After initiating atenolol, how long, before the medication, has reached Maximum Effectiveness?

Absorption of an oral dose is rapid and consistent but incomplete. Approximately 50% of an oral dose is absorbed from the gastrointestinal tract, the remainder being excreted unchanged in the feces. Peak blood levels are reached between two (2) and four (4) hours after ingestion. Over 85% of an intravenous dose is excreted in urine within 24 hours compared with approximately 50% for an oral dose.

The elimination half-life of oral atenolol is approximately 6 to 7 hours. Following intravenous administration, peak plasma levels are reached within 5 minutes. Declines from peak levels are rapid (5- to 10-fold) during the first 7 hours; thereafter, plasma levels decay with a half-life similar to that of orally administered drug. Following oral doses of 50 mg or 100 mg, both beta-blocking and antihypertensive effects persist for at least 24 hours.

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