9. Pharmacokinetics I Flashcards
Name the 4 Key Pharmacokinetic Processes.
-Absorption.
-Distribution.
-Metabolism.
-Excretion.
Describe Absorption.
-The processes that take place between the site of administration and the site of measurement.
Describe the 3 ways Drugs pass through membranes into the general circulation.
Through membrane pores they need low molecular weight or small ions.
Diffusion through the membrane they need to be lipid soluble.
Carrier mediated, these drugs must resemble the natural ligand or substrate.
Name 5 factors effecting absorption.
-Lipid solubility.
-ionisation
-Formulation
-gatro intestinal function
-First pass mechanism
Describe how lipid solubility effects Absorption.
high lipid solubility it will rapidly absorb in gut and get into circulation but slow from intra-muscular injections.
Describe how ionization effects Absorption.
if largely ionised poorly absorbed in gut, different sections of the body have different pH so can effect how they move
Describe how Formulation effects Absorption.
-Drugs need to be able to dissolve for rapid and extensive absorption.
-Smaller drugs with a larger surface area can dissolve quickly.
-Two types of formulation conventional where it is absorbed quickly and is eliminated quickly, and Sustained release where it is absorbed slowly and stays in the therapeutic range for longer.
Describe how Gastro-intestinal effects Absorption.
-Gastric emptying is the process of food leaving the stomach and entering the intestines.
-Drugs are absorbed much faster in the intestines than the stomach so if a meal has been eaten a little before the drug is taken then it can be absorbed faster.
Describe how First pass metabolism effects Absorption.
-Drugs taken orally have to pass through the gut and liver first which can remove a lot of the drug initially.
Each have many enzymes that will change the conformation of the drug, if lots is eliminated will reduce absorption
