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Chemicals can have a wide range of effects on our health. Depending on how the chemical will be used, many kinds of toxicity tests may be required. Since different chemicals cause different toxic effects, comparing the toxicity of one with another is hard.

We could measure the amount of a chemical that causes kidney damage, for example, but not all chemicals will damage the kidney. We could say that nerve damage is observed when 10 grams of chemical A is administered, and kidney damage is observed when 10 grams of chemical B is administered. However, this information does not tell us if A or B is more toxic because we do not know which damage is more critical or harmful.

Therefore, to compare the toxic potency or intensity of different chemicals, researchers must measure the same effect. One way is to carry out lethality testing the LD 50 tests by measuring how much of a chemical is required to cause death. This type of test is also referred to as a "quantal" test because it is measures an effect that "occurs" or "does not occur".

In , J. Trevan attempted to find a way to estimate the relative poisoning potency of drugs and medicines used at that time. He developed the LD 50 test because the use of death as a "target" allows for comparisons between chemicals that poison the body in very different ways.

Since Trevan's early work, other scientists have developed different approaches for more direct, faster methods of determining the LD Acute toxicity is the ability of a chemical to cause ill effects relatively soon after one oral administration or a 4-hour exposure to a chemical in air.

In nearly all cases, LD 50 tests are performed using a pure form of the chemical. Mixtures are rarely studied. The chemical may be given to the animals by mouth oral ; by applying on the skin dermal ; by injection at sites such as the blood veins i.

Researchers can do the test with any animal species but they use rats or mice most often. Other species include dogs, hamsters, cats, guinea-pigs, rabbits, and monkeys.

In each case, the LD 50 value is expressed as the weight of chemical administered per kilogram body weight of the animal and it states the test animal used and route of exposure or administration; e. If the lethal effects from breathing a compound are to be tested, the chemical usually a gas or vapour is first mixed in a known concentration in a special air chamber where the test animals will be placed.

When an LC 50 value is reported, it should also state the kind of test animal studied and the duration of the exposure, e. Inhalation and skin absorption are the most common routes by which workplace chemicals enter the body. Thus, the most relevant from the occupational exposure viewpoint are the inhalation LC 50 and skin application tests LD 50 -skin. Despite this fact, the most frequently performed lethality study is the oral LD This difference occurs because giving chemicals to animals by mouth is much easier and less expensive than other techniques.

EC50 values are often used for acute enviromental hazard classification and calculation of predicted non-effect concentration PNEC. No observed effect concentration NOEC is the concentration in an environmental compartment water, soil, etc which below an unacceptable effect is unlikely to be observed. It is typically obtained from chronic aquatic toxicity studies and terrestrial toxicity studies.

Half-life DT50 is defined as the time it takes for an amount of a compound to be reduced by half through degradation in an environmental compartment water, soil, air, etc.

It is used to measure the persistence of a substance. The unit is day. DT50 is often used in environmental exposure modelling to predict the concentration of a substance in an environmental compartment over a long time of period. We do not provide consultancy services. If you have questions or need any help, please contact our sponsor.

You may also find an expert in CSP business directory below. If you are a consultant, you may get yourself listed in CSP business directory free or sponsor this page to leave your contact info on this page.. Sometimes, ppm is used. Keddis, RN. Chapter Local Anesthetics and Adjuvants. In: Atchabahian A, Gupta R. McGee, DL. Local and topical anesthesia. Amsterdam Netherlands : Elsevier Academic Press; Accessed November 29, Nolan, JP.

Anaesthesia and neuromuscular block. Clinical Pharmacology. Properties, absorption, and disposition of local anesthetic agents. Maximum recommended doses of local anesthetics: a multifactorial concept. Reg Anesth Pain Med. Nov ; 29; Schwartz DR, Kaufman B. A nomogram for calculating the maximum dose of local anaesthetic. Wolfe J. In: Ehrenfeld J.