Autacoids

Question 1

H1 antagonist

Answer 1

Both neutral H 1 antagonists and inverse H 1 agonists reduce or block the actions of histamine by reversible competitive binding to the H 1 receptor. Several have been clearly shown to be inverse agonists, and it is possible that all act by this mechanism. They have negligible potency at the H 2 receptor and little at the H 3 receptor.

example, histamine-induced contraction of bron- chiolar or gastrointestinal smooth muscle can be completely blocked by these agents, but the effects on gastric acid secretion and the heart are unmodified.

Question 2

The first-generation H 1 -receptor antagonists

Answer 2

The large number of these actions probably results from the similarity of the general structure (F igure 16–1) to the structure of drugs that have effects at muscarinic cholinoceptor, α adrenoceptor, serotonin, and local anesthetic receptor sites. Some of these actions are of therapeutic value and some are undesirable.

They are less effective against an episode of motion sickness already present

Question 3

Second- generation H 1 antagonists

Answer 3

These drugs (or their active metabolites) also have far fewer autonomic effects than the first-generation antihistamines.

have little or no sedative or stimulant actions.

Question 4

doxylamine

Answer 4

The first-generation H 1 -receptor antagonists Ethanolamines

were used widely in the past in the treatment of nausea and vomiting of pregnancy

DOA 3-6

Question 5

Serotonin-blocking action—

Answer 5

Strong blocking effects at sero- tonin receptors have been demonstrated for some first-generation H 1 antagonists, notably cyproheptadine

Question 6

Promethazine

Answer 6

First Generation Antihistamines (Phenothiazines)
mostly antiemitic 
all +++
 local anesthetics
4-8

Question 7

First Generation Antihistamines (Alkylamines)++ antiM

First Generation Antihistamines (Ethylaminediamines) + anitM

Answer 7

no antiemitic activity

Question 8

First Generation Antihistamines (Intranasal)

Answer 8

Azelastine

12

Question 9

The piperazines (cyclizine and meclizine) also have significant activity in preventing motion sick- ness and are less sedating than diphenhydramine in most patients

Answer 9

1

Question 10

he second-generation H 1 antagonists are used mainly for the treatment of allergic rhinitis and chronic urticaria

Answer 10

2

Question 11

Like the other hista- mine receptors, the H 2 receptor displays constitutive activity, and some H 2 blockers are inverse agonists

Answer 11

3