gms | German Medical Science

For patients with inner ear ailments, treatments with systemic administration or intratympanic administration are considered applicable. However, systemic route can't be used because of difficulties with blood-labyrinth barrier and systemic side effects while the intratympanic approach is not reliable sometimes on account of troubles with the variation of the round window membrane (RWM). To investigate its feasibility of delivering therapeutics to the inner ear, we compared the postauricular (p.a.) and intravenous (i.v.) pharmacokinetics in the inner ear fluid with magnetic resonance imaging (MRI) by using a T1 contrast agent Gadopentetate Dimeglumine (Gd-DTPA) as in vivo tracer. Normative data were obtained from male albino guinea pigs with weight ranging from 300 to 400 grams (N = 12), which were divided randomly into two groups and each was given a p.a. or i.v. bolus of Gd-DTPA. A Bruker Biospec Avance 70/30 experimental MRI system with a magnetic field strength of 7.0 Tesla was used to obtain the signal intensity of Gd-enhanced image of the scala tympani (ST) as a biomarker for concentration changes in the perilymph for 48 h. It was Gd-enhanced signal other than perilymph concentration that being calculated for pharmacokinetic parameters. Results revealed longer time to peak signal intensity (Tmax), elimination half-life (T1/2) and mean residence time (MRT), and higher levels of area under the signal time curve from pre-injection to the last time point (AUClast) of postauricularly treated guinea pigs than intravenously treated guinea pigs (p<0.05). The present study demonstrates the use of the novel topical administration—p.a. injection—possibly as a potential and efficient drug delivery route to cure inner ear disorders.