Drug Interactions

Have you ever taken a medication and it ‘did not’ work? Well, you may have impeded the action of the medication by a certain food or drug you may have taken with it. This is called drug interaction.

Simply put, a drug interaction occurs when a patient’s response to a drug is modified by food, nutritional supplements, formulation excipients, other drugs or disease.

Drug interactions produce negative effects to the patient as the interaction could either increase the concentration of the drug in the body causing drug toxicity or reduce the concentration of the drug causing therapeutic failure; in other words, ‘the drug did not work’ or ‘I suffered from a terrible side effect to that drug’

There are different types of drug interaction. the common types include:

  • Drug-drug interaction
  • Drug-nonprescription treatment interaction
  • Drug-food interaction
  • Drug-disease interaction, etc.

Drug-drug interaction occurs where two or more drugs are taken simultaneously or within a close time and one of the drugs affects the other by either reducing the absorption of the drug, hence less of the drug in the blood, causing therapeutic failure as the right amount of drug needed to be absorbed into the blood stream for optimization is impeded or by increasing the amount of the drug causing toxicity. An example is Theophylline which is a content of the common drug Franol® used to reduce the symptoms of Asthma and Quinolones a class of antibiotics used to treat infections like typhoid fever, etc. Another common example is Ciprofloxacin (Ciprotab®) and Theophylline . Ciprofloxacin increases the concentration of Theophylline in the blood which can produce harmful effects such as seizures, cardiac arrest, and respiratory failure. These drugs should not be used together.

Drug-food interaction occurs where the action of a drug is impeded by a particular food. An example is Atorvastatin (Lipitor®) a drug used for the treatment of high cholesterol and grapefruit juice. Grapefruit juice would increase the potency of Atorvastatin when taken together which can cause a greater risk of side effects. Another example is Calcium rich foods such as milk, yogurt, and Antibiotics. The antibiotics bind to the calcium in the foods forming an insoluble product which can not be absorbed into the body thus causing therapeutic failure of the antibiotic as the amount absorbed of drug needed to elicit its action is not sufficient

Drug-disease interaction occurs where a drug used to treat a disease in a patient causes the worsening of another disease present in the same patient. An example is NSAIDs e.g., Diclofenac, used as a pain reliever, and asthma. Diclofenac may cause airway constriction worsening an asthmatic condition or even provoking an attack. Another example is Pseudoephedrine, a content of some cough and flu medicines e.g., Actifed® and High blood pressure. Pseudoephedrine can cause an increase in blood pressure which can be detrimental if not monitored.

Other examples like drug-nonprescription interactions can occur when a drug such as a supplement/ blood tonic is taken together with medication, and it reduces the effect of that drug. For example, supplements that contain iron should not be taken with antibiotics as the iron can decrease the amount antibiotic absorbed from the stomach, causing reduced effectiveness of the drug.

Drug-alcohol interactions also exist. For instance, taking Metronidazole (Flagyl®) and alcohol can lead to an unpleasant reaction called Antabuse reaction. Taking alcohol together with drugs that cause sedation e.g., Bromazepam is also not advisable.


  • Always read the patient leaflet of every drug and take note of the potential drug interactions.
  • Know the name of any medication you are currently taking so you can inform your doctor/pharmacist and they can be guided accordingly.
  • Always take your medications as prescribed. Follow the instructions to the letter. There is a reason why a medication is to be taken an hour before or after meals, etc.
  • Review your medications regularly.
  • Ask questions!!! Always ask your pharmacist or doctor to advise on what to avoid while on certain medications.

-Ayanfe Glory Rotimi, Pharmacy Benefits

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