Confusion Over Drug Efficacy & Potency

DRUG EFFICACY & DRUG POTENCY

   - Both of these are like TWO DIFFERENT beds in a single room!!

   - Often these two terms ‘Drug Potency’ & ‘Drug Efficacy’ are used relatively, but these are not synonymous & refer to different characteristics of the drug

   - So, this is the article from where you may clearly understand the difference between these two terms which we mentioned earlier as two different beds in a single room!

                                                                                                                                                                

1. DRUG POTENCY:

   - Amount of Drug Needed to produce maximum effect which is done by the Drug-Receptor Interaction.

   - It is the ability/affinity of drug to bind receptors.

   - Amount of drug is inversely proportional to potency that means lesser the amount of drug required to produce maximum effect, more will be the potency of that drug.

   - It is also known as Drug Strength.

    - Potency refers to the concentration OR dose of a drug required to produce 50% of that drug’s maximal effect.

                                                                                                                                                               

2.DRUG EFFICACY [ E_MAX ]:

   - Efficacy is the concept of a drug after interaction with receptor. 

   - Hence it is an Ability of Drug to produce effect.

   - This is the ability to initiate conformational changes in receptors which leads to certain effects. Efficacy is the concept of a drug after interaction with receptor.

   - In other words, it is the capacity of a drug to produce a maximum response.

   - Hence, it can also be termed as Maximal Efficacy [ E_MAX ]. Maximal Efficacy of a drug assumes that all receptors are occupied by drug & if more drugs are added, no further additive response will be observed.

   - Collectively, it can define as the ability of a drug to elicit a physiological response when it interacts with receptor.

   - Efficacy is depending on:

1. Number of Drug-Receptor Complexes are formed.

2. Efficiency of the coupling of receptor activation to cellular response.

Just_Touch_me to get brief about Difference between Drug Potency & Drug Efficacy.

Both of these Terms are Mathematically Understandable from DOSE RESPONSE CURVE.

                                                                                                                                                                

DOSE RESPONSE CURVE:

    - Two aspects viz;

(I) Dose-Plasma Concentration Relationship

(II) Plasma Concentration-Response Relationship

    - Intensity of Response Increases with Increase in Dose / more Precisely Increase in Concentration at Receptor).

    - Drug-Receptor Interaction obeys Law of Mass Action, which is illustrated by the formula;

    - Where, E is Observed Effect at a Dose [D] of drug; EMAX is Maximal Response; KD is Dissociation Constant of Drug-Receptor Complex.

    - Dose-Response Curve is a Rectangular Hyperbola Logarithmic Dose-Response Curve is Sigmoid Drug Potency & Efficacy can be determined by Drug Response Curve.

    - Potency & Efficacy of Drug can be determined by Dose Response Curve as shown below:

 

Drug B is Less Potent but Equally Efficacious as Drug A

Drug C is Less Potent and Less Efficacious than Drug A

Drug D is More Potent than Drugs A, B, & C, but Less Efficacious than Drugs A & B, & Equally Efficacious as Drug C

    - Log Dose-Response Curves [DRC] IS Plotted because it has several advantages like;

(I) Wide Range of Drug Doses can be Easily Displayed on a Graph

(II) Comparison Between Agonists & Study of Antagonists becomes Easier

Dose-response curves are used to derive Dose Estimates of chemical substances.

                                                                                                                                                               

DOSE ESTIMATES:

There are Three important Dose Estimating classical terms are there which are:

1.Lethal Doses [LDs]

2.Effective Doses [EDs]

3.Toxic Doses [TDs]

1.Lethal Doses [LDs]:

    - Initially, LD50 (Lethal Dose 50%) has been a common dose estimate for acute toxicity.

    - LD50 is statistically derived maximum dose at which 50% of the group of organisms (rat, mouse, or other species) would be expected to die.

    - LD50 testing is no longer the recommended method for assessing toxicity because of the ethics of using large numbers of animals, the variability of responses in animals and humans & the use of mortality as the only endpoint.

    - Regulatory agencies use LD50 only if it is justified by scientific necessity & ethical considerations.

    - Concentrations / Lethal Dose 0% (LD0) represents the dose at which no individuals are expected to die. This is just below the threshold for lethality.

    - Concentrations / Lethal Dose 10% (LD10) represents the dose at which 10% of the individuals will die.

    - Lethal Concentration 50% (LC50) refers for inhalation toxicity, air concentrations are used for exposure values. The LC50 refers to the calculated concentration of a gas lethal to 50% of a group. Very occasionally LC0 and LC10 are also used.

2.Effective Doses [EDs]:  

    - Effective Doses (EDs) are used to indicate the effectiveness of a substance.

    - Normally, effective dose refers to a beneficial effect such as relief of pain.

    - It may also stand for a harmful effect such as paralysis.

    - Thus, the specific endpoint must be indicated.

    - The usual terms are: ED0, ED10, ED50, ED90.

3.Toxic Doses (TDs):

    - Toxic Doses (TDs) are used to indicate doses that cause adverse toxic effects.

    - The usual dose estimates include: TD0, TD10, TD50, TD90. [TD50 is Dose required to produce a toxic effect i 50% of population].

Determining the Pharmaceutical Relative Safety:

    - Toxicologists, pharmacologists & others use effective and toxic dose levels to determine the relative safety of pharmaceuticals.

                                                                                                                                                               

THERAPEUTIC INDEX:

    - Quantitative measurement of relative safety of drug.

    - Therapeutic Index (TI) is used to compare the therapeutically effective dose to the toxic dose of a pharmaceutical agent.

    - TI is a statement of relative safety of a drug.

    - It is the ratio of the dose that produces toxicity to the dose needed to produce the desired therapeutic response.

    - The common method used to derive the TI is to use the 50% dose-response points, including TD50 & ED50.

 

    - Que. If the TD50 is 100 & the ED50 is 20 mg, then TI would be?

 

   - More the Safety if more is TI [TI directly Proportional to Safety]

    - In Low TI i.e., Low Safety Margin, even the smaller increment in the dose would produce toxic effects.

    - Like that, In High TI i.e., High Safety Margin, more reliability of the dose is possible since it would not produce toxic effects after smaller increment in dose.

    - Bioavailability of a drug should be done at Low TI.

    - However, the use of the ED50 & TD50 doses to derive the TI may be misleading about a drug's safety, depending on the slope of the dose-response curves for therapeutic & toxic effects.

    - To overcome this demerit, toxicologists often use another term to denote the safety of a drug i.e., Margin of Safety [MOS].

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Stay tune...

Stay Safe...

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