Background Bacterial keratitis is an infectious ocular disease accompanied by inflammation that can cause severe visual impairment. Commercial eye drops are not effective in many cases, so it is necessary to develop fortified antibiotic eye drops with high drug concentrations in hospital pharmacy departments.

Purpose To develop and characterise imipenem eye drops through release and stability studies of three possible formulations for the treatment of resistant bacterial keratitis.

Material and methods Initially, three different vehicles were used for the development of 5 mg/ml imipenem eye drops: balanced salt solution (BSS); 0.4% hyaluronic acid (HA); and 0.84% ion-sensitive hydrogel composed of gellan gum and kappa carrageenan (ISH). Later, these three formulations were characterised. First, release assays were performed using vertical Franz cells (37°C, 100 rpm orbital shaker, 12–14 kD dialysis membrane) and artificial tears as receptor medium. The drug release was determined spectrophotometrically (298 nm). For the stability study, all formulations were stored at room temperature and at 4°C–8°C for 10 days protected from light. Each day, pH, transparency and concentration were determined.

Results Release studies showed that imipenem is delivered by a Higuchi diffusion in all formulations. However, ISH was more effective than BSS and HA in drug release control.

Stability studies showed that, at day 3, formulations stored at 4°C–8°C of BSS and HA maintain ≥90% of the initial concentration (IC), while in ISH it was 85%. At the same time, room temperature-stored samples preserved 60%–80% of the IC. At day 5, only BSS and HA formulations stored at 4°C–8°C maintain ≥85% of the IC. Finally, after 10 days of study, all samples stored at 4°C–8°C maintain around 70% of the IC, while those stored at room temperature only keep around 20%–30%. On the other hand, no significant pH and transparency variation were shown at both storing conditions.

Conclusion The ISH vehicle shows the best release characteristics. However, its poor physicochemical-stability would make its use difficult in clinical practice. For this reason, the optimal vehicles for the elaboration are BSS and HA.

It is recommended to store these eye drops at 4°C–8°C protected from light. Under these conditions, a validity period of 5 days can be established.

References and/or acknowledgements No conflict of interest.