Round window gentamicin & the human labyrinthine sampling model (HLSM)

Becvarovski Z, Bojrab DI, Michaelides EM, Kartush JM, Zappia JJ, LaRouere MJ.

Michigan Ear Institute, Farmington Hills; Providence Hospital, Southfield; Wayne State University, Department of Otolaryngology, Detroit, Michigan, USA.


OBJECTIVE/HYPOTHESIS Using a novel human labyrinthine sampling model (HLSM), in vivo gentamicin absorption through the round window can be measured.

STUDY DESIGN A prospective study.

METHODS Gentamicin was delivered either transtympanically (preoperative) or through a facial recess approach (intraoperative). The lateral semicircular canal and vestibule were opened, and by means of a microsyringe, labyrinthine fluid was aspirated. A sample of serum was also drawn. In all patients cerebrospinal fluid was also drawn. The samples were analyzed using a standard chemistry analyzer.

RESULTS Intratympanic gentamicin diffused through the round window membrane and achieved concentrations in the labyrinthine fluid ranging from 0 to 16 mg/L. Intratympanic gentamicin was absorbed into the systemic circulation in 4 of 11 patients with serum levels ranging from 0.3 to 0.4 mg/L. No gentamicin was detected in the cerebrospinal fluid.

CONCLUSIONS Intratympanic gentamicin diffuses rapidly through the round window membrane and achieves significant levels in the inner ear. Thus, this new model can be used to assess round window permeability to clinically relevant medications such as steroids and ototopical antibiotics.

Laryngoscope 2002 Sep;112(9):1610-3