Pharmacokinetics 1

Question 1

What is pharmacokinetics

Answer 1

How drugs are absorbed into the body, how they are distributed and how they are eliminated

Question 2

What are the four areas to consider in pharmacokinetics

Answer 2

Absorption, distribution, metabolism, excretion

Question 3

Where does the bulk flow of transfer take place

Answer 3

Through the bloodstream

Question 4

How do lipid soluble drugs cross the membrane of cells

Answer 4

Passivley diffuse down their concentration gradient

Question 5

What will result from a rapid absorption of a drug through the gut

Answer 5

Rapid increase in concentration in the blood and brain - may also mean its rapidly metabolised however

Question 6

What is the partition coefficient

Answer 6

Determines lipid solubility - how quickly the drug will dissolve in oil rather than water

Question 7

How do non-polar molecules interact with cells

Answer 7

Diffuse freely in lipids and penetrate the cell freely

Question 8

What is the best mechanism to achieve fast absorption of drugs

Answer 8

Intravenous injection - preferential in emergency circumstances

Question 9

What effects the rate of absorption in intrauscular injections

Answer 9

Depends on the perfusion of that muscle - greater blood supply = greater rate of absorption

Question 10

What are inrathecal injections

Answer 10

Drugs of the CNS - administered into the cerebrospinal fluid - used in pain relief

Question 11

What is a characteristic needed for oral medication

Answer 11

Has to be resistent to being broken down in the gut - some will be metabolised in the liver and kidneys but not a huge amount

Question 12

How does particle size effect a drugs metabolism

Answer 12

Large particle sized drugs are more easily metabolised/ less is absorbed into the blood stream

Question 13

When would rectally administered drugs be used

Answer 13

For small infants that can’t swallow tablets and for seriously ill patients that can’t stop vomiting.

Question 14

Why is a low pH beneficial to the absorption of weak acids (Many drugs are weak acids or bases)

Answer 14

Shifts the dissociation equation of a weak acid to the associated side - so no longer carries a charge and is able to diffuse across the membrane

Question 15

Give the eqn to show aspirin is in its active form at a pH of 3 in the stomach

Answer 15

pKa= pH + log10 [HA]/[A-]
pKa = 3.5

Question 16

Once aspirin gets into the bloodstream what changes occur

Answer 16

The pH becomes more neutral - so the drug dissociates more - this means it stays in the blood longer as it can’t move across the lipid membrane

Question 17

How does the pH of the kidney effect absorption

Answer 17

pH or 8 so the drug dissociates more readily - This is good as this is where the associated is metabolised

Question 18

How are overdose drug situations combated

Answer 18

Administration of NaHCO3 to neutralise the compartments so drug is in a more dissociated form in the blood so doesn’t act on CNS etc - metabolised at the kidney