Question

Because the interior of cell membranes is made of non-polar molecular regions, drugs with acid-base properties are better absorbed by cells when their most abundant form is not electrically charged (not an ion). In which region of the body will phenobarbital be absorbed at the lowest rate? (stomach, duodenum, jejunum).

it's not stomach

Answer 1

Jejunum is the right answer.

Phenobarbital is primarily absorbed from the intestines.The presence of food decreased the pharmacological activity of phenobarbital by decreasing the rate of absorption and that this decreased absorption rate is due primarily to slowed gastric emptying.

For example, In reports the effect of food on the oral absorption of phenobarbital in the rat was checked. The presence of food was found to lower significantly the serum levels of intact drug and to reduce dramatically (and at low doses, 100 mg./kg., to eliminate) sleeping times induced by phenobarbital. The amounts of drug remaining unabsorbed in the stomach and intestines were determined in fasted and nonfasted rats. Greater than 90% of the amount unabsorbed was found in the stomach in both test conditions, but the amounts unabsorbed were greater in the nonfasted rats. Since the drug is rapidly absorbed in the intestine, the extent of absorption is the same in the nonfasted rat as in the fasted rat.