What is the most likely cause of a rash in a patient after returning from holiday, given the options: co-amoxiclav (Augmentin), clarithromycin (Biaxin), erythromycin, aspirin, or doxycycline?

Most Likely Drug Causing Post-Holiday Rash

Doxycycline is the most likely culprit for causing a rash after returning from holiday, primarily due to its well-documented phototoxicity when combined with sun exposure during travel.

Primary Mechanism: Phototoxicity

• Doxycycline causes photosensitivity reactions manifesting as exaggerated sunburn-like symptoms including burning, erythema, and potentially large-area photodermatitis when exposed to sunlight 1, 2
• The triggering UV spectrum consists mainly of UVA1 (340-400 nm), making tropical sun exposure particularly problematic for travelers taking doxycycline 2
• Clinical manifestations range from mild sunburn-like sensations to severe photodermatitis, and can include onycholysis 2
• The CDC specifically warns that patients taking tetracyclines like doxycycline should avoid prolonged direct sun exposure and use UVA-absorbing sunscreens 1

Context: Holiday Travel

• Doxycycline is commonly prescribed for malaria prophylaxis in travelers to tropical regions where sun exposure is typically high 3, 2
• The combination of doxycycline use and significant sun exposure during holiday travel creates the perfect scenario for phototoxic reactions 2
• Travelers to tropical countries taking doxycycline need thorough counseling to avoid severe phototoxic reactions 2

Comparison with Other Options

Co-amoxiclav (Augmentin):

• Can cause drug-associated rash, with an estimated 8 cases of rash (including 1 severe life-threatening reaction) per 10 cases prevented when used prophylactically 4
• However, this is not specifically associated with sun exposure or holiday travel 4

Clarithromycin and Erythromycin:

• No specific photosensitivity documented in the provided evidence
• These macrolides are not typically used for travel prophylaxis 4

Aspirin:

• Not associated with photosensitivity or travel-related rash in the provided evidence
• Not used for travel prophylaxis

Cephalexin (if considered):

• Specifically noted as preferred over tetracyclines for patients with photosensitivity concerns 1
• Not associated with phototoxic reactions 1

Clinical Pitfall to Avoid

• The key distinguishing feature is the temporal relationship between sun exposure during travel and rash development 2
• Travelers may not connect their antimalarial medication with the skin reaction, attributing it solely to sunburn 2
• UV-protective products must cover the UVA1 range (340-400 nm) for adequate prevention, not just standard UVB protection 2