Grapefruit and antibiotics

Question

I read that the action of some antibiotics changes when you take them together with grapefruit (juice). Is this correct and is this the case with ciprofloxacine? Is the action stronger then?

Answer

Dear questioner,
Patients with cystic fibrosis are taking very many medicines. Sometimes there is ‘interaction’ between medicines which means that the effect of the medicin or the side effects are changed by simultaneous use of both drugs. Interaction is also possible with what you eat. Everybody knows for instance that some medicines need to be taken before a meal whereas others have to be taken with a meal to have the maximal effect or to avoid side effects. Interaction can occur in different ways. The uptake of medicine from the intestine can be influenced: delayed or increased. The breakdown of the medecine by the liver or the clearing of the medicine via the kidneys or via the gallbladder can be diminished or accelerated. This will lead to a change in the concentration of the medicine in the blood which results in increase or decrease of effects or side effects. Simultaneous administration of 2 medicines with the same effect can lead to an increase of their effect or side effect. Grapefruit juice influences the uptake in the intestine and the breakdown in the liver of some medicines. This concerns mainly medicines that are metabolized by a specific pathway (cytochrom P450, an enzyme or specific protein that changes many chemical agents taken up in the body, e.g. CYP3A4). Not everything is known about this topic but for the specific antibiotic precisely ciprofloxacine, the drug that you mention, there is no influence from grapefruit juice. For some medicines (such as sleeping pills, drugs that diminish anxiety, cisapride, cholesterol lowering agents, blood pressure lowering agents, immunosuppressive drugs taken after transplant) interaction is possible, usually with increasing the side effects. Taking ciprofloxacine together with grapefruit juice will thus not alter the effect nor the side effects. It is important to remain attentive for possible interactions with medicines and for questions about this you can always consult your treating physician.
F. Vermeulen

18.05.2009