Formulation and evaluation of ciclopirox olamine loaded liposomal gel for topical delivery

Onychomycosis is a fungal infection of the nail unit caused by dermatophytes, non-dermatophyte molds and yeasts. It commonly affects toenails and is characterized by nail discoloration, thickening, subungual hyperkeratosis and onycholysis. The nail plate is a dense keratinized barrier that can restrict penetration of topically applied antifungal drugs. The supplied project document identifies poor nail penetration as an important limitation of conventional topical ciclopirox therapy and proposes a vesicular delivery system to improve local drug delivery.

Liposomes are phospholipid vesicles capable of incorporating active pharmaceutical ingredients within an aqueous compartment and/or lipid bilayer. Their composition, size, surface charge and lamellarity can be adjusted to modify drug retention and release. Soya lecithin provides the phospholipid component while cholesterol can improve membrane organization and stability. Incorporation of an optimized liposomal dispersion into a Carbopol-based gel may further improve residence time and handling at the application site.

Previous formulation work summarized in the supplied dissertation reports that lipid- and nano-sized systems can improve topical or nail delivery of ciclopirox and that optimized topical systems may provide sustained release. The present work therefore focused on preparation of ciclopirox olamine-loaded liposomes, optimization of lipid composition using a central composite design, incorporation of the optimized dispersion into gel and evaluation of its physicochemical and in-vitro performance.

2. MATERIALS AND METHODS

2.1 Materials

2.2 Preformulation and drug characterization

Organoleptic properties and melting point were assessed. UV spectrophotometric analysis was performed in phosphate buffer pH 7.4. The calibration range reported in the dissertation was 1–5 µg/mL, with analysis at approximately 310.5 nm. Drug–excipient compatibility was evaluated by FTIR spectroscopy, DSC and X-ray diffraction.

2.3 Experimental design and optimization

A central composite design was applied using Design-Expert software. Cholesterol (X1) and soya lecithin (X2) were selected as independent variables, each at low, middle and high levels. Entrapment efficiency (Y1) and in-vitro drug release (Y2) were selected as responses.

2.4 Preparation of ciclopirox olamine-loaded liposomes

Ciclopirox olamine, cholesterol and soya lecithin were combined and dissolved in approximately 10 mL chloroform in a rotary evaporator flask. The organic phase was evaporated under reduced pressure at approximately 50–55 °C to obtain a dry thin lipid film. The film was hydrated with 10 mL phosphate buffer pH 7.4 at 50–55 °C for 1 h with rotation at approximately 250 rpm. The resulting liposomal dispersion was sonicated in a bath sonicator for 2 min and stored at 2–4 °C overnight before characterization.

2.5 Evaluation of liposomes

Vesicle appearance was examined microscopically. Particle size and polydispersity were measured using a particle-size analyzer after dilution. Zeta potential was determined after dilution with distilled water. Entrapment efficiency was evaluated following ultracentrifugation at 10,000 rpm for 30 min at 4 °C and spectrophotometric analysis at approximately 310 nm. In-vitro drug release was assessed by dialysis-bag diffusion using 100 mL phosphate-buffered saline pH 7.4 with sampling over the study period. Surface morphology was examined by scanning electron microscopy.

2.6 Preparation of liposomal gel

Carbopol 934 (1% w/w) was slowly dispersed in distilled water with continuous stirring and allowed to hydrate for approximately 2–3 h. Methyl paraben (0.02% w/w) was dissolved in propylene glycol (5% w/w) and incorporated into the hydrated polymer. Triethanolamine was added dropwise to adjust the pH to approximately 5–6 and produce a clear gel. The optimized liposomal dispersion was then incorporated slowly with gentle stirring to obtain a homogeneous liposomal gel

2.7 Evaluation of liposomal gel

The optimized gel was evaluated for appearance, homogeneity, texture, viscosity, pH, spreadability, drug content and in-vitro diffusion. Antifungal screening was performed by a modified agar-well diffusion method using Candida albicans as reported in the supplied dissertation. Stability was assessed at 40 ± 2 °C/75 ± 5% RH and at 25 ± 2 °C/60 ± 5% RH for up to three months.

3. RESULTS AND DISCUSSION

3.1 Preformulation and compatibility studies

The drug was described as a white, odourless, crystalline solid. The reported melting point was 143–144 °C. The UV study identified an analytical wavelength of approximately 310–310.5 nm. FTIR spectra retained the characteristic functional-group bands of ciclopirox olamine in the presence of formulation excipients, and the dissertation interpreted these findings as indicating no significant chemical interaction. The reported DSC thermogram of ciclopirox olamine showed a sharp endothermic peak at approximately 153.1 °C. The drug–excipient mixture retained the characteristic drug peak without evidence of a well-defined interaction. XRD showed distinct diffraction peaks, consistent with a crystalline drug state.

3.2 Optimization of liposomes

The nine experimental batches showed entrapment efficiencies from 65.50% to 82.10% and 24-h drug release values from 83.20% to 93.80%. Increasing cholesterol and soya lecithin concentrations was associated with increased entrapment efficiency and a reduction in the release rate in the reported design study. Batch F6, containing 150 mg cholesterol and 300 mg soya lecithin, showed the highest experimental entrapment efficiency (82.10 ± 1.25%) and 24-h drug release of 83.20%. Numerical/graphical optimization identified the F6 composition as the selected optimized formulation.

The numerical optimization section of the supplied dissertation reports an estimated optimum of 150 mg cholesterol and 300 mg soya lecithin, with predicted entrapment efficiency of 81.73% and predicted drug release of 84.75%; the reported desirability was 0.914. The experimental F6 batch was subsequently selected as the optimized formulation.

3.3 Characterization of optimized liposomes

The optimized dispersion showed a particle size of 743.7 nm and a low reported polydispersity index of 0.152. The zeta potential of −59.1 mV was interpreted in the dissertation as indicating good physical stability. SEM demonstrated predominantly spherical vesicles with a smooth surface. The combination of high entrapment efficiency and relatively slower drug release at higher lipid concentrations supported selection of F6.

3.4 Evaluation of optimized liposomal gel

The optimized liposomal gel exhibited a white colour, uniform homogeneity and smooth texture. Its viscosity was close to that of the marketed/conventional gel, while the spreadability was slightly higher. The pH of 6.68 was reported as suitable for topical application. Drug content was 96.23%, indicating satisfactory drug incorporation into the final gel system.

3.5 In-vitro diffusion study

The liposomal gel exhibited slower drug diffusion than the marketed/conventional gel. At 8 h, cumulative drug release was 47.23 ± 1.20% from the liposomal gel compared with 66.72 ± 2.35% from the conventional gel. The slower release profile is consistent with retention of drug within the lipid vesicles and subsequent diffusion through the gel matrix.

3.6 Antifungal activity

The supplied dissertation reports that the liposomal gel produced a greater inhibition response than pure drug and marketed gel after 24 h. The activity was reported using a qualitative symbol system rather than exact inhibition-zone measurements: ++ represented moderate activity (5–8 mm) and +++ represented high activity (>9 mm). These findings support the potential of the formulation but should be confirmed using a validated antifungal assay with exact zone measurements and appropriate controls before publication.

3.7 Stability studies

Under accelerated conditions (40 ± 2 °C/75 ± 5% RH), no visible change in colour was reported over three months. Viscosity changed from 5417 ± 0.44 to 5402 ± 0.74 cps, pH from 6.68 ± 0.56 to 6.65 ± 0.85, spreadability from 12.0 ± 1.41 to 10.0 ± 1.34 g·cm/s, and 8-h drug release from 47.23 ± 2.12 to 46.65 ± 1.65%. Under long-term conditions (25 ± 2 °C/60 ± 5% RH), only small changes were reported through three months.