Pharmacology for Dentistry

222 Section 5/ Autacoids

can also stimulate the smooth muscles of uterus.

Nerve endings: 5-HT is less potent than
histamine in releasing catecholamines from
adrenal medulla. 5-HT 3 receptors located on
various sensory neurons mediate a
depolarising response, which may cause
pain & itching.

5-HT ANTAGONISTS

5-HT antagonists are classified in table 5.2.1.

Many of the drugs are partial agonists
or antagonise certain action of 5-HT but
stimulate others. The two drugs that are
usually classified as 5-HT antagonist namely
methysergide and cyproheptadine is used
as a potent 5-HT 1 antagonist, while another
drug, ketanserin is highly selective for
blocking 5HT 2 receptors.

METHYSERGIDE

Chemically, methysergide is 1-methyl-d-
lysergic acid butanolamide, congener of
methylergonovine and of LSD.

It antagonises the vasoconstrictor and

pressor effect of 5-HT as well as the action

of the amine on a variety of extravascular

smooth muscles.

It has been used for migraine prophy-

laxis, vascular headaches, postgastrectomy

dumping syndrome and also used to

combat diarrhoea and malabsorption in car-

cinoid patients.

Common side effects include nausea,

vomiting, heartburn, diarrhoea. Central

effects include drowsiness, weakness,

nervousness, insomnia, confusion, excite-

ment and hallucinations.

CYPROHEPTADINE

Chemically, it is a phenothiazine

derivative and has equal potency at both

H 1 -histamine and 5-HT receptors as an

antagonist. As H 1 -histamine antagonist it

has been used in various allergic

conditions. It increases the appetite and

promotes weight gain.

Table 5.2.1: Classification of 5-HT antagonists.

I. Ergot alkaloids and derivatives

Ergotamine 1-3 mg/day, 0.25-0.5 mg SC/IM

Lysergic acid diethylamide (LSD)

2-Bromolysergic acid amide (BOL)

Methysergide (Congener of LSD; SANSERT) 2 mg BD-TDS

Metergoline

II. Antihistaminics

Cyproheptadine (PERIACTIN) 4 mg/day

Cinnarizine (STUGERON) 25-50 mg/day

III.Phenothiazines

Chlorpromazine (LARGECTIL) 25-100 mg/day, IM

IV.Selective 5-HT blockers

Ketanserin (SUFREXAL) 10-30 mg/day

Pizotifen (PIZOTYLINE) 0.5-1 mg/day