Drug Interactions between azilsartan medoxomil / chlorthalidone and Urapine

GENERALLY AVOID: Agents that can alkalinize the urine such as thiazide diuretics, carbonic anhydrase inhibitors, and antacids may decrease the antibacterial effectiveness of methenamine by inhibiting its conversion to formaldehyde. Methenamine is most effectively converted in an acidic milieu of pH less than 5.5.

MANAGEMENT: Concomitant use of methenamine-containing preparations with thiazide diuretics, carbonic anhydrase inhibitors, or large doses of antacids should be avoided if possible. Otherwise, frequent urine pH testing may be considered. Some methenamine products may be used with antacids if dosing times are separated by at least one hour. Consult the manufacturer's product labeling for specific recommendations.

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MONITOR: Nonsteroidal anti-inflammatory drugs (NSAIDs) may attenuate the antihypertensive effects of angiotensin II receptor antagonists. The proposed mechanism is NSAID-induced inhibition of renal prostaglandin synthesis, which results in unopposed pressor activity producing hypertension. In addition, NSAIDs can cause fluid retention, which also affects blood pressure. Clinical data are limited.

MONITOR: Concomitant use of NSAIDs and angiotensin II receptor antagonists may cause deterioration in renal function, particularly in patients who are elderly or volume-depleted (including those on diuretic therapy) or have compromised renal function. Acute renal failure may occur, although effects are usually reversible. Chronic use of NSAIDs alone may be associated with renal toxicities, including elevations in serum creatinine and BUN, tubular necrosis, glomerulitis, renal papillary necrosis, acute interstitial nephritis, nephrotic syndrome, and renal failure. Additionally, in patients with prerenal conditions whose renal perfusion may be dependent on the function of prostaglandins, NSAIDs may precipitate overt renal decompensation via a dose-related inhibition of prostaglandin synthesis. Angiotensin II receptor antagonists can further worsen renal function by blocking the effect of angiotensin II-mediated efferent arteriolar vasoconstriction, thereby decreasing glomerular filtration.

MANAGEMENT: Patients receiving angiotensin II receptor antagonists who require prolonged (greater than 1 week) concomitant therapy with an NSAID should have blood pressure monitored more closely following initiation, discontinuation, or change of dosage of the NSAID. Renal function should also be evaluated periodically during prolonged coadministration. The interaction is not expected to occur with low doses (e.g., low-dose aspirin) or intermittent short-term administration of NSAIDs.

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Anticholinergic agents may increase the absorption and oral bioavailability of thiazide diuretics. The proposed mechanism involves increased gastrointestinal transit time due to reduction of stomach and intestinal motility by anticholinergic agents. In six healthy volunteers, pretreatment with propantheline prolonged the time to reach peak plasma concentration (Tmax) for hydrochlorothiazide from 2.4 to 4.8 hours and increased its total 48-hour urinary recovery by 36%. Similar results were reported for chlorothiazide in another study. The clinical significance of these changes is unknown.

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