8 Isoniazid Interactions to Watch Out For

Isoniazid is an older antibiotic, which was first developed in 1912. Even though it's been around for a while, it's still used today to prevent and treattuberculosis. Tuberculosis is a serious bacterial infection of the lungs. Treatment for this condition typically lasts several months.

If you've been prescribed isoniazid, it's a good idea to know what side effects and food and drug interactions to look out for. Here, we'll discuss eight notable isoniazid interactions and how to prevent or manage them. But be sure to share your currentmedication list with your prescriber so they can scan it for potential interactions.

1. Alcohol

In rare cases, isoniazid can cause liver inflammation (hepatitis). Daily alcohol use can increase your risk of hepatitis from isoniazid. Drinking alcohol can also increase your risk of nerve problems, another possible isoniazid side effect. That's why it's best toavoid drinking alcohol if you take isoniazid.

Before starting treatment, have an honest conversation with your prescriber about whether it's possible for you to avoid alcohol. They may recommend another tuberculosis medication if you plan to continue drinking during treatment.

If you're having trouble limiting your alcohol consumption, consider talking to a healthcare professional abouthow to cut back.

2. Tyramine- and histamine-containing foods

Certain medications should be taken on anempty stomach, or without food. Isoniazid is one of these medications. Taking isoniazid with food blocks its absorption, making it less effective.

But specific foods, such as those containingtyramine orhistamine, may need to be avoided altogether with isoniazid.Foods that contain tyramine include ripened cheese, red wine, and dried and cured meats. Fermented cheese, meats, and fish are examples offoods that contain histamine.

Isoniazidreduces the activity of certain enzymes (proteins): CYP450 enzymes andmonoamine and diamine oxidases. These enzymes break down (metabolize) several medications and chemicals in the body - including histamine and tyramine. By blocking these enzymes, isoniazid may cause tyramine and histamine to build up in the body. This can lead to a tyramine or histamine reaction. Symptoms of a reaction may include headaches, sweating, and heart palpitations.

Talk with your prescriber about what foods you should avoid while taking isoniazid.

3. Acetaminophen (Tylenol)

Although rare, there's a risk of liver damage with isoniazid. Combining isoniazid with the popular over-the-counter (OTC) pain reliever acetaminophen (Tylenol) increases this risk. Isoniazidspeeds up the metabolism of acetaminophen in the body. This may cause a toxic product of acetaminophen breakdown to build up, which canlead to liver damage.

If you're prescribed isoniazid, it's best to avoid taking acetaminophen. Talk with your prescriber about other OTC pain relief medications that may be safer to take. This may includeibuprofen (Advil, Motrin) ornaproxen (Aleve, Naprosyn).

4. Seizure medications, such as carbamazepine

Isoniazid may block the metabolism of certain seizure medications. Examples includecarbamazepine (Tegretol),phenytoin (Dilantin, Phenytek), and divalproex (Depakote). Blood levels of these medications may increase when they're combined with isoniazid, raising the risk of side effects.

If you've been prescribed isoniazid, make sure the healthcare professional that prescribes your seizure medication is aware. They may want to adjust the dosage of your seizure medication or switch you to another treatment altogether. Alternatively, they may just want to monitor you closely for side effects, likedrowsiness,dizziness, andnausea, or check your blood levels of seizure medication more frequently.

5. Ketoconazole

Ketoconazole is an antifungal medication. Isoniazid may decrease ketoconazole levels in the body when the medications are combined. This can make ketoconazole less effective, leaving your fungal infection undertreated

Some experts recommendagainst taking isoniazid and oral ketoconazole within 2 weeks of each other. The oral form of ketoconazole isn't used as much anymore. And topical ketoconazole products, like shampoo, are less likely to interact with isoniazid. Still, make sure your prescriber knows that you take ketoconazole (no matter what form) before starting treatment with isoniazid.

6. Theophylline

Theophylline (Theo-24, Elixophyllin, Theochron) is an oral medication that treats asthma and chronic obstructive pulmonary disease (COPD). But it's an older medication, and isn't used very often anymore.

Older research shows that isoniazid canincrease levels of theophylline in the body. This raises the risk of theophyllineside effects, such as diarrhea, anxiety, and heart palpitations. If you're taking theophylline and isoniazid together, your prescriber may ask you to do frequent blood tests to measure your theophylline blood levels. Depending on the results of these blood tests, you may need a lower theophylline dosage.

7. Vitamin D

Vitamin D is an essential nutrient that helps maintain bone health and serves other functions in the body. Isoniazid can affect vitamin D levels by blocking an enzyme that's involved in converting vitamin D to its active form. As a result, isoniazid can decrease vitamin D levels in the body. Isoniazid can also makevitamin D supplements less effective.

The effects of this potential interaction are more unpredictable if you're also taking rifampin (Rimactane). Rifampin is another commonly prescribed tuberculosis medication that's often combined with isoniazid. And it can also affect vitamin D levels.

If you're taking vitamin D supplements or you have a knownvitamin D deficiency, let your prescriber know before starting treatment with isoniazid and/or rifampin. They may want to check your vitamin D levels after you start treatment. If your levels are low, they may adjust your vitamin D supplement dosage (or recommend you start taking supplements, if you're not already).

Good to know: Isoniazid can also decrease vitamin B6 levels. So some people, especially those at risk of low vitamin B6 levels, may need to take vitamin B6 supplements (pyridoxine) with isoniazid. This can help prevent nerve problems.

8. Benzodiazepines, such as alprazolam

Benzodiazepines are a group of medications that treat conditions like anxiety and panic disorder. Some benzodiazepines aremetabolized by an enzyme in the liver that isoniazid may block. Examples include alprazolam (Xanax) and diazepam (Valium). Isoniazid can increase the levels of these medications in the body, raising the risk of side effects.

Benzodiazepine side effects include drowsiness, dizziness, and falls. More seriously, high benzodiazepine levels can lead to slowed breathing and overdose. So your prescriber may recommend avoiding these benzodiazepines while you're taking isoniazid.