Q 355 tibiotics can be toxic in large doses. If repeated doses of an antibiotic are to be given, the rate at which the medicine is excreted through the kidne - ooo red by a physician. One measure of kidney function is the glomerular filtration rate, or GFR, which measures the amount of material crossing the glomerular) membrane of the kidney, in milliliters per minute. A normal GFR is about 125 ml/min. Figure 8.40 gives a contour diagram of the percent, P, of a dose of mezlocillin (an antibiotic) excreted, as a function of the patient's GFR and the time, t, in hours since the dose was administered. 3 GFR (ml/min) 100 90 80 70 P = 60 P = 50 P = 40 68968 P = 30 P = 20 P = 10 t (hours) 4 8 12 16 20 24 Figure 8.40 (a) In a patient with a GFR of 50, approximately how long will it take for 30% of the dose to be excreted? Answer (b) In a patient with a GFR of 60, approximately what percent of the dose has been excreted after 5 hours? > Answer (c) Explain how we can tell from the graph that, for a patient with a fixed GFR, the amount excreted changes very little after 12 hours. > Answer (d) Is the percent excreted an increasing or decreasing function of time? Explain why this makes sense. > Answer (e) Is the percent excreted an increasing or decreasing function of GFR? Explain what this means to a physician giving antibiotics to a patient with kidney disease. P. 356 >