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Flashcards in Clinical Applications of Pharmacokinetics Cont. Deck (12):

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


One-compartment model

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


Steady state

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?

  • drugs with narrow therapeutic ranges
  • expected or desired effect of drug is not observed
  • patient has physiological condition that affects therapeutic activity of the drug (i.e. renal insufficiency)