Doxycycline is first line therapy for Rocky Mountain Spotted Fever(RMSF) regardless of age.
RMSF presents initially with fever, myalgias, and can have many other symptoms such as gastrointestinal symptoms, photophobia and focal neurologic signs. It should be considered in those with flu like symptoms in endemic areas seasonally.
Two to five days after fever begins a pink/red macular rash may develop on the wrists and ankles and spreads proximally as well as to the palms and soles. The lesions can become petechial as the condition progresses. Treatment should started as soon as possible to prevent fatal outcomes and often should be started prior to the rash’s appearance.
Doxycycline is first line at any age.
References:
Centers for Disease Control. "Tickborne Diseases of the United States: A Reference Manual for Health Care Providers." 4th edition, 2017. https://www.cdc.gov/lyme/resources/tickbornediseases.pdf.