Dosing and Serum Levels

what is the goal of dosing and serum drug levels?

to maintain a therapeutic level of a drug in the body without causing toxicity

what is serum?

the liquid part of your blood — what’s left after all the blood cells and clotting stuff are removed

how are serum drug levels checked?

draw a blood specimen and measure the drug level in the serum

what do serum drug levels assess?

peak and trough levels

therapeutic range

the blood serum concentration that produces the desired effect without causing toxicity

what happens if a level is above the therapeutic range (peak level)?

increased risk for bad side effects

what happens if a level is below the therapeutic range (trough level)?

the medication does not work well

loading dose

a larger than normal first dose given to reach the therapeutic effect as quickly as possible

why do we give a loading dose?

to get the med to therapeutic level quickly when it may not work well on the first day

example of a loading dose

more pills on the first day of taking meds to reach effect, then fewer pills on following doses

maintenance dose

the lower, usual dose used after a loading dose

peak level

the highest concentration of the drug in the blood

when is peak level generally measured?

when absorption is complete

• typically about 1 hour after administration (depending on route)

trough level

the lowest drug concentration in the blood before the next dose

half-life

the time it takes for the amount of drug in the body to be reduced by half

each medication’s half-life is ____

different for each medication

how do providers use half-life?

to determine dosing frequency

how providers decide when to redose a patient’s medication

aim to give the next dose when the body reaches the half-life so the med works effectively

peak level timing is linked to what pharmacokinetic phase?

completion of absorption

trough level timing is linked to what pharmacokinetic process?

elimination rate just before the next dose