oral dosing Workshop W1

Question 1

Explain the factors which determine the plasma concentrations of the drug after oral administration

Answer 1

1. Absorption
   - 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
2. Distribution
   - 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
3. Metabolism
   - 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
4. Elimination
   - 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
5. Physiochemical properties of the drug
   - 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
6. Patient factors
   - 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
7. Drug interactions
   - other medications: some drugs can order the absorption, metabolism, or elimination of others