What is a two-compartment model?

A two-compartment pharmacokinetic model divides the body into two theoretical spaces:

• Central Compartment (Vc): Represents blood and highly perfused tissues (heart, lungs, kidneys, liver). Drug is administered here and measurements are taken from here.
• Peripheral Compartment (Vp): Represents less perfused tissues (muscle, fat). Drug distributes slowly between central and peripheral compartments.

Key Parameters:

• Vc (L): Volume of the central compartment, calculated as Vc Coefficient × Weight
• Vp (L): Volume of the peripheral compartment
• Q (L/hr): Inter-compartmental clearance - rate of drug transfer between compartments
• CL (L/hr): Total body clearance - rate of permanent drug elimination from the central compartment

Clinical Significance:

Two-compartment models better characterize drugs with significant peripheral distribution like vancomycin and aminoglycosides. They accurately predict the initial distribution phase (rapid decline after infusion) and the terminal elimination phase (slower decline during the dosing interval). This is critical for AUC-guided dosing and extended-interval aminoglycoside protocols.

Available Models:

• Goti Model: Published population parameters for vancomycin with Vc coefficient 0.8343 L/kg, Vp 38.4 L, Q 6.5 L/hr
• Carreno Model: Alternative population parameters derived from obese patients (BMI ≥40, reference weight 110 kg) with Vc coefficient 0.234 L/kg (25.76 L at 110 kg), Vp 40.96 L, Q 58.99 L/hr