L1: Absorbtion and Distribution of Drugs

Question 1

Where should the medicine be introduced to have quick effect?

Answer 1

intravenous route.

Question 2

What is pharmacodynamics?

Answer 2

It is what the drug does to the body.

Question 3

What is pharmacokinetics?

Answer 3

It is what the body does to the drug.

Question 4

What does pharmacokinetics include?

Answer 4

Absorbtion
Distribution
Metabolism
Execration

Question 5

What is elimination?

Answer 5

Metabolism + excretion

Question 6

Why is there some lag in the start of the curve of the time course of drug action (oral)?

Answer 6

Due to Absorption but in intravenous, there is no lag.

Question 7

Where should the drug concentration be kept?

Answer 7

In the therapeutic window.

Question 8

What is absorption?

Answer 8

Absorption is defined as the passage of a drug from the site of administration to plasma.

Question 9

What are the main routes of administration of drugs?

Answer 9

• Sublingual.
• Oral
• Rectal.
• Local.
• Inhalation.
• Injections.

Question 10

Does the sublingual route have any Barriers?

Answer 10

No

Question 11

What are the internal routes of administration?

Answer 11

• Sublingual.
• Oral
• Rectal.

Question 12

What are the external routes of administration of drugs?

Answer 12

• Local.
• Inhalation.
• Injections.

Question 13

What are the factors that affect the rate of Absorption?

Answer 13

A. Factors related to the drug:
• Ionization of the drug (pKa)
B. Factors related to the absorbing surface:
• Rate of the circulation at the site of absorption.

Question 14

What is the ionization constant (pKa)?

Answer 14

It is the pH at which the ionized and non-ionized forms of the drug are equal.

Question 15

Are ionized forms lipid soluble or no?

Answer 15

Unionized forms are more lipid-soluble and rapidly absorbed.

Question 16

Where do acidic drugs become more ionized?

Answer 16

In basic media and vice versa

Question 17

Give an example for acidic and basic drugs respectively?

Answer 17

Aspirin - amphetamine

Question 18

What is the clinical significance of pKa?

Answer 18

-knowing the site of drug absorption on the GIT.

-Treatment of drug toxicity:
• Toxicity with acidic drugs (e.g. aspirin) could be treated by alkalinization of urine, which renders this drug more ionized in urine and less reabsorbable.

• Toxicity with basic drugs (e.g. amphetamine) could be treated by acidification of urine, which renders this drug more ionized in urine and less reabsorbable.

Question 19

What is the action of local anesthetic?

Answer 19

They block voltage-dependent Na+ channels within the nerve fibers →↓ nerve conduction.

Question 20

What is the clinical value of pKa in local anesthetics?

Answer 20

• All local anesthetics are weak bases. So, the addition of bicarbonate to the anesthetic solution maintains the anesthetic in the non-ionized state and this increases lipid solubility and enhances penetration of the anesthetic into the nerve sheath.

Question 21

What is the bioavailability of drugs?

Answer 21

it is the fraction of the drug that becomes available for systemic effect after administration. The bioavailability of drugs given i.v. is 100%.

Question 22

What are the factors that affect drug bioavailability(oral)?

Answer 22

Factors affecting oral availability:

• The same factors of drug absorption.
• Hepatic first-pass metabolism for oral route

Question 23

What is the definition of volume of distribution?

Answer 23

The apparent volume of water into which the drug is distributed in the body after distribution equilibrium

Question 24

How is Vd calculated?

Answer 24

The total amount of the drug in the body
Vd = —————————————————————————— = L Plasma concentration of the drug after distribution equilibrium

Question 25

What is the clinical significance of Vd?

Answer 25

Knowing Sites of distribution of drugs:
1. Plasma (3 liters)
2. Extracellular (9 liters)
3. Intracellular water (29 liters)
• So, Vd more than 41 liters means drug moves to tissues.

Calculation of the loading dose: LD = Vd target Cp

Question 26

Binding of drugs to plasma proteins

Answer 26

• Most drugs are found in the vascular compartment associated with plasma proteins
• The pharmacological effect of the drug is related only to its free part.
• Binding of drugs to plasma proteins prolongs their effects.