A DRUG interaction is defined as a change in the drug’s effect on the body when it is taken with other drug(s), food, beverage, and supplement or in a pre-existing disease condition, which may be triggered by the use of the said drug.

Screening for drug interactions is a proactive exercise done by the pharmacist so as to prevent prolonged illness and enhance medication management. However in the event that the intended outcome of the drug is not achieved or the side effects outweigh the benefits, retroactive investigations can be done on drug interactions.

Drug interactions could either increase the effect of one or more drug, resulting in toxicity or amplified undesirable effects or decrease or reduce the effect of the medication, leading to treatment failure.
For simplification of drug interactions, there is a three category classification; drug-nutrient, drug-disease and drug-drug interactions.
* Drug-nutrient interaction – Nutrient including food, supplements (herbal and traditional) and beverages may have an effect when consumed with certain drugs. For example, a drug such as ketoconazole is metabolized by the liver, so when a substance like alcohol is used concomitantly, the alteration of liver enzymes affect the drug’s metabolism. Hence it is not recommended to use alcohol whilst on such medications. Metronidazole, commonly known as flagyl, is another drug which when taken with alcohol may cause flushing, headaches, palpitations, nausea or vomiting.
* Drug-disease interaction – A patient with a known chronic disease may need a drug for another condition, which may make the underlying chronic ailment worse. For example, an asthmatic experiencing pain or fever should not use Advil or ibuprofen, aspirin or any readily available NSAID (non-steroidal anti-inflammatory drug) since it can exacerbate an asthmatic attack. Likewise, if the asthmatic patient present with cardiac issues later in life and requires a heart rate slowing drug, it is advisable that a highly selective beta-1 blocker such as bisoprolol is prescribed at the lowest effective dose which presents minimal risk of beta-2 blocking bronchospasm.
* Drug-drug interaction– Both POM (prescription only medicines) and OTC (over the counter) products can interact by negating, synergising or altering the effect of drug(s). There are three kinds of drug-drug interactions; duplication, antagonism and alteration.

> Duplication
Duplication occurs where there are two drugs with the same active ingredient or same outcome, causing the resultant effect to be intensified. Often concomitant use of OTC products with multiple active ingredients or when the patient seeks multiple doctors’ opinion with no record of an established medical history can lead to duplication.
Blood thinners’ effects are potentiated by pain killers and can cause a gastric bleed as seen when warfarin is used with diclofenac, ibuprofen or aspirin.
The synergistic vasodilation of Nifedipine and GTN (glycerintrinitrate) may cause hypotension.
The combination of a statin (simvastatin, atorvastatin or rouvastatin) and gemfibrozil increases the frequency of myopathy.
Some OTC potentiated effects are:
* Cold medication and pain reliever since both may contain acetaminophen
* Cold medication and sleep aid since both contain diphenhydramine

> Antagonism
Antagonism occurs when two drugs with opposing mechanism of action are taken together, interfering with the desired effect of one or both medications. Taking an NSAID such as ibuprofen or diclofenac for pain may cause retention of water and elevate the blood pressure. However for those patients who are already on diuretics for their hypertension, acetaminophen will be a better option for the pain.
The combination of HCTZ (hydrochlorothiazide), aldomet or spironolactone along with ramipril, captopril or potassium sparing diuretics and ACE inhibitors may retain too much potassium in the body and can cause hyperkalemia.

> Alteration
Alteration occurs when one of the processes that the drug undergoes in the body is affected; either its absorption, its metabolism, its distribution or its elimination. For example it is not recommended to take the antifungal medication, ketoconazole, if you are on acid reducing agents such as proton pump inhibitors like omeprazole or pantoprazole or H2 blockers like cimetidine, famotidine, nizatidine or ranitidine more popularly known as Tagamet, Pepcid, Axid and Zantac respectively. The reason being ketoconazole is best absorbed in an acid environment.
Omeprazole and clopidogrel together alter the clinical outcome by reducing the inhibition of platelet aggregation.

Additionally, these are not recommended to use concomitantly:
* Furosemide or Lasix and gentamycin since this combination potentiate hearing loss, especially in the elderly or those with pre-existing kidney disease.
* Azithromycin and Benadryl or Piriton or Cetrizine – This is a controversial combination since it has been widely used in many respiratory illnesses but caution must be exercised in two areas; if the duration exceed the usual three day antibiotic dose or if the patient is an elderly with a cardiac issue since there is a risk to prolong QT interval.
Some self-help suggestions to significantly avoid drug interaction:
> Chart your medicines, dosages and chronic illness, if any, for future reference.
> Read the labels and compare active ingredients contained.
> Consult a doctor or pharmacist when considering an additional or new drug, even for a minor illness.
> Stay with one medical practitioner or pharmacist who knows your individualised patient profile or keep records of your history. This will avoid antagonistic interactions.
> Not advisable to share medications with friends and family without the consultation of a doctor or pharmacist although they may be suffering from the presumably same condition. Each person is different and may already be on an established regimen.

For further pharmacological guidance, contact the pharmacist of Medicine Express PHARMACY located at 223 Camp Street, between Lamaha and New Market Streets. If you have any queries, comments or further information on the above topic kindly forward them to medicine.express@gmail.com or send them to 223 Camp Street, N/burg. Tel #225-5142.