Question

You were prescribed codeine, a weak organic base with a pKa of 8. You are a vegetarian and also take certain dietary supplements (green+). A diet rich in vegetables and fruit and herbal extracts has an alkaline influence on urinary pH (pH~7). In contrast, urine pH in a meat eater is more acidic (pH~5). *must show your work*

1. Calculate the ratio of ionized:nonionized in urine for both the vegetarian and meat eater.
2. Does your diet and supplement consumption while taking codeine increase or decrease the elimination of codeine in urine compared to a meat eater? Why?

Answer 1

1. Codeine pKa= 8 and is base

Urine pH= 7 in veg and 5 in non veg

According to Handerson Hasselbalch eq for bases

pH=pKa+log (ratio of unionized: ionized)

for veg 7=8+log (ratio of unionized: ionized)

log (ratio of unionized: ionized)=-1

ratio of unionized: ionized = 0.1

ratio of ionized: unionized= 1/0.1=10

for non veg 5=8 + log (ratio of unionized: ionized)

log ratio of unionized: ionized =-3

ratio of unionized: ionized =0.001

ratio of ionized:un ionized=1/0.001=1000

2. ionized i.e. polar forms in urine remain in urine and are not reabsorbed this process called ion trap. Ratio of ionized form of codeine is higher in meat so its excretion in urine will be higher than vegitarians thus vice versa i.e. vegitarian’s urine will excrete less codeine in comparison ot meat eater’s urine.