What Is a Drug Interaction?

Introduction

According to the Centers for Disease Control and Prevention, more than 20,000 deaths annually happen due to unintentional drug poisoning. Moreover, the US Food and Drug Administration stated that four or more prescribed medications are concurrently taken by 40 percent of Americans, which means that the risks and potential harm of drug interactions affect almost half of the American population. 

If medications are taken along with alcohol, dietary supplements, and certain foods, then the risks increase even more. A drug interaction happens when two medications are taken together and may influence each other by weakening or strengthening each other's actions. Drugs may be prescribed, nonprescribed or a combination of both. 

The risks of drug interaction depend on the age, weight, current illness, and lifestyle of the person. Some drug interactions may occur with certain types of food, dietary supplements, and alcohol.

Drug interactions can be mild or life-threatening and can cause the following:

• Weaken the effect of other medications
• Increased action of a particular drug
• Unexpected side effects

Are drug interactions common?

Drug interactions are relatively common. In fact, there are currently around 800 documented drug interactions, but not all are clinically significant. If a patient is taking more than two medications, the risk of drug interaction is 10-20 percent. The risk also increases as people age. Approximately 5 percent of patients who are 70 years and above are at risk of experiencing serious drug interactions.

Factors That Affect Drug Interactions

Drug interactions may differ from one person to another. The factors that can affect drug interactions include:

• Age of the person
• Amount of exercise
• Genetics
• Diet
• Current medications
• Dosing and time interval between two medications
• Underlying disease

Elderly people tend to take more medications, so they are more at risk of having adverse drug reactions. According to a study done in 2008, over 2 million individuals between the age of 57 and 85 are at a risk of major drug interactions. When people take a new drug or stop taking a particular drug, they are more prone to developing drug interactions.

Types of Drug Interactions

1. Drug-Drug Interaction

When two or more drugs react with each other, drug-drug interaction happens. The way in which the drug works on the body is affected and it can also cause unwanted side effects. For example, for allergy relief, a person takes a sedative and antihistamine. Together, they might interact and cause drowsiness. It can be dangerous when doing any work that requires mental alertness such as driving a car.

Certain drugs may interact with caffeine present in coffee and chocolate. Nicotine in tobacco may interact with other medications as well.

2. Drugs-Supplements

Some interactions between drugs and supplements may cause adverse reactions. An example would be taking a prescription drug along with St. John's wort, Ginkgo biloba, ginseng, and vitamin E.

3. Drug-Food/Alcohol

Drug-food/alcohol interaction occurs when certain food or beverages are taken along with a certain drug. The absorption of the drug can be slowed down by food, which makes the drug less effective. However, to prevent irritation of the stomach, some drugs are taken with food. Sometimes, absorption of nutrients from food can be interfered by certain drugs, which then affects the nutritional value of the food. A person’s appetite can also be artificially increased or decreased by certain drugs. 

Certain drugs have sedative effects and alcohol intensifies such effects. Thus, when alcohol is taken with certain drugs, drowsiness may occur. Alcohol itself is a drug, so a drug-alcohol interaction also may happen. Adverse effects such as slowing down the person's reaction or extreme drowsiness can be caused by combining drugs with alcohol.

4. Drug-Condition Interaction

When a person’s existing medical condition causes some medications to become potentially harmful, then a drug-condition interaction occurs. If you have hypertension or high blood pressure, you may experience certain reactions when you take a nasal decongestant.

Based on the underlying mechanism drug interactions may be categorized into:

• Behavioral - This interaction happens when a patient’s behavior is altered because of drugs to modify compliance with another drug. An example would be a person with depression who is taking antidepressants. 

• Pharmaceutical - This type of interaction occurs before drugs are given to the patient. It usually represents drug incompatibilities, which are intravenously given.

• Pharmacokinetic - Pharmacokinetic interactions happen when a drug modifies the effect of another drug to its target. Drugs may change the distribution, absorption, or elimination of other drugs. 

• Pharmacodynamic - It relates to the actual drug effects on a targeted organ or system. Such interaction may happen at identical receptor sites as well as by diverse mechanisms on related organs.

Pharmacokinetic Drug-Drug Interaction

• Altered bioavailability - happens when the perpetrator drug affects the amount of drug reaching the systemic circulation. Drugs of high bioavailability are seldom affected. The ones affected more are drugs with low bioavailability.

• Altered clearance - occurs when the perpetrator drug affects the excretion or metabolism of the object drug. Particularly vulnerable are the drugs with narrow therapeutic index. Large concentration changes are caused by perpetrator drugs that affect the metabolism of the drug. Thus, it is important to recognize these perpetrators drugs.

• Metabolism - An important cause of unexpected drug interaction is drug metabolism changes. Out of all the enzyme families involved in drug metabolism, the cytochrome enzyme is the most significant.

• Prodrugs - These are vulnerable to changes in metabolism since they are dependent on the single enzyme pathway. For conversion to their active form, some drugs rely on cytochrome P450. Therapeutic failure may be caused when prodrugs are not converted to active form. The concentration of the active drug then decreases.

• Excretion - Some drugs are excreted in active form through the urine or feces.

Drugs Known to Have Interaction Issues

Of the most common prescription drugs, three of them are known to have a potential interaction. Drug interactions may occur if the drug is incorrectly used.

1. Blood Pressure Medications

Common diuretics such as hydrochlorothiazide are known to treat high blood pressure. This drug is known to decrease the blood volume by pulling extra water from the body. However, hydrochlorothiazide should not be taken with heart rhythm medications, since they can cause the levels of potassium to drop to a dangerous level, which can cause cardiac arrhythmia.

Glycyrrhizin in black licorice that is also found in some sweeteners and teas can affect the levels of potassium. The effectiveness of blood pressure medications may also be reduced by over-the-counter decongestants.

2. Antidepressants

The most common drugs prescribed for depression are selective serotonin reuptake inhibitors (SSRIs) such as:

• Prozac (fluoxetine)
• Zoloft (sertraline)
• Wellbutrin (bupropion)
• Lexapro (escitalopram)
• Paxil (paroxetine)

SSRIs raise the serotonin level and ease the symptoms of depression. The problem is that they can also cause drug interactions, side effects, and complications. In young adults, it is not uncommon to have suicidal thoughts and behavior, which can become a serious condition. Serotonin syndrome may occur when St. John's wort is taken.

3. Statins for Cholesterol

About 24 million Americans take statins to lower cholesterol levels. Statins halt the production of cholesterol by a liver enzyme. However, muscle damage and kidney failure may be caused by mixing statins with some foods, drugs, or dietary supplements. Taking statins with oral fungal medications, grapefruit juice, and vitamins can be dangerous.

Steps to Prevent Drug Interactions

The key to avoid a potential drug interaction is by being proactive and reading drug labels. Talk with a doctor or pharmacist if you are uncertain about the possibility of drug interactions. Make a list of all prescription and over-the-counter medications you have taken and share it with the doctor or pharmacist. 

Drug Interaction Lawsuits

Drug companies are expected to be responsible and held accountable if their actions cause harm. Legal recourse is possible if a drug interaction that could have been avoided has occurred. Two valid reasons for a personal injury case are unexpected drug interaction and adverse drug reactions. The legal rights of a person can be determined with the help of a personal injury attorney. They may also help when it comes to navigating options. Partnering with a skilled attorney will help. The legal system can be daunting. However, such cases can be handled in the most professional and efficient manner. 

How to avoid drug-drug interactions?

• Keep a list of prescription drugs, over-the-counter medications, and herbal products. 
• Knowledge of the clinical effects of the involved drugs.
• Since pharmacokinetic drugs are not predictable from the clinical effects of the involved drugs, their anticipation is difficult. Identification will become easier by recognizing drugs that have narrow therapeutic index and major perpetrators of pharmacokinetic interactions.

To manage potential drug-drug interaction, the following rules can be followed:

• If any interaction between existing drugs has occurred in the patient, then they become part of the differential diagnosis.
• It becomes easier to recognize a potential pharmacodynamic drug-drug interaction by having knowledge of the pharmacological effects of the drugs and the physiology of the patient.
• Drugs mostly susceptible to pharmacokinetic drug-drug interaction are those with a narrow therapeutic index.
• Very few drugs are important perpetrators of pharmacokinetic drug-drug interactions.
• Whether to start or stop a drug is a prescribing decision, which may result in drug interaction.
• It is a part of routine care to monitor the patient for less efficacy and drug toxicity. Drug interactions can be checked and detected early if there is a check on the changes in symptoms, drug concentration soon after prescription changes, and biomarkers of effect. 

Clinical Resources for Drug-Drug Interactions

To help clinicians with drug-drug interactions, a number of resources are available:

• Drug information services - they provide access to reference information.

• Prescribing and dispensing software - can generate alerts about drug pairs.