Valsartan is an oral medication that belongs to a class of drugs called angiotensin receptor blockers (ARBs). It is orally active and specific angiotensin II antagonist acting on the AT1 subtype. Angiotensin’s attachment to the receptors cause the blood vessels to narrow (vasoconstrict) which leads to an increase in blood pressure (hypertension). Valsartan blocks the angiotensin II receptor. By blocking the action of angiotensin, Valsartan dilates blood vessels and reduces blood pressure without affecting pulse rate. Valsartan has much greater affinity (about 20,000-fold) for the AT1 receptor than for the AT2 receptor. It does not bind 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 anangiotensin converting enzyme (ACE) inhibitor tends to reverse the potassium loss associated with these diuretics.
Dosage & Administration
Hypertension: A patient whose blood pressure is not controlled with Valsartan and Hydrochlorothiazide monotherapy, should switch to Valsartan and Hydrochlorothiazide combination once daily. Highest allowed dose of Valsartan should not be greater than 320 mg in combination with hydrochlorothiazide 25 mg.
For Elderly: No initial dosage adjustment is necessary for elderly patients.
Pediatric use: Safety and effectiveness in pediatric patients have not been established.
- Diuretics: Patient on diuretics may occasionally experience excessive reduction in blood pressure after initiation of therapy with Valsartan. No drug interaction of clinical significance has been identified with thiazide diuretics.
- Agents increasing Serum Potassium: Since Valsartan decreases the production of aldosterone, potassium supplements or salt containing potassium substitutes may lead to hyperkalemia.
- Lithium Salts: As with other drugs which eliminate sodium, lithium clearance may be reduced. Therefore, serum lithium levels should be monitored carefully if lithium salts are to be administered.
- Other drugs showing interaction are Warfarin, Digoxin.
- When administered concurrently, the following drugs may interact with thiazide diuretics: alcohol, barbiturates, or narcotics may potentiate antihypertensive effect or orthostatic hypotension may occur.
- Antidiabetic drugs (oral agents and insulin): dosage adjustment of the antidiabetic drug may be required.
- Other antihypertensive drugs give additive effect.
- Cholestyramine and colestipol resins: absorption of Hydrochlorothiazide is impaired in the presence of anionic exchange resins.
Pregnancy & Lactation
Pregnancy: Valsartan should not be used in pregnancy, as in 2nd and 3rd trimester it can cause injury and even death to fetus. When pregnancy is detected, Valsartan should be stopped as soon as possible.
Nursing mothers: It is not known whether Valsartan is excreted in human milk. Hydrochlorothiazide is excreted in breast milk.