Acyclovir (ACV) was acquired from Pharmaniaga Research Centre Sdn. Bhd. (Malaysia). Phospholipon® 90G (lecithin) was bought from Lipoid GmbJ, Mattermannallee, Switzerland. Chitosan, propylene glycol (PG), and polyethylene glycol (PEG-2000, MW: 1900–2200) were purchased from Merck Sdn. Bhd (USA). Dialysis bag-110 (molecular weight cut-off (MWCO): 12,000–14,000 Da) was purchased from HiMedia Laboratories Pvt. Ltd. (India). Rabbit intestinal sac was obtained as a gift from SARSHA Riding Centre. HPLC-grade Acetonitrile was procured from Fisher Scientific Inc. (Malaysia). Water is purified using a MilliQ® Integral Water Purification System with a conductivity of 15 MΩ. Other chemicals were of analytical reagent grade.