Pharmacokinetics

Question 1

Describe the route of administration of drugs through the body

Answer 1

Inhalation, ingestion, intravenous, dermal, subcutaneous, muscular

External: via GI
Paraentral: everything else

Salbutamol: inhalation
Betnovate: steroid cream
Cannabis: systemic

Question 2

Describe the absorption mechanism of drugs

Answer 2

Drugs move around in two ways: bulk flow transport (blood) and diffusional transport (over short distances)

Drugs can cross membranes via diffusion, active and Pinocytosis

Bulk flow: drug goes down GI to liver via hepatic portal system and then diffuse into intestinal capillary and join bulk flow

Most drugs are either weak acids or bases. Ionisation state is dependent on PH therefore drugs exist as pola r and non polar.

Eg aspirin and morphine.

Question 3

Describe the factors influencing drug absorption

Answer 3

1. Regional blood flow
2. Extra cellular binding (plasma protein bound) eg warfarin
3. Capillary permeability (water filled gaps allow ionised )
4. Localisation in tissue (drugs that are lipophilic sit in fatty tissue eg LA).

Question 4

Describe the two major routes for excretion

Answer 4

1. Kidneys ionised drugs stay in urine and can’t diffuse out (+ transporters) in PCT there is active secretion of acids and base, in PCT AND DCT lipid soluble is reabsorption.
2. Liver - biliary excretion for large molecules, active transport system into bile acids and glucorinides blood via hepatocytes then via faces. However enterohepatic cycling may occur