Biopharmaceutics and Oral Drug Delivery

Bioavailability

A measure of the quantity of drug which reaches its site of action and the rate at which it gets there.

F = F_a x F_g x F_h

F_a = Fraction absorbed

F_g = Fraction escaping the GI metabolism

F_h = Fraction escaping the hepatic metabolism

F = Net oral bioavailability

Pharmacokinetics

What the body does to the drg

Pharmacodynamics

What the drug does to the body

Determinants of Pharmacokinetics

ADME

Absorption

Distribution

Metabolism

Excretion

What is drug absorption?

The uptake of a non metabolized drug, following its release from its formulation, from the site of delivery to the systemic circulation.

What does drug absorption involve crossing?

A biological barrier

Drug absorption in the GI tract

• Dosage form is swallowed and ends up in the stomach

• Enteric coating around medicine prevents it from dissolving, so medicine passes to the small intestine

• The solid dosage form has to break apart and go to solution. The human body cannot absorb solids.

• Solid dosage form turns to particles in suspension, then becomes molecules in solution, and can then be absorbed across the epithelium (the biological barrier in the GI tract) which can then be absorbed into the blood and transported to the liver

What are some factors that affect absorption of small drugs in the GI tract?

• pH = Ionisation, solubility

• Hydrogen bonding

• Size

• Lipophilicity

Drug Plasma concentration vs Time