Losartan Potassium and Hydrochlorothiazide (Page 4 of 8)
It is not known whether losartan is excreted in human milk, but significant levels of losartan and its active metabolite were shown to be present in rat milk. Thiazides appear in human milk. Because of the potential for adverse effects on the nursing infant, a decision should be made whether to discontinue nursing or discontinue the drug, taking into account the importance of the drug to the mother.
8.4 Pediatric Use
Safety and effectiveness of losartan potassium and hydrochlorothiazide tablets in pediatric patients have not been established.
Neonates with a history of in utero exposure to losartan potassium and hydrochlorothiazide tablets: If oliguria or hypotension occurs, direct attention toward support of blood pressure and renal perfusion. Exchange transfusion or dialysis may be required as means of reversing hypotension and/or substituting for disordered renal function.
8.5 Geriatric Use
In a controlled clinical study for the reduction in the combined risk of cardiovascular death, stroke and myocardial infarction in hypertensive patients with left ventricular hypertrophy, 2857 patients (62%) were 65 years and over, while 808 patients (18%) were 75 years and over. In an effort to control blood pressure in this study, patients were coadministered losartan and hydrochlorothiazide 74% of the total time they were on study drug. No overall differences in effectiveness were observed between these patients and younger patients. Adverse events were somewhat more frequent in the elderly compared to non-elderly patients for both the losartan-hydrochlorothiazide and the control groups [see Clinical Pharmacology (12.3)].
In the Losartan Intervention For Endpoint reduction in hypertension (LIFE) study, Black patients with hypertension and left ventricular hypertrophy treated with atenolol had a lower risk of stroke, the primary composite endpoint, as compared with Black patients treated with losartan (both cotreated with hydrochlorothiazide in the majority of patients). In the subgroup of Black patients (n=533, 6% of the LIFE study patients), there were 29 primary endpoints among 263 patients on atenolol (11%, 26 per 1000 patient-years) and 46 primary endpoints among 270 patients (17%, 42 per 1000 patient-years) on losartan. This finding could not be explained on the basis of differences in the populations other than race or on any imbalances between treatment groups. In addition, blood pressure reductions in both treatment groups were consistent between Black and non-Black patients. Given the difficulty in interpreting subset differences in large trials, it cannot be known whether the observed difference is the result of chance. However, the LIFE study provides no evidence that the benefits of losartan on reducing the risk of cardiovascular events in hypertensive patients with left ventricular hypertrophy apply to Black patients [see Clinical Pharmacology (12.3)].
8.7 Hepatic Impairment
Initiation of losartan potassium and hydrochlorothiazide tablets is not recommended for patients with hepatic impairment because the appropriate starting dose of losartan, 25 mg, is not available.
8.8 Renal Impairment
Changes in renal function have been reported in susceptible individuals [see Dosage and Administration (2.1), Warnings and Precautions (5.4), and Clinical Pharmacology (12.3)]. Safety and effectiveness of losartan potassium and hydrochlorothiazide tablets in patients with severe renal impairment (creatinine clearance < 30 mL/min) have not been established.
Significant lethality was observed in mice and rats after oral administration of 1000 mg/kg and 2000 mg/kg, respectively, about 44 and 170 times the maximum recommended human dose on a mg/m2 basis.
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 active metabolite can be removed by hemodialysis.
The oral LD50 of hydrochlorothiazide is greater than 10 g/kg in both mice and rats. The most common signs and symptoms observed are those caused by electrolyte depletion (hypokalemia, hypochloremia, hyponatremia) 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.
Losartan Potassium and Hydrochlorothiazide Tablets USP, 50 mg/12.5 mg, Losartan Potassium and Hydrochlorothiazide Tablets USP, 100 mg/12.5 mg, and Losartan Potassium and Hydrochlorothiazide Tablets USP, 100 mg/25 mg combine an angiotensin II receptor blocker acting on the AT1 receptor subtype and a diuretic, hydrochlorothiazide, USP.
Losartan potassium USP, a non-peptide molecule, is chemically described as 2-butyl-4-chloro-1-[p -(o -1H -tetrazol-5-ylphenyl)benzyl]imidazole-5-methanol monopotassium salt. Its structural formula is:
C22 H22 ClKN6 O M.W. 461.01
Losartan potassium, USP is a white to off-white free-flowing crystalline powder. It is freely soluble in water, soluble in alcohols, and slightly soluble in common organic solvents, such as acetonitrile and methyl ethyl ketone.
Oxidation of the 5-hydroxymethyl group on the imidazole ring results in the active metabolite of losartan.
Hydrochlorothiazide, USP is 6-chloro-3,4-dihydro-2H -1,2,4-benzothiadiazine-7-sulfonamide 1,1-dioxide. Its structural formula is:
C7 H8 ClN3 O4 S2 M.W. 297.74
Hydrochlorothiazide, USP is a white, or practically white, crystalline powder, which is slightly soluble in water, but freely soluble in sodium hydroxide solution.
Losartan Potassium and Hydrochlorothiazide Tablets USP are available for oral administration in three tablet combinations of losartan and hydrochlorothiazide, USP. Losartan Potassium and Hydrochlorothiazide Tablets USP, 50 mg/12.5 mg contain 50 mg of losartan potassium, USP and 12.5 mg of hydrochlorothiazide, USP. Losartan Potassium and Hydrochlorothiazide Tablets USP, 100 mg/12.5 mg contain 100 mg of losartan potassium, USP and 12.5 mg of hydrochlorothiazide, USP. Losartan Potassium and Hydrochlorothiazide Tablets USP, 100 mg/25 mg contain 100 mg of losartan potassium, USP and 25 mg of hydrochlorothiazide, USP. Inactive ingredients are: lactose monohydrate, magnesium stearate, microcrystalline cellulose, polyethylene glycol, polyvinyl alcohol-part hydrolyzed, pregelatinized corn starch, talc, and titanium dioxide. Additionally, 50 mg/12.5 mg tablets contain D&C Yellow #10 (Aluminum Lake) and FD&C Blue #1 (Aluminum Lake) and the 100 mg/25 mg tablets contain D&C Yellow #10 (Aluminum Lake).
Losartan Potassium and Hydrochlorothiazide Tablets USP, 50 mg/12.5 mg contain 4.24 mg (0.108 mEq) of potassium, Losartan Potassium and Hydrochlorothiazide Tablets USP, 100 mg/12.5 mg contain 8.48 mg (0.216 mEq) of potassium, and Losartan Potassium and Hydrochlorothiazide Tablets USP, 100 mg/25 mg contain 8.48 mg (0.216 mEq) of potassium.
12 CLINICAL PHARMACOLOGY
12.1 Mechanism of Action
Angiotensin II [formed from angiotensin I in a reaction catalyzed by angiotensin converting enzyme (ACE, kininase II)], 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). There is also an AT2 receptor found in many tissues but it is not known to be associated with cardiovascular homeostasis. Neither losartan nor its principal active metabolite exhibits any partial agonist activity at the AT1 receptor, and both have much greater affinity (about 1000-fold) for the AT1 receptor than for the AT2 receptor. In vitro binding studies indicate that losartan is a reversible, competitive inhibitor of the AT1 receptor. The active metabolite is 10 to 40 times more potent by weight than losartan and appears to be a reversible, non-competitive inhibitor of the AT1 receptor.
Neither losartan nor its active metabolite inhibits ACE (kininase 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 coadministration of an angiotensin II receptor antagonist tends to reverse the potassium loss associated with these diuretics. The mechanism of the antihypertensive effect of thiazides is unknown.
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