DEFINE BIOAVAILABILITY:
it is percentage of drug reach systemic circulation and
become
available to do biological effects.-particle size
2-PHARMACEUTICAL FACTORS
-Dosage form and formulation variables
-Dissolution rate
3-PHYSIOLOGICAL FACTORS
-Effect of GIT fluids
-GI Transit
-First pass effect
-Absorbing surface
-Diseased state
Physical factors
pka : at pH = to pKa 50% of ionized form drug and 50% of
unionized form of drug which is readily absorbed.Pharmaceutical factors
-Dosage form and formulation variables
Absorption of aqueous solution >oily solution>oral solid
dosage form
-Dissolution rate : increase in dissolution rate lead to
increase of bioavailability
Physiological factors
-effect of GIT fluids
Mucin forms complex with some drugs lead to
decrease bioavailability.-GI transit time
Delyed gastric emptying time lead to reduced
absorption of aspirin
Food lead to prolong gastric emptying time
Food decrease absorption of amoxil, penicillin and
cephalexin.Some drugs that are greatly effected by first pass
metabolism:
Morphine, Propranolol, Diazepam, Midazolam,
Cimetidine, Lidocaine.First pass effect via hepatic portal system
Lead to small fraction of drug reach systemic
circulation.means reduced bioavailabilty.FACTORS AFFECTING BIOAVAILABILITY:
1-PHYSICAL FACTORS
-pKa
-partition coefficient.E,g Griesofulvin.