What is the difference between lc50 and ec50

The IC50 is the concentration of an inhibitor where the response or binding is reduced by half. Seems simple enough. But when you actually go to fit data to determine these values, there are several complexities and ambiguities. The rest of this article is about IC50 I for inhibition, for downward sloping dose-response curves.

All the ideas can be applied to stimulatory curves and EC50 E for effective as well. Just stand on your head when you view the figures. The green symbols show measurements made with controls.

The data of the experimental dose-response curve red dots extend all the way between the two control values. When fitting this curve, you need to decide how to fit the top plateau of the curve. You have three choices:. The results will be very similar with any of these methods, because the data form a complete dose-response curve with a clear top plateau that is indistinguishable from the blank.

I prefer the third method, as it analyzes all the data, but that is not a strong preference. Similarly, there are three ways to deal with the bottom plateau: Fit the data only, set Bottom to be a constant equal to the average of the NS controls, and put the NS controls into the fit as if they were a very high concentration of inhibitor.

This figure shows an unusual situation where the inhibition curve plateaus well above the control values NS defined by a high concentration of a standard drug. This leads to alternative definitions of IC Clearly, a single value cannot summarize such a curve. You'd need at least two values, one to quantify the middle of the curve the drug's potency and one to quantify how low it gets the drug's maximum effect.

The relative IC50 is by far the most common definition, and the adjective relative is usually omitted. It is the concentration required to bring the curve down to point half way between the top and bottom plateaus of the curve. The NS values are totally ignored with this definition of IC This definition is the one upon which classical pharmacological analysis of agonist and antagonist interactions is based. With appropriate consideration of the biological system and concentrations of interacting ligands, estimated Kd values can often be derived from the IC50 value defined this way not so for the "so-called absolute IC50" mentioned below.

This term is not entirely standard. Since this value does not quantify the potency of a drug, the authors of the International Union of Pharmacology Committee on Receptor Nomenclature 1 think that the concept of absolute IC50 and that term is not useful R.

Neubig, personal communication. I agree. Changing any of these variables e. The LD 50 test was neither designed nor intended to give information on long-term exposure effects of a chemical. Once you have an LD 50 value, it can be compared to other values by using a toxicity scale. Confusion sometimes occurs because several different toxicity scales are in use.

These tables differ in both the numerical rating given to each class and the terms used to describe each class. It is important to reference the scale you used when classifying a compound. It is also important to know that the actual LD 50 value may be different for a given chemical depending on the route of exposure e. For example, some LD 50 s for dichlorvos, an insecticide commonly used in household pesticide strips, are listed below:. Differences in the LD 50 toxicity ratings reflect the different routes of exposure.

The toxicity rating can be different for different animals. The data above show that dichlorvos is much less toxic by ingestion in pigs or dogs than in rats.

Using Table 1, dichlorvos is moderately toxic when swallowed oral LD 50 and extremely toxic when breathed inhalation LC 50 in the rat.

Using Table 2, dichlorvos is considered very toxic when swallowed oral LD 50 by a rat. In general, if the immediate toxicity is similar in all of the different animals tested, the degree of immediate toxicity will probably be similar for humans. When the LD 50 values are different for various animal species, one has to make approximations and assumptions when estimating the probable lethal dose for man.

Tables 1 and 2 have a column for estimated lethal doses in man. Special calculations are used when translating animal LD 50 values to possible lethal dose values for humans. Safety factors of 10, or are usually included in such calculations to allow for the variability between individuals and how they react to a chemical, and for the uncertainties of experiment test results.

The LD 50 is only one source of toxicity information. For a more thorough picture of the immediate or acute toxicity of a chemical, additional information should be considered such as the lowest dose that causes a toxic effect TDLO , the rate of recovery from a toxic effect, and the possibility that exposure to some mixtures may result in increasing the toxic effect of an individual chemical.

Add a badge to your website or intranet so your workers can quickly find answers to their health and safety questions. Although every effort is made to ensure the accuracy, currency and completeness of the information, CCOHS does not guarantee, warrant, represent or undertake that the information provided is correct, accurate or current. CCOHS is not liable for any loss, claim, or demand arising directly or indirectly from any use or reliance upon the information.

OSH Answers Fact Sheets Easy-to-read, question-and-answer fact sheets covering a wide range of workplace health and safety topics, from hazards to diseases to ergonomics to workplace promotion. Search all fact sheets: Search. Type a word, a phrase, or ask a question. Little Pro on In toxicology and eco-toxicology, dose descriptor is the term used to identify the relationship between a specific effect of a chemical substance and the dose at which it takes place.

The dose descriptors will be used later for deriving the no-effect threshold levels for human health i. They are used for GHS hazard classification and risk assessment.

In this article, we will summarize the definition of common toxicology dose descriptors, how they are obtained and what the units are. For inhalation toxicity, air concentrations are used for exposure values.

LD50 and LC50 are typically obtained from acute toxicity studies. The units of LD50 and LC50 are listed as follows:. No Observed Adverse Effect Level NOAEL is the highest exposure level at which there are no biologically significant increases in the frequency or severity of adverse effect between the exposed population and its appropriate control; some effects may be produced at this level, but they are not considered adverse effects.

NOAEL are typically obtained from repeated dose toxicity studies 28d repeated dose toxicity study, 90d repeated dose toxicity study or chronic toxicity and reproductive toxicity studies. NOAELs are very important. Lowest Observed Adverse Effect Level LOAEL is the lowest exposure level at which there are biologically significant increases in frequency or severity of adverse effects between the exposed population and its appropriate control group.