Pharmacology 3620 Lecture Notes - Lecture 10: Enteric Coating, Grapefruit Juice, Intravenous Therapy
1 May 2018
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Lecture 010: Routes of Administration
Objectives
● Describe what happens after a drug is administered orally
● Describe why some drugs must be administered with food and others must be taken on
an empty stomach
● Describe the advantages and disadvantages of various routes of drug administration
● Identify the impact of blood flow and solubility on drug absorption
● Identify factors that influence drug absorption in each of the routes of administration
Oral Drug Administration
● Most common route of drug administration
● Advantages
○ Cheap, easy, safe
● Disadvantages
○ Incomplete or variable absorption
○ Interactions with food
○ Not practical in unconscious patients
● Following oral administration, drugs pass through the esophagus and into the stomach
● Drug absorption in the stomach is minimal due to:
○ Small available surface area
○ Lining of the stomach is covered by a mucous layer
● Majority of drug absorption occurs in the small intestines
○ Due to large surface area provided by the villi
○ Also the site of most of the nutrient absorption
● Drug absorbed from the intention is carried by the portal circulation to the liver
○ Liver is the primary side of drug metabolism
● Why some orally administered drug undergo a large degree of first pass metabolism
○ Relatively predictable, so dose can be adjusted accordingly
○ However, this can become a problem if the metabolism is reduced
■ Grapefruit juice
Enteric Coating
● A special coating on drugs that prevents the disintegration in acidic environment (i.e. the
stomach)
● As enteric coated drugs move from the acidic stomach into the more alkaline duodenum,
the enteric coating dissolves
○ Promoted by the increase in pH
● Drugs that are irritant to the stomach or degraded in the acid environment may be
enteric coated
● Drugs that change the pH of the stomach (i.e. antacids, proton pump inhibitors) can
cause premature disintegration of the enteric coating
○ Problematic!
Rectal
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Document Summary
Describe what happens after a drug is administered orally. Describe why some drugs must be administered with food and others must be taken on an empty stomach. Describe the advantages and disadvantages of various routes of drug administration. Identify the impact of blood flow and solubility on drug absorption. Identify factors that influence drug absorption in each of the routes of administration. Following oral administration, drugs pass through the esophagus and into the stomach. Drug absorption in the stomach is minimal due to: Lining of the stomach is covered by a mucous layer. Majority of drug absorption occurs in the small intestines. Due to large surface area provided by the villi. Also the site of most of the nutrient absorption. Drug absorbed from the intention is carried by the portal circulation to the liver. Liver is the primary side of drug metabolism. Why some orally administered drug undergo a large degree of first pass metabolism.
