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Questions and Answers
What is the most likely effect of complexation in drug absorption?
What is the most likely effect of complexation in drug absorption?
- Only affects fat-soluble drugs
- Decreases absorption (correct)
- Increases absorption
- No effect on absorption
Quinolones are effective against bacterial infections.
Quinolones are effective against bacterial infections.
True (A)
What is the primary mechanism by which cyclosporin is metabolized?
What is the primary mechanism by which cyclosporin is metabolized?
by CYP3A
The enteric-coated formulation of ASA is designed to resist _____.
The enteric-coated formulation of ASA is designed to resist _____.
Match the following drugs with their application or mechanism:
Match the following drugs with their application or mechanism:
What is the formula for calculating absolute bioavailability (F)?
What is the formula for calculating absolute bioavailability (F)?
Relative bioavailability (Frel) can be used to compare the absorption between two different drug formulations.
Relative bioavailability (Frel) can be used to compare the absorption between two different drug formulations.
What role does the cytochrome P450 (CYP450) enzyme play in drug metabolism?
What role does the cytochrome P450 (CYP450) enzyme play in drug metabolism?
The percentage of the oral dose that does not reach the systemic circulation after administration is __________.
The percentage of the oral dose that does not reach the systemic circulation after administration is __________.
Match the following parameters with their descriptions:
Match the following parameters with their descriptions:
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Study Notes
Oral Absorption
- Absolute Bioavailability: Defined as the extent of drug absorption into systemic circulation; calculated using the area under the curve (AUC) for intravenous (iv) vs. oral doses.
- Relative Bioavailability: Compares absorption between two formulations; for example, a bioequivalence study compares a test drug (like generic LOVRAK®) with a reference drug (ZOVIRAX®).
Factors Influencing Oral Bioavailability
- Absorption affected by gut wall and hepatic first-pass effect, which includes presystemic elimination.
- Enzymes/transporters such as CYP450 play a significant role in drug metabolism and absorption.
- CYP450: A superfamily of enzymes involved in the metabolism of various drugs, significant for oral bioavailability.
Example: Cyclosporine
- Total bioavailability formula: ( F = F_a \times F_G \times F_H ).
- F values: Fa (0.86), FG (0.41), FH (0.76) yield a total absorption of merely 27% into systemic circulation.
- 73% of the oral dose is lost due to metabolism and transport effects.
Drug Interaction and Bioavailability
- Certain drugs can affect absorption through various mechanisms, including complexation (e.g., quinolones with polyvalent cations) and efflux pumps (e.g., P-glycoprotein for cyclosporin).
Extended Release Formulations
- Studies indicate mean steady-state plasma concentration profiles between immediate release (IR) and extended release (ER) formulations, using tolterodine as an example.
Enteric-Coated Formulations
- Pharmacokinetics differ based on whether doses are administered on an empty stomach or after a meal; variations in lag time observed with enteric-coated aspirin.
Felodipine Case Study
- Bioavailability varies significantly based on grapefruit juice intake and other factors; inhibition can drastically affect the oral bioavailability (Foral ranging from 0.15 to 0.45).
Oral Transporters
- Fexofenadine: An example of a drug with absorption mediated by transporters like OATP2B1 and MRP3 across the GI tract, highlighting the importance of transport mechanisms on oral bioavailability.
Competing Reactions in GIT
- Drug absorption can be competed by various reactions within the gastrointestinal tract, indicating that dissolution may not always be the rate-limiting step.
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