Drug Interactions: ‘Must-Know’ Facts for Multiple Drug Users

11:34 am May 15, 2016

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Drug Interaction, What does it mean?

Drug Interaction can literally be described as an interaction between two or more drugs, or some food substance within the body of an individual. It can lead to either increase in the effectiveness of the drug, decrease in its effectiveness. It can even lead to some undesirable side effects depending upon the nature of interacting substances.

For example, mixing a drug you take to help you sleep (a sedative) and a drug you take for allergies (an antihistamine) can slow your reactions and make driving a car or operating machinery dangerous.

Drug-food/beverage interactions result from drugs reacting with foods or beverages. For example, mixing alcohol with some drugs may cause you to feel tired or slow your reactions.

Drug-condition interactions may occur when an existing medical condition makes certain drugs potentially harmful. For example, if you have high blood pressure you could experience an unwanted reaction if you take a nasal decongestant.

The likelihood and extent of drug interaction also depends upon the environment in which the individual is living, health status of the individual, his food habits, whether or not he/she /she suffers from any other health complication and if he/she is on multiple drugs at one time.

Generally, taking multiple drugs at a time increase the chances of a person to suffer from the consequences of drug interaction, but the nature of drugs always remains a predominant factor in determining the outcome.

Types of Drug Interactions

Drug interactions are of two types: Pharmacokinetic interactions are straightforward drug interactions with predictable outcomes, which generally result in adding or cancelling out the activity of other drug.

For example, if a person is having two different drugs for hypertension at the same time, the effect would be additive, and BP will be lowered to a greater extent.

Other type of drug interaction, the pharmacodynamics interactions, are more complex ones and depend upon the type of interaction that the two drugs would undergo say, if a person consumes an antibiotic like ciprofloxacin and a supplement of iron or calcium together, there will be decrease in the absorption of both the drug and the supplement and hence the efficiency of both will be decreased.

Drug interaction can comprise the efficiency of drug and cause other side effects like hepatic problems (since the drug components primarily reach to liver for detoxification) and kidney trouble (since kidneys filter out these various substances from blood).

How to Manage the Problem

A person cannot simply stop having medicines to avoid possible Drug Interactions. However, a careful observation of the types of medicines a person is having and some insight into the possible interactions might help the clinician in adjusting the dosages or using alternate medicines in order to improve patient outcomes.

More care should be taken when we are talking about elderly people. The old age people are usually suffering from multiple ailments; using medicines for prolonged time, have mild impairment in liver and kidney functions owing to their age and also are more susceptible to the side effects of Drug Interactions.

Top 10 Drug Interactions

(Devised by The Multidisciplinary Medication Management (M3) Project Advisory Committee)

The medications chosen for this list are based on their frequency of use in older adults, and on the likeliness for negative consequences if the drugs were taken together.

Drug I Drug II (other Interacting Drug)

Warfarin NSAIDs
Warfarin Sulfa Drugs
Warfarin Macrolides
Warfarin Quinolones
Warfarin Phenytoin
ACE Inhibitors Potassium Supplements
ACE Inhibitors Spironolactone
Digoxin Amiodarone
Digoxin Verapamil
Theophylline Quinolones

This table was developed for the Good Fellow Unit Symposium (2007) by Dr Linda Bryant (Clinical Advisory Pharmacist, Department of General Practice and Primary Health Care, University of Auckland).

Warfarin Used as an oral anticoagulant to prevent blood clot formation, prevent extension of clots already formed, and minimize the risk of blood clot embolization in vital organs (lungs, brain).

Some medications can interact to enhance the actions of Warfarin causing excessive blood thinning that can result in life-threatening bleeding.

Non-steroidal Anti-Inflammatory Drugs (NSAIDs):

Used to treat inflammation, mild to moderate pain, fever, headaches, arthritis, and menstrual cramps.

Examples: Aspirin, Ibuprofen (Motrin), Naproxen (Aleve), Oxaprozin (Daypro), RofeCoxib (Vioxx), CeleCoxib (Celebrex), interacts with Warfarin resulting in a potential for serious gastrointestinal bleeding.

Sulfa Drugs: Used as antibiotics to treat bacterial and some fungal infections. Most commonly used to treat urinary tract infections (UTIs). Examples: Bactrim DS, Bactrim SS, Gantanol, Sulfatrim, Thiosulfil Forte, interacts with Warfarin by increasing the effects with a potential for excessive bleeding.

Macrolides: Used as an antibiotic to treat common bacterial infections. Examples: Erythromycin, Pediazole, Zithromax, interacts to increase the effects of Warfarin with a potential for excessive bleeding.

Quinolones: Used as a primary agent in the treatment of UTIs. Examples: ciprofloxacin, norfloxacin, Cipro, Levaquin, Noroxin, Penetrex, interacts with Warfarin to increase its effects and potential for bleeding.

Phenytoin: Used either orally or through injections as anti-convulsant, particularly used to prevent grand mal seizures and psychomotor seizures. Example: Dilantin, interaction can increase the effects of Warfarin and/or Phenytoin.

Angiotensin Converting Enzyme (ACE) Inhibitors: Used for controlling blood pressure, preventing kidney damage and treating heart failure in patients with diabetes and/or hypertension. Examples: Lotensin, Aceon, Altace and Accupril, interacts with Potassium supplements and spironolactone by increasing blood concentrations.

Digoxin: Used to treat congestive heart failure, and to slow the heart rate down if there is a disturbance in rhythm. Example: Lanoxin, interacts with amiodarone and verapamil by causing great toxicity in the body and slowing the heart rate down too much.

Theophylline: Used to provide relief and prevention of airway narrowing in asthmatic patients. Examples: Theo-Dur, Respbid, Uniphyl, interacts with Quinolones and increases the chances of having a higher toxicity level in the blood.

Spironolactone: Used as a diuretic to remove excess fluid caused by many different diseases. Examples: Aldactone, interacts with ACE inhibitors by lowering the blood sodium levels while raising blood potassium levels.

Amiodarone: Prescribed for many serious arrhythmias of the heart Examples: Cordarone, interacts with Digoxin by excessively lowering the heart rate.

Verapamil: Prescribed for chest pain that occurs due to insufficient oxygen in the heart muscle, also used for high blood pressure. Examples: Calan, Isoptin, Verelan, interacts with digoxin by increasing the blood levels of this medication.

How to Prevent Drug Interactions

A person on multiple drugs and/or supplements should make a list of all the medications that he/she is currently using, or has been using for at least last 3-4 weeks and show it to his healthcare provider or physician.

Also, any changes in medicine dosage, route of administration or change in medicine should also be noted and compared with the medicines which are currently in use to assess any possibility of Drug Interactions.

Avoid smoking, drug abuse and alcohol consumption which not only lead to complications in terms of Drug Interactions but are detrimental for health in every sense of the term.

Any changes in lifestyle, for example, sleep-wake cycle, exercise, dietary changes, changes in stress levels due to work or otherwise should also be reported to the healthcare provider from time to time in order to eliminate or minimize any chances of Drug Interactions and to benefit from the prescribed Drugs to the best possible limit.

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