Torlos-50 Drug Interactions

No significant drug-drug pharmacokinetic interactions have been found in interaction studies with hydrochlorothiazide, digoxin, warfarin, cimetidine and phenobarbital. Rifampin, an inducer of drug metabolism, decreased the concentrations of Losartan and its active metabolite. In humans, two inhibitors of P450 3A4 have been studied. Ketoconazole did not affect the conversion of Losartan to the active metabolite after intravenous administration of Losartan, and erythromycin had no clinically significant effect after oral administration. Fluconazole, an inhibitor of P450 2C9, decreased active metabolite concentration and increased Losartan concentration. The pharmacodynamic consequences of concomitant use of Losartan and inhibitors of P450 2C9 have not been examined. Subjects who do not metabolize Losartan to active metabolite have been shown to have a specific, rare defect in cytochrome P450 2C9. These data suggest that the conversion of Losartan to its active metabolite is mediated primarily by P450 2C9 and not P450 3A4.
As with other drugs that block angiotensin II or its effects, concomitant use of potassium-sparing diuretics (e.g., spironolactone, triamterene, amiloride), potassium supplements, or salt substitutes containing potassium may lead to increases in serum potassium.
Lithium: Increases in serum lithium concentrations and lithium toxicity have been reported during concomitant administration of lithium with angiotensin II receptor antagonists. Monitor serum lithium levels during concomitant use.
Non-Steroidal Anti-Inflammatory Drugs (NSAIDs) Including Selective Cyclooxygenase-2 Inhibitors (COX-2 Inhibitors): In patients who are elderly, volume-depleted (including those on diuretic therapy), or with compromised renal function, co-administration of NSAIDs, including selective COX-2 inhibitors, with angiotensin II receptor antagonists (including Losartan) may result in deterioration of renal function, including possible acute renal failure. These effects are usually reversible. Monitor renal function periodically in patients receiving Losartan and NSAID therapy.
The antihypertensive effect of angiotensin II receptor antagonists, including Losartan, may be attenuated by NSAIDs, including selective COX-2 inhibitors.
Dual Blockade of the Renin-Angiotensin System (RAS): Dual blockade of the RAS with angiotensin receptor blockers, ACE inhibitors, or aliskiren is associated with increased risks of hypotension, syncope, hyperkalemia, and changes in renal function (including acute renal failure) compared to monotherapy.
In most patients no benefit has been associated with using two RAS inhibitors concomitantly. In general, avoid combined use of RAS Inhibitors. Closely monitor blood pressure, renal function, and electrolytes in patients on Losartan potassium and other agents that affect the RAS.
Do not co-administer aliskiren with Losartan potassium in patients with diabetes. Avoid use of aliskiren with Losartan potassium in patients with renal impairment (GFR <60 mL/min).