Grapefruit and Medication

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Grapefruit and Medication

Healthylife Pharmacy29 January 2019|4 min read

Ever wondered why your doctor tells you to avoid eating grapefruit when taking certain medications. Eating grapefruit can be seen as a healthy part of the diet, unfortunately it can interfere with how medicine are metabolized in the body. This can be most concerning when you are relying on that medication for serious health conditions such as high blood pressure or heart health. Individual drug metabolism rates are influenced by genetic factors, coexisting disorders (particularly chronic liver disorders and advanced heart failure), and drug interactions, especially those involving metabolism - step forward grapefruit.

We are not suggesting grapefruit is a bad fruit to eat, on the contrary, they are high in important health nutrients such as vitamin C, vitamin A, magnesium, potassium and fibre. Consideration just needs to be taken when on certain medications. 

How is Eating Grapefruit a Problem?

The simple answer is grapefruit increases the amount of medication that enters the blood stream. Whilst you may think this could be good, it actually can be quite dangerous.

When you are prescribed an amount of medication to take it has been carefully researched to be the specific amount the body needs to preform the action required. The medication is metabolized over a certain period of time and excreted.

What is Metabolism?

Metabolism is the sum of all chemical processes that occur in the body to sustain life. It includes the breakdown of chemical substances into simpler components (catabolism) and building up of complex substances from simpler, smaller components (anabolism). Think of the digestion of food into individual proteins – amino acids, as an example of catabolism, and the new amino acids into protein to use as the building blocks for muscles and bones as an example of anabolism.

Medication can be metabolized in the body by different methods, these include: oxidation, reduction, hydrolysis, hydration, conjugation, condensation, or isomerization; with the goal in mind to make the drug easier to excrete. The enzymes involved in metabolism are present in many tissues of the body but generally are found more concentrated in the liver and intestines.

Some bodies metabolize their medications too quickly which mean the therapeutic effect in the blood and tissue concentrations are not reached; in others, metabolism may be so slow causing a toxic effect.

Because grapefruit blocks the metabolic process needed to break your medicine down to a useable product, specifically the vital enzyme called cytochrome P450 3A4 (CYP3A4), it means your medication stays in the blood stream longer and can increase as you take more doses. The increased drug can then have serious side effects depending on which medication you are on and how much CYP3A4 enzyme you have in your intestines. For instance, an increase in cholesterol medication can increase the risk of damage to the liver, kidneys and muscles.

Drug Transporters

Not only does grapefruit potentially increase drugs in the blood, it has recently been noted that it may also decrease systemic concentrations by inhibiting drug transporters. These transporters play pivotal roles in the absorption, distribution and excretion of xenobiotic molecules (from outside the body -medication for example) and endogenous molecules (coming from inside the body).

Other things can influence metabolism

These include:

  • Physical activity - such as exercise
  • Hormonal influences – for example insulin, thyroxin and adrenaline
  • Increased heat – as in fever

Grapefruit and some other similar citrus fruits contain chemical substances called furanocoumarins. It is these chemical substances that causes the inactivation to the enzyme needed for metabolism of the medication. Seville oranges, limes and pomelos also contain furanocoumarins.

Many of the drugs that interact with grapefruit are commonly prescribed and are essential for the treatment of important or common medical conditions.

Medications

The medications affected have three essential characteristics:

  • Oral administration (taken by mouth)
  • Low intrinsic oral bioavailability (low absorption)
  • Metabolized by CYP3A4

Some Medications that need to be considered include:

  • Cholesterol lowering drugs - such as Zocor (simvastatin) and Lipitor (atorvastatin)
  • High blood pressure drugs - such as Procardia and Adalat CC (both nifedipine)
  • Abnormal heart rhythm medication - such as Pacerone and Nexterone (both amiodarone)
  • Organ-transplant rejection drugs, such as Sandimmune and Neoral (both cyclosporine)
  • Anti-anxiety drugs - such as buspirone
  • Corticosteroids for Crohn’s disease or ulcerative colitis - such as Entocort EC and Uceris (both budesonide)
  • Antihistamines, such as Allegra (fexofenadine)

Not all the medications used to treat these conditions will interact with grapefruit or grapefruit juice. It can depend on the amount of fruit/juice consumed, the person and the particular drug. It is important to check with your doctor or pharmacist and read the warnings and any information provided with your medication.

Serious Side Effects

Serious adverse side effects that have been found include:

  • torsade de pointes (a specific type of abnormal heart rhythm that can lead to sudden cardiac arrest),
  • rhabdomyolysis (death of muscle fibres and release of their content into the blood stream)
  • myelotoxicity
  • respiratory depression
  • gastrointestinal bleeding 
  • nephrotoxicity

Due to grapefruits ability to block the enzyme responsible for metabolising medication means these medications increase in systemic circulation.

How Much is Too Much?

The amount of grapefruit consumed could be a small as one grapefruit or a glass of grapefruit juice for it to potentially cause an increase in medication. 

This interaction can last for several days and have serious consequences depending on the particular medications or health condition. Ask your Doctor if your medication/s are affected by eating grapefruit and if so, how much can you eat.  

The bottom line

Grapefruit and certain other citrus fruits are considered healthy foods but with the potential for a drug interaction.  

References

  1. Henry, Osiecki; The Nutrient Bible 9th Edition, Bio Concepts, AG Publishing; QLD, Australia
  2. Tortora, Gerald J and Derrickson, Bryan 2006 Principles of Anatomy and Physiology 11th edition, John Wiley and sons, Inc, USA
  3. https://www.betterhealth.vic.gov.au/health/ingredientsprofiles/Grapefruit
  4. https://www.fda.gov/ForConsumers/ConsumerUpdates/ucm292276.htm
  5. https://medical-dictionary.thefreedictionary.com/Metabolism
  6. https://www.msdmanuals.com/en-au/professional/clinical-pharmacology/pharmacokinetics/drug-metabolism
  7. The physiological role of drug transporters https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4417677/
  8. https://www.webmd.com/a-to-z-guides/rhabdomyolysis-symptoms-causes-treatments#1
  9. Grapefruit–medication interactions: Forbidden fruit or avoidable consequences? http://www.cmaj.ca/content/185/4/309
  10. https://www.nps.org.au/medical-info/consumer-info/understanding-interactions?c=mixing-grapefruit-with-medicines-aba01dfa