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A loading dose is most useful for drugs that are eliminated from the body relatively slowly, i.e. have a long systemic half-life. Such drugs need only a low maintenance dose in order to keep the amount of the drug in the body at the appropriate therapeutic level, but this also means that, without an initial higher dose, it would take a long ...
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 ...
Clark's rule is a medical term referring to a mathematical formula used to calculate the proper dosage of medicine for children aged 2–17 based on the weight of the patient and the appropriate adult dose. [1] The formula was named after Cecil Belfield Clarke (1894–1970), a Barbadian physician who practiced throughout the UK, the West Indies ...
For example, gentamicin is an antibiotic that can be nephrotoxic (kidney damaging) and ototoxic (hearing damaging); measurement of gentamicin through concentrations in a patient's plasma and calculation of the AUC is used to guide the dosage of this drug. [3] AUC becomes useful for knowing the average concentration over a time interval, AUC/t.
Therefore, if a drug has a bioavailability of 0.8 (or 80%) and it is administered in a dose of 100 mg, the equation will demonstrate the following: De = 0.8 × 100 mg = 80 mg That is the 100 mg administered represents a blood plasma concentration of 80 mg that has the capacity to have a pharmaceutical effect.
The solution of this differential equation is useful in calculating the concentration after the administration of a single dose of drug via IV bolus injection: = C t is concentration after time t; C 0 is the initial concentration (t=0) K is the elimination rate constant
In clinical practice, this means that it takes 4 to 5 times the half-life for a drug's serum concentration to reach steady state after regular dosing is started, stopped, or the dose changed. So, for example, digoxin has a half-life (or t 1 / 2 ) of 24–36 h; this means that a change in the dose will take the best part of a week to ...
Therefore the dose required to give a certain plasma concentration can be determined if the V D for that drug is known. The V D is not a real volume; it is more a reflection of how a drug will distribute throughout the body depending on several physicochemical properties, e.g. solubility, charge, size, etc.