Absorption and administration Flashcards
What form does the drug have to be in in order to be absorbed by the GI tract?
Unionised, it is more lipophilic.
What is the pH of stomach contents?
1.0-3.0
What is the pH of the small intestine?
4.8-7.6
What is the pH of the large intestine?
7.6-8.0
What two factors does the extent of ionisation depend on?
- The pH of the solution, the acid or the base it is dissolved in
- On the strength of the weak acid or base
What is the strength of the acid or base measured by?
pKa
What does it mean if the pH and pKa values are the same?
Half the molecules will be ionised and half will be unionised.
What form will many weak acids exist in the stomach?
Unionised
What environment will weak acids be preferentially absorbed by?
Acidic
Why is the main site for absorption the small intestine?
Largest SA
Thinnest membrane
Highest blood flow
give the name for an ATP powered efflux pump
P-glycoprotein
Where is P-glycoprotein found?
Apical surface epithelial cells of the small intestine
What does P-glycoprotein do?
Pumps a wide range of drug substrates out of the cell and back into the gut lumen, reducing permeability.
What sort of diffusion is absorption normally?
Transcellular passive diffusion
How else can drugs be absorbed other than trancellular passive diffusion?
Carrier-mediated transport
Give an example of a drug absorbed by carrier mediated transport and why it can be
L-DOPA (treating Parkinson’s disease), its an amino acid and the body has evolved to absorb them from the gut lumen.
What is the transporter for penicillins and cephalosporins?
Oligopeptide transporter
What is the transporter for privastatin (antihyperlipidaemic agent)?
Monocarboxylic acid transporters
What is the transporter for Iron?
Divalent metal transporter and bound to haem by the haem carrier protein
Where do drugs go once they have passed from the GI tract?
Enter the hepatic portal vein, to the liver and then to the inferior vena cava.
What are the 3 major metabolic barriers for oral drugs?
- Intestinal lumen (digestive enzymes)
- Intestinal wall (intestinal first pass metabolism)
- The liver (hepatic first pass metabolism)
Why is it called the first pass effect?
It occurs on the first passage of the drug from the gut lumen into the body
What is sublingual drug administration?
Drug is placed under the tongue and sucked.
Why is absorption from sublingual drug administration rapid?
Good blood supply under the tongue, which drains into the jugular vein and then into the heart
When is rectal drug administration useful?
When oral route is compromised.
describe I.V. administration.
- 100% bioavailable
- Risks, requires supervised care and only used when necessary
- Useful in emergency situations due to immediate onset
Where is the drug placed in I.M. and S.C. administration?
Connective tissue matrix
What is the form of absorption into the blood and lymphatic vessels?
Paracellular passive diffusion
Give 2 disadvantages of using I.M and S.C administration
- Invasive, may require supervised care
2. Costly in comparison with oral drugs.
What is lung parenchyma?
Term used to describe the functioning parts of the lung
What does intranasal administration allow?
Direct absorption into the systematic circulation via the jugular vein, may enable drugs to cross the brain barrier
What is tropical administration?
Local effects, drug is applied directly to the site.
What is transdermal administration?
Patches-a depot of drug targeted for systematic absorption, must be lipid soluble.
