Antihypertensive Agents 179It selectively and competitively
antagonises the action of catecholamines
mediated through adrenergic receptors. It
decreases heart rate, force of cardiac contrac-
tion. During longterm therapy, the blood
pressure falls in patients of hypertension.
The renin secretion is inhibited.
After oral administration it is absorbed
almost completely but a large portion of the
dose is metabolised in liver before reaching
systemic circulation as a result the
bioavailability of propranolol is reduced. It
is highly bound to plasma proteins.
Adverse effects include fatigue,
tiredness, skin rash, fever, depression,
nightmares, sexual dysfunction, nausea,
epigastric distress, cold extremities and
hypoglycaemia.
It is indicated in hypertension, cardiac
arrhythmias, longterm management of MI,
hypertrophic subaortic stenosis, pheochro-
mocytoma, migraine prophylaxis, angina pec-
toris, essential tremors.
The detailed pharmacology of propra-
nolol is discussed in chapter ‘Adrenergic
blocking agents.’
METOPROLOL
It is a relatively selective βββββ 1 adrenergic
antagonist with no agonist activity. It
reduces plasma renin activity in
hypertensive patients.
After oral administration its absorption
is good and rapid. It is metabolised
extensively in body and shows first pass
metabolism in liver (less than propranolol).
Adverse effects include headache, dizzi-ness, nausea, vomiting, skin rash, diarrhoea,
nightmares, hypotension and bradycardia.
It is indicated in hypertension, angina
pectoris, cardiac arrhythmia, post MI
patients, adjunctive management of
thyrotoxicosis and prophylaxis of migraine.ATENOLOL
It is a cardioselective βββββ 1 blocker with
insignificant intrinsic sympathomimetic
activity.
After oral administration it is
incompletely absorbed, excreted largely in
urine as unchanged drug.
Adverse effects include bradycardia,
nausea, vomiting, epigastric discomfort,
dizziness, fatigue, tiredness, skin rash, leg
pain, cold extremities because of peripheral
arterial insufficiency.
It is indicated in hypertension, angina
pectoris and acute MI.PINDOLOL
It is a non-selective βββββ adrenergic
blocker with partial agonist activity.
It is absorbed efficiently after oral
administration and is metabolised in liver.
Adverse effects include dizziness, nausea,
vomiting, headache and sleep disturbances.CARVEDILOL
It competitively blocks βββββ 1 , βββββ 2 and ααααα 1
adreno-receptors. It lacks sympathomi-
metic activity and has vasodilating prop-
erties which are exerted mainly through
β 1 blockade. It reduces both systolic and
diastolic blood pressure without reflex
tachycardia.