My 91-year-old mother-in-law is generally in good health and lives unassisted. She takes omeprazole (Prilosec) for gastrointestinal reflux and was recently prescribed clopidogrel (Plavix) for a mild stroke. She called her daughter — my wife who is a nurse — with concern that the patient information for clopidogrel indicated it should not be taken with omeprazole. Her question: “Is it safe to take both drugs?”

Today’s Mountain Medicine overviews drug interactions. The goal is to provide reliable information to discuss with your health care practitioners.

There are two common ways that one drug can interact with another and result in undesirable clinical outcomes.

First, one drug may change the absorption of a second drug. For example, if the antibiotic ciprofloxacin (Cipro) is taken by mouth with magnesium-aluminum antacids (Maalox), or drug products containing calcium, iron or zinc, ciprofloxacin absorption is significantly reduced. Consequently the infection may remain untreated. Your prescription bottle should have an auxiliary label to warn you of these interactions.

The opposite effect is when one drug increases absorption of another. Pepper extracts are included with some turmeric products intended to increase absorption of curcumin, its active ingredient (see Mountain Medicine, July 4, 2018). Another example is grapefruit juice that increases absorption of many drugs, such as sildenafil (Viagra). This interaction may result in adverse cardiovascular effects such as low blood pressure. An auxiliary label may advise you to avoid grapefruit juice for some of the more than 80 drugs so affected.

The second common mechanism is when one drug changes the breakdown, i.g., the metabolism of another drug resulting in either too little drug to accomplish its goal, or too much drug — causing adverse effects. For example, the dietary supplement St. John’s Wort increases metabolism of many drugs, including some used to treat HIV and hepatitis C virus infections. Since there is less drug in the body, viral growth may continue and lead to progression of disease.

In my mother-in-law’s case, clopidogrel is metabolized by a specific human enzyme to become the active drug that decreases clot formation. Omeprazole inhibits this enzyme, reducing the amount of the active form of clopidogrel and its effectiveness, possibly leading to another stroke.

Here is what you should know:

No clinician can remember all potential interactions, including those that are serious. You can make an important contribution by reading the patient prescribing information to see if you are receiving drugs that may interact. This is especially important for new prescriptions. If so, ask your prescriber or pharmacist for their advice.

One advantage to having all your prescriptions filled by the same pharmacy is your pharmacist can access software to identify drug interactions and their clinical significance. He or she can discuss options with you and your prescriber to avoid important interactions, including deprescribing (discontinuation of unnecessary drugs; see Dr. Maly’s Mountain Medicine, March 6, 2019), changing the timing of administration or switching to drugs that don’t interact.

Alternatively, you have access to many online resources — e.g., Google: “drug interaction checker”. I recommend that you check two or three programs to see if they give similar advice. Each will score the clinical importance of an interaction, such as “high,” signalling to avoid use, “moderate,” indicating to use with caution, and “low,” meaning probably safe. In five such programs, the interaction of omeprazole and clopidogrel was consistently reported as clinically important and best to avoid, although not all sources agree. Many online programs automatically check for interactions with grapefruit juice, alcohol, and foods.

In summary, the more you know about your drugs, the greater probability that you, with your health care providers, will maximize their benefit and minimize the potential for harm.

Mountain Medicine is a collaboration between Ron Polk and Dr. Kelsey Allen with Wallowa County medical practitioners.

Ron Polk is Emeritus Professor, now retired, at Virginia Commonwealth University.

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