When discussing interactions, we should first understand their brief, general definition: an interaction is an effect that occurs when two or more medicines or active substances are used simultaneously, resulting in a change in the properties of one or more medicines.
In the following examples, we will look at some interactions between medicines and food containing substances or interacting agents similar to those found in medicines. The interaction between two substances may increase, reduce or completely cancel out the effect of a medicine intended for treatment. Depending on our knowledge of the interaction and the patient’s benefit, interactions may be classified as beneficial or adverse.
Let us take a look at the table below, which lists the most common adverse interactions encountered in everyday practice:
| Medicines | Food and drink | Interaction |
|---|---|---|
| Tetracycline antibiotics, such as Vibramycin and Clinofug D50 | Milk and cheese | Incomplete absorption of the antibiotic |
| Tetracycline antibiotics, such as Vibramycin and Clinofug D50 | Liver and pumpkin seeds | The antibiotic does not work as intended due to an incomplete mechanism of action |
| Antidepressants belonging to the MAO inhibitor group; the only registered medicine is Aurorix | Fermented cheeses, wine, beer, salami | Risk of a sudden increase in blood pressure |
| Heart medicines containing digoxin or metildigoxin as active ingredients, such as Lanicor and Lanitop | Vegetables, cereals and fibre-rich foods | Incomplete absorption, resulting in reduced effectiveness of the medicine |
| Antifungal medicines: griseofulvin, ketoconazole (Oronazol, Sporanox) | Fatty meat and animal fats | Double the absorption of the active ingredient, increasing the risk of toxicity |
| Medicines for intestinal infections containing furazolidone (Furoxone) | Fermented cheeses, red wine, salami, broad beans | Risk of increased blood pressure, particularly dangerous for people with heart conditions |
| Medicines for the treatment of hypertension, such as Amlopin, Nimotop and Unipres | Grapefruit juice | Their effects may increase by 20%, potentially causing an excessive drop in blood pressure |
| Antihistamines for the treatment of allergies, such as Teridin | Grapefruit juice | Accumulation of the active ingredient in the body, with a resulting risk of cardiotoxicity |
| Antidepressants, anxiolytics and medicines for insomnia | Liver and foods rich in vitamin B12 | Reduced effectiveness of the medicines, potentially requiring a dosage increase |
| Antidepressants based on lithium salts (Lithii carbonatis) | Insufficient salt intake | Reduced sodium intake increases lithium salt concentrations, thereby increasing the risk of side effects |
| Antiparkinsonian medicines, such as Madopar, Nakom and Akineton | Protein-rich foods containing pyridoxine or vitamin B6, particularly meat, cheese, soy, yeast, fish and whole grains | Reduced effectiveness of the medicine because food proteins and medicines share the same transport mechanism. Food proteins compete with the medicine for transport, reducing its passage into the brain |
| Contraceptive pills, such as Minulet, Femoden, all Stediril products and Cilest | Vitamin C | Slower metabolism of oestrogens, causing them to remain in circulation for longer and reducing their effectiveness |
| Contraceptive pills, such as Minulet, Femoden, all Stediril products and Cilest | Coffee | Oestrogens slow down caffeine metabolism, potentially causing harmless nervousness and insomnia |
| Anticoagulants or antithrombotic medicines, such as Marivarin and Pelentan | Vegetables rich in vitamin K, particularly cereals, broccoli and spinach | Reduce or even completely cancel out the effectiveness of the medicines. Increasing the dosage in response can therefore be dangerous |
| Lipid-lowering medicines or preparations used to reduce serum lipid levels, such as Sortis, Lipobay, Artein, Holetar, Sinvacor and Vasilip | Grapefruit juice | Significant increase in serum concentrations of the active ingredient, increasing the risk of toxicity, such as muscle damage |
| Immunosuppressive medicines, such as Sandimmun | Grapefruit juice | Increased serum concentrations of ciclosporin, resulting in a higher risk of nephrotoxicity |
| Certain medicines for which significant interactions are suspected and caution is therefore advised, such as Viagra, Digenol and Heptanon | Grapefruit juice | Significant increase in serum concentrations, resulting in an increased risk of side effects |
If you would like to learn more about somewhat more complex interactions, including interactions between different medicines, please contact us via our website. We will be happy to provide you with professional information.
Prepared by: Samo Mahovič, MSc in Pharmacy.