TRC: Steady state

Reaching steady-state

This graphic shows that the amount infused over a period of time is halved at each half-life of the drug. Because not all drug is eliminated in the next time period, a certain amount of accumulation occurs. Thus the cleared amount will be half the sum of the accumulated amount and the infused amount.

Assuming that the rate of infusion is constant, the steady-state concentration is entirely dependent upon the clearance. The time it takes before reaching steady-state depends on the half-life. A simple rule of thumb is that the steady-state is reached after approximately 4-5 half-lives, but that you are within 10% after 3½ half-lives.

A patient with atrial fibrillation is treated with a twice daily, oral dose of acenocoumarol (anticoagulant). Acenocoumarol has a half-life time of 10h. Around how many days of therapy can you expect a steady state concentration?

Extra info: Steady state is achieved around 4-5 half lives (40-50 hours), thus 1.7-2.1 days).

Option explanation:

0.5-1 day

1.5-2.5 days

5-6 days

7-14 days

Reaching steady-state

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