Purpose:
The aim of this study was to compare, in the rabbit, the ocular bioavailability of three different ophthalmic dosage forms (eye drops, ointment and a new hydrogel formulation) containing 3 mg/ml of netilmicin.
Methods:
A volume of 50µl (eye drops) or a quantity of 50 mg (ophthalmic ointment or hydrogel ) of each formulation was instilled (single administration) into the conjunctival sac of the right eye of New Zealand albino rabbits. Sampling was performed 15,30,60 minutes and 2,4,6 and 12 hours after treatment. Cornea, conjunctiva and aqueous humour, were collected and netilmicin measured by HPLC/fluorimetric method.
Results:
The pharmacokinetic parameters obtained in conjunctiva and cornea are showed in the table. In the aqueous humour the concentration values were always below the detection limit (0.1µg/ml).*p<0.01 **p<0.001Netilmicin concentrations for the three different ophthalmic formulations were consistently above the MICs of the most common ocular pathogens responsible of external ocular diseases. AUC and Cmax showed a high presence of netilmicin in the cornea for ointment formulation, while netilmicin hydrogel revealed a better affinity for conjunctiva. These effects are attributable to the high mucoadhesive characteristic of the hydrogel containing xanthan gum and sodium hyaluronate(ARVO 2006) and to the lipidic texture of the ophthalmic ointment.
Conclusions:
The choice of the three ophthalmic formulations could be related to the main site target (cornea or conjunctiva) and to the pathology to treat without neglecting the patient’s compliance. The eyedrop could be also used in association with one of the two semisolid formulation depending on the severity of the disease. Moreover considering the re-epithelialization effect of xanthan gum and sodium hyaluronate, netilmicin hydrogel could be used in the treatment of post-surgery or post-traumatic ocular surface disease, promoting the healing process and ensuring at the same time an antibacterial prophylaxis.
Keywords: anterior segment • antibiotics/antifungals/antiparasitics • pH regulation/protons