<prompt> After oral administration the fraction of drug reaching the systemic circulation in unchanged form is:EliminationDistributionBioavailabilityMetabolism  <response>: Ref: KD Tripathi, 7th ed. pg. 16BIOAVAILABILITYBioavailability is a measure of the fraction of administered dose of a drug that reaches the systemic circulation in the unchanged form.Bioavailability of drug injected IV is 100, but isfrequently lower after oral ingestion because--The drug may be incompletely absorbed.The absorbed drug may undergo first pass metabolism in the intestinal wallliver or be excreted in bile. 