US EPA

2733535 

Journal Article 

Quantitative determination of hydrophobic compound entrapment in dipalmitoylphosphatidylcholine liposomes by differential scanning calorimetry 

Montenegro, L; Panico, AM; Bonina, F 

1996 

Yes 

International Journal of Pharmaceutics
ISSN: 0378-5173
EISSN: 1873-3476 

IPA/97/1120361 

J 

REF 17 

191-197 

English 

IPA COPYRIGHT: ASHP Multilamellar dipalmitoyllecithin (dipalmitoylphosphatidylcholine) liposomes encapsulating 1 mg and 0.36 muCi of radiolabeled testosterone, 1 mg of d-alpha-tocopheryl acetate (vitamin E acetate), or 400 mug of tretinoin (retinoic acid) were prepared, and the percentage of drug entrapment (PDE) values obtained using differential scanning calorimetry (DSC) was compared to those obtained using dialysis and centrifugation. Dialysis was performed at 3, 6, 9, and 12 h intervals. Centrifugation was carried out at 6000, 9000, and 12,000 rpm. PDE values of testosterone, tocopheryl, and tretinoin determined by DSC analysis, applying the Van't Hoff equation, were 6.3, 68.9, and 87.8, respectively. The duration of dialysis slightly influenced the quantification of tocopheryl and tretinoin, but strongly affected that of testosterone. Plateaus for tocopheryl and tretinoin and for testosterone were observed at 6 h and 9 h, respectively. No significant differences were observed between PDE values obtained at different centrifugation rates. For each compound, linear relationships were observed between PDE values obtained by dialysis at 9 and 12 h and centrifugation and the values determined by DSC. The results suggested that DSC can be used for the determination of PDE of hydrophobic compounds entrapped in dipalmitoyllecithin liposomes.