Drug Absorption

Question 1

Define bioavailabilty

Answer 1

Fraction of unchanged drug that reaches the systemic circulation

Question 2

Define Bioequivalence

Answer 2

Generic vs Theraputic substitutions

Question 3

What is a generic subsitution?

Answer 3

It is when a different formulation of the same drug is substituted. They must have a bioavailability of 80-125% compared to the reference product

Question 4

What is theraputic substitution?

Answer 4

Replacement of the originally-prescribed drug with an alternative molecule with assumed equivalent theraputic effect

Question 5

What are the advantages and disadvantages of the oral route?

Answer 5

A - Cheap, safe and convenient.

D - Patient compliance and variation in bioavailability of drug

Question 6

Describe the journey of an oral drug into the systemic circulation

Answer 6

Some of the dose will be destroyed by the gut, some won’t be absorbed, some will be destroyed by the gut wall, some will be destroyed by the liver and then it will enter the systemic circulation.

Question 7

Describe the buccal/sublingual mucosa routes?

Answer 7

It allows for direct absorption into the bloodstream, avoids first pass metabolism but it is not ideal for surface absorption

Question 8

Describe where weak acids/bases are ionised and where they are absorbed

Answer 8

Weak bases - Ionised in acidic pH and are absorbed in the small intestines.
Weak acids - Unionised in acidic pH but are also absorbed in small intestines due to the large surface area in the intestines

Question 9

What is the Henderson-Hasselbalch equation?

Answer 9

pKa - pH = log(10) ionised/unionised.

Question 10

Describe the effect of food on drug absorbtion

Answer 10

• No effect,
• Cause decreased absorption due to increased motility, interactions with food and presystemic metabolism,
• Delayed absorption due to gastric emptying and the Cmax may decrease.
• Increased absorption (poorly water soluble drugs) due to increased solubilisation

Question 11

What are some of the additional considerations for the effects of food on the GI?

Answer 11

Type of meal - Solid v liquid, protein and fat content and other dietary factors. Also is the drug a GI irritant

Question 12

What is first pass metabolism?

Answer 12

Some of the drug is absorbed from the GI tract and passed into the liver via the portal vein where some of the drug is metabolised. Therefore only a proportion reaches systemic circulation.

Question 13

Explain how drugs interactions can effect absorption

Answer 13

Drugs can alter the ability for other drugs to be absorped, for example. Antacids and PPIs change the gastric and intestinal pH. Laxitives/anticholinergics change GI motility. Vasodilators change GI perfusion

Question 14

Explain how GI motility can be effected by intestinal disease

Answer 14

• Altered rate of drug absorption due to disease state eg, increased GI motility or compromised GI integrity

Question 15

What are the physiochemical factors?

Answer 15

Direct drug interactions, dietary factors and varying pH

Question 16

Name some parenteral routes and their features.

Answer 16

• Subcutaneous (slow absorption dur to blood flow),
• IM (lipophilic drugs rapidly and polar drugs via bulk flow and endothelial junctions) Rate of onset changed by extent of capillary perfusion, drug vehicle.

Question 17

Describe features of inhalation route

Answer 17

• Will effect alveolar epithelium and bronchial mucosa.
• Systemic effects - Lipid-soluble drugs, drugs of abuse and accidental poisoning.
• Local effects - Modify structure, particulate size, selectivity for receptors and rapidly broken-down in circulation.

Question 18

Describe features of intranasal route

Answer 18

Advantages - Avoids hepatic first pass metabolism, easy convenience and saftey.
Disadvantages - Limited drugs suitable

Question 19

Describe features of the topical route

Answer 19

Local effects - corticosteroids for eczema, antihistamine cream for insect bites and local anaesthetics.
Systemic effects - Transdermal patches and accidental poisoning.