Basic Pharmacokinetic Parameters Flashcards
(14 cards)
What is Biopharmaceutics?
Biopharmaceutics examines how a drugs formulation influences its absorption and availability in the body.
What is Pharmacokinetics?
Pharmacokinetics explores the bodys handling of a drug, encompassing absorption, distribution, metabolism, and excretion.
What is pharmacodynamics?
Pharmacodynamics is the study of how drugs interact with the body to produce effects at a molecular level.
What is Cmax?
Cmax is the peak (max) plasma concentration reached in the body post administration of a drug. For many drugs the Cmax is related to the therapeutic benefit and/or the likelihood of adverse effects.
What is Tmax?
Tmax is the time it takes to reach the maximum plasma concentration (Cmax). Calculating Tmax can help to predict how long it might take to provide max therapeutic benefit or AE’s.
What is Half-life?
Half-life is defined as the time taken for the amount of drug in the body (or the plasma concentration) to fall by half. This is useful for calculating when repeat doses should be given and how long a medicine with persist in the body. It is applied to drugs that follow first order kinetics but NOT zero order kinetics.
How do you calculate Half-life?
There are several ways to calculate half life: you can use the elimination rate constant (multiple equations available).
What is the area under the curve (AUC)?
The AUC calculates the total exposure to a drug that the body receives. It is calculated using a concentration Vs time graph.
What is steady state concentration (Css)?
Steady state concentration is the drug concentration achieved when the amount of drug entering the body is equivalent to the amount of drug being excreted (i.e. drug in = drug out).
How long does it take to achieve Css?
It takes generally 4-5 half-lives of continuous dosing (or at least chronic doing every half-life) to reach Css. NOTE that if there is a dose change it will take 4-5 half-lives for a new Css to be achieved.
What are the important factors to consider before providing a loading dose?
- The drug should have a direct mechanism of action. Drugs with an indirect mechanism of action (e.g. SSRIs) are unlikely to be more effective when given as a loading dose.
- Loading doses are associated with an increased risk of adverse effects. We need to consider whether the risk of adverse effects outweighs the potential.
- Only certain clinical scenarios will require a fast onset of action. We need to balance the risk of adverse effects against the potential benefit.
For which drugs is it particularly important to consider fluctuations in concentration?
- Require a steady drug concentration (i.e., minimal fluctuations in concentration)
- Have a direct and reversible mechanism of action
- Have a narrow therapeutic index
How can we reduce fluctuation in concentration?
- Evenly space dosing
- Using a controlled-release product
- Using a medication in the same therapeutic drug class that has a longer half-life (e.g. pravastatin versus atorvastatin)
What is dose forgiveness?
- Dose forgiveness is the difference between the medications post-dose duration of beneficial action and the prescribed dosing interval (i.e. it relates to how many doses can be skipped (or forgotten) without causing a detectable disease relapse).
