Pharmacology for Dentistry

Antihypertensive Agents 177

CENTRALLY ACTING DRUGS

CLONIDINE

It is an imidazoline derivative with a par-
tial agonist action. It stimulates presynap-
tic, α 2 receptors in vasomotor centre of brain
causing decreased sympathetic outflow
which results in fall of blood pressure and
bradycardia.

After oral administration the absorption
is almost complete and rapid. It penetrates
easily into CNS. Half to two third of oral
dose is excreted unchanged in urine.

Adverse effects include drowsiness, dry
mouth, sedation, restlessness, anxiety,
nightmares, dizziness, sleep disturbances,
skin rash, urticaria, nausea, constipation,
indigestion and impotence.

Abrupt withdrawal may result in severe
rebound hypertension, hepatic dysfunction
and renal dysfunction.

It is indicated in hypertension of all grades
except pheochromocytoma, glaucoma and
migraine. It is also useful in opiate, alcohol and
nicotine withdrawal. It also attenuates vaso-
motor symptoms of menopausal syndrome.

METHYLDOPA

It is α-methyl analogue of DOPA, the
precursor of dopamine and noradrenaline.

It is converted to alpha methyl
noradrenaline which stimulates central
alpha 2 adrenergic receptors in brain thereby
decreasing sympathetic outflow. It
decreases peripheral resistance more than
heart rate or cardiac output.

After oral administration bioavailability
is low because of extensive metabolism. It

is partly metabolized and partly excreted

unchanged in urine.

Adverse effects include dizziness, pos-

tural hypotension, sedation, dry mouth,

headache, sleep disturbances, depression,

anxiety, impotence, blurred vision, consti-

pation, skin rash, arthralgia, fatigue, anor-

exia, haemolytic anemia, parkinsonian

signs, drug fever and hepatitis.

It is indicated in mild to moderate

hypertension.

ADRENERGIC NEURONE BLOCKERS

RESERPINE

It is an alkaloid obtained from the roots of

‘Rauwolfia serpentina.’ It is known to deplete

the catecholamines – adrenaline,

noradrenaline and dopamine from the

various sites in the body. It also depletes 5-

hydroxytryptamine (serotonin).

Hypotension develops gradually and is

due to depletion of noradrenaline from

peripheral adrenergic nerve endings.

Adverse effects include nasal

congestion, flushing, bradycardia, postural

hypotension, water and salt retention and

CHF may be precipitated.

It also causes miosis, salivation,

increased gastric acid secretion. CNS side

effects include lethargy, apathy, psychic

depression which may result in suicidal

tendencies and weight gain.

Endocrinal disturbances include

gynecomastia and impotence.

Because of its serious side effects and

limited efficacy, it is not much used now

clinically.