Systemic availability of orally administered meperidine.

A comparison of the areas under the plasma concentration-time curves after intravenous and oral administration of meperidine in 4 normal subjects indicated that 48% to 56% of the oral dose avoided "first-pass" metabolism and was systemically available. Similar estimates were obtained by applying the Loo-Riegelman method for calculating drug absorption viz, 47% to 60%. Oral availability predicted from a knowledge of drug clearance (blood) after intravenouration-time curves after oral administration exhibited irregularities and double peaks possibly indicative of the action of meperidine on the gut or a recycling process.