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Chapter 16 Review Question Answers
1. The following functional group interactions between the catecholamines and
adrenoceptors are most likely:
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Cationic amino group and aspartic acid 113 in TMD III
3’-OH group and serine 204 in TMDV
4’-OH group and serine 204 in TMD V
1-OH group and asparagines 293 in TMD VI
Catechol ring and phenylalanine 290 in TMD VI
The first four functional groups are considered the pharmacophores of the catecholamines
and are important for their direct-acting activity.
2. Drugs A, B, and C would resist COMT. The COMT enzyme O-methylates 3’-OH group
of catecholamines to 3’-methoxyl group to give inactive metabolites. The methylation
occurs almost exclusively on the 3’-OH group of the catechol. Since Drugs A, B, and C
are not catechols, they are not substrates of the enzyme and thus are resistant to its
metabolism.
3. Drug E (norepinephrine) is the least orally active and has the shortest duration of action,
for the following reasons:
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It is polar and ionized at physically pH and therefore is has poor absorption.
MOA and COMT can metabolically degrade the drug.
4. Drugs B (colterol), C (albuterol), and D (terbutaline)
5. All of the choices except Drug D are considered to be prodrugs. Drug A (Dipivefrin) is
hydrolyzed by esterases to its active metabolite, epinephrine. Drug B (Midodrine) is
hydrolyzed by amidases to its active metabolite, desglymidodrine. Drug C (Bitolterol) is
hydrolyzed slowly by esterases to its active metabolite, colterol. Drug D (Esmolol) is
hydrolyzed by esterases to its inactive metabolite. Drug E (Methyldopate) is hydrolyzed,
decarboxylated, and -hydroxylated to its active metabolite, (1R, 2S)-methylnorepinephrine.
Ch. 16 Review Question Answers
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