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In pharmacokinetics, a loading dose is an initial higher dose of a drug that may be given at the beginning of a course of treatment before dropping down to a lower maintenance dose. [ 1 ] A loading dose is most useful for drugs that are eliminated from the body relatively slowly, i.e. have a long systemic half-life .
A V D greater than the total volume of body water (approximately 42 liters in humans [5]) is possible, and would indicate that the drug is highly distributed into tissue. In other words, the volume of distribution is smaller in the drug staying in the plasma than that of a drug that is widely distributed in tissues.
Continuing the maintenance dose for about 4 to 5 half-lives (t 1/2) of the drug will approximate the steady state level. [1] One or more doses higher than the maintenance dose can be given together at the beginning of therapy with a loading dose. [2] A loading dose is most useful for drugs that are eliminated from the body relatively slowly ...
It can be determined from the following formula: = Where: is total amount of the drug in the body and is the drug's plasma concentration. As the value for A b {\displaystyle Ab} is equivalent to the dose of the drug that has been administered the formula shows us that there is an inversely proportional relationship between V d {\displaystyle Vd ...
Consideration has to be given to what is known as "drug loading" - the ratio of the active drug to the total contents of the dose. A low drug load may cause homogeneity problems. A high drug load may pose flow problems or require large capsules if the compound has a low bulk density.
Clearance of a substance is sometimes expressed as the inverse of the time constant that describes its removal rate from the body divided by its volume of distribution (or total body water). In steady-state, it is defined as the mass generation rate of a substance (which equals the mass removal rate) divided by its concentration in the blood .
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The median effective dose is the dose that produces a quantal effect (all or nothing) in 50% of the population that takes it (median referring to the 50% population base). [6] It is also sometimes abbreviated as the ED 50, meaning "effective dose for 50% of the population". The ED50 is commonly used as a measure of the reasonable expectancy of ...