Most people have the mistaken belief
that being natural, all herbs and foods are safe. It cannot be said to be true.
The herbs and foods may interact with medications taken, that may result in
serious side reactions. For the simple reason that like oral medication, food
and herbs also traverse the same gastrointestinal path. Hence co-administration of drugs and
food/herbs may affect the absorption of the drugs by altering gastric pH,
secretion, gastrointestinal motility and transit time; and consequently
therapeutic efficacy (1).
In order to understand drug-food /
drug-nutrition interaction, it is important to understand the ADME of the drug
in question (2). The impact of drug-food interaction can be assigned to
multitude of factors namely, age, weight, sex and state of health of the
person; dosage of the drug and the time of administration of the interacting
components. Sufficient information about the drug and the timing of medication
around food intake can help avoid drug-food interaction (3). Food may alter hepatic metabolism of some
drugs. The flavonoids in grapefruit juice inhibit cytochrome P 450 metabolism
of antihypertensives namely felodipine and nifedipine causing enhanced
bioavailability (4). This interaction could increase both the efficacy and
toxicity of the drugs. There is potential clinical significance, because citrus
juices are frequently consumed in breakfast when many medications are taken.
Apart from interference in absorption, the foods may alter the urinary pH,
which may affect the activity of certain drugs that may influence excretion and
hence the half- life. The half-life of
an acidic drug will be extended in acidic urinary pH whereas it would be
reduced in alkaline urine. Foods such as milk, vegetables, etc. may alkalinize
the urine whereas meats, fish, cheese and eggs can acidify the urine.
Foods may interact with medications by
altering their pharmacologic actions. Diets high in vitamin K (turnip greens,
green tea, cauliflower, spinach, broccoli, brussels sprouts, chickpeas, pork
liver, beef liver) may cause antagonism of warfarin and decrease its
therapeutic efficacy (5). As stated the timing of administration is very
important to avoid drug food interaction. For example to avoid interaction,
calcium rich dairy products and calcium supplements should be taken two hours
before or six hours after administration of
fluoroquinolones ( ciprofloxacin, norfloxacin)/ tetracyclines/
biphosphonates( aldendronate, risedronate & ibadronate).
When fruit juices or vegetables are
co-administered with drugs, interaction at pharmacokinetic level is possible.
The drug-phytochemical interaction may not be manifested as therapeutic failure
but certain adverse events may take place. For e.g. grape juice blocks
cytochrome P 450 and IA2 (CYP3A4 and CYO1A2) in intestinal area; hence should
not be taken with certain antihypertensive drugs and cyclosporine as it may
lead to higher levels of drugs (6). Thus the interactions need to be well
Extensive research inputs are needed
for identification of this kind of interactions. Possibly some alterations/
evolution of drug release test methodologies may be seen as methods to forecast
the interactions. In future, this may become integral part of new drug approval
process. However, in the current scenario, a pharmacist can help avoid
drug-food interactions by practicing proactively.
- Yaheya M, Ismail M,
Drug food interactions and role of pharmacist, Asian J Pharm Clin Res,
- Zyl VM, The effects
of food on nutrition, S Afr J Clin, Nutr, 2011, 24, 38-41.
- Hepler CD, Strand
LM, Opportunities and responsibilities in pharmaceutical care, Am J Hosp Pharm,
1990, 47, 533-43.
- Bailey DG, Spence
JD, Munoz C, Arnold JMO. Interaction of citrus juices with felodipine and
nifedipine. Lancet. 1991; 337:268–269.
Accessed 21 June 2017.
- Bailey DG, Malcom
J, Arnold O, Spence JD, Grapefruit juice-drug interactions, Br J Clin
Pharmacol, 1998, 46(2): 101–110.