Pharmacology - Absorption

Question 1

What is Pharmacokinetics

Answer 1

This is the study of how a drug moves around the body and what the body does to the drug. The usual response would be to remove the drug by metabolising it (breaking it down)

Question 2

What are the 4 phases of Parmocokinetics

Answer 2

Absorbstion
Distribution
Metabolism
Excretion

Question 3

What is Absorbtion give examples of administration

Answer 3

Absorption refers to the Location of Administration of a drug to the bodycirculation system :
Injection
* IV - intravenous (Bloodstream)
* IM - Intramuscular (Muscle area e.g vaccine)
* SQ - Subcutaneous (Fat area e.g Insulin)

Oral/enteral
* PO - Per Oral
* SL - Sublingual (under the tongue)

Rectal
* Per Rectal Suppository

Lungs
* Inhaled (Albuterol or Steroids)

Transderamal
* Skin Absorption (e.g nicotine, fentanyl

Question 4

Give an overview of absorption

Answer 4

• Absorption refers to the location of administration of a drug to the bodys circulation system.
• This can be determined by the chemistry or the size of a molecule
• A cobination of lipid and water loving charecteristics is useuful and can be determined by weak acids and bases
• (e.g. for a drug to dissolve it is helpful if some is charged (ionised) at a given PH) as well as Uncharged (unionised) to facilitate movement across the lipid membrane.

Question 5

What is Bioavailabilty and its significance to Absorption

Answer 5

• Bioavalibilty refers to the fraction of an administered drug that reaches the systemic circulation
• This can be affected by first pass metabolism which is the process which a drug is metabolised at a specific location in the body resulting in a reduced concentration of the drug at the desired site of action
• This should be considered when detremining drug dosage

Absorption - First Pass Metabolism - Bioavalibility

Question 6

What is the Only route to 100% bioavalibility

Answer 6

IV - Intravenous delivery

Question 7

What factors can affect absorption

Answer 7

Plasma protein concentrations
Enzymatic activity
Gastrointestinal movment - Diarhea would decrease the contact time of a drug
Blood flow - Any condition where blood flow is affected will decrease absorption e.g. any shock state, Peripheral Arterial Disease

Question 8

What are the mechanisms of Absorption (How do drugs get across tissue mambranes)

Answer 8

• Passive diffusion (down concentration gradient) e.g small hydrophobic molecule
• Facilitated diffusion (Using Transport Proteins) Larger hydrophilic
• Active transport (Ustalising energy ATP) (Low concetration to High concentration) e.g. Larger Hydrophilic drug against a concentration gradeint
• Bulk Transport (Invagination where cell membrane envelopes a molecule to form a vesicle ENDOCYTOSIS it will then be expelled via exocytosis into the vasculature) drug like B12 which is too big to use active transport

Question 9

What Factors affect Bioavailability

Answer 9

Solubility
e.g. Hydrophobic lipid soluble molecule will pass through a cell membrane easier entering the bloodstream quicker meaning more of the drug is available and increasing the Bioavalbilty

Instability
e.g. The drug itself may have instability in the gi tract due to the acidic environment or the extent of metabolism due to enzymes in the gut, this can impact the bioavilable fraction of the drug

First pass effect
Process which a drug is metabolised at a specific location in the body (Liver) resulting in a reduced concentration of the drug at the desired site of action. e.g. The drug is given orally is absorbed from the GI tract and passes via the portal vein into the liver where some drugs are metabolised. Sometimes the result of first pass metabolism means that only a proportion of the drug reaches the circulation.