- On 3 Aug 2006 at 12:08:08, Eric Siu (esiu74.at.yahoo.ca) sent the message

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Dear all,

Just wondering how I can determine the time it'd take for a drug to

reach steady state from a subcutaneous osmotic mini-pump.

I already know the rate of drug delivery, absorption and elimination

rate constants for the drug in question.

Thanks in advance,

Eric Siu - On 4 Aug 2006 at 09:11:46, "attivi david assion" (assion.-at-.hotmail.com) sent the message

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The following message was posted to: PharmPK

If you know the half time of elimination, first, in a simple model

you steady state could be achieve in 4 to 7 half time of elimination

Thanks

David - On 11 Aug 2006 at 14:15:36, RLepage.aaa.pharmamedica.com sent the message

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Eric Siu,

The answer to your question can be found in Gibaldi and Perrier

(Pharmacokinetics 2nd Edition, Volume 15). The authors make a clear

mathematical argument for the time to reach steady state.

The conclusion of the exercise states, "For a drug with one-

compartment model characteristics the time required to reach a

particular fraction of steady state is independent of the number of

doses administered and the interval between administrations, but it

is directly proportional to the half-life."

Ultimately:

90% of steady state will be reached in 3.32 half-lives

99% of steady state will be reached in 6.64 half-lives.

Since you have a pump system, you can easily equate your system to a

continuous IV infusion. The concentration-time profile will look

similar to a continuous IV infusion, with concentration starting at

zero and gradually increasing and leveling out until plateau

Thank you

Robert Lepage, M.Sc. CCRP

Pharmacokineticist & Assistant Study Director

Pharma Medica Research Inc.

E-Mail: rlepage.-a-.pharmamedica.com

Phone: (905) 624-9115 x3300

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