Pharmacovigilance

What Are The Types Of Adverse Drug Reaction (ADR)?

An adverse drug reaction (ADR) can be defined as ‘an appreciably harmful or unpleasant reaction resulting from an intervention related to the use of a medicinal product; adverse effects usually predict hazard from future administration and warrant prevention or specific treatment or alteration of the dosage regimen.

Monitoring of adverse drug reaction is an important aspect of pharmacovigilance defined as the science and activities relating to the detection, assessment, understanding and prevention of adverse effects or any other drug-related problem. Regarding marketed medicinal products, a well-accepted definition of an adverse drug reaction in the post-marketing setting is as follows: A response to a drug which is noxious and unintended and which occurs at doses normally used in man for prophylaxis, diagnosis, or therapy of disease or for modification of physiological function (WHO, 1972).

What are the types of adverse drug reaction (ADR)?

There are various classifications of ADRs they include:

Augmented. An effect that is higher in intensity or magnitude than the expected pharmacological effect. It can occur either as an extension effect or part of the therapeutic effect or can occur as not part of the intended therapeutic effect (as a side-effect). It has usually a dose-dependent mechanism.

  • Augmented extension effect – For instance a hypertensive patient is on a beta-blocker. Since the management of hypertension includes the lowering of cardiac output, and the resultant blood pressure, beta-blocker is ideal. Heart rate also plays a role in the pathophysiology of hypertension, and hence as part of therapeutic management beta-blocker can be useful because it has in part, the expected pharmacological action of slowing the heart rate. However, let’s say that the bradycardia seen in this hypertensive patient was less than 60 and the patient feels some discomfort, then this is a form of beta-blocker augmented extension effect. It is expected and can be managed with dose reduction or shifting to another class of hypertensive agent.
  • Augmented side effect – on the other hand, let us say that the same patient experienced bronchospasm as a result of beta-blocker use, this is a form of an augmented Side-effect. We know that this can happen as part of beta-blocker actions but bronchospasm is not an intended effect of treating hypertension unlike the earlier example, where lowering of the heart rate with beta-blocker can confer some lowering of cardiac output and blood pressure. The management in this ADR case will have to be shifting to another class of hypertensive agent. On the other hand, phenothiazines or haloperidols used to treat psychiatric conditions may induce extra-pyramidal side reactions that can be managed with small doses of benztropine or diphenhydramine. Anti-cancer drugs that induce nausea and vomiting can be given anti-emetic agents.

Bizarre.This effect can be likened to a hypersensitivity or idiosyncratic reactions. It is often unpredictable. There are no conventional tests to demonstrate which patients might experience this ADR in order to theoretically prevent its occurrence. It is not dose dependent to the medicine used. Some can occur immediately, such as penicillin hypersensitivity and acute anaphylactic reactions. But some can occur at a much later time, even months later, such as Steven-Johnson Syndrome following use of phenytoin, carbamazepine, Phenobarbital or sulfa-containing drugs. Not all cases can be explained by known pharmacological actions of the suspected drug.

Continuous. This ADR happens after a prolonged use of a drug even at normal dosage. It affects organ systems. An example is phenacetin causing renal papillary necrosis. Another is Cushing’s syndrome from long-term use of steroids. Hypokalemia and dehydration can happen from long furosemide use. Because of the accumulation of the epileptogenic metabolites of meperidine following prolonged use, seizures can occur. Even large dose & long term use of pyridoxine can lead to neuropathy.

Delayed. This is seen when a drug used at some earlier time has some adverse effects that are observed much later on, such as affecting the next generation. Diethylstilbestrol taken by women can cause vaginal and other reproductive organ damage in female offspring. In the 1960’s thalidomide used by pregnant women invariably leads to the development of congenital malformations.

Ending of use.  This is when a drug that was used on long term is suddenly stopped, the patient suffers a form of withdrawal reaction. These drugs exhibit tolerance phenomenon or have some dependency potential. Examples are: rebound hypertension following sudden cessation of clonidine, adrenal insufficiency after stopping prolonged steroid use, seizures from acutely ceasing anticonvulsants, and uncomfortable withdrawal syndromes from benzodiazepines and narcotics.

Failure of treatment. This is a new form of ADR recently recognized as a public health threat. ADR monitoring systems can pick up unusual and unexpected drug inefficacy and can detect possible fake or substandard quality medicines. But the doctor has to be astute and keep an open, objective and critical mind to even suspect these. But once they do, they can be useful to the drug regulators, concerned industry and to the institutions that use these drugs. Patients’ lives and the public health is the ultimate beneficiary.

ADR symptoms can be described as mild, moderate, severe. These are descriptive terms of the intensity of a particular sign or symptom. Serious, on the other hand defines the urgency and the impending critical threat to the life of the patient.

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