Medication Summary
The best outcomes in Rocky Mountain spotted fever (RMSF) are achieved when treatment is started within 5 days of symptom onset. Doxycycline is the antibiotic of choice.
Chloramphenicol was previously recommended for the treatment of children younger than 9 years. In national surveillance data, however, patients treated with chloramphenicol were more likely to die than those treated with a tetracycline. Chloramphenicol poses a risk of permanent aplastic anemia and should be avoided if at all possible.
Antibiotic Agents
Class Summary
Tetracyclines are the drugs of choice. Although tetracyclines should not be routinely prescribed to children younger than 8 years, the benefits far exceed the risks in RMSF. Doxycycline is the agent of choice because the risk of dental staining is less with this agent than with other tetracyclines.
Doxycycline (Adoxa, Doxy 100, Vibramycin, Monodox)
Doxycycline is the drug of choice for RMSF. It is a broad-spectrum, synthetically derived bacteriostatic antibiotic in the tetracycline class. When given orally, it is almost completely absorbed.
It concentrates in bile and is excreted in urine and feces as a biologically active metabolite in high concentrations. This agent is the only tetracycline that does not need dosing adjustment in renal failure.
Doxycycline inhibits protein synthesis and, therefore, bacterial growth by binding to 30S and possibly 50S ribosomal subunits of susceptible bacteria. It may block dissociation of peptidyl transfer RNA (tRNA) from ribosomes, arresting RNA-dependent protein synthesis.
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Geographic distribution of Rocky Mountain spotted fever incidence in 2010, cases per million: Courtesy of the US Centers for Disease Control and Prevention.
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Annual incidence (per million persons) for Spotted Fever Rickettsiosis (SFR) in the United States, 2017. Courtesy of the CDC.
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Under a magnification of 98X, this scanning electron microscopic (SEM) image depicts the dorsal view of the head region from an American dog tick, Dermacentor variabilis, magnified 98X. D. variabilis is a known carrier of Rocky Mountain Spotted Fever (RMSF) caused by the bacterium, Rickettsia rickettsii. Courtesy of the Public Health Image Library (PHIL), CDC, photo credit Janice Haney Carr.
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Rocky Mountain Spotted Fever (RMSF) rash in a child. It appears day 3-5 of illness, begins in ankles and wrists, and typically involves palms and soles. In early stages it is macular and later it is petechial. Courtesy of the Morbidity and Mortality Weekly Report (MMWR), CDC.
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Tick identification. (i) American dog tick (Dermacentor variabilis), ii) Rocky Mountain wood tick (Dermacentor andersoni), and, iii) brown dog tick (Rhipicephalus sanguineus) iv) Lone star tick (Amblyomma americanum). Courtesy of the CDC.