What is the general 'Rule of Thumb' for medication half-life?

A general rule of thumb is to take the elimination half-life of a medication (the time it takes for a drug in the body to be reduced by 50%) and multiply it by five to allow for 'clearance.'

For example, a medication with a half-life of 8 hours (8 x 5 = 40) would take 40 hours to fully 'clear' from the body.

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Note: with certain medications, the drug itself may have cleared the body, but the effect of the medication may be longer lasting. It is important to realize that there is a great deal of variability in the circulating levels and metabolic clearance rates of medications and dietary supplements. In addition, clearance rates are affected by episodic fluctuations, diurnal rhythm, genetics, age, biological sex, menstrual cycle phase, renal function, liver function, immune function, and comorbidities. 

 

 

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