Mirikizumab is a first-in-class monoclonal antibody that targets the p19 subunit of interleukin-23. It is approved for moderate-to-severe active ulcerative colitis and, as of January 2025, Crohn’s disease in adults, giving clinicians a newer option across the inflammatory bowel disease spectrum. As with any biologic, individual patients respond differently, and knowing where a patient’s drug exposure actually sits can help clinicians interpret that response and decide what to do next.

With iDose® GEN7.0, Baysient now supports PK-informed therapeutic drug monitoring (TDM) for both intravenous and subcutaneous mirikizumab. By combining Bayesian modeling with individual patient data, iDose gives clinicians an individualized view of exposure, turning a patient’s own drug concentrations and lab results into actionable pharmacokinetic (PK) insight.

Individual Pharmacokinetics Vary From Patient to Patient

Mirikizumab has linear, dose-proportional pharmacokinetics, but individual exposure still differs meaningfully between patients. Increased body weight and decreased serum albumin are associated with higher mirikizumab clearance, and higher body weight is associated with lower drug concentrations. Because standard dosing does not account for these individual differences, two patients on the same regimen can reach different exposures. Measuring where a given patient actually sits is where TDM earns its place.

Immunogenicity Is Measurable and Worth Watching

Mirikizumab also carries a meaningful immunogenicity profile. In the registration trials, anti-drug antibodies developed in roughly 23% of ulcerative colitis and 13% of Crohn’s disease patients, without a clinically significant effect on safety. Immunogenicity of that magnitude is one more reason a patient’s exposure can diverge from the population average, and it is worth evaluating when a previously responding patient begins to lose response. Monitoring both drug concentration and antibody status gives clinicians a fuller picture than either measure alone.

What TDM Does for Mirikizumab

For mirikizumab, TDM is a tool for clarity. It is most useful when assessing response is difficult, or when a clinician wants to confirm a patient is above a concentration that may improve the odds of response, and to inform decisions about continuing, adjusting, or de-escalating therapy.

The most valuable moment is loss of response. When a patient stops responding, a PK-informed view helps distinguish a patient who is underexposed and may benefit from a dosing change from one whose disease is simply not responding to IL-23 inhibition, who may need a different therapy altogether. That distinction changes the clinical decision, and it is difficult to make from symptoms alone.

Where iDose Adds Value for Mirikizumab Dosing

iDose gives clinicians an individualized estimate of a patient’s exposure, built from their own drug concentrations and lab data rather than assumed from the label. For a drug where body weight, albumin, and immunogenicity all shift individual exposure, that PK view helps clinicians interpret response, evaluate loss of response, and support decisions about the path forward.

iDose informs clinical judgment. Clinicians choose a target concentration, and iDose can forecast the dose and interval expected to reach it. Just as importantly, it can simply show where a patient’s exposure sits today, which is often exactly the information a treatment decision needs.

The Patient Populations Where This Applies

Mirikizumab is currently approved for ulcerative colitis and Crohn’s disease, two inflammatory bowel disease indications. iDose GEN7.0 supports PK-informed TDM for both intravenous and subcutaneous mirikizumab.

Across both, the same reasoning applies. Exposure varies between patients and immunogenicity is measurable, so an individualized PK view can support clinical decisions and help clinicians act with more confidence.

How iDose Brings PK-Informed Monitoring to Mirikizumab

iDose is a cloud-based clinical decision support software service that uses Bayesian estimation and population pharmacokinetic modeling to integrate an individual patient’s data, including drug concentrations, routine lab results, and demographics. From that information, it can estimate individual exposure and, where a clinician chooses to target a concentration, forecast the dose and interval expected to reach it. Because any such target is not defined in FDA-approved labeling, iDose is built to inform the clinician’s decision rather than to direct therapy.

For mirikizumab, which is given intravenously for induction and subcutaneously for maintenance, this gives clinicians a structured way to:

• See where an individual patient’s exposure sits rather than assuming it from the label
• Account for patient factors, such as body weight and albumin, that shift clearance
• Interpret loss of response in light of exposure and immunogenicity
• Use the routine labs and patient data already collected in practice

As precision dosing matures across inflammatory disease, an accurate, individualized view of exposure gives clinicians a clearer basis for every treatment decision.

To see how iDose can be integrated into your practice, schedule a demo today.