A lipophilic drug with a pK = 6.0 is taken orally and dissolves in the gastric environment of the stomach (pH = 1.0).

âWhat is the degree of ionization of the drug in the stomach and the blood plasma (pH = 7.4)?

âIn what direction will this drug tend to passively diffuse between the two compartments?

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. Hydrochloric acid is secreted into the stomach by parietal cells (also known as oxyntic cells) in the gastric lining. These cells contain a H+/K+ ATPase antiporter in their apical membrane. Gastric juice (pH 1.5) is produced by pumping HCl from blood plasma (pH 7.4) into the stomach. Calculate the amount of free energy required to concentrate the H+ in 1 L of gastric juice at 37 Â°C. Assume that [K+]outside = [K+]inside and that the net [K+] and [H+] remain constant both inside and outside the cell. Note that this is an electroneutral reaction, therefore the change in charge does not need to be calculated.

Aspirin is a monoprotic weak acid with a K a of 3.98 x 10-4 and one dose of aspirin is 500mg.

Write the reaction that controls the pH of aspirin (HC9H7O4)

Given that the average stomach has a pH of 1.4 and a volume of approximately 1 liter, calculate the concentration of aspirin (HA) and its conjugate (A - ) in the stomach.

The conjugate of aspirin is the active drug, and it is absorbed from the stomach into the bloodstream. The pH of the blood stream is 7.4. Assume that all the A - you calculated in (b) is initially absorbed into the bloodstream and calculate what the new ratio of A - /HA will become at this pH.

The absorption of drug molecules such as aspirin (acetylsalicylic acid) depends on their ability to penetrate nonpolar cell membranes. A large KP value indicates that the drug is able to do this efficiently. AH2O â Amembrane [A]membrane KP = â¯ï£§â¯ï£§â¯ï£§â¯ï£§ [A]H2O A. Aspirin has a carboxyl group with a pKa = 3.5 Calculate the exact percent of the drug in the uncharged (neutral) form at pH = 2. Calculate exactly the KP value in the stomach at pH = 2. Explain your reasoning and any simplifying assumptions. Show all work. B. If the large intestine has a pH = 5.5, estimate the percent in the uncharged form at this pH. What do you predict will be the ÎGÂ°transfer into the membrane? Explain your reasoning and any assumptions and show all work. ï¿¼C. Do you expect aspirin to cross the cell membrane more efficiently in the stomach or in the intestine? Quantify how much better. Explain your reasoning and any assumptions.

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