Calculate the half-life of a drug from two plasma levels separated by a time interval.

Note: The "peak" should be obtained after the drug has been fully distributed, and the "trough" obtained at some interval later. These levels need not be the "true" peak or trough, as long as they are separated in time. The longer the time interval between the levels, the better the estimate.

If the levels are drawn around a dose (peak, dose, trough) rather than after the same dose (dose, peak, trough), the calculations here would be invalid if steady-state conditions are not satisfied.

Also note that the time interval entered is not the same as the dosing interval.

The formulae used are:

kelim =	(ln(Cpeak) - ln(Ctrough)
	tinterval

t_½ = 0.693 / k_elim