Grapefruit–medicine interactions: what we already know
Chemicals in grapefruit can affect how medicines work in the body
It has been known for some time that certain chemicals in grapefruit (known as furanocoumarins) can interfere with the way your body metabolises or processes many medicines in the intestine (gut) or liver before they reach your bloodstream. When this happens, more of a medicine may get into your body, making it work too strongly or causing unwanted side effects.This happens because of their effect on ‘CYP3A4’ — an enzyme involved in metabolising many medicines. Medicines need to be taken orally (e.g. in the form of a tablet or liquid) to be affected by grapefruit because grapefruit mainly affects this enzyme in the gut.
Some other citrus fruits might have a similar effect
Bitter oranges (e.g. Seville oranges) and limes may also cause interactions with medicines. Other citrus fruits such as sweet oranges and lemons don’t have this same effect.Many medicines are already known to interact with grapefruit
Several prescription, over-the-counter or complementary medicines (herbal, ‘natural’, vitamin and mineral) are known to interact, or potentially interact, with grapefruit. Common examples include some types of medicines for heart conditions, high blood pressure, high cholesterol, infections, epilepsy, depression, anxiety and sleep problems.Side effects that are caused by these interactions
The exact side effects from interactions vary and depend on the medicine, but some are serious.Serious side effects have occurred when certain medicines are taken with grapefruit, including:- complete heart block (resulting in a very slow heart beat)
- torsade de pointes (rapid heartbeats that can lead to sudden death)
- rhabdomyolysis (severe damage to skeletal muscle that can lead to kidney damage)
- nephrotoxicity (kidney damage)
- myelotoxicity (damage to bone marrow)
- respiratory depression (reduced or slowed breathing).
Consuming any part or form of grapefruit can cause an interaction
The whole fruit including the juice and peel contain furanocoumarins, the chemicals that can interact with medicines. For this reason, people who take medicines that may interact with grapefruit are usually advised not to eat grapefruit or drink grapefruit juice at all. People may also be advised to avoid other related fruits that could interact with medicines.Interactions can result from just one serve of grapefruit
Even one glass of juice or one grapefruit can have an effect on a medicine, and an interaction can occur even when the grapefruit or juice is eaten or drunk at a different time. The severity of the interaction may also depend on how often you consume grapefruit or grapefruit juice.What the review says
The review raised four key points about grapefruit–medicine interactions. Information was obtained by looking at existing published reviews and case reports of interactions, in addition to product monographs and prescribing information sheets for recently marketed medicines in Canada.The number of medicines that interact with grapefruit is rising
The introduction of new medicines over the last few years has seen an increase in the number of potential grapefruit–medicine interactions.The review indicates that between 2008 and 2012, the number of medicines that may interact with grapefruit to cause serious side effects has risen from 17 to 43.
Certain medicines are more likely to have serious interactions with grapefruit than others
Medicines that normally reach your bloodstream in very small to moderate amounts are more likely to have significant interactions with grapefruit. This is because the effect of grapefruit can cause much larger amounts of the medicine to get into your bloodstream and cause side effects.Affected medicines should not taken with grapefruit at any time
An interaction is possible no matter when you ingest grapefruit during treatment.You don’t need to consume large quantities of grapefruit either for problems to occur: eating a whole grapefruit or drinking 200–250 mL of juice can cause significant interactions, especially if you consume this repeatedly.
The review also suggests that another non-interacting medicine may need to be considered if you can’t avoid eating grapefruit.
Older people could be more vulnerable to serious interactions
The likelihood of people experiencing grapefruit interactions with medicines can vary — and some may be more at risk than others.People over the age of 45 years appear to be most vulnerable as they are the main buyers of grapefruit and are more likely to receive prescriptions for medicines. People over the age of 70 years may be at particularly high risk of experiencing harmful effects from an interaction.
Which medicines can interact?
The review provided a risk ranking for 89 medicines that have, or could result in, interactions with grapefruit. The authors ranked medicines by assessing:- How much more of the medicine is absorbed into the body than usual, because of grapefruit.
- How serious the side effects are that result from this increased amount of medicine.
go to the link for entire article and the list of current meds.