intro 3 (bioavailability)

what is bioavailability?

the fraction of the administered drug that reaches the systemic circulation in a chemically unchanged form

what are factors that affect bioavailability?

1. first-pass metabolism

2. solubility of the drug

3. chemically instability

4. nature of the formulation of the drug

what is first-pass metabolism?

any loss or inactivation of the administered material by transmucosal or hepatic metabolism after absorption and before reaching the systemic circulation

what is the example of a drug impacted by first-pass metabolism via the GIT?

• benzylpenicillin, which is partially broken down in the gut, so it is not effective orally and is usually given parenterally.

• insulin, which is destroyed in the gastrointestinal tract (enzymes + gut metabolism), so it cannot be given orally.

what is the example of a drug impacted by first-pass metabolism via the liver?

• propranolol, which undergoes extensive hepatic first-pass metabolism, reducing its oral bioavailability.

• lidocaine (lignocaine), which is completely metabolized by the liver, and cannot be given orally as it is ineffective

how can the solubility of a drug impact bioavailability?

it plays a critical role in drug effectiveness. without it, a drug substance cannot be absorbed, leading to low bioavailability. in simple terms, it must first dissolve in body fluids before it can be absorbed into the bloodstream. poor solubility leads to reduced absorption, which causes low bioavailability

what is the chemical stability of a drug refer to?

the drug’s ability to remain in the same chemical form when exposed to various environmental conditions that may cause it to deteriorate, such as heat, light, moisture, or changes in the pH

what is the most common form of chemical drug degradation?

hydrolysis, which is when the drug interacts with water, breaks down and thus reduces its effectiveness

what occurs when a drug is chemically unstable?

• decomposes

• loses potency

• forms inactive or harmful products

what are the types of ways drugs can be formulated?

1. solution

2. suspension

3. tablet

how does the nature of the formulation impact drug bioavailability?

based on how it is formulated, it can have the highest bioavailability but low stability, moderate bioavailability and stability, or low initial absorption but high stability

based on how a drug is formulated, how can they be ranked from highest bioavailability to lowest?

1. solutions

2. suspensions

3. tablets