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October 20, 2009
3:00 PM - 4:30 PM
Room Room 356
Inhibition of the GABA(A) Receptor by a Macrolide but Not by a Lincosamide Antibiotic
  **   Paul S. Garcia, M.D., Ph.D., Andrew Jenkins, Ph.D.
Anesthesiology, Emory University, Atlanta, Georgia
Introduction. With the exception of flumazenil [1], research on inhibition or reversal of general anesthesia has been largely overlooked, despite the obvious clinical benefits of improved operating room efficiency or potential improvements in patient safety. We began to investigate the macrolide antibiotic clarithromycin as a potential inhibitor of anesthesia and sedation after reviewing case reports of insomnia and mania in patients receiving oral clarithromycin [2]. Gamma-aminobutyric acid (GABA), is the major inhibitory neurotransmitter in the mammalian CNS and its most common receptor (GABA(A)) is the site of action of several anesthetic agents both intravenous (e.g. propofol) and inhaled (e.g. volatile anesthetics). We examined the effect of clarithromycin on the GABA(A) receptor and compared its action as a potential inhibitor of anesthesia and sedation to a common lincosamide antibiotic, clindamycin, and to the negative modulator of GABA(A) function, flumazenil.

Methods. For this study, our laboratory electrophysiologically recorded the current passing through the most common subtype of GABA(A) receptor expressed in immortal cell lines. Alpha1, beta2, gamma2s GABA(A) receptor and AAV-GFP cDNAs were transfected into human embryonic kidney (HEK) cells grown on glass cover slips using a calcium phosphate transfection method. 36-72 hours after transfection, coverslips were transferred to a perfusion chamber to assay receptor function. Fluorescing cells were whole-cell patch clamped and exposed to different concentrations of GABA and drugs. Chemicals were delivered to the cells using two 10-channel infusion pumps and a rapid solution exchanger. Whole cell currents were recorded using a 700B amplifier, digitized using a 1322A interface and analyzed using pClamp9.2 (All Axon Instr., Foster City, CA).

Results. The macrolide antibiotic,clarithromycin, inhibited GABA(A) currents at concentrations as low as 3 µM (17.8±10.7 %). Nearly 50% inhibition occurred at concentrations of 300 µM clarithromycin (45.3±11.9%). The lincosamide antibiotic, clindamycin, demonstrated only a modest inhibition (from 0 to 17.6±13.8%) of GABA(A) current through a range of concentrations (3 – 3000 µM). The addition of 100 µM clarithromycin resulted in a fractional shift of EC50 of 51.2% with no change in maximal current for the GABA dose-response curves. The application of 4 µM flumazenil had no effect on fractional shift of EC50 but reduced the maximal GABA current to 74.9% of control conditions.

Conclusions. Clarithromycin but not clindamycin inhibits GABA(A) current at clinically relevant concentrations and may have potential for general anesthesia reversal. Clarithromycin's mechanism for GABA antagonism is unique from that of flumazenil.

1. Schwieger, I.M., F. Szlam, and C.C. Hug, Jr., Anesthesiology, 1989. 70 (3): p. 477-80.

2. Geiderman, J.M., Clin Infect Dis, 1999. 29 (2): p. 464-5.[figure1]

From Proceedings of the 2009 Annual Meeting of the American Society Anesthesiologists.
Figure 1