Scientists create medications based on the ability of that specific chemical compound to produce a promising effect against a specific biological target. Most drugs, however, not only affect that target, but also affect other systems throughout the body. An adverse drug reaction describes the unwanted, uncomfortable or dangerous effects a medication produces within the body, as described by the Merck Manual. Because any drug can produce an adverse drug reaction, doctors analyze the risk versus benefit for each patient prior to determining appropriate treatment.
Dose Related
Dose related adverse drug reactions, often referred to as side effects of the drug; occur at the normal doses prescribed by doctors. This type of reaction is predictable, meaning that doctors know the side effects that can occur with the drug. Mild adverse drug reactions, such as stomach upset, do not require treatment and may subside as the body gets used to the drug. Doctors treat moderate adverse reactions by modifying the dose of the medication. More severe adverse drug reactions can result in hospitalization and require immediate discontinuation of the medication.
Allergic
Sometimes, a drug can illicit an immune response within the body. This type of reaction, referred to as an allergic reaction or drug hypersensitivity, occurs soon after the patient takes the medication, but usually fails to occur after the first dose. The first dose of medication provides the body with the initial exposure that triggers the body to produce antibodies against the drug. When the patient ingests the medication again, those antibodies recognize the medication triggering an immune-mediated reaction.
Allergic drug reactions account for approximately 5 percent to 10 percent of all adverse drug reactions, according to the American Academy of Family Physicians. An allergic reaction ranges from a mild reaction producing symptoms such as a rash, to a severe reaction resulting in anaphylactic shock---a life-threatening emergency. Patients experiencing allergic adverse reactions should discontinue the use of the medication and not take that medication again.
Idiosyncratic
Idiosyncratic drug reactions describe a type of drug reactions that doctors cannot predict. Idiosyncratic drug reactions can cause any type of symptom, making it difficult to determine the relationship between the drug and the reaction. Symptoms that occur soon after the patient ingests the drug make it easy to connect the drug with the symptoms. When symptoms occur later, doctors have difficulty determining the drug as the cause of the symptoms.
The American Academy of Family Physicians report that approximately 20 to 25 percent of all adverse drug reactions occur as a result of unpredictable effects. To conclusively determine the relationship between the drug and the reaction, doctors may need to rechallenge the patient by allowing the patient to take the medication again to try to illicit the same symptoms.
Toxic
Toxic adverse drug reactions, also called a drug overdose, occur when a patient ingests too much of a certain medication, either accidentally or intentionally. The symptoms of toxic adverse events vary depending upon the drug, but may cause liver and kidney damage.
