{"title":"Target-Mediated Drug Disposition (TMDD) Revisited: High Versus Low-Affinity Approximations of the TMDD Model.","authors":"Ronny Straube","doi":"10.1002/psp4.70048","DOIUrl":null,"url":null,"abstract":"<p><p>Target-mediated drug disposition (TMDD) is often associated with high-affinity binding to a target resulting in nonlinear pharmacokinetics. For large molecules, such as monoclonal antibodies, this can lead to increased clearance at sub-saturating concentrations. However, for small molecules, target binding can protect the drug from a fast systemic clearance. Here, we show that both types of behaviors can be described by simple expressions arising from a high-affinity approximation of the standard TMDD model. Interestingly, the celebrated Michaelis-Menten (MM) approximation arises in the opposite limit of low affinity and if the systemic drug clearance is sufficiently slow. Our derivation contains a previously missing factor in front of the MM constant that becomes important when target and drug-target complex elimination rates are different. As a measure of target suppression, we also derive simple expressions for the free target to baseline ratio and compare our approximations with data from large and small molecules.</p>","PeriodicalId":10774,"journal":{"name":"CPT: Pharmacometrics & Systems Pharmacology","volume":" ","pages":""},"PeriodicalIF":3.1000,"publicationDate":"2025-05-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"CPT: Pharmacometrics & Systems Pharmacology","FirstCategoryId":"3","ListUrlMain":"https://doi.org/10.1002/psp4.70048","RegionNum":3,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q2","JCRName":"PHARMACOLOGY & PHARMACY","Score":null,"Total":0}
引用次数: 0
Abstract
Target-mediated drug disposition (TMDD) is often associated with high-affinity binding to a target resulting in nonlinear pharmacokinetics. For large molecules, such as monoclonal antibodies, this can lead to increased clearance at sub-saturating concentrations. However, for small molecules, target binding can protect the drug from a fast systemic clearance. Here, we show that both types of behaviors can be described by simple expressions arising from a high-affinity approximation of the standard TMDD model. Interestingly, the celebrated Michaelis-Menten (MM) approximation arises in the opposite limit of low affinity and if the systemic drug clearance is sufficiently slow. Our derivation contains a previously missing factor in front of the MM constant that becomes important when target and drug-target complex elimination rates are different. As a measure of target suppression, we also derive simple expressions for the free target to baseline ratio and compare our approximations with data from large and small molecules.