Diuretic and other antihypertensive agents: Other antihypertensive agents may increase the hypotensive effects of Irbesartan; however this drug has been safely administered with other antihypertensive agents, such as beta-blockers, long-acting calcium channel blockers, and thiazide diuretics. Prior treatment with high dose diuretics may result in volume depletion and a risk of hypotension when initiating therapy with this drug.
Potassium supplements and potassium-sparing diuretics: Based on experience with the use of potassium-sparing diuretics potassium supplements, salt substitutes containing potassium or other medicinal products what may increase serum potassium levels (e.g. heparin) may lead to increase in serum potassium and is therefore, not recommended.
Lithium: Reversible increase in serum lithium concentrations and toxicity have been reported during concomitant administration of lithium with angiotensin converting enzyme inhibitors. Similar effects have been very rarely reported with irbesartan so far. Therefore, this combination is not recommended. If the combination proves necessary careful, monitoring of serum lithium levels is recommended.
Non-steroidal anti-inflammatory drugs: when angiotensin II antagonists are administered simultaneously with non-steroidal anti-inflammatory drugs (i.e. selective COX-2 inhibitors, acetylsalicylic acid (> 3g/day) and non-selective NSAIDs), attenuation of the antihypertensive effect may occur.
As with ACE inhibitors concomitant use of angiotensin II antagonists and NSAIDs may lead to in increased risk of worsening of renal function, including possible acute renal failure, and an increase serum potassium, especially in patients with poor pre-existing renal function. The combination should be administered with caution, especially in the elderly. Patients should be adequately hydrated and consideration should be given to monitoring renal function after initiation of concomitant therapy, and periodically thereafter.
Additional information on irbesartan interactions: In clinical studies, the pharmacokinetic of irbesartan is not affected by hydrochlorothiazide. Irbesartan is mainly metabolized by CYP2C9 and to a lesser extent by glucuronidation. No significant pharmacokinetics or pharmacodynamics interactions were observed when irbesartan was coadministered with warfarin, a medicinal product metabolized by CYP2C9. The effects of CYP2C9 inducers such as rifampicin on the pharmacokinetic of irbesartan have not been evaluated. The pharmacokinetic of digoxin was not altered by coadministration of irbesartan.