peptic ulcer comprises heterogeneous disorders , which manifest as a break in the lining of the gastrointestinal mucosa bathed by acid and pepsin . it is the most predominant of the gastrointestinal diseases with a worldwide prevalence of about 40% in the developed countries and 80% in the developing countries . in recent years large advance in chemical and pharmacological studies has contributed to the knowledge about new therapeutically active compounds and control drug delivery systems for peptic ulcer . out of the available category of drugs for the treatment of ulcer , h2 antagonist 's class of drugs like famotidine and ranitidine is considered to be the safest drugs available . famotidine is n-(amino sulfonyl)-3-[[[2-[(diamine methylene ) amino]-4-thiazolyl ] methyl ] thio ] propanimidamide a model bcs class - iii drug . it is a potent h2 receptor antagonist used to treat peptic ulcer and hence effectively heals gastric and duodenal ulcers and is also effective in zollinger - ellison syndrome . the bcs classification provided new quantitative data of importance for modern drug development , especially within the area of drug permeability . it gives clear and easy applied rules for determining the rate limiting factors of gi absorption process . for a bcs class - iii drug we need to increase its permeability to improve its oral bioavailability because , here , in class iii drugs they have high solubility but low permeability . the absolute bioavailability of famotidine after oral administration is about 4045%   and absorbance only in the initial part of small intestine may be due to low intestinal permeability . microemulsions as colloidal carriers are one of the promising systems that have nowadays attracted the main interest in intestinal permeability enhancement . they are optically isotropic , transparent , and thermodynamically stable homogeneous solutions of oil and water , stabilized by addition of a surfactant and usually a cosurfactant [ 3 , 4 ] . hence , an olive oil based microemulsion formulation with tween-80 as surfactant and peg-400 as cosurfactant was developed by using water titration method with an aim of enhancing the intestinal permeability as well as oral bioavailability . the surfactant and cosurfactant ( tween-80 and peg-400 ) may have contributed to an increase in the permeability of the intestinal membrane or improved the affinity between lipid particles and the intestinal membrane . famotidine usp was obtained from micro labs ( bangalore , india ) as free gift sample . hplc - grade methanol , ammonium acetate , and ethyl acetate were purchased from sigma - aldrich , india . all other chemicals used in this study were obtained commercially and were of analytical ( ar ) grade . olive oil based microemulsion formulations were developed ( phase titration method ) with tween-80 as surfactant and peg-400 as cosurfactant , keeping constant weight ratio of surfactant / cosurfactant ( 2  :  1 ) . drug loaded microemulsion system ( f-1 ) was prepared by dispersing famotidine ( 40  mg ) into the mixture of surfactant cosurfactant and oil followed by precise addition of water drop by drop to the oily phases with magnetic stirring at ambient temperature . droplet size distribution of optimized microemulsion was determined by using a delsa nano - c ( beckman coulter instruments ) based on light scattering phenomenon , which analyzes the fluctuations in light scattering . percentage transmittance of samples was measured at 650 and 400  nm with distilled water taken as blank and three replicates were performed for each sample . the ph values of the microemulsion were measured by a ph meter ( digital systronics , mumbai , india ) at ambient temperature with glass electrode . the viscosity measurement of the prepared microemulsion was performed using brookfield 's viscometer ( brookfield lvdv - ii + proviscometer ) at single mode using spindle number cpe41 at 32  0.5c . all aspects of testing were controlled using rheocalc software . to check the intraduodenal permeability , the duodenal part of the intestine was isolated and taken for the in vitro permeation study . then this tissue was thoroughly washed with phosphate - buffered saline ( ph 6.8 ) solution to remove the mucous and lumen contents . the microemulsion sample of approximately 1  ml was injected into the lumen of the duodenum using syringe , and the two sides of the intestine were tightly closed . the receiver compartment was filled with 45  ml of phosphate - buffered saline ( ph 6.8 ) with continuous aeration and a constant temperature of 37c . mixing was performed by means of a magnetic stirrer at 50  rpm , 1  ml samples were withdrawn periodically from the receiver compartment at time intervals of 30 minutes , 1  h , 2  h , 3  h , 4  h , 5  h , 6  h , and 7  h up to 8  h and diluted to 10  ml with phosphate - buffered saline ( ph 6.8 ) solution and replaced with an equal volume of fresh transport medium . the absorbance was measured using a uv - vis spectrophotometer at wavelength of 265  nm , keeping the respective blanks ( phosphate - buffered saline ) . in order to predict and correlate the in vitro intestinal permeation behavior from these famotidine - loaded microemulsions through excised goat intestine , it is necessary to fit into a suitable mathematical model . the in vitro famotidine permeation data from microemulsions containing famotidine through excised goat intestine were evaluated kinetically by various mathematical models like zero - order , first - order , higuchi , and korsmeyer - peppas model . all animal procedures were performed in accordance with protocols reviewed and approved by the committee for the purpose of control and supervision on experimental animals ( cpcsea ) . the pharmacokinetic study of the microemulsion containing famotidine was conducted in new zealand rabbits weighing 2.53.0  kg . the rabbits have been chosen as the model for study because there have been many bioavailability studies done using this animal model . a 12  h light/12  h dark cycle was held to keep a normal circadian rhythm in the animals . control batch was fed with normal saline , test batch was fed with 6  mg / kg famotidine ( pure drug ) , and the test batch was given the formulation equivalent to 6  mg / kg of drug . the blood samples ( approximately 300400  l ) were collected from the marginal ear vein of the rabbits using heparinized needle ( 2024 size ) at predetermined time intervals , specifically at 0.5 , 2 , 6 , 8 , 10 , 12 , and 24 hours after oral administration . the heparinized blood samples were immediately collected in centrifugation tubes ( 5  ml ) and centrifuged at 20000  rpm at 0c for 15 minutes . supernatant layer of plasma was separated into another centrifugation tube and stored at 20c until analysis . the 1200 series hplc system ( agilent technologies , waldbronn , germany ) was used . mass spectrometric detection was performed on an api 3200 triple - quadrupole instrument ( applied biosystems / mds sciex , toronto , canada ) . the mobile phase was composed of methanol : 20  mm ammonium acetate ( 55  :  45 , v / v ) . the flow rate of the mobile phase was set at 0.6  ml / min and the injection volume was 10  l . the retention time of famotidine was found to be approximately 1.37  min as shown in table 1 . all samples and standards were made slightly acidic by addition of 10  l of 0.1  m aqueous ammonium acetate ( ph 6 ) and were extracted into 3  ml of ethyl acetate . the extraction tubes were shaken at high speed for 5  min followed by centrifugation at 6000  rpm for 5  min . the organic phase was transferred to clean glass tubes and evaporated to dryness in a 45c water bath under a nitrogen stream . the samples were reconstituted within 200  l of mobile phase and vortexed for 30  sec . after transfer into glass inserts of autosampler vials , an aliquot of 10  l of each sample was injected onto the lc - ms / ms system . after oral administration of the microemulsion and standard drug , plasma samples were analyzed by lc - ms / ms for their famotidine content . a curve of cumulative drug absorbed vs time curved from 0 to 24 hours was plotted to calculate the area under curve ( auc ) . other pharmacokinetic parameters , that is , peak plasma level ( cmax ) and time to reach peak plasma level ( tmax ) , were obtained after analysis of the individual plasma concentration - time curves . the calculations were made by computer using win nonlin tm professional version 3.1 software ( pharsight corporation , california , usa ) . microemulsion formulation containing olive oil was prepared using tween-80 and peg 400 fixed smix ratios of 2  :  1 ( table 2 ) . the narrow globule size range of 170.1  1  nm and polydispersity index 0.415  0.029 for f-1 indicated that the microemulsion approached a monodispersed stable system and could deliver the drug effectively owing to larger surface area . the presence of zeta potential to the tune of 6.58  0.32  mv on the globules of f-1 conferred physical stability to the system . the microemulsions were expected to have good physical stability ( phase separation ) as zeta potential is less than 30 to 40  mv [ 1012 ] . the ph of the optimized famotidine microemulsion was found to be 7.1  1.46 , approximating the normal blood ph ( 7.4 ) . it was observed that the viscosity of the microemulsion formulation generally was very low ( 138.5  0.96  cp ) . this was expected , because one of the characteristics of microemulsion formulations is of lower viscosity [ 1315 ] . 
 in vitro drug permeation was examined through goat intestine over a period of 8  h in 0.1 ( n ) hcl solution at 37  0.5c for the optimized microemulsions and the corresponding pure drug . there was an increase in intestinal permeability for optimized formulation compared to pure drug due to presence of surfactants and cosurfactants combination , generally used as permeation enhancers . 
 in vitro drug permeation in intestine after 8  h for all formulations varied from 30.42% to 78.39% ( table 4 and figures 1 , 2 , and 3 ) and most of the formulations showed enhanced permeation compared to pure drug ( 48.92% ) ( table 5 and figure 4 ) . formulation f-1 ( 78.39% ) shows highest permeation and f-9 ( 30.42% ) shows lowest permeation in intestine . the maximum permeation could be due to having the lowest droplet size and lowest viscosity of all the formulations . thus the drug diffused at a faster rate from the microemulsion system . in order to predict and correlate the in vitro intestinal permeation behavior from these famotidine - loaded microemulsions through excised goat intestine , it is necessary to fit into a suitable mathematical model . the in vitro famotidine permeation data from microemulsions containing famotidine through excised goat intestine were evaluated kinetically by various mathematical models like zero - order , first - order , higuchi , and korsmeyer - peppas model . based on intestinal permeation behavior of famotidine - loaded microemulsions formulations f-1 to f-7 have been selected for kinetic evaluation . the results of the curve fitting into these above - mentioned mathematical models indicate the in vitro intestinal permeation behavior of famotidine - loaded microemulsions ( f-1 to f-7 ) shown in table 6 . when respective correlation coefficients were compared , f-1 followed the zero - order model ( r = 0.986 ) , whereas f-2 , f-3 , and f-4 formulations followed korsmeyer - peppas model ( r = 0.990 , 0.998 , and 0.989 ) , and formulation f-5 , f-6 , and f-7 followed the first - order release ( r = 0.995 , 0.994 , and 0.998 ) over a period of 8 hours . the determined values of diffusion exponent ( n ) ranged between 0.610 and 1.329 , indicating that the intestinal drug permeation from these famotidine - loaded microemulsions followed the supercase ii transport . the in vivo study was performed to quantify famotidine , after oral administration of formulation containing drug . the plasma concentration time profiles of the drug in male new zealand albino rabbits following oral administration of the microemulsion formulation ( f-1 ) and standard drug were compared . figure 5 shows mean plasma concentration - time curve of famotidine after a single oral administration of standard drug and test formulation . famotidine microemulsions ( f-1 ) demonstrated a longer tmax ( 6  h ) compared with standard drugs ( 2  h ) and sustained the release of drugs over 24  h because the drug needs to be released out from the oil phase thereby resulting in a delayed tmax . after oral administration , f-1 exhibited the higher absorption and cmax achieved from the optimized famotidine test formulation ( 456.20  ngh / ml ) represents greater improvement than the standard drug ( 126.80  ngh / ml ) . the drug content of the test formulation was significantly higher at all time periods after administration than that of the standard formulation . it was found that auc024  h obtained from the optimized famotidine test formulation ( 3023.5  ngh / ml ) was significantly higher than the standard famotidine ( 1663.3  ngh / ml ) . area under the curve ( auc ) for microemulsion showed almost a 1.8-fold increment from auc generated after administering standard famotidine indicating a significant enhancement of famotidine bioavailability when given orally as microemulsions . the significant differences of the factors leading drug absorption in vivo between the microemulsion preparations and standard drugs were probably attributed to the following . famotidine belongs to bcs class - iii drug and the oral absorption as well as the bioavailability of both drugs is mainly limited due to low intestinal permeability . the surfactant and cosurfactant ( tween-80 and peg 400 ) may have contributed to an increase in the permeability of the intestinal membrane or improved the affinity between lipid particles and the intestinal membrane . further , due to small particle size , microemulsions may adhere to the gut membrane or enter the inter - villar spaces thus extending gastrointestinal residence time in the gastrointestinal tract . moreover , microsized preparation ensures greater surface area and also the presence of tween-80 as a surfactant in the microemulsion formulation might modulate the intestinal membrane permeability through apically polarized efflux system leading to enhanced oral bioavailability . the results from these studies demonstrated that microemulsion is a viable approach for developing a liquid dosage form of famotidine with enhanced intestinal permeability as well as bioavailability . enhancing permeability correlates with improved pharmacokinetic profile . the pharmacokinetic studies reveal that the oral administration of famotidine microemulsion sustained the release of drugs over 24  h. as a consequence of this , decrease in the dose and frequency of administration for drugs is possible to achieve the desired therapeutic activity . this study proved the utilization of microemulsion as a carrier for oral delivery of famotidine .
the absolute bioavailability of famotidine after oral administration is about 4045% and absorbance only in the initial part of small intestine may be due to low intestinal permeability . 
 hence , an olive oil based microemulsion formulation with tween-80 as surfactant and peg-400 as cosurfactant was developed by using water titration method with the aim of enhancing the intestinal permeability as well as oral bioavailability . in vitro drug permeation in intestine after 8  h for all formulations varied from 30.42% to 78.39% and most of the formulations showed enhanced permeation compared to pure drug ( 48.92% ) . 
 famotidine microemulsion exhibited the higher absorption and cmax achieved from the optimized famotidine formulation ( 456.20  ngh / ml ) was higher than the standard ( 126.80  ngh / ml ) . 
 it was found that auc024  h obtained from the optimized famotidine test formulation ( 3023.5  ngh / ml ) was significantly higher than the standard famotidine ( 1663.3  ngh / ml ) . 
 f-1 demonstrated a longer ( 6  h ) tmax compared with standard drug ( 2  h ) and sustained the release of drug over 24  h. the bioavailability of f-1 formulation was about 1.8-fold higher than that of standard drug . 
 this enhanced bioavailability of famotidine loaded in microemulsion system might be due to increased intestinal permeability .