Pharmacology for Dentistry

178 Section 4/ Drugs Acting on Cardiovascular & Urinary System

Guanethidine is another agent which
inhibits release of noradrenaline. Causes
sodium and water retention and may
precipitate CHF. Endocrinal side effects are
more common e.g. impotence and inhibition
of ejaculation. It is also not used now
clinically.

ADRENERGIC RECEPTOR ANTAGONISTS

The detailed pharmacology of alpha and
beta blockers is already discussed in chapter
‘Adrenergic blocking agents’. Only
adrenergic blockers used in hypertension
are discussed here.

PRAZOSIN

It selectively blocks post synaptic α 1 adr-
energic receptors due to which vasodilata-
tion occurs. The haemodynamic effects are
decreased arterial pressure and reduction in
venous and arterial tone.

It shows first pass metabolism in liver
and it is highly bound to plasma proteins.

Adverse effects include postural
hypotension, dizziness, tachycardia,
palpitation, headache, weight gain, dry
mouth, nausea, diarrhoea, constipation,
nasal stuffiness, priapism and skin rash.

TERAZOSIN

It is an ααααα 1 adrenoceptor antagonist and
is a close structural analog of prazosin. It has
a long duration of action.

It selectively blocks α 1 adrenoceptors
due to which vasodilatation occurs and the
blood pressure is reduced.

After oral administration it is almost
completely absorbed. It is highly bound to

plasma proteins and is metabolised in liver.

About 10% terazosin is excreted unchanged

in urine. It crosses the placenta.

Adverse effects include marked hy-

potension with first dose of terazosin, drowsi-

ness, dizziness, nausea, blurred vision, nasal

congestion, peripheral edema, syncopal epi-

sodes and headache. In patients with BPH

postural hypotension has been reported more

than in those with hypertension.

It is indicated in mild to moderate

hypertension, symptomatic relief of urinary

obstruction in patients of benign prostatic

hypertrophy.

DOXAZOSIN

It effectively controls blood pressure

over 24 hours suppressing early morning BP

rise. It increases insulin sensitivity, improves

lipid profile.

It is extensively metabolised in the liver

mainly by O-demethylation or hydroxyla-

tion. Approximately 4.8% is excreted in the

faeces as unchanged drug.

Adverse effects include postural hy-

potension (rarely associated with fainting),

dizziness, headache, fatigue/malaise, ver-

tigo, edema, asthenia, somnolence, nausea

and rhinitis.

It is indicated in mild to moderate,

hypertension, treatment of both urinary

outflow obstruction, obstructive and

irritative symptoms associated with BPH.

PROPRANOLOL

It is βββββ 1 , βββββ 2 adrenergic receptor blocker

with membrane stabilising activity.