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PharmPK PK/PD Discussion Group:
Azithromycin is an antibiotic which might be useful in providing
oral treatment of Chronic Lyme Disease, which can include a CNS
infection with Borrelia burgdorferi (Bb). Bb is noted as being
sensitive to azithromycin at concentrations above 0.015 mg/L
(MIC90) to 0.04 mg/L (MBC). Additionally, azithromycin is
concentrated in tissues (up to > 1000-fold).
While published studies of brain tissue in cats, rats and rabbits
support entrance into the CNS and concentration in brain tissue,
similar studies in humans are not available (and would probably be
difficult to plan!). The package insert for azithromycin states that
after 5 days therapy "only very low concentrations are noted in
cerebrospinal fluid (less than 0.01 mg/L) in the presence of non-
If azithromycin crosses the blood-brain barrier, its concentration
in CSF may remain low while the drug is concentrated in brain tissue.
This would be consistent with both animal studies and the
azithromycin package insert and would suggest that prolonged
treatment with azithromycin might successfully treat chronic Lyme
Does anyone in our group know of any information dealing with the
distribution of azithromycin into the human central nervous system? I
am hoping that appropriate data is available for pharmacokinetic
modeling and to suggest rational doses and duration of treatment.
Peter J. Rice, Ph.D., R.Ph.
Associate Professor of Pharmacology
East Tennessee State University
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