Antacid Drug Interactions

Antacids have long been used to treat ulcers and serious stomach upset due caused by stomach acid, as well as to relieve heartburn, but they can interfere with the body’s absorption of other drugs.

They should be used no earlier than two hours prior to or four hours after taking interacting medications (see Tables 1 and 2).

As opposed to other drugs that control problems from an acidic stomach such as cimetidine (TAGAMET) or omeprazole (PRILOSEC) that reduce production of acid by the stomach, antacids directly neutralize acid.

Antacids generally interact with other drugs in one of two ways: by binding to the molecules that make up those drugs or by interfering with drug absorption by reducing the acidity of the stomach.

Drugs that bind strongly with antacids

Commonly used antacids contain aluminum, magnesium or calcium salts, alone or in combination. These "cations" can bind moderately to strongly in the stomach with certain drugs, thus reducing their absorption and decreasing those drugs’ effect.

Antacids also may bind loosely with many other drugs, thus producing mild reductions in drug absorption and effect. The good news is that the magnitude of loose binding usually is not sufficient to cause difficulties for patients.

Tetracyclines. The classic example of drugs that bind strongly with antacids, decreasing absorption and effect, are tetracyclines. Tetracyclines are antibiotics; drugs of this class have been on the market for many decades.

The absorption of oral tetracyclines can be drastically reduced if antacids are taken at the same time. Some tetracyclines interact more than others with antacids, but all of them are affected (see Table 1 for a list of tetracyclines).

Quinolones. Quinolone antibiotics also bind strongly with antacids, and in some cases quinolone absorption can be almost completely blocked if antacids are given at the same time (see Table 2 for a list of quinolone antibiotics).

Thyroid hormones. Antacids tend to bind more moderately with thyroid hormones, but in some patients taking thyroid replacement therapy this effect may be enough to cause symptoms of hypothyroidism.

Other. Other drugs that may bind moderately with antacids include allopurinol (ZYLOPRIM), atenolol (TENORMIN), gabapentin (NEURONTIN), halofantrine (HALFAN), isoniazid (INH), iron preparations, mycophenolate (CELLCEPT), and penicillamine (CUPRIMINE).

If used with an antacid, taking the other drug no less than two hours before or four hours after the antacid is likely to minimize any binding in the stomach.

For drugs that bind strongly or moderately with antacids in the stomach, the interaction can be avoided by using "acid reducers" instead of antacids. This could include H2-receptor antagonists such as cimetidine (TAGAMET), ranitidine (ZANTAC), famotidine (PEPCID) or nizatidine (AXID) or proton pump inhibitors such as omeprazole (PRILOSEC).

Drug absorption affected by changes in stomach acidity

The absorption of some drugs used for diabetes, such glipizide (GLUCOTROL) and glyburide (DIABETA) can actually be increased when antacids reduce the acidity of the stomach.

The opposite (decreased absorption) occurs when antacids are given with the antifungal agents itraconazole (SPORANOX) or ketoconazole (NIZORAL), or the antibiotics cefditoren (SPECTRACEF), cefpodoxime (VANTIN), or cefuroxime (CEFTIN).

For these interactions, as with the binding interactions discussed above, taking the other drug no less than two hours before or four hours after the antacid should minimize any interaction.

Unlike the binding interactions, interactions caused by reduced levels of stomach acidity cannot be avoided by substituting "acid reducers" for the antacid, since reduced acid is exactly what is causing the interaction.

What You Can Do

To minimize your risk of antacid drug interactions by, try not to take any medication less than two hours before or four hours after taking antacids.

Always check the auxiliary labels on your prescription bottles; if the drug interacts with antacids, there will usually be a warning sticker.

When in doubt, ask your pharmacist or prescriber if your medications interact with antacids.

* Do Not Use in Worst Pills, Best Pills
** Limited Use in Worst Pills, Best Pills