Development of a Self-Emulsifying Lipid Based Formulation Using Clotrimazole as Model Compound
Posted on January 16, 2017
By Martin Piest, Ad Bernaerts, Katerina Rousou & Marjolein van Baest
Patheon Softgels B.V. De Posthoornstraat 7, 5048 AS The Netherlands
Clotrimazole is an antifungal, typically dosed as vaginal tablet or oral lozenge or topical cream, but Clotrimazole can also be used as a potential antimalarial drug. When administered orally Clotrimazole exhibited poor and erratic absorption from the gastrointestinal tract . Lipid formulations are regularly applied as enabling formulation and considered the most used dosage form utilized for bioavailability improvement for approved drugs.
Figure 1. Solubility of Clotrimazole in lipid excipients and aqueous dispersion of saturated solutions.
Clotrimazole was has poor aqueous solubility of 29.84 μg/ml and high log P of 6.1 (www.DrugBank.ca). Target solubility of 20 wt.% of Clotrimazole in the final formulation was perceived as suitable for development of a Softgel product.
Table 1. Excipients selected for screening
Solubility of the Clotrimazole was determined by UHPLC in >20 excipients covering medium and long chain triglycerides, lipid surfactants, and non-lipid cosolvents, see Table 1. Excess of Clotrimazole was added to each excipient in a 2 ml Eppendorf tube. Samples were stored at 37°C for 24 hours on a shaker-incubator. Samples were centrifuged at 4000 rpm for 15 minutes and an aliquot was taken for UHPLC analysis. Next, samples were subjected to an excursion to 65°C for 24 hours, followed by overnight storage at 37°C. Samples were again centrifuged at 4000 rpm for 15 minutes and equilibrium solubility was determined by UHPLC. Supernatant solutions were evaluated by for their self-emulsifying properties upon aqueous dispersion in MilliQ water.
Formulations were prepared by mixing Clotrimazole with Capryol 90, Labrasol, and/or Phosal and/or Povidone, and heated to 80°C until dissolved. Formulations were subject to three repeated freeze-thaw cycles (>24 hr./cycle) to assess physical stability of the formulation.
Table 2. Lead formulation composition
Formulation Evaluation by Dispersion in SGF
Lead formulations were evaluated for aqueous dispersion by addition of 2 g formulation to 400 ml Simulated Gastric Fluid in dissolution apparatus with Paddle at 37°C and 100 rpm. Duplicate samples were taken after 60 minutes and assayed by UHPLC.
Figure 2. Dispersion of lead formulations in SGF
Formulation Evaluation by Lipid Digestion
Lipid digestion screening was performed according to lipid digestion studies following the procedure described by the LFCS consortium . In short 1 g lipid formulation is digested by pancreatin at pH 6.5 using a Metrohm Titrando to perform a pH-stat titration. Samples were collected after 0, 15, 30, 45, and 60 minutes, respectively. After adding the enzyme inhibitor to stop the digestion, samples are centrifuged at 14,000 rpm for 30 minutes at 37°C. Next, supernatant is collected for analysis by UHPLC and the 60 minute sample is analyzed by DLS.
Figure 3. Example of lipid digestion experiment after 15 minutes and after 45 minutes of digestion.
Capryol 90 was selected as main excipient as solubility of Clotrimazole was highest. Labrasol was selected as a lipid surfactant. Next, different co-surfactants and stabilizers were investigated. Up to 24 prototype formulations were prepared by mixing excipients with Clotrimazole, heated to 80°C until dissolved. Addition of Phosal and Povidone were found to further increase the solubility to the target value of 20% in the vehicle upon activation with a small amount of water. Five prototype formulations showed complete solubility at target 20% w/w concentration, also after three repeated freeze-thaw cycles.
Aqueous dispersion in Simulated Gastric Fluid (SGF) showed good recoveries by UHPLC analysis of ca 80-85% but lipid digestion studies showed low recovery. DLS results were poor due to sedimentation of the sample during analysis. Next two control formulations were prepared at 20 wt% and 5 wt% load of Clotrimazole, see Table 1. Lipid digestion testing was repeated and it was found that the control with only 5wt% showed complete recovery and aqueous solubility in the digestion medium was increased twentyfold from 0.057 to 1.32 mg/ml.
Table 3. Recovery by UPLC after SGF and Lipid Digestion
Figure 4. Samples taken from control formulations 1 and 2 with 5% and 20% load respectively after 60 minutes of lipid digestion and centrifugation.
We used our standard Lipid Based Formulation approach to develop a SEDDS. Reducing the Clotrimazole load in the formulation from 20 wt% (control 2) to 5 wt% (control 1) improved the self-emulsifying properties as demonstrated by the full recovery after lipid digestion.
Figure 5. Recovery of clotrimazole by UHPLC for control 1 (96% = 1.32 mg/ml) and control 2 (1% = 0.057 mg/ml)
 Borhade et al. International Journal of Pharmaceutics, (2012), 431, 149–160
 Williams et al. Journal of Pharmaceutical Sciences, (2012), 101, 3360 – 3380
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