Dose adjustment

Question 1

Explain why age might affect Absorption?

Children

Answer 1

Children can usually absorb drug more quickly than others (more children under 3 years)

Gastric emptying can be slower and peristalsis can be less regular (which affects transit time and gives a great opportunity for drug absorption)

If drug is given via the intramuscular route, absorption in children may be inhibited.
This is because children have less well-developed musculature and may use it less than adults, so blood supply would be less there.

Question 2

Explain why age might affect Absorption?

Elderly

Answer 2

Gastric emptying may be delayed, which will delay absorption.

Reduced peristalsis - movement of food through the digestive tract

Active transport may be decreased – so if a drug is absorbed by active transport, then less absorption.

These impact drug absorption to a certain extent.

Question 3

Explain why age might affect Distribution?

Children

Answer 3

Children are smaller and have a smaller weight so the volume of distribution will be less.

So if you give the same dose of adult to a children, they will end up with a higher plasma concentration

Binding to plasma protein may be decreased in children.

Most drugs are highly plasma protein bound so if there is a reduction in the plasma protein being produced, you could end up with a higher free drug concentration.

Question 4

Explain why age might affect Distribution?

Elderly

Answer 4

As people age, there may be changes in body composition.
If the drug normally distributes through those then this might change the volume of distribution.

If cardiac output is reduced, the distribution of certain drugs will get affected.

There may be increased peripheral resistance, which could reduce the distribution of drugs.

The blood brain barrier (BBB) permeability may increase, so the volume of distribution may change.

Question 5

Explain why age might affect Metabolism?

Children

Answer 5

With children under 6 months of age drug metabolic activity is less

So drugs will be metabolised more slowly, so you would end up with a higher drug concentration.

The drugs half-life would be longer than anticipated

Question 6

Explain why age might affect Metabolism?

Elderly

Answer 6

P450 metabolism decreases with age

Decreased hepatic blood flow

Question 7

Explain why age might affect Excretion?

Children

Answer 7

With children under 6 months of age, glomerular filtration rate (GFR) increases

This is from birth – 6months

Question 8

Explain why age might affect Excretion?

Elderly

Answer 8

Glomerular filtration rate - GFR decreases with age but can vary