Dr Michelle O'Driscoll: Have you heard about medicine interactions?

HAVE you ever been asked by your doctor or pharmacist whether you drink grapefruit, or advised not to eat too many green leafy vegetables?

There’s a very valid reason for these seemingly random questions about your diet.

Similarly, there’s a reason why you’re always supposed to tell the pharmacist or other healthcare professionals who are looking after you if you’re taking any medicines before adding anything else onto the list by prescription, over the counter or even from a herbal medicine perspective.

The action of a drug is in the body is a delicate balance of many different elements and factors. Many drugs themselves have come from plant sources originally, e.g. digoxin for the heart comes from foxgloves! 

The things we take into our body are not all neutral in terms of their action. Our food or herbal products can have unanticipated effects on how drugs act in our bodies and are broken down.

Our bodies work to break down a drug once we take it into our systems, a process known as metabolism. This is how the body breaks down a drug to (usually) an inactive version of itself, to allow it then be released. This breakdown occurs with the help of enzymes which catalyse or influence the speed of the process.

Back to the good old Junior Cert definition, enzymes speed up or slow down a chemical reaction, without themselves being used in the reaction. They’re like little chemical assistants in the body – the more there is of a particular type of enzyme, the more work it can do to affect the breakdown process. Some drugs are acted upon by the same enzyme however, and you can imagine that this then leads to competition for its attention and action, and a reduction in the speed that it can affect each of the drugs.

It’s very common for two different drugs to interact with one another for this reason, the competition increases, or one can block the other for example. This is less common with food but it can occur occasionally, and the main examples of this should be flagged with you when you begin taking the drug.

Grapefruit is a strong enzyme inhibitor, and this means it will stop certain enzymes such as cytochrome P450 3A4 and others from working. This particular enzyme is responsible for the breakdown of a large number of drugs.

This means that any drugs broken down by this enzyme will not be broken down at the same speed if you’re taking in large quantities of grapefruit very suddenly. Too much drug left in the system can then lead to side-effects or even overdose. It’s an interesting and important consideration to bear in mind, which will affect some but not all drugs.

For green leafy veg as another example, they contain lots of vitamin K. If you’re taking a drug called warfarin which keeps the blood thin to prevent a clot, too much vitamin K helps enzymes that make the clotting factors in the body work better, and reduces the effectiveness of the warfarin. Keeping your intake of green leafy veg constant from week to week will help to make sure the body strikes a balance with the dose of warfarin you’re on.

Another consideration in the breakdown of some drugs is smoking. Giving up is the single best thing you could ever do for your health. However, it’s always a good idea to let your doctor or pharmacist know first if you’re attempting to give it up, especially if you’re taking medications. There are a few medicines occasionally prescribed that are broken down by enzymes which are affected by smoking.

Smoking increases the action of an enzyme in the body, which means it breaks down certain drugs more quickly. This is fine because your drug dose is adjusted to this if you’re a smoker. However, if you decide to give up smoking, the enzymes are going to slow down – and you could be left with too much drug in your system. This would need a change in your dose to balance all of this out. This is very manageable, but important to flag before stopping the smoking, in the case of some drugs.

Overall, a good rule of thumb is to ask when starting a medicine whether there are any particular food or other lifestyle considerations with it. 

Don’t make any drastic lifestyle or diet changes if you’re unsure about their effects on your medications, and always feel free to ask at the pharmacy or doctor if unsure.

ABOUT THE AUTHOR

Dr Michelle O’Driscoll is a pharmacist, re searcher and founder of InTuition, a health and wellness education company. Her research lies in the area of mental health education, and through InTuition she delivers health promotion workshops to corporate and academic organi sations nationally.