The blood-to-plasma ratio is important for understanding and predicting the concentration of a drug in the blood, and the blood-to-plasma ratio (Rb) is defined as Cb (the blood concentration of the compound) / Cp (the compound’s plasma concentration). It is an important clinical parameter for the calculation of pharmacokinetic (PK) parameters based on blood concentrations and those based on plasma concentrations.
The ratio of blood to plasma determines the concentration of the drug in whole blood compared to plasma and provides an indication of drug binding to erythrocytes, some compounds may have a high affinity for the erythrocyte fraction of whole blood and therefore have a larger blood compared to plasma concentrations. For this class of compounds, PK parameters (eg, blood clearance) determined from plasma data can be misleading; therefore, PK parameters need to be determined by analyzing whole blood rather than plasma. BPP is usually reflected by red blood cell partition (RBC partition), which indicates the degree of drug accumulation in red blood cells.
The meaning of blood plasma ratio
Pharmacokinetic parameters are usually determined by analyzing drug concentrations in plasma rather than whole blood.
Parameters determined using plasma data may be misleading if drug concentrations between plasma and red blood cells differ due to different binding to specific components in the blood.
The blood-to-plasma ratio determines the concentration of the drug in whole blood compared to plasma and provides an indication of the drug’s binding to red blood cells.
When the blood-to-plasma ratio is greater than 1 (usually due to drug distribution into red blood cells), plasma clearance significantly overestimates blood clearance and may exceed hepatic blood flow.
The blood-to-plasma ratio is an important parameter combined with other ADMEs and physicochemical properties to predict systemic pharmacokinetics.
Why is the blood to plasma ratio important?
Calculation of pharmacokinetic parameters is usually performed by analyzing drug concentrations in plasma rather than whole blood. Therefore, pharmacokinetic parameters calculated from plasma data may be misleading if there are differences between the concentrations of the drug in plasma and red blood cells due to different binding to specific components in the blood. When the blood-to-plasma ratio is greater than 1 (usually due to drug distribution into red blood cells), plasma clearance significantly overestimates blood clearance and may exceed hepatic blood flow. Blood to plasma ratio can also be used to understand potential blood toxicity.
Axispharm provides blood plasma ratio measurement services to understand drug distribution in red blood cells and plasma. We regularly measure and compare K-RBC/PL from the following species: mice, mice, dogs, monkeys, humans.
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Blood to Plasma Ratio