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Melatonin may be useful in the treatment of delayed sleep phase syndrome. [9] Melatonin is known to reduce jet lag, especially in eastward travel. However, if it is not taken at the correct time, it can instead delay adaptation. [30] Melatonin appears to have limited use against the sleep problems of people who work shift work. [31]
MDCalc was founded by two emergency physicians, Graham Walker, MD, and Joseph Habboushe, MD, MBA, [5] and provides over 500 medical calculators and other clinical decision-support tools. [6] The MDCalc.com website was launched in 2005. [5] In 2016, MDCalc launched an iOS app, [7] followed by an Android app in 2017. [8]
Thus, total body clearance is equal to the sum clearance of the substance by each organ (e.g., renal clearance + hepatic clearance + pulmonary clearance = total body clearance). For many drugs, however, clearance is solely a function of renal excretion. In these cases, clearance is almost synonymous with renal clearance or renal plasma clearance.
Clearance is therefore expressed as the plasma volume totally free of the drug per unit of time, and it is measured in units of volume per units of time. Clearance can be determined on an overall, organism level («systemic clearance») or at an organ level (hepatic clearance, renal clearance etc.). The equation that describes this concept is:
Caesium in the body has a biological half-life of about one to four months. Mercury (as methylmercury) in the body has a half-life of about 65 days. Lead in the blood has a half life of 28–36 days. [29] [30] Lead in bone has a biological half-life of about ten years. Cadmium in bone has a biological half-life of about 30 years.
t 1/2 is the half-life time of the drug, which is the time needed for the plasma drug concentration to drop to its half Therefore, the amount of drug present in the body at time t A t {\displaystyle A_{t}} is;
It was proposed to be used instead of AUC in animal-to-human dose translation, as computer simulation shows that it could cope better with half-life and dosing schedule variations than AUC. This is an example of a PK/PD model, which combines pharmacokinetics and pharmacodynamics. [13]
The melatonin receptors are G protein-coupled receptors and are expressed in various tissues of the body. There are two subtypes of the receptor in humans, melatonin receptor 1 (MT 1) and melatonin receptor 2 (MT 2). [2] Melatonin and melatonin receptor agonists, on market or in clinical trials, all bind to and activate both receptor types. [1]