Pharmacology 2060A/B Lecture Notes - Lecture 10: Histamine Receptor, Allergy, Drug Allergy
15 May 2018
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Module 10 – Adverse Drug Reactions
10.1 – Adverse Drug Reactions
- Adverse drug reactions (ADRs) are the unintended and undesired responses from drugs
- Adverse drug reactions are an enormous societal health problem
- Canadian research suggests that 7.5% of hospital admissions in Canada are attributed to adverse
drug reactions. This represents 185,000 people per year!
- Adverse drug reactions can include:
o 1. Side effects
o 2. Drug toxicity
o 3. Allergic Reaction
o 4. Idiosyncratic Reaction
o 5. Carcinogenic Effects
o 6. Mutagenic Effects
o 7. Teratogenic Effects
1) Side effects
- Side effects are secondary to the main therapeutic effect of the drug and are expected
- Side effects occur at normal therapeutic doses and are often unavoidable
- Side effects are often due to poor specificity or poor selectivity of the drug and what it binds to
- Example:
o Antihistamines act by blocking H1 histamine receptors to prevent the symptoms of
allergy (i.e. runny nose, watery eyes)
▪ Histamine bound = vasodilation = allergy symptoms
▪ Anti-histamine bound = vasoconstriction = no symptoms
o Side effects include drowsiness, dry mouth and urinary retention
▪ This is because the drug is acting at a different location in the body
o Histamine binding to the histamine receptor in sinuses causes vasodilation which results
in runny nose and watery eyes
o Antihistamines act by blocking the effect of histamine = no allergy symptoms
o Side effects occur when antihistamines bind histamine receptors in the brain = produces
side effect of drowsiness (sedation)
o When the anti histamines bind to other receptors in the brain, it produces dry mouth
and urinary retention
- Side effects are caused by poor specificity and poor selectivity of the drug
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2) Drug toxicity
- Drug toxicity can be considered as any severe adverse drug event
- Drug toxicity is often mediated by overdose where patients unintentionally or intentionally take
too much medication (over dose situations)
- These types of reactions are often extensions of the therapeutic effect (too much therapeutic
effect)
- For example, a patient who takes too much insulin will experience hypoglycemia (low blood
glucose – can be in a coma)
o Normal response: as insulin rises in the blood, blood glucose decreases
3) Allergic reaction
- Allergic reactions are mediated by the immune system
- Allergy requires a prior sensitization where a patient is exposed to the allergen (i.e. drug) and
does’t hae a allergi reatio
- Upon subsequent exposure to the drug an allergic reaction will occur
- During allergic reactions, mast cells (immune cell) release chemical mediators such as histamine
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- Sensitization does not cause an allergic reaction but does cause the sensitization which
produces antibodies on the surface of the cell
o The next time the patient is exposed to the drug, there is an allergic reaction mediated
by the release of histamine from mast cells
o Release of histamine causes symptoms of allergies
- Release of histamine from mast cells causes the symptoms of allergy (rash, itching, anaphylaxis)
- Allergic reactions can vary from itching and rash, to life threatening anaphylaxis (bronchospasm,
edema and severe hypotension)
- The intensity of allergic reactions are independent of dosage size
o Increasing the dose does not increase the response
o Therefore even small doses can produce severe allergy
- ~ 10% of all ADRs are related to drug allergy
- Very few drugs cause allergic reactions but the drugs that do cause it are:
o The most common drug class to cause drug allergy are the penicillins
o Sulfonamides (an antibiotic)
o Nonsteroidal anti-inflammatory drugs (NSAID) are also known to cause drug allergy
- Sites where allergic reaction is most likely to show its effects:
o Trunk area of body is the site where most allergic reactions occur
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Adverse drug reactions (adrs) are the unintended and undesired responses from drugs. Adverse drug reactions are an enormous societal health problem. Canadian research suggests that 7. 5% of hospital admissions in canada are attributed to adverse drug reactions. Adverse drug reactions can include: 1. Side effects are secondary to the main therapeutic effect of the drug and are expected. Side effects occur at normal therapeutic doses and are often unavoidable. Side effects are often due to poor specificity or poor selectivity of the drug and what it binds to. Side effects are caused by poor specificity and poor selectivity of the drug: drug toxicity. Drug toxicity can be considered as any severe adverse drug event. Drug toxicity is often mediated by overdose where patients unintentionally or intentionally take too much medication (over dose situations) These types of reactions are often extensions of the therapeutic effect (too much therapeutic effect)
