An in vitro study of the susceptibility of mobile and cystic forms of Borrelia burgdorferi to hydroxychloroquine.
Level 5 - mechanism / opinion, no new human data
Bench research (in vitro laboratory study)
PubMed 12102233 · doi:10.1007/s10123-002-0055-2
What was done
The researchers evaluated the in vitro susceptibility of mobile and cystic forms (1-day-old and 1-week-old cysts) of *Borrelia burgdorferi* to hydroxychloroquine (HCQ) at 30°C and 37°C. They measured minimal bactericidal concentrations (MBC) and evaluated morphological changes using acridine orange staining, dark-field microscopy, and transmission electron microscopy.
What was found
The MBC of HCQ against mobile spirochetes was > 32 µg/ml at 37°C and > 128 µg/ml at 30°C. HCQ significantly reduced the conversion of mobile spirochetes to cystic forms. For 1-day-old biologically active cysts incubated at 37°C, the MBC was > 8 µg/ml, compared to > 32 µg/ml for 1-week-old cysts. At HCQ concentrations at or above the MBC, cyst contents were partly degraded, core structures failed to develop, and RNA content decreased significantly. At 256 µg/ml, approximately 95% of cysts ruptured and internal spirochetal structures dissolved.
Why it matters
The study shows direct in vitro activity of hydroxychloroquine against both spirochetal and cystic forms of *B. burgdorferi*, offering a mechanistic rationale for further preclinical research.
Limits
This was entirely an in vitro laboratory study without animal models or human clinical data. The bactericidal concentrations identified in culture (8 to >256 µg/ml) substantially exceed typical achievable and safe plasma concentrations in humans.
Cited by
- supports Hydroxychloroquine (Plaquenil) alkalizes the intracellular compartment, enhances antibiotic efficacy, and targets cystic forms of Borrelia burgdorferi.