Plasma Protein Binding Calculator
Calculate plasma fraction unbound, protein binding, and recovery from equilibrium-dialysis concentrations.
Plasma protein binding results
Enter valid concentrations and volumes.
For equilibrium dialysis, use buffer and plasma concentrations quantified in the same analytical units after equilibrium. Separately review pH, temperature, equilibration time, volume shift, nonspecific binding, stability, matrix effects, and LOQ. Diluted plasma or tissue homogenate requires a separate dilution correction that this tool does not apply automatically.
Sources: FDA clinical pharmacology reviews; equilibrium dialysis and mass-balance methods (PMCID: PMC3545278).
Tool Guide
Definition
Plasma Protein Binding Calculator — After equilibrium dialysis, divide the unbound drug concentration in buffer (Cᵤ) by the plasma concentration (Cₚ) to calculate plasma fraction unbound (fu,p), unbound percent, and protein-bound percent. Optional initial and final compartment volumes provide mass-balance recovery.
Purpose
(1) Cross-check equilibrium-dialysis PPB results (2) Convert between fu,p and percent protein bound (3) Calculate mass-balance recovery across mixed µL and mL volumes (4) Prepare PK-report values and flag analytical anomalies
How to Use
① Enter post-dialysis plasma Cₚ and buffer Cᵤ in the same concentration unit. ② For recovery, add initial plasma C₀ and initial/post-dialysis compartment volumes. ③ Copy fu,p, unbound percent, protein-bound percent, and recovery. Dilution correction for diluted plasma or tissue homogenate is not included. Separately review pH, temperature, equilibrium, volume shift, nonspecific binding, stability, matrix effects, and LOQ.
Examples
Example) Post-dialysis Cₚ=9 µM and Cᵤ=1 µM → fu,p=0.1111, unbound=11.1111%, protein bound=88.8889% With initial C₀=10 µM, initial plasma=150 µL, post-dialysis plasma=150 µL, and buffer=150 µL → mass-balance recovery=100% The calculator does not correct fu>1 or abnormal recovery automatically; review analytical conditions.