Angiotensin II formed from angiotensin I in a reaction catalyzed by angiotensin converting enzyme (ACE), is a potent vasoconstrictor, the primary vasoactive hormone of the renin-angiotensin system and an important component in the pathophysiology of hypertension. It also stimulates aldosterone secretion by the adrenal cortex. Losartan and its principal active metabolite block the vasoconstrictor and aldosterone-secreting effects of angiotensin II by selectively blocking the binding of angiotensin II to the AT₁ receptor found in many tissues, (e.g. vascular smooth muscle, adrenal gland). In vitro binding studies indicate that losartan is a reversible, competitive inhibitor of the AT₁ receptor. Neither Losartan nor its active metabolite inhibits ACE (kinase II, the enzyme that converts angiotensin I to angiotensin II and degrades bradykinin); nor do they bind to or block other hormone receptors or ion channels known to be important in cardiovascular regulation.

Hydrochlorothiazide is a thiazide diuretic. Thiazides affect the renal tubular mechanisms of electrolyte reabsorption, directly increasing excretion of Sodium and Chloride in approximately equivalent amounts. Indirectly, the diuretic action of Hydrochlorothiazide reduces plasma volume, with consequent increases in plasma renin activity, increases in Aldosterone secretion, increases in urinary Potassium loss, and decreases in serum Potassium. The renin-aldosterone link is mediated by angiotensin II, so co-administration of an angiotensin II receptor antagonist tends to reverse the Potassium loss associated with these diuretics.

This is indicated for the treatment of hypertension. It is also indicated to reduce the risk of stroke in patients with hypertension and left ventricular hypertrophy.

Hypertension-

• The usual starting dose of 50/12.5 is one tablet once daily.
• For patients who do not respond adequately to one tablet the dosage may be increased to 100/25 once daily.
• A patient whose blood pressure is not adequately controlled with Losartan 100 mg monotherapy may be switched to this combination 100/12.5 once daily.
• In hypertensive patients with left ventricular hypertrophy initial dose is 50/12.5, if additional blood pressure reduction is needed, 100/12.5 may be given, followed by 100/25 if required. The maximum dose is 100/25 once daily.
• In general, the antihypertensive effect is attained within three weeks after initiation of therapy.
• No initial dosage adjustment of 50/12.5 is necessary for elderly patients. But maximum dose of 100/25 once daily dose should not be used as initial therapy in elderly patients.

Severe Hypertension:

• The starting dose for initial treatment of severe hypertension is one tablet of 50/12.5 once daily.
• For patients who do not respond adequately to this dose after 2 to 4 weeks of therapy, the dosage may be increased to 100/25 once daily. The maximum dose is one tablet of 100/25 once daily.

Administration

This preparation may be administered with other antihypertensive agents. This may be administered with or without food.

The combination of Losartan and Hydrochlorothiazide is contraindicated in patients who are hypersensitive to any component of this product. Because of the Hydrochlorothiazide component, this product is contraindicated in patients with anuria or hypersensitivity to other sulfonamide-derived drugs.

Side-effects are usually mild. Symptomatic hypotension including dizziness may occur, particularly in patients with intravascular volume depletion (e.g. those taking high-dose diuretics). Hyperkalaemia occurs occasionally; angioedema has also been reported with some angiotensin-II receptor antagonists. Vertigo; less commonly gastro-intestinal disturbances, angina, palpitation, oedema, dyspnoea, headache, sleep disorders, malaise, urticaria, pruritus, rash; rarely hepatitis, atrial fibrillation, cerebrovascular accident, syncope, paraesthesia; also reported pancreatitis, anaphylaxis, cough, depression, erectile dysfunction, anaemia, thrombocytopenia, hyponatraemia, arthralgia, myalgia, renal impairment, rhabdomyolysis, tinnitus, photosensitivity, and vasculitis (including Henoch-Schonlein purpura)

Overdose Effects

Losartan Potassium: Limited data are available in regard to overdosage in humans. The most likely manifestation of overdosage would be hypotension and tachycardia; bradycardia could occur from parasympathetic (vagal) stimulation. If symptomatic hypotension should occur, supportive treatment should be instituted. Neither losartan nor its metabolite can be removed by hemodialysis.

Hydrochlorothiazide: The most common signs and symptoms observed are those caused by electrolyte depletion (hypokalemia, hypochloremia, and dehydration resulting from excessive diuresis. If digitalis has also been administered, hypokalemia, may accentuate cardiac arrhythmias. The degree to which Hydrochlorothiazide is removed by hemodialysis has not been established.

• Hypersensitivity: Angiooedema
• Periodic determination of serum electrolytes to detect possible electrolyte imbalance should be performed at appropriate intervals
• Hypokalemia may rarely develop, especially with brisk diuresis, when severe cirrhosis is present, or after prolonged therapy
• Impaired renal function and
• Symptomatic hypotension

Use in Special Populations

Use in Patients with Renal Impairment: The usual regimens of therapy with 50/12.5 may be followed as long as the patient's creatinine clearance is >30 ml/min. In patients with more severe renal impairment, loop diuretics are preferred to thiazides. In that case, hydrochlorothiazide is not recommended.

Use in Patients with Hepatic Impairment: The combination of Losartan and Hydrochlorothiazide is not recommended for titration in patients with hepatic impairment because the appropriate 25 mg starting dose of Losartan cannot be given.

Use in pediatric patients: The safety and effectiveness in pediatric patients have not been established.

Pregnancy & Lactation

Angiotensin-II receptor antagonists should be avoided in pregnancy unless essential. They may adversely affect fetal and neonatal blood pressure control and renal function; skull defects and oligohy dramnios have also been reported. Information on the use of angiotensin-II receptor antagonists in breastfeeding is limited. They are not recommended in breastfeeding and alternative treatment options, with better-established safety information during breastfeeding, are available.