Adverse Drug Reactions | Causes and Prevention | Roles of Pharmacists

More than 10 percent of hospitalized patients are due to Adverse drug reactions (ADRs) which account for several thousands of deaths yearly; being the 4th to 6th cause of death in the USA.



What is Adverse Drug Reaction?

National agency for food and drug administration and control (NAFDAC) defines Adverse Drug Reactions (ADRs) as A response to a medicine that is noxious (harmful) and unintended and which occurs at doses normally used in man for the prophylaxis (prevention), diagnosis or therapy (treatment) of diseases, or for the modification of physiological function’.


Therefore, for a drug effect to be tagged as an Adverse drug reaction, it must have the following characteristics.

  • It must be harmful or noxious to health.
  • The effect is intended
  • Dose used is normal

Relationship between Adverse Drug Reactions (ADR) and DTPs

Adverse drug reactions are one of the 8 classes of drug therapy problems. It is a Drug Therapy Problem because it is an undesired outcome of drug therapy.

Nevertheless, it is the only DTP that occurs with little or no contribution from the Physician. According to the Tanzania Food and drug authority “ADR is an unexpected consequence of drug usage and its risk of occurrence can not be predetermined”.

Almost all effective drugs, no matter how skillfully used, may cause adverse reactions. The fact that an adverse reaction has occurred does not reflect in any way discreditable on the healthcare professional who prescribed, dispensed, or sold the drug.


Difference between ADR and side effects

The knowledge of the mechanism of actions of drugs makes it easier to predict a side effect, unlike an adverse effect that happens without warning. E.g., Side effects like slowing of heartbeat or shortness of breath will occur while using Cholinergic drugs since they enhance the actions of acetylcholine and the parasympathetic system.

ADR usually occurs when there is an incomplete or malfunctioning of the metabolism or the elimination mechanism (pharmacokinetics) while side effects occur at the pharmacodynamic level. However, the pharmacokinetic properties of a drug can also superimpose the clinical side effects of a drug.

ADR of any drug is usually rare, it occurs in below 1% of the population (e.g., the Stephen Johnson syndrome associated with cotrimoxazole) while side effects occur in greater than 50% of the population.

Causes of Adverse drug reactions

• Dose-related ADRs

This type of ADR occurs as a result of a high dose of the drug in the system due to insufficient elimination or metabolism mechanism. Drug-drug interaction and Drug-disease interaction ( especially one that has to do with renal or hepatic impairment) fall under this category.

• Allergic ADRs

Allergic ADRs occur when drugs are acts as an immunogen or an antigen to the patient’s immune system. after first exposure, sensitization to the drug occurs and subsequent build of antibodies against the drug.

On subsequent exposure, a serious hypersensitive reaction occurs e.g., hypersensitivity reaction of Abacavir to some patients.

• Idiosyncratic ADRs

Idiosyncratic ADRs are neither dose-related nor allergic, it defines reactions that have no defined cause. However, most Idiosyncratic ADRs occurs as a genetic predisposition. This means it occurs to a few individuals due to the presence or absence of some genetic components. E.g., the reaction of slow and fast acetylators to some drugs like Isoniazid, hydralazine, and Procainamide.

Role of a pharmacist in preventing Adverse drug reactions

The Pharmacist is the last gateway to ensuring the patient gets the best outcome of his drug. He must check medication appropriateness, perform medication reconciliation, and medication reviews, develop a care plan, and monitor patients.

Meanwhile, people refer to Adverse drug reactions as ‘side effects’ which impinges on pharmacovigilance and proper diagnosis. Good safety monitoring encourages healthcare practitioners to take fuller responsibility for their medicines. It improves clinical effectiveness and increases the confidence with which they and their patients use medicines. (6)

Tips for reducing Adverse drug reactions

  1. There is always the need for the Pharmacist to assess patients’ Prescriptions for an appropriate indication, safety, efficacy, and also possible drug interactions.
  2. a pharmacist must educate patients about possible side effects or drug therapy problems that may arise from using their medications and what to do if any come up.
  3. Good Pharmacy Communication skills will enable the patient to be part of the team. Therefore,information on the side effects of the drug can easily be related to the Pharmacists for proper action.
  4. The pharmacist should monitor and address issues of Polypharmacy, especially in the elderly, which may give rise to uncontrollable drug interactions and non-adherence.
  5. Integration of Prescription drug monitoring programmes (PDMPs) into pharmacy databases to track the prescription and dispensing of harmful controlled drugs by pharmacists such as Opioids. (
  6. Pharmacists through pharmacovigilance or proper documentation of adverse drug reactions can provide data for research tools to determine the effective ways of using a medicinal agent

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