Least-Squares Regression Model Calculations
Phoenix includes a library of nineteen pharmacokinetic (PK) models. The PK models are one to three compartment models with intravenous or first-order absorption, and can be used with or without a lag time to the start of absorption. For more on Phoenix’s PK models, see the “Pharmacokinetic models” section.
Phoenix includes a library of eight pharmacodynamic (PD) models. The PD models include simple and sigmoidal Emax models, and inhibitory effect models. For more on Phoenix’s PD models, see the “Pharmacodynamic models” section.
Phoenix’s Michaelis-Menten models are one-compartment models with intravenous or 1st order absorption, and can be used with or without a lag time to the start of absorption. For more on Phoenix’s Michaelis-Menten models, see the “Michaelis-Menten models” section. Information on required constants is available in the “Dosing constants for Michaelis-Menten models” section.
Indirect Pharmacodynamic Response Models
Four basic models have been developed for characterizing indirect pharmacodynamic responses after drug administration. These models are based on the effects (inhibition or stimulation) that drugs have on the factors controlling either the input or the dissipation of drug response. See the “Indirect Response models” section for more details.
When pharmacological effects are seen immediately and are directly related to the drug concentration, a pharmacodynamic model is applied to characterize the relationship between drug concentrations and effect. When the pharmacologic response takes time to develop and the observed response is not directly related to plasma concentrations of the drug a linked model is usually applied to relate the pharmacokinetics of the drug to its pharmacodynamics.
The PK/PD linked models can use any combination of Phoenix’s Pharmacokinetic models and Pharmacodynamic models. The PK model is used to predict concentrations, and these concentrations are then used as input to the PD model. This means that the PK data are not modeled, so the linked PK/PD models treat the pharmacokinetic parameters as fixed, and generate concentrations at the effect site to be used by the PD model. Model parameter information is required for the PK model in order to simulate the concentration data. Refer to the “PD output parameters in a PK-PD model” section for parameter details.
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