pharmacokinetics FOM

Question 1

How are enteral formulations administered?

Answer 1

• mostly oral but also sublingual and rectal

Question 2

Example of enteral formulation

Answer 2

• tablet: compressed. has enteric coating which prevents disintegration until passage through stomach
• extended/sustained/modified release, have permeable coating allowing slow release from osmotic core

Question 3

How are parenteral formulations administered?

Answer 3

• straight into vein, skin, muscle

Question 4

Examples of topical formulations

Answer 4

• cutaneous: cream, ointment, gel ,paste
• inhaled: MDI, nebuliser
• eye drops, nasal sprays, suppositories, dermal implants

Question 5

What state can drugs cross the lipid membrane?

Answer 5

• non-ionised

Question 6

How is non-ionised state achieved by drug?

Answer 6

• acid drug in basic environment
• basic drug in acidic environment

Question 7

What is bioavailability?

Answer 7

• fraction of administered dose reaching general circulation unchanged

Question 8

How is bioavailable dose worked out?

Answer 8

• administered dose x bioavailability

Question 9

What is volume of distribution?

Answer 9

• volume of plasma in which the total amount of drug would need to be dissolved to give observed drug conc.in blood or plasma
• relatively fixed characteristic for each drug and is independent of drug dose
• units are litres but is often expressed per body weight to compare individuals

Question 10

What is the main organ involved in metabolism?

Answer 10

• liver: catabolises lipophilic drugs typically inactive and water-soluble metabolites

Question 11

Why is the rate of elimination important?

Answer 11

• determines the rate of drug administration needed to maintain drug concentration in the body

Question 12

What are the two phases of drug metabolism?

Answer 12

• phase 1: inactivation
• phase 2: conjugation

Question 13

What occurs in phase 1 of drug metabolism?

Answer 13

• drugs undergo chemical modification by CYP450 enzymes by addition or exposure to functional groups
• purpose is to drug more water-soluble

Question 14

What occurs in phase 2 of drug metabolism?

Answer 14

• become chemically linked to larger, more water-soluble molecules
• increases drug’s water solubility for faster elimination from body

Question 15

Describe the first pass effect

Answer 15

• when passing through liver, enzymes may metabolise a significant portion of the drug before it reaches the bloodstream
• can reduce bioavailability of certain orally administered drugs

Question 16

What is a prodrug?

Answer 16

• drug administered inactive with metabolism needed to activate them

Question 17

Examples of routes excretion

Answer 17

• pulmonary, renal, faecal
• glomerular filtration, reabsorption and secretion

Question 18

What are the different pharmacodynamic effects?

Answer 18

• additive: overall effect is sum of each effect
• synergistic: overall effect is greater than additive
• antagonistic: overall effect is less than additive some of each drug

Question 19

What are zero-order kinetics?

Answer 19

• constant amount of drug is eliminated from body over given amount of time
• regardless of plasma conc.
• fixed amount of drug is metabolised/excreted per unit time

Question 20

What are first-order kinetics?

Answer 20

• proportionally increase elimination as plasma conc. increases
• constant fraction % of drug is eliminated per unit time in a particular organ

Question 21

What is clearance?

Answer 21

• volume of blood from which all drug is cleared per unit of time in a particular organ
• constant for particular drug and independent of drug dose