Target-Mediated Drug Disposition
Also known as: TMDD, target-driven clearance
Target-mediated drug disposition (TMDD) is a mechanistic framework describing nonlinear pharmacokinetics arising from drug binding to a target receptor or protein. Developed by Mager and Jusko in 2001, TMDD explains saturable clearance, dose-dependent half-lives, and time-dependent changes in plasma concentrations observed with protein therapeutics and some small-molecule drugs.
Key highlights
- Mechanistically sound approach explicitly modeling drug-target binding and its impact on clearance
- Explains nonlinear PK and dose-dependent half-lives arising from target saturation
- Enables rational dose optimization by identifying saturation regimes and free drug target
- Applicable across diverse drug classes (proteins, small molecules) with target-driven clearance
Intuition
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How it works
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When to use it
Use TMDD modeling for antibodies, cytokines, and receptor-binding protein therapeutics that exhibit nonlinear PK. Also applies to small-molecule drugs with very high target affinity or when target depletion affects clearance.
Strengths & limitations
- Mechanistically sound approach explicitly modeling drug-target binding and its impact on clearance
- Explains nonlinear PK and dose-dependent half-lives arising from target saturation
- Enables rational dose optimization by identifying saturation regimes and free drug target
- Applicable across diverse drug classes (proteins, small molecules) with target-driven clearance
- Requires target protein expression data (concentration, turnover) which is often unavailable
- Fit complexity increases with number of parameters; risk of overfit without adequate data and constraints
- Assumes simple binding model; does not account for multiple target populations or allosteric effects
- Difficult to distinguish TMDD from other nonlinear clearance mechanisms without target occupancy measurements
Common pitfalls
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Applications
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Frequently asked
What is the difference between TMDD and linear pharmacokinetics?
Linear PK assumes clearance is independent of dose; doubling dose doubles exposure. TMDD arises when drug binds its target; at low doses more drug is bound (slow clearance), at high doses less is bound (fast clearance). This saturation creates nonlinear, dose-dependent PK.
How do I know if my drug exhibits TMDD?
Signs include non-proportional dose escalation (doubling dose increases exposure more than 2-fold), dose-dependent half-life (longer at lower doses), or biexponential (or more complex) disposition. These observations suggest target-mediated mechanism; confirm with target occupancy data if possible.
What parameters define TMDD?
Key parameters are Kd (drug-target dissociation constant; lower = tighter binding), Kon (binding rate), Koff (dissociation rate), target concentration, and target turnover rate. These mechanistic parameters control the degree and dose-dependence of nonlinearity.
Can TMDD occur with small-molecule drugs?
Yes, if the small molecule has very high target affinity (low Kd) and the target is not highly expressed. However, TMDD is most common in protein therapeutics where high affinity and large target concentration produce pronounced nonlinearity.
Sources
- 1.Mager, D. E., & Jusko, W. J. (2001). General pharmacokinetic model for drugs exhibiting target-mediated drug disposition. Journal of Pharmacokinetics and Pharmacodynamics, 28(6), 507-532.
- 2.Levy, G. (2004). Carrier-mediated active transport: pharmacokinetic consequences and examples in humans. Clinical Pharmacokinetics, 37(6), 429-445.
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Cite this page
ScholarGate. (2026, June 3). Target-Mediated Drug Disposition. ScholarGate. https://scholargate.app/pharmacology/target-mediated-drug-disposition