Toxicology of antimicrobial drugs P2

What are the learning outcomes for this lecture? (4 points)

1. Understand how common antimicrobials cause photoallergy

2. Understand the difference between phototoxicity and photoallergy

3. Appreciate the biochemical mechanisms behind photoallergy

4. Outline patient risk factors for photoallerg

What is photoallergy and how does it manifest? (3 points)

1. Photoallergy occurs through dermal exposure to drugs and UV light

2. Manifests as reddening, swelling, and blistering of the skin

3. Represents approximately 8% of adverse dermatological drug reactions

What is the mechanism behind photoallergy? (4 points)

1. Involves an immune response once the patient is sensitised

2. Sensitisation is permanent

3. Chemical must be activated by UV light to become reactive

4. Only occurs with skin exposure to UV light (e.g., sun or sunbeds)

What is haptenation and how does it relate to photoallergy? (2 points)

1. Haptenation is the binding of a small molecule to a protein forming an antigen

2. UV-activated chemicals can become haptens, triggering an immune response

How do fluoroquinolones cause photoallergy? (4 points)

1. Driven by bond cleavage at the C8 position

2. C-H and C-halogen bonds are easily broken by UV light

3. Produces reactive intermediates that haptenate skin proteins

4. Fluoroquinolones with halogen or hydrogen in C8 are commonly linked to photoallergy

Which fluoroquinolones are safer regarding photoallergy? (2 points)

. Those without halogen or hydrogen at the C8 position

2. Preferred for patients with sun exposure risk (e.g., summer travel)

What is the summary of photoallergy mechanisms and risks? (5 points)

1. Photoallergy is driven by UV-induced chemical activation

2. Reactive molecules can bind proteins and trigger an immune response

3. Only a subset of exposed individuals will react

4. Risk is highest in patients with previous dermatitis from chemicals

5. Other drug classes can also cause photoallergy