Photosensitive drug reactions

Question 1

Photosensitizing drug reactions can either be _____ (most common) or _______

Answer 1

• phototoxic (most common)
• photoallergic

Question 2

What is the basic mechanism of phototoxic drug reaction?

Answer 2

direct interaction between UVR (UVA mostly) and drug or drug metabolites-→ free radicals→ damage to skin cells

Question 3

Presentation of phototoxic drug reaction:

Answer 3

exaggerated sunburn-like eruption in sun exposed areas +/- blistering, heals with hyperpigmentation

Question 4

Histopathology of phototoxic drug reaction:

Answer 4

• necrotic keratinocytes, dermal edema, minimal dermal inflam, and vasodilation (same as sunburn)

Question 5

What are the most common drugs causing phototoxic reactions:

Answer 5

• tetracyclines
• NSAIDS
• Fluoroquinolones
• psoralens
• voriconazole (XP-like presentation w/ increased risk of aggressive SCC, eruptive lentigines, premature aging)
• HCTZ
• St. Johns wart

Question 6

pseudoporphyria is a clinical variant of a ______

Answer 6

phototoxic drug reaction

Question 7

drugs associated with pseudoporphyria include:

Answer 7

• NSAIDS (naproxen is #1)
• thiazides
• voriconazole
• furosemide
• TCNs

Not The Fucking Verdad (NSAIDS, thiazies, TCNS, furosemide, voriconazole)

as in its not the true porphyria but pseudo

Question 8

How can you tell the difference between porphyria and pseudoporphyria?

Answer 8

• clinically pseudo will lack the hypertrichosis, sclerodermoid features, and hyperpigmentation
• psuedo will have normal porphyrin studies

Question 9

Drugs that can cause photooncycholysis:

Answer 9

Tetracyclines and psoralens

Question 10

Drugs that cause slate gray hyperpigmentation:

Answer 10

amiodarone, TCA’s, diltiazem

Question 11

most common drugs causing photo-lichenoid eruption:

Answer 11

HCTZ and NSAIDs

Question 12

Drugs that cause UV recall:

Answer 12

Methotrexate

Question 13

basic mechanism of photoallergic drug reaction:

Answer 13

cell-mediated hypersensitivity (requires sensitization)

• UVR (especially UVA) induces chemical change in drug→ becomes photoallergen

Question 14

presentation of photoallergic drug reaction

Answer 14

• eczematous to lichenoid eruption on sun-exposed areas initially, then can generalize

Question 15

Most common drugs causing photoallergic reaction:

Answer 15

• sunscreens containing oxybenzone
• fragrances (musk ambrette, sandalwood)
• *NSAIDS**
• Griseofulvin
• quinine, sulfonamides, quinolones

Question 16

How to confirm diagnosis of photoallergen?

Answer 16

photo patch testing