Do amiodarone or Macrobid (nitrofurantoin) cause a sun-related rash?

Amiodarone and Nitrofurantoin (Macrobid) Sun-Related Rash Risk

Yes, amiodarone causes sun-related rashes in >50% of patients, while there is no evidence that nitrofurantoin (Macrobid) causes photosensitivity reactions. 1, 2

Amiodarone-Induced Photosensitivity

Mechanism and Presentation

• Amiodarone is a well-documented photosensitizer that causes photosensitivity reactions in more than 50% of treated patients 1
• The typical presentation includes:
  • Burning and tingling sensation in sun-exposed skin
  • Associated erythema (redness)
  • Develops shortly after sun exposure 3
  • Primarily activated by long-wave UV-A spectrum (350-380 nm) 3

Severity and Timeline

• Photosensitivity typically develops after approximately 4 months of continuous treatment 4
• Requires a minimum cumulative dose of approximately 40g 4
• Can persist for months to years after discontinuation of the medication 5
  • In rare cases, photosensitivity can persist for over 17 years after discontinuation 5

Long-term Effects

• With prolonged use and sun exposure, amiodarone induces a distinctive blue-grey pigmentation on sun-exposed sites in 1-2% of patients 1
• This hyperpigmentation typically develops after:
  • An average of 20 months of continuous treatment
  • A minimum total dose of 160g 4
• Hyperpigmentation is generally reversible after drug discontinuation, though resolution may take many months 4

Prevention and Management

Sun Protection Measures

• Patients taking amiodarone should be advised to:
  • Seek shade when outside, particularly around midday 1
  • Wear protective clothing covering as much of the body as possible
  • Use broad-brimmed hats and sunglasses
  • Apply broad-spectrum sunscreens with SPF 30 or higher 1, 2
  • Consider sunscreens containing dioxybenzone, which has been shown to reduce phototest reactions 3

Monitoring and Follow-up

• Regular skin examinations should be included in routine follow-up 2
• Patients should be counseled about photosensitivity risk before starting amiodarone
• If severe photosensitivity occurs, consider:
  • Dose reduction if clinically feasible
  • Alternative anti-arrhythmic agents if the patient's cardiac condition allows

Clinical Pearls and Pitfalls

• Photosensitivity appears to be a phototoxic reaction rather than photoallergic, as it occurs in nearly all patients receiving sufficient doses 3
• The risk is unrelated to skin type, though hyperpigmentation is more common in patients with skin type I 4
• Photosensitivity can occur even with brief sun exposure and may be exacerbated by factors such as altitude, reflective surfaces (water, snow, sand), and time of day 1
• Unlike many photosensitizing drugs that primarily react to UVB, amiodarone photosensitivity is primarily triggered by UVA wavelengths 3

In summary, amiodarone carries a significant risk of photosensitivity reactions, while nitrofurantoin (Macrobid) is not associated with sun-related rashes based on the available evidence.