Special populations: drug interactions

Question 1

List the different populations that may require special consideration when prescribing.

Answer 1

• Drug companies design PIII studies to be successful. Therefore, often does not reflect the real-world patient.
• Groups:
  1. Children
  2. Women
  3. Pregnant women
  4. Elderly
  5. Ethnic groups
  6. Patients with other diseases – Patients on other medications

Question 2

How these populations can differ in their response to drugs.

Answer 2

• Responses differ because:
  1. Different pharmacokinetics
  2. Different rates of clearance
  3. Different metabolism
  4. Different pharmacodynamics

Question 3

Discuss the difference in response to drugs in elderly people.

Answer 3

• Changes in body composition e.g. reduced lean mass, ^ fat content.
• Changes in clearance: decreased renal function
• Changes in metabolism: Decreased hepatic blood flow and liver mass. Decreased cytP450 levels

Question 4

Describe the effect of liver disease on prescribing

Answer 4

• In the elderly: Changes in metabolism of the drug due to decreased hepatic blood flow and liver mass. Decreased cytP450 levels but not in conjugation enzymes.
• Results in:
  1. Increased sensitivity to CNS depressants
  2. Increased sensitivity to adverse effects
  3. Often due to impaired compensatory mechanisms.

Question 5

Describe the effect of kidney disease on prescribing

Answer 5

• In the elderly: changes in clearance due to decreased renal function.
• Results in elimination half-life being increased.
• Increased volume of distribution of lipid-soluble drugs.

Question 6

Describe the basis of drug-drug interactions?

Answer 6

• Occurs when one drug alters the concentration of another drug with clinical consequences.
• 3 types:
  1. Duplication: 2 drugs with the same effect are taken, side effects ^.
  2. Opposition (antagonism): 2 drugs with opposing actions can interact, thereby reducing the effectiveness of one or both.
  3. Alteration: 1 drug may alter how the body absorbs, distributes, metabolises, or excretes another drug.