P582 Adalimumab therapeutic drug monitoring: Does time of testing matter?

Background Whilst anti-TNF drugs such as adalimumab (ADL) have revolutionised the management of inflammatory bowel disease treatment outcomes are not universally favourable with 30% primary non-response (PNR) and 46% secondary loss of response (SLOR) rates reported.1,2 Therapeutic drug monitoring (TDM)—the measurement of serum drug levels and anti-drug antibodies—has become popular with clinicians who use it to optimise biologic therapy through serum drug-level guided dose adjustment. Conventionally TDM is based on the interpretation of trough drug levels (DL) which are obtained by drawing a blood sample immediately prior to the next drug dose. Obtaining an ADL trough DL can be challenging as the drug is administered as a subcutaneous injection usually in the patient’s own home. The aim of this project was to determine the current use of non-trough ADL TDM in clinical practice and determine whether timing of ADL TDM in relation to the next planned dose is clinically important. Methods All ADL DLs performed in 2018 in the Scottish Biologic TDM service3 were identified. DLs were included for patients in sustained clinical remission (SCR), on 40mg every other week dosing, and if the time from the last dose was ≤14 days. TDM performed during induction and for PNR or SLOR were excluded, as were patients on nonstandard dosing or with missing data on dose and interval. Results were analysed by quartile according to time from the last drug dose. Results 338 DLs were included. Median DL is 8µg/ml (range <0.4–36). Median time from last dose is 12 (range 0–14) days. The first quartile (n = 83, median 5 (range 0–7) days) had a median DL of 8.2µg/ml (<0.4–28.1). The second quartile (n = 90, median 11 (8–12) days) had a median DL of 7.9µg/ml (<0.4–36). The third quartile (n = 80, 13 days from last dose) had a median DL of 8µg/ml (<0.4 – 28.1). fourth quartile samples (n = 85, 14 days from last dose – true trough DLs) had a median DL of 8 µg/ml (<0.4–34.8). No relationship was identified between observed DL and the time of DL testing (ρ= -0.3162, p = 0.23). Conclusion It is not necessary to use trough DLs when performing ADL TDM for individuals in SCR. These data should give clinicians the confidence to use opportunistic ADL TDM testing in a clinical setting. Further work should be undertaken on non-trough testing of ADL DLs in other clinical scenarios. Disclosure Biogen GmbH contributed funding for this research. Authors had full editorial control and approval of all content. References

Retrospective analysis of goal drug level attainment of posaconazole for invasive fungal infection prophylaxis in patients with acute myeloid leukemia pre- and post-switch to tablet formulation

Background Posaconazole is approved for invasive fungal infection prophylaxis in patients with hematologic malignancies. Posaconazole suspension is plagued by poor oral absorption and dietary requirements that are difficult for patients to meet. The delayed-release tablet formulation of posaconazole may be taken without regards to meals and has significantly better oral absorption than posaconazole suspension. Objectives We sought to determine if a switch to posaconazole tablets improved steady-state drug level attainment for invasive fungal infection prophylaxis in patients with acute myeloid leukemia. Methods All adult inpatients with acute myeloid leukemia undergoing chemotherapy, who received posaconazole for invasive fungal infection prophylaxis between 2012 and 2015, were included. The primary outcome was proportion of patients with first posaconazole level greater than 700 ng/mL. Secondary outcomes included proportion of patients with first posaconazole level greater than 1000 ng/mL, invasive fungal infection within 100 days, and adverse drug events. Results Forty patients received posaconazole tablets and 34 patients received suspension. Posaconazole levels were significantly higher at first measurement in patients receiving tablet than suspension (1296 ng/mL vs. 788 ng/mL, p < 0.01). Thirty-seven patients receiving tablets had a serum drug level greater than 700 ng/mL on first measurement versus 18 receiving suspension (p < 0.01). Patients receiving tablets were also more likely to have a serum drug level over 1000 ng/mL on first measurement (26 vs. 11, p < 0.01). Rates of invasive fungal infection and adverse events were not statistically different. Conclusions Patients receiving posaconazole tablets attained significantly higher serum drug levels than those receiving suspension.

Predicting serum drug level using the principles of pharmacokinetics after an overdose: a case of lithium overdose

Objective: In cases of drug overdose, clinicians often find it challenging to predict serum drug level and decide the optimum time for recommencing the overdosed drug. Method: This paper describes how to predict serum drug level using the principles of pharmacokinetics. Results: The proposed method and recommencement of the overdosed drug is demonstrated using a clinical case of lithium overdose. Conclusion: The proposed method can assist clinicians in predicting serum drug levels and deciding the optimum time for recommencing the overdosed drug safely. Therefore, it may reduce unnecessary repeat serum drug level procedures.

ASSESSING ANTI-TNF TROUGH LEVELS AND ITS APPLICABILITY IN DAILY PRACTICE IN SPONDYLOARTHRITIS PATIENTS

Objective. The purpose of the present study was to assess the relevance of therapeutic drug monitoring in spondyloarthritis patients, by determining drug serum levels and anti-drug antibodies and estimating cut-off values for three TNF inhibitors. Methods. Over one year, we enrolled 100 patients with SpA, under consequent treatment with adalimumab (ADL), etanercept (ETA) or infliximab (IFX). Demographic, clinical (BASDAI, ASDAS) and laboratory (ESR, CRP) data was collected together with drug serum level and anti-drug antibodies using the ELISA technique. The statistical analysis was performed using the SPSS software, version 20.0 with the aid of Student t-test, Spearman and Pearson tests. Results. Out of the study cohort, 35% were on ADL, 33% on IFX, and 32% under ETA treatment. Undetectable drug levels correlated to the presence of anti-drug antibodies and to disease activity scores. There were no identified anti-ETA antibodies. For this study lot trough levels are estimated between 2 and 4 μg/mL for an ASDAS-CRP under 2.1. Conclusion. Serum drug level measurement and anti-drug antibody detection can be used as a completion to a clinician’s tools in assessing disease activity, leading to an optimal and personalized manner of patient management.

Monitoring Drug and Antidrug Levels: A Rational Approach in Rheumatoid Arthritis Patients Treated with Biologic Agents Who Experience Inadequate Response While Being on a Stable Biologic Treatment

Clinical response in patients with rheumatoid arthritis (RA) treated with biologic agents can be influenced by their pharmacokinetics and immunogenicity. The present study evaluated the concordance between serum drug and antidrug levels as well as the clinical response in RA patients treated with biological agents who experience their first disease exacerbation while being on a stable biologic treatment. 154 RA patients treated with rituximab (RTX), infliximab (IFX), adalimumab (ADL), or etanercept (ETN) were included. DAS28, SDAI, and EULAR response were assessed at baseline and reevaluated at precise time intervals. At the time of their first sign of inadequate response, patients were tested for both serum drug level and antidrug antibodies level. At the next reevaluation, patients retreated with RTX that had detectable drug level had a better EULAR response (P=0.038) with lower DAS28 and SDAI scores (P=0.01andP=0.03). The same tendency was observed in patients treated with IFX and ETN regarding EULAR response (P=0.002andP=0.023), DAS28 score (P=0.002andP=0.003), and SDAI score (P=0.001andP=0.026). Detectable biologic drug levels correlated with a better clinical response in patients experiencing their first RA inadequate response while being on a stable biologic treatment with RTX, IFX, and ETN.