Mod 3 - Pharmacokinetics: the study of the movement of drug molecules
Excretion
Feces
Exact reversal of duodenal absorption
Intact molecules cross the membrane and are immediately ionized
Urine
Active Transport
penicillins and cephalosporins.
slow penicillin’s rate of excretion by giving the patient probenecid
Affected by lipophilicity, protein binding and ionization.
KIDNEY
kidney excretes and retrieves
Re-collects water, glucose, back sodium, potassium, etc
20% free flowing through glomerulus
Transport across lipid membrane
Types of cell transport/passage
Factors that affect transport and passage
Affinity for protein molecules
serum proteins (albumin)
When a molecule that is bound to a protein molecule is going to be temporarily tied up and not available for transport.
Lipophilicity
(hydrophilic) will never get into the lipid membrane.
Tendency to ionize
Urine has highest variability
heavily defined by the pH
Ionized molecules cannot cross lipid membranes.
Oral antifungals are too big to get through. they remain in stomach. this is used to our advantage
Slip through holes
Actively transported across the membrane by enzyme systems.
Passive diffusion
Absorbed through gut wall
complications:
may be lost to bile circulation
may require reabsorption to reach heart and become systemic
much gets excreted w/o being absorbed
capillaries and venules --> Liver --> heart --> lungs -->back to the heart --> systemic circulation
