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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.

DEFINE BIOAVAILABILITY:
it is percentage of drug reach systemic circulation and
become
available to do biological effects.
First Pass Metabolism
• It is metabolism of some drugs before reaching
systemic circulation, sites
• * hepatic site
• *Pulmonary site
• *intestine site.
• Liver is a major site of drug metabolism by oral route.
• Alternate routes to avoids first pass metabolism
1- suppositories. 2-I.V 3-I.M
4-Aerosols 5-T.D.D.S 5- Subligual
By above routes drug absorbed directly and reach to
systemic circulation and avoid 1st pass effect.
Some drugs that are greatly effected by first pass
metabolism:
Morphine, Propranolol, Diazepam, Midazolam,
Cimetidine, Lidocaine.
FACTORS AFFECTING BIOAVAILABILITY:
1-PHYSICAL FACTORS
-pKa
-partition coefficient.
-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.
Partition coeficient increase lead to absorption increase
then bioavailability increase.
Particle size: decrease in particle size lead to increase in
surface area lead to increase in dissolution rate ,increase in
dissolution rate lead to increase in bioavailability.
E,g Griesofulvin.
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.
First pass effect via hepatic portal system
Lead to small fraction of drug reach systemic
circulation.means reduced bioavailabilty.
Absorbing surface
Skin is poor absorbing surface as compared to GI
Sublingual route faster absorption
Intestine large surface area more absorption as compared
to stomach
Diseases state
Drugs excreted through kidney lead to bioavailabilty
increases in kidney failure.
Drugs excreted through liver lead to bioavailability
increases in liver dysfunction
So dose adjusment is needed for these two cases.