Adverse Drug Reactions: Types, Mechanisms, and Management

Adverse Drug Reactions (ADRs)

Types of Adverse Drug Reactions

Adverse drug reactions (ADRs) are unintended, harmful events attributed to the use of medicines. They can occur as a cause of and during significant proportions of unscheduled hospital admissions, during hospitalization, and after discharge. ADRs can be classified into two main types:

1. Type A (Pharmacological): These reactions represent an augmentation of the pharmacological actions of a drug. They are dose-dependent and are therefore readily reversible on reducing the dose or withdrawing the drug. Examples include hypotension from an antihypertensive drug or nausea from a chemotherapeutic agent.

2. Type B (Idiosyncratic): These reactions are not related to the known pharmacology of the drug, do not show any simple dose-response relation, and resolve only when treatment is discontinued. Examples include Stevens-Johnson syndrome from an antibiotic or agranulocytosis from an anticonvulsant.

Mechanisms of Adverse Drug Reactions

The mechanisms of ADRs can be complex and multifaceted. Some reactions are predictable based on a drug's known pharmacology, while others are not. Factors affecting the occurrence of ADRs include the patient's age, sex, genetic makeup, concurrent diseases, and concomitant medications.

Prevention of Adverse Drug Reactions

Preventing ADRs depends on avoiding treatment in cohorts of patients who are at increased susceptibility or providing monitoring and blood test results. A careful medication history can assist a prescriber in understanding the patient's previous experiences with drugs, particularly in identifying previous ADRs that may preclude re-exposure to the drug. Prudent prescribing is also key to reducing errors that can contribute to ADRs.

Management of Adverse Drug Reactions

Management of ADRs involves identifying and managing the underlying drug-related problem, which may include changing the dose, switching to an alternative medication, or withdrawing the drug altogether. Spontaneous reporting, such as the Yellow Card Scheme in the UK, is an important part of overall ADR surveillance and management.

Common Medications Causing Adverse Reactions

Many medications can cause ADRs, and the risk varies depending on the drug and the individual patient. Some common examples include:

• Antibiotics: Certain antibiotics, such as penicillins and cephalosporins, can cause hypersensitivity reactions, including anaphylaxis and serum sickness.
• Nonsteroidal anti-inflammatory drugs (NSAIDs): NSAIDs are associated with gastrointestinal bleeding, renal toxicity, and other adverse reactions.
• Cardiovascular medications: Antihypertensives, antiarrhythmics, and anticoagulants can cause hypotension, arrhythmias, and bleeding, respectively.
• Chemotherapeutic agents: These drugs can cause a wide range of adverse reactions, including nausea, alopecia, and bone marrow suppression.

In conclusion, understanding and managing adverse drug reactions is crucial for optimizing the safety and efficacy of drug therapy. By recognizing the various types of ADRs, their mechanisms, and effective prevention strategies, healthcare professionals can minimize the risk of ADRs and improve patient outcomes.