Common Drug-Disease Interactions

Instructor: Patricia Jankowski

Patricia is an experienced registered nurse who has worked in various acute care areas as well as in legal nurse consulting. She also has a BSChE.

Many drugs that are intended for therapeutic purposes can cause harmful effects when they are given to patients with certain diseases. In this lesson, we will examine how these harmful interactions happen and how elderly patients are at greater risk.

What is a Drug-Disease Interaction?

A drug-disease interaction is an event in which a drug that is intended for therapeutic use causes some harmful effects in a patient because of a disease or condition that the patient has. There are some diseases that alter the body's ability to metabolize, or break down, a drug so that it can have the intended effect. This can be true of both prescription and over-the-counter drugs. When it is known that a patient has such a disease, care must be taken to choose therapeutic drugs accordingly and to adjust the doses when necessary.

Common Types of Drug-Disease Interactions

Every time a patient takes a drug, the drug has to travel through their unique body. The process by which a drug is metabolized can vary from patient to patient and it can depend on the bacteria that dwell in the intestines, on the patient's age, or on the general health of their excretory organs, such as the liver or kidneys. As the drug passes through the body, chemical reactions occur that make it water-soluble so that it can eventually be excreted and will not accumulate to toxic levels within the bloodstream. However, because of various disease conditions, sometimes this process doesn't go quite as planned. Let's look at some of these disease conditions and how they affect the patient's ability to metabolize various medications.

Chronic Kidney Disease

In chronic kidney disease, or CKD, the kidneys have been damaged and their function has been compromised. This means that any drug that is toxic to the kidneys, or is nephrotoxic, must be prescribed with care, especially in more advanced stages of CKD. Also, any drug that is converted to a metabolite, or water-soluble form, and is then excreted through the kidneys may have delayed excretion in a patient with CKD and may accumulate in the body to toxic levels. The kidneys also play a role in endocrine function, and when they are diseased, some of this function is lost. This may affect how a drug is metabolized. For these reasons, a clinician needs to consider if there is a less toxic drug to prescribe for the patient with CKD, or if an adjusted dose would be appropriate.

Cardiovascular Disease

There are many pre-existing cardiac conditions that don't work well with certain drugs. One of these is hypertension, or high blood pressure. Many over-the-counter decongestants, like pseudoephedrine, are great for clearing up the congestion of a bad cold, but since they shrink the blood vessels, they raise the blood pressure. This can be dangerous for a patient whose blood pressure is difficult to control. Non-steroidal anti-inflammatory drugs, or NSAIDS, may also be dangerous in the context of high blood pressure because they cause fluid retention. Antacids also cause fluid retention and often contain magnesium, which can affect the heart rhythm.

Digestive Disease

Of all the drugs that are hard on the digestive system, NSAIDs are probably the worst, as they wear away the stomach lining and increase stomach acidity. Patients with peptic ulcer disease should not take NSAIDS. In inflammatory bowel diseases, such as Crohn's disease, the walls of the intestines are often thickened, which slows the absorption of any drug. Many drugs are metabolized in the liver, so liver diseases, like cirrhosis, cause the drugs to accumulate in the blood, which, again, may lead to toxicity.

Other Types Of Disease

There are also other conditions that make taking certain drugs riskier, such as asthma and gout. Beta blockers are drugs commonly given for heart failure and hypertension, but these must be given with caution to those with asthma because their blocking action on beta receptors, which is therapeutic for hypertension, also causes constriction of the airways.

In a patient who has gout, taking diuretics can cause the retention of uric acid. Gout is caused by the buildup of uric acid in the joints, so the retention of more uric acid simply worsens the disease.

High-Risk Elderly Patients

Anyone with a chronic disease that affects the metabolism and elimination of drugs is at risk for a drug-disease interaction, but it is most often the elderly patient who has a chronic disease. For this reason, the Beers Criteria were developed. Furthermore, dementia and frequent falls are, unfortunately, not uncommon conditions in elderly patients, and they warrant special consideration when medications are prescribed.

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