Adverse Drug Effects

ADVERSE DRUG EFFECTS

Adverse effect is ‘any undesirable or unintended consequence of drug administration’. It is a broad term, includes all kinds of noxious effect—trivial, serious or even fatal.

For the purposes of detecting and quantifying only those adverse effects of a drug which are of some import and occur in ordinary therapeutic setting, the term adverse drug reaction (ADR) has been defined as ‘any noxious change which is suspected to be due to a drug, occurs at doses normally used in man, requires treatment or decrease in dose or indicates caution in the future use of the same drug’. This definition excludes trivial or expected side effects and poisonings or overdose.

Another term ‘adverse drug event’ (ADE) has been used to mean ‘any untoward medical occurrence that may present during treatment with a medicine, but which does not necessarily have a causal relationship with the treatment’. The idea is to record all adverse events first, and look for causality only while analyzing pooled data.

All drugs are capable of producing adverse effects and whenever a drug is given a risk is taken. The magnitude of risk has to be considered along with the magnitude of expected therapeutic benefit in deciding whether to use or not to use a particular drug in a given patient, e.g. even risk of bone marrow depression may be justified in treating cancer while mild drowsiness caused by an antihistaminic in treating common cold may be unacceptable.

Adverse effects may develop promptly or only after prolonged medication or even after stoppage of the drug. Adverse effects are not rare; an incidence of 10–25% has been documented in different clinical settings. They are more common with multiple drug therapy and in the elderly. Adverse effects have been classified in many ways. One may divide them into: Predictable (Type A or Augmented) reactions (mechanism based adverse reactions) These are based on the pharmacological properties of the drug, which means that they are augmented, but qualitatively normal response to the drug; include side effects, toxic effects and consequences of drug withdrawal. They are more common, dose related and mostly preventable and reversible.

Unpredictable (Type B or Bizarre) reactions

These are based on peculiarities of the patient and not on drug’s known actions; include allergy and idiosyncrasy. They are less common, often nondose related, generally more serious and require withdrawal of the drug. Some of these reactions can be predicted and prevented if their genetic basis is known and suitable test to characterize the individual’s phenotype is performed.

Severity of adverse drug reactions has been graded as:

Minor: No therapy, antidote or prolongation of hospitalization is required.

Moderate: Requires change in drug therapy, specific treatment or prolongs hospital stay by atleast one day.

Severe: Potentially life-threatening, causes permanent damage or requires intensive medical treatment.

Lethal: Directly or indirectly contributes to death of the patient.