Bioavailability

Question 1

IV administration

Answer 1

Entire dose reaches the
systemic circulation, i.e. 100% bioavailability

Question 2

What determines bioavailability?

Answer 2

• Permeability of the biological membrane, drug properties,and other route-dependent factors,
  e.g. stomach contents for oral route

Question 3

Absolute bioavailability (F)

Answer 3

fraction of administered
dose of drug which reaches
system circulation

Question 4

First pass metabolism

Answer 4

• Absorbed from the stomach, small
  intestines and upper colon pass into the hepatic
  portal system liver

Question 5

Naloxone

Answer 5

• Used to combat opiate overdose
• Rapid onset required
• Undergoes first pass metabolism
• Oral bioavailability of 0.9% to 2%

Question 6

Blood plasma concentration – time curves

Answer 6

• Samples of blood withdrawn from a patient/volunteer at time intervals after a dose is administered
• The same patient would have both the i.v. and oral dose administered
• Compare area under curve

Question 7

Compare AUC(oral) to AUC(IV)

Answer 7

• Bioavailability of the oral formulation is therefore 0.5
• Repeated for diffrent patients and volenteers
• Reduced bioavailability may be due to
  incomplete absorption

Question 8

Absolute bioavailability (F) equation

Answer 8

• AUC(oral)/ AUC(I.V.)

Question 9

Not the same dose absolute bioavailability

Answer 9

AUC(oral) Dose(i.v.)/AUC(i.v.) Dose(oral)

Question 10

How is bioavailability determined?

Answer 10

• Area of a trapezoid = 0.5 (a + b) h on a drug conc time graph
• Where a & b are the two parallel sides and h the distance between them

Question 11

Relative bioavailability (Frel)

Answer 11

• Comparing the amount absorbed from a test formulation, e.g. an oral drug solution, to a standard formulation such as a tablet

Question 12

Equation for relative bioavailability

Answer 12

Frel = AUCtest/AUCstandard

Question 13

What is Frel used to measure?

Answer 13

• Changes in formulation parameters, e.g. dosage form, excipients, processes

Question 14

Bioequivalence

Answer 14

• Relative bioavailability evaluated from 2 products containing the same drug
• generic equivalent of an innovator product is launched

Question 15

Salt factor

Answer 15

Fraction of the dose (which may be in the form of a salt or ester) that is the active drug

Question 16

True value

Answer 16

• S value x ioavailability (F)