Drug Interactions between aspirin / omeprazole and eprosartan / hydrochlorothiazide

MONITOR: Chronic use of proton pump inhibitors (PPIs) may induce hypomagnesemia, and the risk may be increased during concomitant use of diuretics or other agents that can cause magnesium loss. The mechanism via which hypomagnesemia may occur during long-term PPI use is unknown, although changes in intestinal absorption of magnesium may be involved. Hypomagnesemia has been reported rarely in patients treated with PPIs for at least three months, but in most cases, after a year or more. Serious adverse events include tetany, seizures, tremor, carpopedal spasm, atrial fibrillation, supraventricular tachycardia, and abnormal QT interval; however, patients do not always exhibit these symptoms. Hypomagnesemia can also cause impaired parathyroid hormone secretion, which may lead to hypocalcemia. In approximately 25% of the cases of PPI-associated hypomagnesemia reviewed by the FDA, the condition did not resolve with magnesium supplementation alone but also required discontinuation of the PPI. Both positive dechallenge as well as positive rechallenge (i.e., resolution of hypomagnesemia with PPI cessation and recurrence with PPI resumption) were reported in some cases. After discontinuing the PPI, the median time required for magnesium levels to normalize was one week. After restarting the PPI, the median time for hypomagnesemia to recur was two weeks.

MANAGEMENT: Monitoring of serum magnesium levels is recommended prior to initiation of therapy and periodically thereafter if prolonged treatment with a proton pump inhibitor is anticipated or when combined with other agents that can cause hypomagnesemia such as diuretics, aminoglycosides, cation exchange resins, amphotericin B, cetuximab, cisplatin, cyclosporine, foscarnet, panitumumab, pentamidine, and tacrolimus. Patients should be advised to seek immediate medical attention if they develop potential signs and symptoms of hypomagnesemia such as palpitations, arrhythmia, muscle spasm, tremor, or convulsions. In children, abnormal heart rates may cause fatigue, upset stomach, dizziness, and lightheadedness. Magnesium replacement as well as discontinuation of the PPI may be required in some patients.

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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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Coadministration with proton pump inhibitors may decrease the oral bioavailability of aspirin and other salicylates. The interaction has been studied with omeprazole and aspirin, although data are conflicting. In one study, pretreatment with omeprazole (20 mg/day for 2 days) in 11 healthy volunteers led to a significant and progressively greater reduction in the mean serum salicylate level at 30, 60, and 90 minutes after administration of aspirin (650 mg single dose). The investigators suggest that acid suppression may reduce the lipophilic nature of aspirin, thereby adversely affecting its absorption from the gastrointestinal tract. Another study found no effect of omeprazole pretreatment (20 mg/day for 4 days) on plasma salicylate and aspirin levels, skin bleeding times, or antiplatelet effect of low-dose aspirin (125 mg single dose) in 14 healthy volunteers. However, these results do not exclude the possibility that omeprazole might interfere with the analgesic, antipyretic, or anti-inflammatory effects of aspirin, which has been demonstrated in rats.

Proton pump inhibitors may enhance the release rate of salicylates from enteric-coated formulations due to premature disruption of the coating and intragastric release of the drug secondary to an increase in gastric pH. In eight healthy volunteers, omeprazole pretreatment (20 mg/day for 4 days) did not affect the bioavailability of salicylate from uncoated aspirin tablets but significantly increased the absorption rate of salicylate from enteric-coated sodium salicylate tablets. The clinical significance of this interaction is unknown. Theoretically, it may increase the risk of gastric adverse effects associated with salicylates.

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