An adverse drug reaction (ADR) is defined as any injury caused by taking medication. ADRs may occur following a single dose or prolonged administration of a drug or result from the combination of two or more drugs. It can be considered a form of toxicity; however, toxicity is most commonly applied to effects of over-ingestion (accidental or intentional) or to elevated blood levels or enhanced drug effects that occur during appropriate use (e.g., when drug metabolism is temporarily inhibited by a disorder or another drug).
Adverse drug reaction (ADR) is a global drug therapy problem. It has been rated as one of the top leading causes of morbidity and mortality. In developing countries, not much is known about ADRs especially with the existing weak post marketing surveillance for monitoring drug use, and its effect on the population.
In the US, 3 to 7% of all hospitalizations are due to adverse drug reactions. ADRs occur during 10 to 20% of hospitalizations; about 10 to 20% of these ADRs are severe. These statistics do not include the number of ADRs that occur in ambulatory and nursing home patients.
What are the types of adverse drug reaction?
There are 3 broad classes of adverse drug reaction namely:
Dose-related adverse drug reactions. This represent an exaggeration of the drug’s therapeutic effects. For example, a person taking a drug to reduce high blood pressure may feel dizzy or light-headed if the drug reduces blood pressure too much. A person with diabetes may develop weakness, sweating, nausea, and palpitations if insulin or another antidiabetic drug reduces the blood sugar level too much. This type of adverse drug reaction is usually predictable but sometimes unavoidable. It may occur if a drug dose is too high (overdose reaction), if the person is unusually sensitive to the drug, or if another drug slows the metabolism of the first drug and thus increases its level in the blood (see Drug Interactions). Dose-related reactions may or may not be serious, but they are relatively common.
Allergic drug reactions. This are not dose-related but require prior exposure to a drug. Allergic reactions develop when the body’s immune system develops an inappropriate reaction to a drug (sometimes referred to as sensitization). After a person is sensitized, later exposures to the drug produce one of several different types of allergic reaction. Sometimes doctors do skin tests to help predict allergic drug reactions.
Idiosyncratic adverse drug reactions. This result from mechanisms that are not currently understood. This type of adverse drug reaction is largely unpredictable. Examples of such adverse drug reactions include rashes, jaundice, anemia, a decrease in the white blood cell count, kidney damage, and nerve injury that may impair vision or hearing. These reactions tend to be more serious but typically occur in a very small number of people. Affected people may have genetic differences in the way their body metabolizes or responds to drugs.
Some adverse drug reactions are not related to the drug’s therapeutic effect but are usually predictable, because the mechanisms involved are largely understood. For example, stomach irritation and bleeding often occur in people who regularly use aspirin or other nonsteroidal anti-inflammatory drugs (NSAIDs). The reason is that these drugs reduce the production of prostaglandins, which help protect the digestive tract from stomach acid.
What are the symptoms of ADR?
Adverse drug reactions are usually classified as mild, moderate, severe, or lethal. Severe or lethal ADRs may be specifically mentioned in black box warnings in the physician prescribing information provided by the manufacturer.
Symptoms and signs may manifest soon after the first dose or only after chronic use. They may obviously result from drug use or be too subtle to identify as drug-related. In older adults, subtle ADRs can cause functional deterioration, changes in mental status, failure to thrive, loss of appetite, confusion, and depression.
Allergic ADRs typically occur soon after a drug is taken but generally do not occur after the first dose; typically, they occur when the drug is given after an initial exposure. Symptoms include itching, rash, fixed-drug eruption, upper or lower airway edema with difficulty breathing, and hypotension. Idiosyncratic ADRs can produce almost any symptom or sign and usually cannot be predicted.
In general, some symptoms that may occur as an adverse reaction following the administration of a drug or medication can include:
- Skin rashes
- Gastrointestinal bleeding.
- Nausea and diarrhea.
- Lightheadedness or dizziness.
- Diarrhea or constipation.