Lyme Disease & Rocky Mountain Spotted Fever

• Rickettsial/vector-borne illnesses are a board exam favorite.

Lyme Disease

• This illness is a commonly tested vector-borne disease, second only to malaria.
• The vector for Lyme disease is the Ixodes tick.
• A bull's-eye rash, or erythema migrans, appears 7-10 days after infection.
• Flu-like symptoms are indicative of Lyme disease.
• These rashes often occur in the northeastern United States.
• In endemic areas, prophylaxis can include doxycycline treatment for 10-21 days.
• Stage one Lyme disease presents with erythema migrans and flu-like symptoms, and it is treated with doxycycline for 10-21 days.
• Amoxicillin is recommended for children, pregnant women, or those with a tetracycline allergy, as doxycycline is contraindicated.

Rocky Mountain Spotted Fever (RMSF)

• Doxycycline is the treatment of choice for RMSF.
• For special populations like children, pregnant women, or those with a tetracycline allergy, chloramphenicol is used instead of doxycycline.
• The presentation of RMSF is slightly different from Lyme disease, because it has a characteristic full-body rash.

Ehrlichiosis

• Doxycycline is the treatment of choice for Ehrlichiosis.
• For special populations like children, pregnant women, or those with a tetracycline allergy, Rifampin is used instead of doxycycline.

Babesiosis

• Mild to non-severe cases are treated with atovaquone and azithromycin.
• Severe cases are treated with quinine and clindamycin.
• Doxycycline can be added if Lyme disease or Anaplasma co-infection is suspected.

Tetracyclines: Doxycycline

• They inhibit bacterial protein synthesis by binding to the 30S subunit of the bacterial ribosome.
• They prevent aminoacyl-tRNA binding to ribosomes and are bacteriostatic.
• Treats gram-positive organisms (Streptococcus, MSSA), gram-negative organisms (H. influenza), atypical organisms (Chlamydia pneumoniae, Legionella, Mycoplasma pneumoniae).
• It's effective against community-acquired MRSA and Rickettsia.
• Contraindications include children under eight and pregnant/breastfeeding women due to the risk of permanent teeth discoloration and impaired teeth/bone growth.
• Side effects include photosensitivity and intracranial hypertension (pseudotumor cerebri).
• Absorption decreases with antacids, dairy products, and products containing iron, magnesium, aluminum, calcium, or zinc.
• It may increase the risk of bleeding with warfarin.
• Doxycycline is the drug of choice for Lyme disease and can be used for malaria prophylaxis.
• Dose adjustment is needed for all tetracyclines except doxycycline in cases of renal impairment.

Aminopenicillins: Amoxicillin and Ampicillin

• These inhibit bacterial cell wall synthesis and are bactericidal.
• Same activity as natural penicillin (Strep. viridans, Strep. pyrogenes, Strep. pneumoniae, mouth anaerobes, and Neisseria meningitidis).
• Better coverage of Streptococcus pneumoniae, H. influenzae, E. coli, Proteus mirabilis, Salmonella, and Shigella.
• Amoxicillin can be used in a 3 or 4-drug regimen for H. pylori.
• Adjust dose in renal impairment.

Chloramphenicol

• It inhibits bacterial protein synthesis by binding to the 50S ribosomal subunit at the peptidyltransferase site
• It inhibits ribosomal transpeptidation.
• Treats meningitis (H. influenza, N. meningitidis, S. pneumoniae), BLP (E. coli, Klebsiella pneumoniae, H. influenza), anaerobes (Bacteroides), and Rickettsia rickettsii.
• Contraindicated in neonates due to the increased risk of gray baby syndrome.
• Side effects include anemia (dose-dependent), aplastic anemia (dose-independent), and gray baby syndrome.
• Only used for life-threatening infections due to toxicity.
• Gray baby syndrome presents with vomiting, lethargy, respiratory depression, and death.

Rifamycins

• Specific antibiotics include rifampin, rifabutin, and rifapentine.
• They inhibit RNA polymerase by binding to the beta subunit of the DNA-dependent RNA polymerase (bactericidal).
• Used with other mechanisms to improve effectiveness; resistance occurs rapidly when used alone with active TB.
• It is used for meningococcal prophylaxis and given to household contacts of children with Haemophilus influenzae type B (HiB) to prevent severe infections.
• Variable gram-positive activity is shown, depending on the site of infection.
• A side effect is the red discoloration of bodily fluids.
• Many drug interactions, particularly with rifampin which decreases blood levels of many medications, and rifabutin has a much lower impact.
• Rifampin is a strong inducer of cytochrome P450 enzymes (CYP450), leading to reduced effectiveness of critical care drugs.

Quinine

• Side effects include cinchonism, leading to flushing, tinnitus, blurred vision, confusion, reversible high-frequency hearing loss, rash, and lichenoid photosensitivity.
• Treats malaria and babesiosis.
• Tinnitus is a characteristic symptom.

Atovaquone

• Treats babesiosis, toxoplasmosis, and PCP prophylaxis.