9 Fosinopril Interactions to Watch For

Fosinopril is an angiotensin-converting enzyme (ACE) inhibitor that treats high blood pressure (hypertension). It’s also prescribed together with other medications to treat heart failure.

When starting fosinopril, it’s helpful to be aware of possible drug interactions. Interactions can impact how well your medications work and increase your risk for side effects. So knowing which medications may lead to a fosinopril interaction can help you avoid or manage the risks.

1. Thiazide and loop diuretics

Diuretics (water pills) are used to get rid of fluid from the body. They’re prescribed for many health conditions, including hypertension and heart failure. Common diuretics include thiazides like hydrochlorothiazide (Microzide) and loop diuretics like furosemide (Lasix).

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Fosinopril may be prescribed with diuretics to treat hypertension and heart failure. In fact, fosinopril is available in a combination pill with hydrochlorothiazide. But both medications lower your blood pressure. Your blood pressure could drop too low (hypotension) — especially when you first start taking fosinopril and a diuretic. This can cause symptoms like dizziness, weakness, and fatigue.

It’s often possible to prevent or manage this interaction. Your prescriber may recommend:

• Stopping your diuretic temporarily before starting fosinopril

• Starting with a lower fosinopril dosage

• Consuming more salt before starting fosinopril, because salt causes your body to hold onto water, which helps maintain blood pressure

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Don’t make any changes to your diuretic or fosinopril dosages, or to your diet, without talking to your prescriber first. They’ll let you know the best way to handle this potential interaction.

2. Potassium-sparing diuretics

Fosinopril also interacts with a group of diuretics called potassium-sparing diuretics. Examples include spironolactone (Aldactone), triamterene (Dyrenium), and eplerenone (Inspra).

Potassium-sparing diuretics help your body hold onto potassium. ACE inhibitors like fosinopril can also increase blood levels of potassium. So this combination increases your risk for high blood potassium (hyperkalemia). Hyperkalemia doesn’t always cause symptoms, but if it does you might experience numbness, fatigue, and muscle weakness.

It’s best to avoid taking fosinopril with potassium-sparing diuretics. But if the combination is necessary, your prescriber will closely monitor your potassium levels. Make sure to complete any blood tests they order for you.

3. Potassium supplements

Fosinopril can also interact with other medications that increase potassium, including potassium supplements. Some are available over the counter (OTC), and others are available only by prescription. Examples include potassium chloride (Klor-Con) and potassium citrate (Urocit-K). Some multivitamins also contain potassium in small amounts.

Potassium supplements can help prevent or treat low blood potassium (hypokalemia). Fosinopril may also increase potassium levels. So taking these medications together can cause hyperkalemia.

Let your prescriber know if you’re taking a potassium supplement. They may recommend stopping the supplement. Or they may just monitor your potassium levels more closely if you need the supplement. So be sure to complete any lab tests they order for you.

4. Angiotensin II receptor blockers (ARBs)

Like ACE inhibitors, angiotensin II receptor blockers (ARBs) are a group of blood pressure medications. Common examples include losartan (Cozaar) and valsartan (Diovan). 

ARBs and ACE inhibitors work in similar ways to lower blood pressure and have many of the same uses. Combining ARBs and ACE inhibitors typically isn’t recommended. Studies show combining them increases the risk of side effects. Risks include hypotension, kidney problems, and hyperkalemia. It’s unlikely your prescriber will recommend taking an ARB with fosinopril.

Good to know: Make sure your prescriber and pharmacist have a list of all the medications you take. Some combination medications may contain ARBs, and it might not be obvious to you. For example, a heart failure medication called Entresto (sacubitril / valsartan) contains an ARB (valsartan). Entresto shouldn’t be taken with ACE inhibitors like fosinopril.

5. Aliskiren

Aliskren (Tekturna) is prescribed to treat high blood pressure in adults. It works similarly to ACE inhibitors and ARBs.

Combining aliskiren and fosinopril usually isn’t recommended. Hyperkalemia, hypotension, and kidney problems become more likely with this combination. This risk is higher if you have diabetes or kidney disease. If you have these health conditions, aliskiren shouldn’t be combined with fosinopril.

6. NSAIDs

Nonsteroidal anti-inflammatory drugs (NSAIDs) are commonly used to treat pain and inflammation. Examples include naproxen (Aleve, Naprosyn), ibuprofen (Advil, Motrin), and celecoxib (Celebrex).

Using an NSAID while you’re taking fosinopril raises your risk for kidney problems. In rare but severe cases, acute kidney damage can happen. Symptoms include peeing less or not at all and swelling in your ankles and feet.

Many NSAIDs are available OTC. If you don’t know whether a product you take contains an NSAID, ask your pharmacist to check for you. Even if you don’t take NSAIDs every day, let your prescriber know if you use them at all. They’ll let you know if it’s safe for you to take NSAIDs while taking fosinopril. They may want to monitor your kidney function more closely.

7. Antacids

Antacids are medications used to treat heartburn symptoms. Examples include calcium carbonate (Tums) and calcium carbonate / magnesium hydroxide (Rolaids). They’re available OTC, but even OTC medications can interact with fosinopril.

Antacids may prevent fosinopril from being fully absorbed by the body. This can reduce fosinopril’s effectiveness. And if fosinopril isn’t working well, your blood pressure could increase.

You can minimize the effects of this interaction by taking your antacid and fosinopril at least 2 hours apart. If you’re not sure whether a medication you take is an antacid, check with your pharmacist or prescriber.

8. Certain cancer and transplant medications

Fosinopril may interact with a group of medications called mammalian target of rapamycin (mTOR) inhibitors. These medications may be used after an organ transplant. Some may also be used to treat certain cancers. Examples of mTOR inhibitors include sirolimus (Rapamune) and everolimus (Zortress, Afinitor).

Taking an mTOR inhibitor with fosinopril increases your risk of angioedema. Angioedema is an allergic reaction that can happen with ACE inhibitors. It can cause swelling in your face, mouth, and neck. In serious cases, it can cause difficulty breathing and be life-threatening.

If you’re taking an mTOR inhibitor, your prescriber may recommend avoiding fosinopril. They may suggest an ARB like losartan instead. ARBs don’t increase the risk for angioedema as much as ACE inhibitors do.

9. Lithium

Lithium (Lithobid) is a medication that treats bipolar disorder. Fosinopril may increase lithium levels if you take them together. This can be dangerous because lithium is a “narrow therapeutic index medication.” This means that even a slight change in blood levels of lithium can lead to side effects and lithium toxicity.

Typical lithium side effects may include peeing more often, feeling thirsty, and nausea. More serious risks of toxicity include: 

• Rapid heartbeat

• Confusion

• Agitation

• Hard-to-control tremors

• Vomiting

• Slurred speech

If you experience any of these symptoms, let your prescriber know immediately. If they feel severe, or you’re experiencing seizures or trouble breathing, seek emergency care.

If you take lithium, your prescriber will check your lithium levels regularly. So make sure to complete any blood work they order for you. This is especially important if you’re prescribed fosinopril along with lithium. In this case, they may ask you to complete blood work even more often.

When should you contact your healthcare team about fosinopril interactions?

Before you start taking fosinopril, give your prescriber and pharmacist a list of medications you take. Include any OTC products or supplements you use. This will help them check for possible fosinopril interactions.

Sometimes, taking a medication that can interact with fosinopril may be unavoidable. As long as your prescriber is aware of the potential interaction, it may be manageable. They may order lab tests more frequently to check for signs of an interaction. But if you develop unusual side effects like hypotension or peeing less than usual, let your prescriber know immediately. If you have severe symptoms like seizures, confusion, or difficulty breathing, seek emergency care.

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Written by:

Alex Brewer, PharmD, MBA

Alex Brewer, PharmD, MBA, is a licensed pharmacist specializing in chronic disease and health and wellness. Upon completing his residency, he worked in the managed care field, conducting medication therapy management and adherence counseling sessions with Medicaid, Medicare, and private insurance patients, before transitioning to a career in medical writing.

Edited by:

Amy B. Gragnolati, PharmD, BCPS

Amy Gragnolati, PharmD, BCPS, is a pharmacy editor for GoodRx. Amy currently holds her pharmacist license in Georgia and California.

Reviewed by:

Austin Ulrich, PharmD, BCACP

Austin Ulrich, PharmD, BCACP, is a board-certified ambulatory care clinical pharmacist. In his early career, he provided direct patient care in a variety of settings, including hospital and community pharmacies, and in a primary care clinic as a clinical pharmacist.

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