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A 29-year-old man comes to a community outreach clinic concerned that he may have œcaught something from one of his many girlfriends. Although he has not felt ill, he has heard that one woman he used to have sex with was treated for a sexually transmitted disease earlier in the month. He states he does not regularly wear a condom. Originally he was not going to get tested. Now, however, he has noticed a new sore on his penis and wants it treated. Aside from this complaint, he has felt well. Review of systems is unremarkable, as is past medical history. However, he does tell you that when he was younger he was treated with amoxicillin for an ear infection and had a bad reaction, where his face became swollen and his skin broke out in hives. Vital signs are: blood pressure 122/79 mm Hg, pulse 72/min, respirations 20/min, and temperature 37 C (98.6 F). Genitourinary examination shows a 1-cm ulcerated area of skin on the proximal glans penis. The lesion is firm and painless, with an indurated border. The surface of the lesion is slightly crusted, while the borders and surrounding skin are red and œmeaty-colored. Inguinal lymph nodes are palpable; the nodes are discrete, firm, rubbery, and nontender. A VDRL is drawn and comes back positive. In addition to testing this patient for additional sexually transmitted diseases, reporting the illness to public health authorities, and counseling the patient on safer sexual practices, which of the following is the most appropriate treatment?

A. Benzathine penicillin G, 2.4 million units IM x 1
B. Ceftriaxone, 1 g IM x 1
C. Desensitization, then intravenous penicillin
D. Doxycycline, 100 mg PO BID x 14 days
E. Trimethoprim-sulfamethoxazole, double strength, PO QD x 14 days

D. Doxycycline, 100 mg PO BID x 14 days
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The correct answer is D. For patients with any form of syphilis other than neurosyphilis, doxycycline can be used to treat the infection. While it is not as efficacious as penicillin, it is adequate in patients with a penicillin allergy. This patient™s lesion is classic for primary syphilis, which has an incubation period averaging 3 to 4 weeks. A VDRL is sensitive, but not as specific as an FTA-ABS. However, given a classic presentation, treatment is warranted.

Benzathine penicillin (choice A) is the traditional treatment for syphilis. However, given this patient™s severe allergy to a very similar compound, amoxicillin, it should be avoided.

Ceftriaxone (choice B) can be used for syphilis, but requires more than a one-time dose; however, this dose will treat gonorrhea. Further, there is thought to be 10% cross-reactivity with the cephalosporins for patients allergic to penicillin.

Desensitization (choice C) is risky, and should not be performed when other agents are available. For neurosyphilis, patients may require desensitization and treatment, because the ability of the macrolides to cross the blood“brain barrier is limited.

Trimethoprim-sulfamethoxazole (choice E) is not used to treat syphilis.