Drug Absorption and Bioavailability Flashcards
Oral route:
Most preferred route because of ease of administration
Rapid and complete absorption into blood stream is targeted
The higher the drug concentration….
the greater the magnitude of response
Generally, the more rapid and complete absorption…
The more uniform and reproducible the response
The faster absorption…
the lesser the chance for drug degradation or interaction with GIT constituents.
Transposition of a drug from an oral dosage form into circulation is a four step process:
Delivery of drug to absorption site
Getting drug into solution
Movement of dissolved drug through membranes of gastrointestinal tract
What is the slowest step for transposition of a drug?
The slowest of the 4 steps is the determinant of rate of availability from an oral dosage form.
The intestine is favored over stomach for absoprtion
Surface area is increased and thickness is decreased
Stomach pH
1-3
Ileum pH
7-8
Small Intestine
60% of the length of GIT
Primarily, digestive and absorptive functions
Primary site for drub absorption
Gastric emptying may be the rate limiting step in drub absorption
Factors that affect stomach emptying..
Exercise (light.increase) (Strenous… decrease)
Emotional state
Pathological conditions
Drugs that affect GI motility
Lying on the left side: contents moving uphill due to stomach anatomy
What does the stomach do..?
Stomach protects intestine from extreme conditions
Nitrofurantoin
Antimicrobial for prevention and treatment of UTI’s
Highly soluble in urine in which it may impart a brown color
Available in two forms:
Macrocrystals- more slowly and less completely absorbed
Microcrystals- Absorbed rapidly and completely
Macrodantin
a larger crystal form of Furadantin (nitrofurantoin)
The absorption of this is slower and its excretion is somewhat less when compared to Furadantin
The presence of food or agents delaying gastric emptying can increase…
The bioavailability
Allowing better dissolution in gastric juices
