What Are The Types Of Adverse Drug Reactions?

Surely you have ever heard of adverse reactions or side effects of medications. 7% of the population has some type of adverse reaction to medications, which represents a public health problem.

An adverse drug reaction, whose acronym is ADR, is any response to a drug that is harmful or unintended and that develops at normally applied doses. They can be doses for the prophylaxis, diagnosis or treatment of diseases, as well as for the restoration, correction or modification of biological functions.

Among the drugs that most frequently produce adverse reactions are:

• Non-steroidal anti-inflammatory drugs
• Antibiotics

How can I know the possible adverse reactions of a medicine?

The Spanish Agency for Medicines and Health Products (AEMPS) reminds us of the importance of always informing us about the drugs that have been indicated to us or those that we buy freely at the pharmacy. It is essential to ask our doctor and pharmacist about the possible adverse reactions that the drug can cause, as well as the situations in which its use is contraindicated.

In addition, you can also review the package insert of the drug. It will list these known side effects and what to do if they occur.

All the marketed medicines can trigger some adverse effect. However, it is decided to market them because the benefit obtained with their use is greater than the risks they have on health.

Type of adverse reactions

A general classification of adverse drug reactions groups them into two large groups: predictable reactions and unpredictable reactions.

Predictable reactions

They represent 80% of the adverse effects. They are dose dependent, that is, the higher the doses, the higher the adverse effects of these drugs. In addition, they are related to the pharmacological actions of the drug, such as:

• A side effect of its mechanism of action
• An interaction with another drug or substance
• Overdose

Unpredictable reactions

These reactions, unlike the previous ones, are not predictable doses, so they can develop at any administered amount. They are also not related to the pharmacological actions of the drug. They are linked to patient-dependent factors, since they occur in people with immune sensitivity or susceptible due to genetic differences.

Among the unpredictable adverse reactions we can differentiate the following:

• Intolerance: when at minimal doses we are not able to tolerate the drug. For example, some patients experience tremor at the lowest doses of salbutamol.
• Idiosyncrasy: these are reactions that are genetically determined and consist of an abnormal response to the drug, because the patient has an enzyme deficiency or abnormalities in the metabolism of the drug. These reactions are usually more serious, but they occur in a small number of people.

• Hypersensitivity reactions or allergic reactions : these are abnormal responses caused by an immune mechanism. For example, allergy to penicillin.
• Pseudoallergic or anaphylactoid reaction : they are clinically indistinguishable from the previous reactions, but they are produced by a different mechanism, in which the immune system is not involved. They have been described with opioid drugs, among others.

Other types of adverse drug reactions

In addition to those mentioned, there are also other unwanted effects that can occur in a drug treatment. Some of these other reactions are known as type C.

They appear after prolonged administration of a drug and, in general, are predictable and known. This group includes drug dependencies -as can occur with benzodiazepines-, tardive dyskinesia due to neuroleptic drugs or Cushing’s syndrome produced by corticosteroids.

Type D reactions are rare and appear some time after finishing treatment. Some of these types of reactions are teratogenesis, which are malformations in fetuses, and carcinogenesis.

On the other hand, there are type E reactions, which are those that occur after the very abrupt withdrawal of a drug. An example of this type of adverse reaction is adrenal insufficiency after withdrawal of corticosteroids, seizures after withdrawal of antiepileptic drugs, or angina after withdrawal of beta-blockers.

Conclution

It is very important to find out about the medicine we are going to take, since all those that are available can trigger an adverse reaction capable of evolving into a dangerous reaction. We recommend that you always ask your doctor and pharmacist for the drug’s instructions for use, as well as any contraindications you may have.