1411 ISSN 0326-2383 KEY WORDS: Acyclovir, Aloe vera, Chausath prahar pippa, Natural permeation enhancer. * Author to whom correspondence should be addressed. E-mail: rjdias75@rediffmail.com Latin American Journal of Pharmacy (formerly Acta Farmacéutica Bonaerense) Lat. Am. J. Pharm. 29 (8): 1411-8 (2010) Original Article Received: January 22, 2010 Revised version: April 13, 2010 Accepted: April 16, 2010 In Vitro Absorption Studies of Acyclovir Using Natural Permeation Enhancers Remeth J. DIAS*, Kailas K. MALI, Vishwajeet S. GHORPADE, Sandeep B. GARJE, & Vijay D. HAVALDAR Department of Pharmaceutics, Satara College of Pharmacy, India Plot no. 1539, New Additional M.I.D.C., Behind Spicer India Ltd. Degaon, Satara-415004, India SUMMARY. Gastroretentive Delivery Systems are employed to improve the bioavailability of drugs which are absorbed through upper part of GIT, by increasing their retention time. Incorporation of permeability enhancers in the formulations of such drugs can further increase their bioavailability; however their use in the formulations is questionable due to the toxicity exhibited by them. Acyclovir is a class III drug hav- ing low oral bioavailability due to improper absorption. Mucoadhesive tablets of acyclovir containing nat- ural permeation enhancers were prepared by direct compression and evaluated for mucoadhesion strength, in-vitro dissolution parameters and in-vitro absorption studies. The formulations containing Aloe vera extract showed increase in the mucoadhesion strength and retarded the drug release. The in-vitro ab- sorption studies revealed that the formulations containing Aloe vera extract (Enhancement Ratio 1.94) and chausath prahar pippal (Enhancement Ratio 1.87) showed significant increase in the permeation of the drug. The studies led to the conclusion that by formulating mucoadhesive tablets of acyclovir containing natural permeation enhancers increased the permeability, thus proving to be the cheaper and easily avail- able alternative to the other permeation enhancers. INTRODUCTION Acyclovir, 9-(2-hydroxyethoxylmethyl) gua- nine, is used in the treatment of disease caused by herpes simplex virus (HSV) and varicella zoster virus. According to the Biopharmaceutical Classification System, acyclovir is categorized as class-III drug i.e. having high solubility and less permeability 1 . Acyclovir has narrow absorption window in gastrointestinal tract (GIT) due to er- ratic absorption. Therefore, the average bioavail- ability of acyclovir is about 10 % to 20 %. Re- peated administration of high dose of acyclovir is required for effective treatment. Normal dosage regimen of acyclovir in case of genital HSV infection is 200 mg 5 times/day and herpes zoster infection is 800 mg 5 times per day 2 . Prolonging the gastric retention of a delivery system is sometimes desirable for achieving therapeutic benefit of drugs that are absorbed from the proximal part of the GIT or that are less soluble in or are degraded by the alkaline pH in the lower part of GIT. Gastroretentive de- livery systems (GRDSs) are thus beneficial for such drugs by improving their bioavailability, therapeutic efficacy and by possible reduction of dose 3 . The permeability of drug candidates across the gastrointestinal mucosa is one of the most critical factors in defining drug bioavailability and biological activity 4 . The permeation en- hancers such as sodium lauryl sulphate, sodium deoxycholate, dimethyl sulfoxide (DMSO) are mostly used to enhance the penetration of the drugs having low permeability 5 . The increase in the permeability of acyclovir from the mucoad- hesive tablet containing sodium lauryl sulphate has been reported 6 . However, due to certain toxic effects, such as irritation of the mucous