Medication Effectiveness Drug effectiveness decreases over time. If, each
hour, a drug is only \(90 \%\) as effective as the previous hour, at some point
the patient will not be receiving enough medication and must receive another
dose. If the initial dose was \(200 \mathrm{mg}\) and the drug was administered
\(3 \mathrm{hr}\) ago, the expression \(200(0.90)^{3},\) which equals \(145.8,\)
represents the amount of effective medication still in the system. (The
exponent is equal to the number of hours since the drug was administered.)