Losartan and admistration
Losartan is an angiotensin II
receptor antagonist with antihypertensive activity due mainly to selective
blockade of AT1 receptors and the consequent reduced pressor effect
of angiotensin II. It is used in the management of hypertension and may
have a role in patients who develop cough with ACE inhibitors it has also been
tried in heart failure (below) and in myocardial infarction (p.805), and is
under investigation in diabetic nephropathy.
Losartan is given by mouth
as the
potassium salt. The maximum hypertensive effect is achieved in about 3
to 6 weeks after initiating treatment
In hypertension the usual
dose is 50
mg ones daily.
The dose maybe increased, if
necessary, to 100mg daily as a single dose of 25mg ones daily maybe used in the
elderly over 75 years, and for patient with moderate to severe renal impairment
(creatinine) clearance less than 20 ml per minute), intravascular fluid
depletion. A reduced dose should also be considered for patient with hepatic
impairment.
Pharmacokinetics
Losartan is readily absorbed
from the gastrointestinal tract following oral administration with an oral
bioavailability of out 33% it undergoes first-pass metabolism to form an active
carboxylic acid
metabolites.
Peak plasma concentrations
of losartan and E-3174 occur about 1 hour and 3 to 4 hours, respectively, after
an oral dose both losartan and E-3174 are more than 98% bound to plasma
proteins. Losartan is
excreted in the
urine, and in the feaces via bile, as
unchanged drug and metabolites, the oral dosing about 35% of the dose is
excreted in the urine and about 60% in the faeces. The terminal elimination
half-lives of losartan and e-3174 are about 1.5 to 2.5 hour and 3 to 9 hours
respectively.
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