Multi-Dose Treatment Regimens
Many drugs are administered repeatedly over an extended period of time, with the goal to achieve and maintain an effective drug level without causing harm to the animal "Goldilocks or Just Right" Zone - balance b/t adverse/toxic effects and lack of therapeutic efficacy
Half life of a drug is dependent upon which two things?
Clearance and volume of distribution T1/2 = 0.693*Vd/Clb Half-life is useful to estimate time that a drug will stay in a therapeutic range
Factors affecting Vd
Aging = possible decrease Obesity = greater distribution into adipose Ascites = greater distribution into fluid
Describes distribution and elimination after an IV bolus dose; entire body viewed as one single compartment -follows first order kinetics
Two compartment model
Includes a peripheral compartment that drugs may distribute to
Central = blood and well-perfused organs
Peripheral = poorly perfused tissues
Describes the plasma drug concentration that is reached when the rate of drug entry into the body and the rate of drug elimination equal one another
The time it takes a drug to achieve steady state concentrations in the plasma is solely dependent on _________________
The half-life of the drug
How many half lives of sustained drug administration does it take for a drug to achieve a steady state?
At what point is the next dose in a multi-dose treatment given?
When the previous dose has reached its half life
How can you achieve steady state more rapidly?
- Provide a loading dose (Vd * Cpss)
- Shorten the dosage interval (small fluctuations)
- Slow absorption (e.g. PO)
- Renal insufficiency
Therapeutic drug monitoring
Drug concentrations are measured in the patient, using pharmacokinetics to analyze blood plasma concentrations and make drug dosage adjustments
When do you use therapeutic drug monitoring?