What are drug interactions?

Drug interactions (or technically speaking, drug-drug interactions), are a phenomenon whereby the pharmacological effects of a medication in a person's body are altered by the presence of another medication. In scientific terms, these medications are sometimes referred to as a victim drug and a perpetrator drug, respectively. 

Drug interactions may involve more than two medications. Medications may include those that are prescribed, and those that are available over-the-counter (including supplements and natural products). Drug interactions can also involve alcohol, recreational drugs, nicotine and caffeine, as they too can impact, or be impacted by, interactions with other drugs.

Drug interactions can be complex and not readily apparent. Broadly speaking, there are two types of drug interactions, which align with typical approaches to pharmacology at large. These two ways involve the perpetrator drug changing how a victim drug's effect(s) impact the body, and, how it affects the body's handling of the victim drug.

The first classification of drug interactions (those that involve how the victim drug affects the body) can be demonstrated by what can happen when a common combination of medications is given prior various medical/dental procedures. Specifically, the administration of an opioid painkiller to help manage pain is supplemented by a sedative that helps calm an individual during the procedure. Many people report feeling drowsy for a reasonable amount of time after the procedure is over - this is because this is a side effect of the opioid that is made worse by the presence of the sedative. 

Amongst common medication interactions affecting the body's ability to handle a drug is the combination of certain cholesterol-lowering medications (including atorvastatin and simvastatin) and a common antibiotic called clarithromycin that is used for a number of infections. This includes pneumonia, and stomach ulcers caused by the bacteria H Pylori. When clarithromycin is taken, it inactivates a key enzyme in the body that breaks down these cholesterol medications. Normally, this enzyme prevents these cholesterol medications from significantly building up in the body over multiple doses. When clarithromycin is started in someone taking these cholesterol medications, the cholesterol medication can build up and become more like to cause side effects in the muscles, including severe forms that can significantly break down muscle cells. 

Though drug interactions are usually not desirable, there are some cases where interactions between medications are beneficial. Health care providers sometimes prescribe combinations with these beneficial effects to better help the person they are treating.

Other types of interactions involving medications

Medications interact with other consumables, and other aspects of the body’s functioning, respectively. These additional medication interactions can also be important considerations when health care providers select which medication to prescribe or advise someone to take.

Specifically, these can include drug-nutrient interactions, drug-disease interactions and drug-gene interactions.

Drug-nutrient interactions typically involve specific nutrients in the foods we eat but can also overlap with the nutrients found in supplements (that are often considered a drug-drug interaction). This can include someone suddenly consuming a large amount of food containing vitamin K (like certain leafy green vegetables) that is regularly taking a certain blood thinner (warfarin). Vitamin K is an essential factor in supporting the body's ability to create blood clots in the case of an open wound or hemorrhage. However, when someone requires thinner than usual blood because they are at an elevated risk of experiencing a stroke due to blood clots, this surge in vitamin K counteracts the blood thinning medication's effectiveness.

Drug-disease interactions involve altered effects of the medication because of an underlying medical condition that typically predisposes someone to experiencing altered effects of a medication. A common example would be the impact of opioid painkillers on breathing. In an otherwise healthy individual appropriately using prescribed opioids, side effects impacting their breathing will generally be minor, insignificant and/or unnoticeable. However, someone with uncontrolled asthma, whose breathing is already impaired, may be more at-risk of experiencing noticeably slower or more laborious breathing when using opioid painkillers.

Drug-gene interactions involve modified responses to medications due to the presence of variations in gene(s) that code the various bodily machinery (consisting of proteins) relevant to that medication. A common example would be those with variations in genes programming key proteins that process a medication (azathioprine) used to calm the immune system in auto-immune disorders like Crohn's disease and rheumatoid arthritis. Those with genetic variations that impair the functioning of these enzymes are at risk of experiencing immune-lowering effects beyond what is necessary. This can increase the risk that the individual's body may not have the ability to fight infections they may develop.

How are interactions dealt with?

Drug-drug interactions, as well as other types of medication-related interactions, are complex and involve a careful assessment of the individual, including the risk and severity of the interaction, the underlying need for the medication, available alternatives, test results (like blood work), other current medication use, medical history, lifestyle factors, diet, organ functioning and genetics. Oftentimes, multiple types of interactions are present at the same time and can amplify certain medication effects even further. Health care providers are responsible for assessing, preventing or otherwise managing the presence or risk of interactions. Where needed, they collaborate with other members of the individual's health care team to ensure that a holistic and optimal approach is taken, given the specific circumstances. Depending on the treatment setting, pharmacists typically play a key role in managing various interaction types, with key collaborations and contributions from physicians, nurse, dentists, dietitians and others as well.

Testing for Drug-Gene Interactions

Pharmacogenetic testing is a process involving an analysis of someone's DNA for variations known to impact effectiveness and/or side effects associated with a number of medications. This information can then be used to inform the choice of the medication selected, or the dose, monitoring, or further investigations needed when prescribers select a certain medication.

This process supplements usual prescribing approaches, allowing health care providers to supplement usual considerations (including drug-drug, drug-disease and drug-nutrient interactions) with insights related to potential drug-gene interactions. This can mean that prescribers may use dosing that differs from the norm, select an alternative medication, order additional tests, and/or more closely monitors the individual's condition and medication response. This improves the chances of finding success with a medication by reducing the risk and severity of side effects, and improving the likelihood of experiencing a beneficial response.

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