Drug-drug interactions

Drug-drug interactions

In a country like Lesotho where Pharmacovigilance is just a topic in a classroom setting, is there a possibility that the high morbidity and mortality rate in our nation is partly due to Drug-Drug interactions left unidentified and hence unreported?
Drug interactions occur when the effects of a drug are modified by the concomitant administration of another substance, most commonly another prescription medication or Over–The Counter (OTC) drug.
Drug-drug interaction can delay, decrease, or enhance absorption of either drug, resulting in the decrease or increase in the action of either or both drugs or can cause adverse and toxic effects.

Although most drug interactions are between two or more drugs, other important drug interactions can involve drugs – herbs interactions, drugs – foods, as well as drug-disease interactions. However our focus for today shall be on drug-drug interaction.
In general, drug interactions must be avoided due to unexpected adverse outcomes. However, certain drug interactions are produced intentionally because they can be clinically beneficial.
These clinically useful interactions are known as pharmacologic augmentations or pharmacologic synergisms.

A modern example is the use of carbidopa with levodopa in the management of Parkinson’s disease. Levodopa, when used individually, is metabolised in the peripheral tissues.
This decreases the availability of levodopa in the brain and increases the risk of adverse effects. Carbidopa inhibits the peripheral metabolism of levodopa, allowing more un-metabolised levodopa to reach the brain, therefore increasing clinical efficacy and reducing the risk of peripheral side-effects.

The population at risk of developing adverse drug interactions:
The elderly are at risk of developing drug interactions due to their overall increased risk of developing illness such as hypertension, diabetes, cardiac and pulmonary diseases and, therefore, increasing their use of prescription and over-the-counter medications.
This increased use of medications in the elderly, combined with their decreased metabolism and impaired clearance of medications, greatly increases their risk for developing drug interactions.
Poly-drug misusers and abusers; and patients in undeveloped countries who self-medicate with prescription medications easily obtained over-the-counter. (Lesotho has no Drug Regulatory Authority, drugs are not under the full custody of Pharmacists, hence the nation is at risk!)

Critically ill patients are also at risk of developing drug interactions due to the fact that they are exposed to a large number of drugs during their illness. In addition, critically ill patients are likely to have organ dysfunction resulting in impaired metabolism and clearance of drugs.
Psychiatric patients; patients taking high doses or multiple medications due to resistant medical conditions; patients who have low albumin levels from chronic lung disease; Alcoholics or the malnourished are also at risk of developing significant drug interactions due to altered protein binding.
Patients should be educated about drug interactions and instructed to seek medical evaluation if symptoms occur.

Some useful patient tips include:

  • Read labels; Know drug warnings; Keep drugs in original containers; Ask your doctor about drug, food, and dietary supplement interactions; Ask your pharmacist before taking over-the-counter medications if you are taking a prescription medicine; Inform all your doctors about all your medicines, including supplements; Keep a list of all your medicines, including supplements; Don’t save medicines for future use; Don’t share medicines; Don’t double dose medicines in case you missed a dose.
    The drug-related morbidity and mortality have been estimated to cost more than $130 billion per year in the United States, however a study in the medical intensive care unit in the US showed that having a clinical pharmacist during ward rounds decreased potential drug interactions by 65 percent and decreased length of hospital stay.
    Doctors and Pharmacists in our nation must thus work together to minimise the risk of drug-drug interaction morbidity and mortality. The area of drug-drug interactions and their effects on morbidity and mortality in Lesotho is an open field for research; Pharmacists with interest in Pharmacovigilance may take up the challenge and publish concrete studies for Lesotho.

Retšelisitsoe Nkhahle is Mosotho pharmacist based in Botswana. She is pursuing an Msc.

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