L05 - Adverse Reactions to Antibiotics Flashcards
Define ADR
Adverse Drug Reactions are injuries caused by taking medication
What are the six main determinants of toxicity?
Genetic Chemical Metabolic Drug Interactions Altered Microbial Flora Hypersensitivity
Define Type A Reactions
Type A = Augmented Response
Normal pharmacological response is undesirable
Dose related, predictable, managed by adjustment
Define Type B Reactions
Type B = Bizzare or Idiosyncratic
Unrelated to pharmacology
Unpredictable, rare, often severe
Related to genetics/immunology
Describe Penicillin allergies
Penicillins couple to proteins, form immunogens (Type 1 hypersensitivity)
Ranges from mild rashes to anaphylaxis
Occurs in 1-10% (risk 6x if prev. reaction or parenteral administration)
What is the time course of ADRs to Beta Lactam antibiotics?
0-60 mins = Acute
1-24 hours = Subacute
1 day to several weeks = Latent
What is the most commonly affected organ in ADRs?
Skin
Give four examples of ADRs affecting the skin
Urticaria
Erythematous Eruptiosn
Toxic Epidermal Necrolysis
Stevens-Johnson Syndrome
Define Drug Interactions
When the effects of one drug are changed by the presence of another:
drug/food/drink/environmental chemical agent
(increase toxicity OR reduce activity)
Give two examples of factors that may increase the risk of drug interactions
Polypharmacy
Renal Impairment
What are CYP450 enzymes?
Enzymes involved in metabolism of toxic compounds. Drugs may be metabolised my multiple/single CYPs
What are the two possible interaction mechanisms of CYPs
Inhibition
Induction (CYP2D6 not inducible)
Describe enzyme induction - Give an example
Increased activity of metabolising enzymes, thereby reducing the plasma concentration of drugs
May take 1/2 weeks for effect and may persist
Rifampicin is a potent inducer
Describe enzyme inhibition
Decreased activity of metabolising enzymes, thereby increasing the plasma concentration of drugs
Rapid onset (1-2 days) and reverses quickly
Ketoconoazole (antifungal agents) and Erythromycin are potent inhibitors
Define the Therapeutic Range
The window between Toxic and Therapeutic drug concentrations