What Is the Bioavailability of Drugs

1
What Is the Bioavailability of Drugs?
2

• The term bioavailability of drugs means the level
  to which the nutrient present in a certain drug
  reaches the action site. This site
• of action can also sometimes indicate the
  biological or body fluid that provides access to
  the action site.
• Simply put, it specifies the amount of active
  ingredient present in
• the drug that would be absorbed by the site of
  action.
• For instance, talking about most of the orally
  consumed medication, gastrointestinal (GI) tract
  receives the active ingredient of the drug. Then,
  through systemic circulation, the ingredients
  reach the site of action. Here, the concentration
  of the active metabolite or ingredient in the
  blood becomes a marker for measuring
  bioavailability.

3

• The blood concertation mentioned above not only
  indicates the release or absorption of the active
  ingredient from the drug but also includes other
  factors. These factors are elimination, systemic
  metabolism, and distribution.
• Mainly, three pharmacokinetic variables are
  utilized for bioavailability
• The highest blood concertation Cmax.
• The time required to reach this highest
  concentration Tmax.
• The time curve versus the area covered under
  blood
• concentration of drug AUC.

4

• An Example of Bioavailability
• Consider that a drug A has 60 or 0.6
  bioavailability. This is derived as
• Only 80 of the consumed drug initially reaches
  the GI tract.
• Further, 20 is used in metabolism before the
  drug achieves
• systemic circulation.
• The combined effect leaves 60 dose of the drug
  ingredient that
• reaches the site of action.
• What Is Bioequivalence?
• Bioequivalence refers to the drug products that
  are pharmaceutically equivalent in relevance to
  the extent of bioavailability. It only means that
  if you have two medicines with the same
  bioavailability, these drugs are bioequivalent.

5

• For instance, we often ask for a different
  medicine with the same function if the chemist
  doesnt have a particular drug. Here, we are
  actually asking for a drug with the same
  bioavailability as the drug prescribed by our
  doctor. This means that if a Drug A has 50
  bioavailability, the Drug B (a similar drug given
  by the chemist) should also have the same or
  nearly similar bioavailability.
• It is assumed that if the plasma concentration
  corresponding to the active ingredient present in
  the drugs is similar, then thesedrugs would react
  similarly. This is to say that the same
  concentration of nutrient of the drug will reach
  the site of action.
• However, it is interesting to note that only
  animal studies or in vitro test cant determine
  bioequivalence. Through established measures, the
  drugs made for humans must be regulated in humans
  only.

6

• The Acceptance Criteria for Bioequivalence Study
• For the acceptance of the bioequivalence of two
  drugs, the criteria to be followed is given
  below
• You have two drugs one is generic and other
  belongs to some brand. For these drugs to be
  bioequivalent, the difference arising in the Cmax
  and AUC of the drugs should not be more than 20.
• Both, bioequivalence and bioavailability of drug
  are related to each other, but these terms are
  not the same. While bioavailability defines how a
  drug will impact the site of action,
  bioequivalence simply gives similarity in
  bioavailability of different drugs.

7

• Thank You