BIO AVAILABILITY
| A | Amount of drug that reach the systemic circulation | |
| B |
Drug metabolized in liver before the drug reaches the systemic circulation |
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| C |
Drug metabolized in liver after the drug reaches the systemic circulation |
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| D |
Maximum by rectral route |
Bioavailability is-
| A |
Amount of drug that reach the systemic circulation |
|
| B |
Drug metabolized in liver before the drug reaches the systemic circulation |
|
| C |
Drug metabolized in liver after the drug reaches the systemic circulation |
|
| D |
Maximum by rectral route |
Ans. is ‘a’ i.e., Amount of drug that reach the systemic circulation
All of the following statements regarding bioavailability of a drug are true except –
| A |
It is the proportion (fraction) of unchanged drug that reaches the systemic circulation |
|
| B |
Bioavailability of an orally administered drug can be calculated by comparing the Area Under Curve after oral and intravenous (iv) administration |
|
| C |
Low oral bioavailability always and necessarily mean poor absorption |
|
| D |
Bioavailability can be determined from plasma concentration or urinary excretion data |
Ans. is ‘c’ i.e., Low oral bioavailability always and necessarily means poor absorption
o Bioavailability of a drug is frequently lower after oral ingestion because of two factors (not poor absorption alone):
1. Extent of absorption
2. First pass metabolism in intestinal wall, portal blood or liver (most common).
About other options
o Bioavailability of a drug is a measure of fraction of administered dose of a drug that reaches the systemic circulation in unchanged form.
o Biovailability is determined by the area under the plasma concentration – time curve. Area under the curve of an orally administered drug when compared to the area under the curve for an I.V. administered drug (100%) can certainly give an idea of its bioavailability.
o The systemic bioavailability of a drug can be predicted from the extent of absorption (function of concentration in plasma) and extraction ratio.
o Bioavailability can also be calculated by comparing the excretion in urine.
| A |
High first pass metabolism |
|
| B |
Increased absorption |
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| C |
IV drug administration |
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| D |
High solubility |
Ans. is ‘a’ i.e., High first pass metabolism
o Causes for less bioavailability.
Incomplete absorption
o High first pass metabolism.
About other options
- Increased absorption increases bioavailability.
o I.V. administration has 100% bioavailahi I ity.
- High lipid solubility causes more absorption and better bioavailability.
| A | First pass metabolism | |
| B |
Second pass metabolism |
|
| C |
Volume of distribution |
|
| D |
Excretion |
Ans. is ‘a’ i.e., First pass metabolism
Bioavilability depends on :
i) Extent of absorption.
it) First pass metabolism.
| A | Short t1/2 in plasma | |
| B |
Hepatic first pass metabolism |
|
| C |
Lower bioavailability by oral route |
|
| D |
Extensive protein binding |
Ans. is ‘b’ i.e., Hepatic first pass metabolism
o This question is tricky one as option b & c literally have the same meaning, i.e. any drug with high hepatic first pass metabolism will have lower oral bioavailability.
o But, we use sublingual nitroglycerine to produce immediate relief of symptoms in angina By sublingual route there is direct absortiption into systemic circulation bypassing liver.
“The sublingual route is used when terminating an attack or aborting an imminent one is the aim. The tablet may be crushed under the teeth and spread over buccal mucosa. It acts within 1-2 min because of direct absorption into systemic circulation (bypassing liver where almost 90% is metabolized)”
| A |
16% |
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| B |
24% |
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| C |
20% |
|
| D |
28% |
Ans. is ‘a’ i.e., 16%
Absortion of drug is 40% i. e. if 100 mg of drug is taken 40 mg will be absorbed.
Hepatic extraction ratio is 0.6 i.e. out of the absorbed dose 60% will be removed by liver; so from the absorbed 40 mg 60% removed i. e. 24 mg removed.
Thus finally the remaining 16 mg of the total dose taken reaches the systemic circulation. So bioavailability is 16% as 16mg of the total 100 mg finally reached the systemic circulation
| A | Area of oral/ area of IV | |
| B |
Area of IV/ area of oral |
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| C |
Area of oral/ area of IV x 100 |
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| D |
Area of IV/ area of oral x 100 |
Ans. is ‘c’ i.e., Area of oral/ area of IV x 100
Bioavailability
- Refers to the rate and extent of absorption of drug from a dosage form as determined by its concentration-time curvein blood or by its excretion in urine.
- It is the measure of fraction (F) of drug, which reaches the systemic circulation in unchanged form.
- Bioavailability of a drug given by i.v.route is 100%. So the bioavailability of drug dosage form is determined by comparing it with the i.v.route.
