Common and life-threatening drug interactions
A drug interaction is a reaction between:
- Two (or more) drugs, or
- A drug and a food, beverage, or supplement
Drug interactions are commonly classified as:
- Drug-drug interactions
- Drug-food/beverage interactions
- Drug-condition/disease interactions
- Drug-laboratory interactions
An interaction can:
- Increase or decrease the effect of one or more drugs, or
- Cause unwanted side effects, including severe or lethal effects
Serious outcomes of drug interactions can include bleeding, bone marrow suppression, arrhythmias, liver failure, seizures, and renal failure.
Some medication classes have a higher risk of interactions. One practical way to reduce risk is to read drug labels and check for warnings about combining products.
Drug classes with a high risk of drug interactions
| Drug class | Example |
|---|---|
| Antiarrhythmics | Digoxin |
| Anticoagulants | Warfarin |
| Antibiotics | Erythromycin |
| Platelet inhibitors | Clopidogrel, aspirin |
| Anti-epileptics | Phenytoin |
| Immunosuppressants | Cyclosporine |
| MAO inhibitors | Phenelzine |
| Antipsychotics | Lithium |
| Supplements | St.John’s wort |
Drug-drug interactions: Drug-drug interactions can occur inside the body (pharmacological) or outside the body (pharmaceutical).
Pharmaceutical interactions happen when drugs come into contact before administration (for example, during storage, preparation, or mixing). These interactions may be physical or chemical.
Types of pharmaceutical interactions
| Type of interaction | Examples |
|---|---|
| Physical | Exposure to light humidity can degrade drugs faster; crushing a tablet may cause it to be absorbed faster than expected |
| Chemical | Potassium phosphate and calcium chloride mixed together in intravenous lines precipitate as calcium phosphate; Phenytoin (Dilantin) and lorazepam (Ativan) become ineffective if mixed together |