Possible drug-drug and drug- food interactions in every day life

When we take a drug we expect it to cause an effect.  This effect can be altered by the presence of another drug.  This is called drug-drug interaction.

Drug effect can also be altered by the presence of food substances.  This is called drug-food interaction. The interaction of another drug or food can increase of decrease the effect of a drug.

Interactions must be avoided for a drug that has a narrow therapeutic index.  This means that the effective dose of the drug is close to the toxic dose of the drug and the presence of another drug or food substance that causes an increase of the drug in the body easily leads to toxicity reactions.  For example, at the therapeutic dose, warfarin prevents blood clots and stroke but at a slightly higher dose, it will cause excessive internal bleeding.  The toxic dose is close to the therapeutic dose and its therapeutic effectiveness can be disturbed by various drugs resulting in either increased clotting or increased bleeding.

Interactions should also be avoided for drugs that are life sustaining or important for sustaining an important biologic function.  For such drugs, if their effects are eliminated by drug-drug or drug-food interactions, there can be serious consequence, life threatening crises, or even sudden death. For example if the effect of blood thinner warfarin should fail, a person who is prone to blood clots may end up with a stroke.  If the effects of an antiepileptic drug should fail a person may end up with a seizure while driving or while operating a dangerous machine.  If the effect of an oral contraceptive should fail, a person may end up having an abortion. Various foods, vitamins and dietary supplements, herbs in foods and herbal medicines, alcohol, and tobacco have a potential for interacting with our common drugs but more often than not, this is of no consequence. Some interactions, however,  should not be overlooked.  For example, the antibiotics called fluoroquinolones, such as ciprofloxacin, bind to calcium and iron in food or multivitamin products. This can prevent the antibiotic from being well absorbed. If the effect of an antibiotic should fail, an infection can overwhelm the body.

Some foods are noteworthy. For example, grapefruit juice inhibits the activity of the liver enzyme called cytochrome P450 3A4 (CYP3A4).  This enzyme is important for the processing (metabolism) of certain drugs and toxins.  Thus the target drugs will not be adequately metabolized for excretion and may become toxic in the body.

Pharmacologists study the effects of drugs on the body and this is called pharmacodynamics.  When a drug relieves a headache, this is a pharmacodynamic effect. Pharmacologists also study the effects of the body on the drug and this is called pharmacokinetics. When the body destroys the drug and eliminates it in urine, these are pharmacokinetic effects.  Drug-drug interactions can be at the level of pharmacodynamics or at the level of pharmacokinetics.  The presence of a second drug or food can change the pharmacodynamics or the pharmacokinetics of a first drug.

Pharmacokinetic drug-drug or drug-food interactions can be at the level of drug absorption from the stomach or intestines, distribution of the drug around the body, or at the level of processing of the drug by liver enzymes and elimination of the end products by the kidney which forms urine.  Thus the normal destination of the drug within the body can be changed by another drug or by a food substance.

Mid-lifers who have chronic non-curable illnesses or medical conditions such as diabetes and hypertension have to take a drug for a long time or for life and are often given multiple drugs.  They have a continual chance of drug-drug and drug-food interactions if they liberally take other drugs, especially non-prescription drugs. Many adults buy over the counter drugs and may use several different drugs at once in self-medication.  This entails a risk of drug-drug and drug-food interactions.

Elders tend to have altered liver and kidney functions that affect the way drugs are processed and eliminated from the body.  Hence, drug-drug and drug-food interactions may affect an elder specially.

Serious consequences of drug-drug and drug-food interactions include sickness and absence from work, life threatening conditions, hospitalization, disability, and death.

Doctors know how to deal with possible drug-drug interactions. For example, they may adjust the dose a drug, adjust the dosing times of different drugs, and monitor various parameters of a patient.  However drug-drug interactions and drug-food interactions that may occur from non-clinical self-medication is something we should all watch out for.  We were taught to give thanks and pray before meals.  Indeed, now we know we should pray with everything we consume, including drugs.  Next, we consider specific examples of interactions.

Theresa Adebola John is a lecturer at Lagos State University College of Medicine (LASUCOM) and an affiliated researcher at the College of Medicine, University of Tennessee, Memphis.  For any comments or questions on this column, please email bolajohnwritings@yahoo.com or call 08160944635