BiophRmaceutics Flashcards
Which physics chemical factors of th drug will affect absorption?
Solubility and dissolution
Lipid solubility and log p
Molecular weight
Which physiological factors influence absorption from the GI tract?
Surface are of absorption sites Ph of Gi fluids Gastric emptying rate Intestinal motility Chemical degradation in Gi Liver metabolism Diet
Which excipients properties will affect absorption?
Diligent Surfactants Viscosity enhancers Lubricant Binder
What types of dosage form will affect absorption?
Aqueous solution Aqueous suspension Soft gelatin capsule Hard gelatin capsule U coated tablet Coated tablet Enteric/gastrocnemius tang tablet
What is a diffusion layer?
This is formed because of interfacial tension between the drug particle and the liquid. The drug particle must be wetted and dissolve and pass across the diffusion layer before it can be absorbed rom Gi tract.
What is F in bio pharmaceutics?
It is the fraction of administered dose which reaches the systemic circulation.
Where are weak acids and weak bases most soluble?
Weak acids more soluble in intestine than stomach
Weak bases more soluble in stomach than intestines.
How do salt forms of a drug help overcome solubility problems ?
Weak acid becomes a basic salt. This means that when it meets the Gi fluid and forms a diffusion layer, the basic ions cause th oh to increase. This means the drug dissolution rate will increase. When the drug molecules leave the diffusion layer, they are converted back to free acid and precipitate into smaller drug particles.
The same happens in revers for weakly basic molecules
What is the difference between salts and hydrates/solvated?
A solvate/hydrate are produced by recrystallisation in organic solvent or water, where as a salt is in weak acid or base
Solvates/hydrates are usually less soluble in Gi whereas r salts are more soluble
What are the four classes of the biopharmeceutical classification system in terms of solubility,permeability and bioavalibility?
The two measures used are solubility IE water in Gi fluid and permeability IE lipid solubility in membranes.
Class 1 have high permeability and high solubility so has a high bioavalibility.
Class 2 has high permeability but poor solubility and so bioavalibility is limite by dissolution rate in GI fluid
Class 3 have low permeability and high solubility so their bioavalibility is limited by their permeability through the membrane
Class 4 have low permeability and solubility so their bioavalibility is low.
Where will acids and bases be more ionized?
Acid will be more ionized above their pKA and bases will be more ionized below their PKA.
The ionized forms are hydrophilic, and unionized are lipophilic therefore their dissolution rate is dictated by what proportion of the drug is ionized, and absorption is dictated by what proportion is unionized.
