Case study | Chemistry | Minnesota State Colleges and Universities - St. Paul, MN

1. (6 points) Th e amount of medication that is in the blood (and available to reach cells and treat the underlying condition) is often diff erent than the dose that was given. Th e fraction of a dose of medication that is in the blood stream and has not been chemically modifi ed (metabolized) by the body is referred to as its bioavailability. When a medication is administered intravenously, its bioavailability is considered to be 100 % at the time of administration and this decreases with time as it is metabolized and/or excreted. However, when a medication is administered orally, its bioavailability is much less due to incomplete absorption and being metabolized on passing through the liver.

Th e paper referenced below compares (in Figure 2) the concentration of azithromycin in the blood in subjects who were administered 500 mg of the medication orally and in other groups who were given the same dose intravenously. From the graphs, determine for the healthy patients: (a) When were the peak concentrations achieved for intravenous and for oral administration of the medication? (b) What were the peak concentrations for intravenous and for oral administration of the medication? (c) What were the concentrations after 12 hours for intravenous and for oral administration of the medication? Note that the graphs in Figure 2 of the article use a logarithmic scale for the azithromycin concentration. Reference: Beringer, P., et al. 2005. Antimicrob Agents Chemother. 49(12): 5013–5017. Th e paper can be accessed at: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1315964/