DOSE RESPONSE CURVE

ED50 refers to Effective Dose of a drug needed to produce a particular response in 50% of population. It is a quantitative measure of the potency of a drug. Smaller the ED50 value, more potent is the drug.

Ref: Encyclopedia of Psychopharmacology By Ian P. Stolerman, Volume 2, Page 456

Therapeutic index is a measure of the margin of safety of a drug.  

Therapeutic index = Median lethal dose/Median effective dose. 

One estimate of a drug’s margin of safety is the ratio LD50/ED50, the therapeutic index, which is a statement of how selective the drug is in producing it’s desired versus its adverse effects.

Ans. is ‘c’ i.e., Efficacy

– Refers to maximal response that can be produced by a drug. Potency

– Amount of drug needed to produce a given response.

Ans. is ‘c’ i.e., Potency

Median effective dose

o The dose that will produce half the maximum (50%) response. o More the ED,  is the potency.

Ans. is b’ i.e., Safety

“Therapeutic index is the ratio between the toxic dose and the therapeutic dose of a drug, and is used as a measure of the relative safety of the drug for a particular treatment.”

Ans. D: Plasma clearance of a drug

The area under the plasma concentration time curve (AUC) is very useful for calculating the relative efficiency of different drug.

It can used to calculate the total body clearance (CL) and the apparent volume of distribution.

The area under the plasma (serum, or blood) concentration versus time curve (AUC) has an number of important uses in toxicology, biopharmaceutics and pharmacokinetics.

Toxicology-AUC can be used as a measure of drug exposure. It is derived from drug concentration and time so it gives a measure how much – how long a drug stays in a body. A long, low concentration exposure may be as important as shorter but higher concentration.

• Biopharmaceutics-The AUC measured after administration of a drug product is an important parameter in the comparison of drug products. Studies can be performed whereby different drug products may be given to a panel of subject on separate equations.
• Pharmacokinetics-Drug AUC values can be used to determine other pharmacokinetic parameters, such as clearance or bioavailability.

Ans. is ‘a’ i.e., Therapeutic index

Therapeutic index

• Drugs usually have more than one action.
• The maximal response for different action of a drug may be different ie the DRCs (Dose response curves) for different effects of a drug may be different.
• The extent of separation of DRCs of a drug for different effects is a measure of its selectivity, e.g. the DRCs for bronchodilatation and cardiac stimulation are quite similar in case of isoprenaline but far apart in case of salbutamol – the latter is more selective.
• The gap between the therapeutic effect DRC and the adverse effect DRC defines the safety margin or the therapeutic index.

Ans. is ‘a’ i.e., Dose Response Curve

Dose-response relationship

When a drug is administered systemically, the dose-response relationship has two components :

1. Dose-plasma concentration relationship (DPCR)

2.Plasma concentration – response relationship (PCRR)

Ans. is ‘a’ i.e., Potency reduced

Competitive antagonist

1. Antagonist bind to the same receptors as an agonist
2. Antagonist resembles chemically with the agonist
3. The same maximal response can be obtained
4. The potency is reduced (Right shift of DRC)
5. Km is increased but Vmax is unchanged

Non-competitive antagonist

1. Binds to another site of the receptor
2. Does not resemble
3. The maximal response is suppressed
4. Efficacy is reduced (Flattening of DRC)
5. Km is unchanged but Vmax is reduced.

Ans. is ‘a’ i.e., Efficacy

POTENCY

• Refers to the amount of Drug needed to produce a given response
• Potency is indicated by the position of curve on the dose axis.
• i.e. a DRC positioned rightward has lower potency
• Potency is less decisive factor in the choice of drug in comparison to efficacy
• Competitive antagonist act by decreasing the potency of a drug, such that maximal response (efficacy) can still be attained by increasing dose of agonist
• cause rightward shift of DRC

EFFICACY

• Refers to the maximal response that can be produced by the Drug
• Efficacy is indicated by the upper limit/height of the dose response curve. (DRC).
• Efficacy is a more decisive factor in the choice of a Drug.
• Non competitive agonist act by decreasing efficacy of a drug. Maximal response is suppressed and unsurmountable.
• flattening of DRC