Adverse effects
Classify and describe adverse drug effects.
An adverse effect is:
- A noxious or unintended effect associated with administration of a drug at the normal dose
- i.e., not an overdose
- Occur:
- Mainly in young and middle-aged individuals
- Twice as common in women
- May be exacerbated by asthma and pregnancy.
- Distinct from an adverse event, which is an untoward occurrence during treatment that does not necessarily have a causal relationship to drug administration
Adverse effects can be classified by mechanism as follows:
Type A Adverse Reactions
These are related to the pharmacological action of the drug. They are:
- Common
- Related to dose (dose-response relationship)
- Temporally associated with drug administration
- Reproducible
- Pharmacologically predictable based on understanding of the drug in question
- e.g hypokalaemia secondary to diuretic use
They typically result in:
- Organ-selective injury
- More pronounced with long-term use and in risk groups:
- Extremes of age
- Pregnancy
- Renal failure
- High morbidity but low mortality
Treatment is to decrease dose.
Type B Adverse Reactions
These are patient-specific or idiosyncratic reactions. They are:
- Rare
Potentially genetic, but poorly understood. - Independent of dose
- Occur with low doses
- Do not have a dose-response relationship
- Not pharmacologically predictable
Important causes include:- Acetylator status
- CYP450 variants
- Receptor abnormalities
- Enzyme alterations/deficiencies
- e.g. Suxamethonium apnoea
- Not necessarily reproducible
They typically result in:
- Immuno-allergic reactions
- Pseudo-allergy
- Idiosyncratic reaction
- Low morbidity but high mortality
- e.g. Stevens-Johnson Syndrome or anaphylaxis following penicillin administration
Treatment is to cease the medication.
Type C Adverse Reactions
These are 'statistical effects' associated with monitoring. They are:
- Typically an increased frequency of background disease that is detected due to increased screening
- Atypical for a drug reaction and not pharmacological predictable
- No identifiable temporal relationship
- Not reproducible
References
- RHB Meyboom, M Lindquist, ACG Egberts. An ABC of Drug-Related Problems. Drug Safety 2000;22:415-23.
- Pirmohamed M, Breckenridge AM, Kitteringham NR, Park BK. Adverse drug reactions. BMJ. 1998 Apr 25;316(7140):1295-8. Open Access Review.
- Lazarou J, Pomeranz BH, Corey PN. Incidence of adverse drug reactions in hospitalized patients—a meta-analysis of prospective studies. JAMA 1998;279: 1200-5.