oral dosing Workshop W1

Question 1

What are the factors which determine the plasma concentrations of the drug after oral administration (7)

Answer 1

1. Absorption
2. Distribution
3. Metabolism
4. Elimination
5. Physiochemical properties of the drug
6. Patient factors
7. Drug interactions

Question 2

1. Absorption

Answer 2

• Bio availability: refers to the fraction of the oral dose that reaches the systemic circulation in an active form
• GI properties: drug absorption primarily occurs in the small intestine and the rate of this depends on factors such as the solubility and pH of the GI
• Presence of food: food can delay gastric emptying therefore affecting drug dissolution and altering absorption

Question 3

2. Distribution

Answer 3

• Blood flow to the site of absorption: the rate of which a drug reaches systemic circulation depends on blood flow to the intestines a higher blood flow facilitates faster absorption
• Plasma protein binding: drugs that are bound plasma proteins have lower free concentration in the bloodstream and only unbound drugs can cross cell membranes and exert their effects

Question 4

3. Metabolism

Answer 4

• First past effect: when a jug is absorbed from the GIT it passes through the liver where enzymes made metabolite it reducing the amount of drug that reaches systemic circulation
• Hepatic blood Flow: if liver blood flow is reduced, the metabolism of drugs may slow down leading to higher plasma concentrations

Question 5

4. Elimination

Answer 5

• Excretion via the kidneys: the kidneys are responsible for eliminating many dogs from the body and renal function plays a major role
• Urine pH: the pH of urine can influence the excretion of drugs

Question 6

5. Physiochemical properties of the drug

Answer 6

• Solubility: drug drugs made us over the gastrointestinal fluids to be absorbed and poor solubility can limit the amount of drug drugs absorb
• stability of the GIT: some drugs may degrade in the aesthetic environment of the stomach which can reduce the amount of active drug reaching the blood

Question 7

6. Patient factors

Answer 7

• Age: young and elderly individual individuals may have differences in drug absorption metabolism
• body weight and composition: fat and muscle distribution can affect the volume of distribution
• health conditions: diseases affecting the liver, kidney or GIT can alter the drugs pharmacokinetics

Question 8

7. Drug interactions

Answer 8

• other medications: some drugs can order the absorption, metabolism, or elimination of others