Therapeutic drug monitoring of biologics in psoriasis.

Biologics are an important component of the armamentarium of drugs in the treatment of moderate to severe psoriasis. There is increasing evidence that therapeutic drug monitoring (TDM) encompassing the measurement of trough concentrations and anti-drug antibodies (ADA), together with clinical response is emerging as a valuable tool for clinical decision making. It aids in targeted dose adjustments in patients with low drug concentrations, monitoring of adherence and assessment of patients who lose response to biologics or do not respond at all. The high prevalence of psoriasis, its impact on patients' lives and costs spent on therapy motivate an evidence-based and cost-effective utility of biologics. We performed a literature review on the TDM of TNF alpha antagonists (adalimumab, infliximab, etanercept), IL12/23 antagonists (ustekinumab, guselkumab, tildrakizumab), IL17A inhibitors (secukinumab, ixekizumab) and biosimilars used in the treatment of psoriasis. Although establishing target therapeutic ranges for biologics is ideal, this has only been explored in adalimumab. We also propose a treatment algorithm for the practical application of TDM depending on drug trough concentrations, presence/absence of anti-drug antibodies and clinical response of patients. The practice of TDM is recommended in routine clinical practice where possible.