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Biological half-life (elimination half-life, pharmacological half-life) is the time taken for concentration of a biological substance (such as a medication) to decrease from its maximum concentration (C max) to half of C max in the blood plasma.
The main discussion of these abbreviations in the context of drug prescriptions and other medical prescriptions is at List of abbreviations used in medical prescriptions. Some of these abbreviations are best not used, as marked and explained here.
In this situation it is generally uncommon to talk about half-life in the first place, but sometimes people will describe the decay in terms of its "first half-life", "second half-life", etc., where the first half-life is defined as the time required for decay from the initial value to 50%, the second half-life is from 50% to 25%, and so on.
This is a list of abbreviations used in medical prescriptions, including hospital orders (the patient-directed part of which is referred to as sig codes). This list does not include abbreviations for pharmaceuticals or drug name suffixes such as CD, CR, ER, XT (See Time release technology § List of abbreviations for those).
Meaning Δ: diagnosis; change: ΔΔ: differential diagnosis (the list of possible diagnoses, and the effort to narrow that list) +ve: positive (as in the result of a test) # fracture: #NOF: fracture to the neck of the femur ℞ (R with crossed tail) prescription: Ψ: psychiatry, psychosis: Σ: sigmoidoscopy: x/12: x number of months x/40: x ...
But is also equivalent to divided by elimination rate half-life /, = /. Thus, = /. This means, for example, that an increase in total clearance results in a decrease in elimination rate half-life, provided distribution volume is constant.
The plasma half-life or half life of elimination is the time required to eliminate 50% of the absorbed dose of a drug from an organism. Or put another way, the time that it takes for the plasma concentration to fall by half from its maximum levels.
The AUC (from zero to infinity) represents the total drug exposure across time.AUC is a useful metric when trying to determine whether two formulations of the same dose (for example a capsule and a tablet) result in equal amounts of tissue or plasma exposure.