Valsartan/hydrochlorothiazide is a fixed-dose (valsartan 80, 160 or 320mg plus hydrochlorothiazide 12.5 or 25mg) angiotensin II receptor blocker/diuretic drug combination indicated for the treatment of patients with essential hypertension not adequately controlled by monotherapy. There is ample evidence that valsartan/hydrochlorothiazide is an effective fixed-dose combination antihypertensive agent. However, efficacy and tolerability data pertaining to the 320mg dose of valsartan in the combination are currently relatively few. There is also some evidence of potential benefits associated with the relatively favourable tolerability profile of the combination, the low occurrence of new-onset diabetes mellitus versus amlodipine and the valsartan-associated improvements in cardiac and endothelial function. Pharmacological Properties: Valsartan is a selective antagonist of the angiotensin II type 1 receptor. This drug has established antihypertensive effects and is associated with improvements in cardiac function (reduced left ventricular mass), endothelial function (improved basal nitric oxide availability, reduced formation of reactive oxygen species, reduced C-reactive protein levels) and lipid profiles. Hydrochlorothiazide is a thiazide diuretic which inhibits Na-Cl transport in the kidney and reduces plasma volume. It has been associated with improvements in cardiac output, mean arterial pressure, stroke volume, heart rate and total peripheral resistance in patients with hypertension. It has also been linked with dyslipidaemia, hyperglycaemia and increased risk of developing type 2 diabetes mellitus in some patients, and it may increase levels of some inflammatory biomarkers. Coadministration of valsartan and hydrochlorothiazide does not have a clinically relevant pharmacokinetic effect on either drug. Plasma concentrations of both components increase dose-proportionally, with peak concentrations reached in 2-5 hours. The elimination half-life of the components ranges from 2.5 to 19 hours, mainly because of variability in hydrochlorothiazide values. Clearance is 2.2 L/h for valsartan and 20-22 L/h for hydrochlorothiazide. Excretion of valsartan is mainly faecal and that of hydrochlorothiazide is mainly renal. While the systemic clearance of hydrochlorothiazide is decreased in older patients, the effects of age on valsartan pharmacokinetics are not considered clinically significant. Exposure to hydrochlorothiazide is increased in patients with renal dysfunction and exposure to valsartan is increased in patients with hepatic dysfunction. Therapeutic Efficacy: The superior antihypertensive efficacy of once-daily valsartan 80-320mg plus hydrochlorothiazide 12.5 or 25mg over the individual components has been demonstrated in well designed trials in patients with hypertension unresponsive to monotherapy or with moderate to severe hypertension. In the only trial investigating comparative clinical cardiovascular outcomes, valsartan- and amlodipine-based therapy regimens had similar results for the primary efficacy parameter (total cardiac morbidity and mortality 10.6% vs 10.4%), despite not achieving the prespecified equivalent reduction in blood pressure (BP). Patients (aged ≥50 years) at high cardiovascular risk received increased dosages of monotherapy and then additional hydrochlorothiazide as required for a mean of 4.2 years. BP reduction and occurrence of myocardial infarction favoured amlodipine-based therapy, while the rate of new-onset diabetes mellitus favoured valsartan-based therapy. In contrast, equivalent BP reduction was seen in a 6-month comparison of valsartan-based and amlodipine-based therapy in elderly patients with moderate to severe isolated systolic hypertension. Valsartan/hydrochlorothiazide recipients had similar BP reductions to those in patients receiving amlodipine monotherapy in two double-blind trials; a significantly greater reduction in systolic BP was seen with the higher hydrochlorothiazide dose in another double-blind trial. One single-blind trial indicated superior systolic/diastolic BP reductions with the combination. Noninferiority for valsartan/ hydrochlorothiazide versus amlodipine monotherapy has been demonstrated in Black African-American patients with mild to moderate hypertension. There are preliminary indications that valsartan/hydrochlorothiazide has generally similar antihypertensive efficacy to that of other angiotensin receptor blocker/hydrochlorothiazide combinations. Tolerability: Valsartan/ hydrochlorothiazide is well tolerated. Adverse events (most commonly dizziness, headache and fatigue) are generally mild and transient. Serious adverse events that have rarely been associated with the combination include orthostatic hypotension, syncope, angioneurotic oedema, angina pectoris and atrial fibrillation. The tolerability profile of the combination was superior to that of lisinopril/ hydrochlorothiazide (similar efficacy profile). Hypokalaemia occurs less often with the valsartan/hydrochlorothiazide combination than with hydrochlorothiazide monotherapy or amlodipine/hydrochlorothiazide.
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