A 46-year-old farmer presents to the office for a follow-up visit. He was seen 4 days ago for a new lesion on his arm that had been present for 1 week prior to that visit. A photograph of the lesion is shown in Figure A. At that time, he was prescribed treatment for the lesion and instructed to follow up as necessary. Today, he reports that he became sunburned this morning within an hour of beginning his workday, despite wearing appropriate sunscreen. He has a medical history significant for type 2 diabetes mellitus that is controlled with metformin. He has no known medical allergies. He smokes 1 pack of cigarettes per day and denies alcohol or illicit drug use. His temperature is 98.6°F (37.0°C), blood pressure is 125/70 mmHg, pulse is 65/min, and respirations are 12/min. On exam, there is a blistering erythematous rash on the arms and shoulders. The previous skin lesion appears unchanged. Which of the following is the most likely explanation for the patient's new rash?
Allergic reaction to prescribed therapy
Progression of disease and alternative therapy is indicated
Progression of disease and surgical debridement is necessary
Adverse effect of doxycycline
Adverse effect of doxycycline
This farmer has a cutaneous black eschar most consistent with cutaneous anthrax for which doxycycline is an appropriate treatment. A new blistering, erythematous rash after spending an hour outside that appears 4 days after starting treatment is consistent with a photosensitivity reaction, a known adverse effect of doxycycline.

Cutaneous anthrax is the most common form of infection caused by Bacillus anthracis. The infection is contracted during contact with infected livestock. The first-line treatment is doxycycline, ciprofloxacin, levofloxacin, or moxifloxacin. Progression to systemic anthrax would result in pulmonary (flu-like symptoms and hemoptysis) or gastrointestinal (nausea, vomiting, and dysentery) symptoms and would require treatment with clindamycin plus ciprofloxacin. Patients with meningitis due to anthrax require antibiotic therapy with ciprofloxacin plus meropenem plus linezolid. Additionally, antitoxins such as raxibacumab and adjunctive therapies such as glucocorticoids should be considered. In addition to photosensitivity, adverse effects of doxycycline include gastrointestinal upset (most common), teeth discoloration, and inhibition of bone growth in children. Doxycycline is teratogenic and should not be prescribed during pregnancy.

Migone et al. discuss the use of raxibacumab, a monoclonal antibody against a component of the anthrax toxin, in treating inhalational anthrax. The authors found that in monkeys, raxibacumab significantly increased survival after exposure to anthrax. The authors recommend the use of antitoxins such as raxibacumab in any patient suspected of having systemic anthrax.

Figure/Illustration A demonstrates the characteristic black eschar (blue circle) of cutaneous anthrax.

Incorrect Answers:
Answer A: Adverse effects of ciprofloxacin do not include photosensitivity, though it is an appropriate antibiotic choice for cutaneous anthrax treatment. Adverse effects of ciprofloxacin include gastrointestinal upset, risk of tendon rupture, and QT prolongation.

Answer C: Allergic reactions to prescribed therapy would be characterized by urticaria and wheals. In severe cases, anaphylaxis may be present.

Answer D: Progression of disease and alternative therapy is indicated does not fit this case. The patient's symptoms (blistering, erythematous rash) are not concerning for the progression of cutaneous anthrax to systemic disease, which would result in pulmonary or gastrointestinal symptoms. Alternative therapy for systemic anthrax is not indicated in this case.

Answer E: Progression of disease and surgical debridement is not indicated. The patient's symptoms (blistering, erythematous rash) are not concerning for the progression of cutaneous anthrax to systemic disease, which would result in pulmonary or gastrointestinal symptoms. Additionally, surgical debridement is not indicated for cutaneous anthrax.

Bullet Summary:
Cutaneous anthrax presents with a black eschar and is treated with antitoxin and either doxycycline or ciprofloxacin, the former of which can cause a photosensitivity reaction.