

• The FDA-approved dosing regimen for psoriatic arthritis is 160 mg subcutaneously every 4 weeks, not every 8 weeks 1
• This differs from plaque psoriasis dosing, where 320 mg every 8 weeks is an option after the initial loading period 1
• For psoriatic arthritis patients with coexistent moderate-to-severe plaque psoriasis, use the plaque psoriasis dosing regimen (320 mg at weeks 0,4,8,12,16, then every 8 weeks) 1

Pre-Treatment Liver Monitoring Requirements

• The FDA label mandates testing liver enzymes, alkaline phosphatase, and bilirubin prior to initiating bimekizumab treatment 1
• However, the label does not specify dose modifications, discontinuation thresholds, or interval extensions based on liver enzyme elevations 1
• This pre-treatment screening is intended to identify baseline hepatic function, not to contraindicate therapy for mild elevations 1

Why Every-Other-Month Dosing Is Not Appropriate

There is no FDA-approved every-8-week (every other month) dosing regimen for psoriatic arthritis without coexistent moderate-to-severe plaque psoriasis. 1

• The 160 mg every 4 weeks regimen was specifically studied and approved for psoriatic arthritis efficacy endpoints 1, 2
• In the BE COMPLETE trial of psoriatic arthritis patients with prior TNF-α inhibitor inadequate response, 43% achieved ACR50 at week 16 with the every-4-week dosing 2
• Extending the interval to every 8 weeks would reduce drug exposure below the studied therapeutic level for joint disease 1

Clinical Context: Dose Tapering Evidence

While dose tapering or interval extension has been studied in plaque psoriasis with other biologics, this approach:

• Requires sustained remission (typically PASI ≤5 or PASI 90-100) for 6-12 months before considering tapering 3
• Most commonly involves 33-50% dose reduction after achieving stable disease control 3
• Has not been systematically studied or validated for psoriatic arthritis joint outcomes 3
• Should not be applied to bimekizumab in psoriatic arthritis based solely on mild liver enzyme elevations, as this is not an evidence-based indication for dose modification 1

Monitoring Strategy for Elevated Liver Enzymes

Monitor liver enzymes periodically during treatment, but do not automatically extend dosing intervals for mild elevations. 1

• Assess for alternative causes of liver enzyme elevation (alcohol, medications, fatty liver disease, viral hepatitis) 1
• Consider hepatology consultation if enzymes are significantly elevated (>3-5× upper limit of normal) or progressively worsening 1
• Discontinue bimekizumab only if clinically significant hepatotoxicity develops, not for stable mild elevations 1

Common Pitfall to Avoid

Do not conflate plaque psoriasis dosing flexibility with psoriatic arthritis dosing requirements. The every-8-week maintenance option exists only for plaque psoriasis (after initial loading with 320 mg doses) or for psoriatic arthritis patients who also have moderate-to-severe plaque psoriasis requiring that specific regimen 1. For psoriatic arthritis alone, the 160 mg every 4 weeks schedule is the only approved and studied regimen 1, 2.