Mod 3 - Pharmacokinetics: the study of the movement of drug molecules

capillaries and venules --> Liver --> heart --> lungs -->back to the heart --> systemic circulation

complications:

much gets excreted w/o being absorbed

may require reabsorption to reach heart and become systemic

may be lost to bile circulation

Passive diffusion

Actively transported across the membrane by enzyme systems.

Slip through holes

Oral antifungals are too big to get through. they remain in stomach. this is used to our advantage

Factors that affect transport and passage

Tendency to ionize

Ionized molecules cannot cross lipid membranes.

heavily defined by the pH

Urine has highest variability

Lipophilicity

(hydrophilic) will never get into the lipid membrane.

Affinity for protein molecules

When a molecule that is bound to a protein molecule is going to be temporarily tied up and not available for transport.

serum proteins (albumin)

KIDNEY

20% free flowing through glomerulus

kidney excretes and retrieves

Re-collects water, glucose, back sodium, potassium, etc

Affected by lipophilicity, protein binding and ionization.

Urine

Active Transport

penicillins and cephalosporins.

slow penicillin’s rate of excretion by giving the patient probenecid

Feces

Exact reversal of duodenal absorption

Intact molecules cross the membrane and are immediately ionized