Inflammatory bowel diseases (IBDs), which include ulcerative colitis (UC) and Crohn’s disease (CD), consist of chronic recurrent inflammatory diseases of unknown etiology that affect the gastrointestinal tract (GIT).^[1] While the inflammation in UC is limited to the colon and rectum, the inflammation in CD can affect all parts of the GIT, from the mouth to the anus, and is linked to discontinuous transmural lesions of the gut wall.^[2] Regardless of sex, IBD can start at any age; however, the most significant peak of onset occurs between the ages of 15 and 45. The incidence is steadily rising to the point that it qualifies as a global health issue.^[3]

The pathogenesis of ulcerative colitis involves the activation of different immune cells, which results in the secretion of pro-inflammatory cytokines, i.e., TNF-α, interleukin-1 (IL-1), IFN-γ, IL-6, and IL-23, which increases the permeability of the intestinal barrier and thus promotes inflammation in the intestinal mucosa.^[4]

Tumor necrosis factor alpha (TNF-α) inhibitors are frequently employed in treating autoimmune diseases such as IBD (for both moderate-to-severe CD and UC).^[5,6] Infliximab, adalimumab, golimumab, and certolizumab are TNF-α inhibitors that have been employed in the clinical setting of IBD; each has a unique pharmacological profile and varying efficacy.^[5] They are utilized when other treatments are ineffective in improving the disease’s signs and symptoms.^[7] Despite anti-TNF-α biologics showing favorable therapeutic effects in achieving clinical, endoscopic, and histologic remission in IBD^[8], they are not without drawbacks, namely a higher risk of serious infection and loss of response in 30–50% of patients.^[9] This encompasses a gradual decline in responsiveness over time as well as an initial absence of response.^[10] Additionally, response may be changed by patient variables (such as smoking status and the duration of the condition). Lastly, the response seems to be influenced by genetic differences.^[11]

Three major mechanisms of biologic treatment failure have been proposed. The first one is the non-immune-mediated pharmacokinetic failure related to the rapid drug clearance. The second mechanism is the immune-mediated pharmacokinetic failure caused by the production of neutralizing anti-drug antibodies (ADAs) against biologics (presenting as secondary loss of response during the maintenance phase of biologics treatment). The third mechanism is the mechanistic failure where the IBD may be driven by inflammatory mechanisms not blocked by the applied biologics.^[12]

Drug trough concentrations refer to measuring drug levels just before the subsequent dose.^[13] Higher trough levels (TL) of the drug equate to higher exposure and result in better clinical outcomes.^[14]

In order to optimize treatment for IBD and to achieve more demanding, objective end goals, therapeutic drug monitoring (TDM) has become a popular approach. Since low trough levels/concentrations or the development of ADAs are variously linked to treatment failure, the TDM of biological drugs includes measuring levels of serum drug concentrations and ADAs to explain primary non-response or secondary loss of response.^[15]

The TDM can be implemented in two main ways: reactive TDM and proactive TDM. Reactive TDM involves measuring drug and ADAs levels in patients experiencing a primary non-response or secondary loss of response. This approach helps in rationalizing management by identifying reasons for treatment failure.^[16] Proactive TDM, on the other hand, involves monitoring drug trough levels/concentrations at regular intervals in patients in remission to maintain therapeutic concentrations and potentially prevent loss of response.^[17]

Adalimumab is a fully humanized IgG1 monoclonal antibody that is administered by the subcutaneous (SC) route. When used for UC, adalimumab is given at a dose of 160 mg (day 1), and then 80 mg 2 weeks later (day 15), followed by a maintenance dose (beginning week 4, day 29) of 40 mg SC every 2 weeks.^[18] The recommended target TL of adalimumab at maintenance when used for IBD is 8–12 µg/mL.^[19] In order to provide more individualized and efficient patient care, studies are still being done to determine the best way to use TDM in adalimumab therapy for IBD.^[20]

This study aims to evaluate TL, the development of ADAs, and their relationships with clinical and laboratory variables in Iraqi patients with ulcerative colitis receiving adalimumab therapy.

In the current study, 44 UC patients receiving adalimumab were included. Therapeutic drug monitoring was used to assess adalimumab TL and the existence of ADAs to adalimumab, which can help with therapy optimization. The observed differences in patients’ outcomes directly informed clinical recommendations, with a significant proportion of patients requiring a change in treatment strategy. This highlights the potential for using these markers to stratify patients early in their treatment, leading to more timely and effective therapeutic adjustments and potentially improving overall outcomes.

Concerning the TL, ADAs, and disease activity of the patients, recommendations were made to increase the dose or shorten the intervals between doses and monitor the response for patients who had low TL with negative ADAs and were in active disease (non-immune pharmacokinetic failure) and for patients who had low TL and were in remission.^[26,27] Furthermore, recommendations were made to switch therapy for patients who were in active disease despite achieving target TL (mechanistic failure) and for patients who did not achieve target TL and were in active disease with high positive ADAs (immune pharmacokinetic failure).^[28] Additionally, for patients who were in remission with the achievement of target TL, recommendations were made to continue therapy, and for those who were in remission with TL above the target, recommendations were made to de-escalate the dose or lengthen the interval between doses. Studies in real-world settings continue to confirm TDM effectiveness with observed clinical remission rates. The optimal adalimumab TL for UC are often considered similar to those for CD, aiming for levels associated with mucosal healing and sustained remission.^[28-31]

Additionally, the current study shows that ADAs were higher in patients with TL below the therapeutic range when compared to patients with TL within or above the therapeutic range. A Saudi cohort study (n=392 IBD patients receiving anti-TNF therapy, including adalimumab): ADAs were negative in 73.1% of patients and weakly positive in 9.8%; 17.1% of patients had positive ADAs, with sub-therapeutic anti-TNF drug levels significantly associated with ADAs positivity (p<0.001).^[32]

Furthermore, routine inflammatory markers (CRP and ESR) and routine blood tests (HGB, PCV, MCV, white blood cell count, lymphocyte count, neutrophil count, MPV, and platelet count) were examined in the current study. It was found that neutrophil count, ESR, and CRP were higher, and HGB and PCV were lower in patients with TL below the therapeutic range. An IBD cohort study published in 2020 showed a significant negative correlation between anti-TNF trough levels and some laboratory markers, including serum CRP.^[33] According to a study by Roblin et al., a combination of CRP, TL, and ADAs can be used to accurately predict a loss of response to infliximab.^[34] Also, the current study demonstrates that CRP could be used as a new noninvasive biomarker to predict a loss of response to adalimumab. Moreover, and for routine disease activity assessment, the recent guidelines for UC management suggest measuring CRP and fecal calprotectin in asymptomatic patients to avoid more expensive and invasive testing, such as endoscopy.^[35] For IBD patients achieving mucosal healing, their WBC count, PLT count, ESR, CRP, and neutrophil/lymphocyte ratio levels were significantly lower than those in patients that did not achieve mucosal healing (all p<0.05) and could be used as noninvasive markers for predicting mucosal healing in patients with IBD.^[36] Anemia (low HGB and PCV) is highly prevalent in IBD patients and directly linked to chronic inflammation.

The higher level of HGB and PCV in patients with TL within or above the therapeutic range is consistent with a prior study showing that anti-TNF treatment, such as adalimumab, raises HGB levels and lowers anemia rates in IBD patients. This benefit occurred concurrently with a decrease in disease activity measured by CRP and was unrelated to iron supplementation during treatment.^[37]

Calprotectin is an acute-phase protein that regulates neutrophil migration. Its quantity corresponds with neutrophil migration and indicates the intensity of inflammation in IBD.^[38]

However, this is the first study, to the best of our knowledge, to examine the association between serum CALP and adalimumab TL and find that serum CALP was higher in UC patients with TL below the therapeutic range, in spite of not being statistically significant. A previous study in Japan (2019) found that serum CALP is an inflammatory biomarker in IBD, but it might be more effective in evaluating CD patients than UC patients.^[39]

A recent Iraqi study by Saleh HH et al. concluded that serum CALP is a new marker that could be used in evaluating and predicting how well CD patients will respond to infliximab and achieve target infliximab TL.^[40]

The present study is not without its limitations, which can be enumerated as follows: firstly, the sample size is limited; secondly, TDM results (TL and ADAs) were delayed because samples were obtained from patients and stored for approximately six months before laboratory measurements were completed, resulting in delayed therapy recommendations to physicians and patients.

Therapeutic drug monitoring for adalimumab (through the measurement of TL and ADAs) has the potential to serve as a valuable instrument in formulating suitable recommendations to optimize UC treatment (escalating the dose for 13 patients, switching therapy for 16 patients, de-escalating the dose for 10 patients, and continuing therapy for 5 patients). Multivariate analysis of the studied variables indicates that PCV, neutrophil count, and CRP could serve as indicators to predict TL accomplishment and subsequent response to adalimumab therapy.

Ethical approval for the study was granted by the Scientific and Ethical Committee of the College of Pharmacy in the University of Baghdad (Protocol IDRECAUBCP742024k, date: 7-4-2024). The Iraqi Ministry of Health also gave its clearance.

The authors have declared that they have no conflict of interest, financial or otherwise.

No use of AI was reported.

The authors have no funding to report.

Each named author has substantially contributed to conducting the underlying research and drafting this manuscript—conceptualization and methodology: AM and DJ; investigation: AM, RJ; formal analysis: AM and DJ; visualization and writing–original draft: AM and DJ; project administration: AM, DJ, and RJ; writing–review and editing: AM, DJ, and RJ; funding acquisition: AM; supervision: DJ, RJ. All authors have read and agreed to the final version of the manuscript and have agreed to the Folia Medica’s submission policies.

All data used are referenced or included in the article.