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Bioavailability Calculator

Calculate drug absorption and bioavailability with pharmacokinetic parameters

Dose given orally

Intravenous dose

Area under curve - oral

Area under curve - IV

Hepatic extraction (0-1)

Liver clearance

Pharmacokinetic Results
Common Drug Examples
DrugF (%)Note
Propranolol30%High first-pass metabolism
Morphine25%Extensive hepatic metabolism
Verapamil20%CYP3A4 substrate
Atenolol50%Moderate bioavailability
Digoxin70%Good oral absorption
Factors Affecting Bioavailability
Hepatic Blood FlowAffects first-pass extraction
Drug SolubilityDetermines dissolution rate
GI Transit TimeAffects absorption window
Food EffectsCan increase or decrease absorption
Drug InteractionsP-gp and CYP enzyme effects
Disease StatesLiver/kidney function changes
Understanding the Results

The fraction of administered drug that reaches systemic circulation unchanged. F = 1.0 (100%) for IV administration. Oral bioavailability is typically lower due to incomplete absorption and first-pass metabolism.

The reduction in drug concentration before it reaches systemic circulation, primarily due to hepatic metabolism. High first-pass effect results in low oral bioavailability.

Low bioavailability may require higher oral doses. Individual variations in metabolism can affect drug response. Consider alternative routes for drugs with very low bioavailability.

Understanding Drug Bioavailability

Bioavailability is a crucial pharmacokinetic parameter that measures the fraction of an administered drug that reaches systemic circulation unchanged. This tool helps healthcare professionals, pharmacists, and students calculate and understand various aspects of drug absorption and metabolism.

Key Concepts

  • Absolute Bioavailability: Compares oral administration to intravenous administration
  • Relative Bioavailability: Compares different formulations of the same drug
  • First-Pass Effect: The reduction in drug concentration due to hepatic metabolism
  • AUC (Area Under the Curve): Represents total drug exposure over time

Clinical Applications

Understanding bioavailability is essential for:

  • Dose adjustments when switching between formulations
  • Predicting drug interactions affecting absorption
  • Designing appropriate dosing regimens
  • Evaluating generic drug equivalence
  • Understanding individual patient variability

Factors Affecting Bioavailability

Several factors can influence drug bioavailability:

  • Physicochemical properties: Solubility, permeability, stability
  • Formulation factors: Tablet disintegration, dissolution rate
  • Physiological factors: GI pH, transit time, blood flow
  • Patient factors: Age, disease states, genetic polymorphisms
  • Drug interactions: Enzyme induction/inhibition, transporter effects

Regulatory Considerations

Bioavailability studies are required by regulatory agencies to ensure drug safety and efficacy. The FDA typically requires bioavailability studies for new drug applications and generic drug approvals to demonstrate bioequivalence to the reference product.