Flashcards in Pharm Deck (14):
What is a drug?
A chemical substance that interacts with a biological system to produce a physiological effect
Target sites: 4
List routes of administration: groupings
Entral (involves the GI tract): Oral, Rectal, Buccal, Sublingual
Parentral (doesn’t involve the GI tract): Intravenous, Intramuscular, Intradermal, Subcutaneous, Inhalation
What type of drugs will cross membranes?
Non-polar drugs (without charge) will cross the phospholipid bilayer as they are lipophilic (lipid soluble)
Polar drugs (with charge) cannot do this passively (ie. Need transporters)
Tell me about asprin
Aspirin is a weak acid pKa of 3.5
Acidic environment like the stomach pH of 2? has a high h+ concentration so does not need to contribute. Drug is unionised.
Alkaline environment like the intestine? will donate H+ ions and become ionised
Where is it preferentially absorbed?
Factos affecting distribution
Regional blood flow
Localisation in tissue
Kidney (major): Most drugs ultimately eliminated here
Liver: Some drugs excreted here via biliary system (into gut).
Enterohepatic recycling: A drug or its metabolite is reabsorbed in the gut after biliary excretion and taken to the liver via the hepatic portal vein.
AIM OF METABOLISM IS TO Conversion of lipophilic chemicals to polar derivatives (so can’t be reabsorbed in kidney tubule)
First pass metabolism
First pass metabolism is the metabolism of the drug in the body before it reaches the systemic circulation
Phase 1 vs Phase 2 Metabolism
Oxidation/reduction creates new functional groups, hydrolysis unmasks them.
Important – functional group serves as a point of attachment for phase II reactions
Phase I reactions often inactivate chemicals, but can also activate (e.g. a prodrug).
After phase I metabolism, there is little change in polarity of the drug
USUALLY CYTOCHROME P450
Uses conjugating agents
Conjugate is almost always pharmacologically inactive
Easier to excrete
Glucuronidation, Acetylation, Amino acid conjugation, Sulphation, Methylation, Glutathione Conjugation
proportion of administered drug that is available within the body to exert its pharmacological effect
The volume of plasma cleared of a drug per unit time
M1 – Neural
M2 – Cardiac
M3 – Exocrine & smooth muscle