Self Micro-Emulsifying Drug Delivery System for Lymphatic Uptake of Darunavir

Research Article

J Drug Discov Develop and Deliv. 2016; 3(2): 1024.

Self Micro-Emulsifying Drug Delivery System for Lymphatic Uptake of Darunavir

Bhalekar MR*, Pokale R, Bandivadekar M, Madgulkar A and Nagore P

Department of Pharmaceutics, AISSMS College of Pharmacy, India

*Corresponding author: Bhalekar MR, Department of Pharmaceutics, AISSMS College of Pharmacy, Pune, Maharashtra, India

Received: July 18, 2016; Accepted: August 24, 2016; Published: September 09, 2016


The aim of the present study was to target Darunavir (DRV); an antiretroviral Protease Inhibitors (PI) drug to lymphatic system using Self Micro Emulsifying Drug Delivery System (SMEDDS) to increase its solubility and bioavailability. SMEDDS system compromising of Imwitor 988 as oil phase, Tween 20 and Span 20 as binary surfactant system were optimized with respect to drug solubilization, particle size, zeta potential, dispersibility, optical clarity, cloud point, in-vitro release and thermodynamic stability. The selected formulation was subjected to ex-vivo lymphatic uptake studies using everted sac method in presence and absence of lymphatic uptake blocker Pluronic-F68. In-vivo pharmacokinetic studies were performed and lymphatic transport of DRV SMEDDS was studied. SMEDDS system containing Imwitor 988 (20%) and Surfactant mix (Smix) (80%) showed maximum drug solubility with least particle size. The ex-vivo lymphatic uptake studies of DRV loaded SMEDDS in presence of lymphatic uptake blocker showed 36.69% drug permeation which increased to 64.24% in absences of lymphatic blocker, indicating the drug transport by lymphatic path. Cmax of DRV loaded SMEDDS was higher as compared to marketed tablet. Also, Pluronic F68 treated rats show lesser plasma concentration as compared to those administered with SMEDDS. The results suggest that SMEDDS is a promising drug delivery system to improve solubility and lymphatic transport of anti-HIV drug DRV.

Keywords: Structured lipid; Imwitor 988; Ternary phase; Everted sac method; Pluronic F68; Lymphatic uptake


PI: Protease Inhibitor; HIV: Human Immunodeficiency Virus; AIDS: Acquired Immune Deficiency Syndrome; Pgp: Polyglycoprotein


SMEDDS is an isotropic, thermodynamically stable mixture of oil, surfactant/co-surfactant and drug which in contact with aqueous fluids spontaneously forms oil-in-water (o/w) microemulsion. SMEDDS have attracted growing interest as promising means for the delivery of poorly water-soluble drugs. SMEDDS have gained this popularity largely due to their excellent efficiency in improving the drug solubility, increasing bioavailability and simplicity of preparation. The nano-sized droplets have very high surface to volume ratios which are able to efficiently solubilize the drug. The drug is released in a more reproducible manner which will become less dependent on the GI physiology and the fed/fasted state of the patient [1].

DRV, a non-peptide protease inhibitor, has been shown to be extremely potent against wild type HIV and active against large panel of protease inhibitor-resistant clinical isolates. It has shown a high genetic barrier to the development of antiretroviral resistance [2]. DRV suffers from poor oral absolute bioavailability (37%), the reasons can be assumed as 1) poor aqueous solubility (0.15mg/ mL) 2) substrate to Pgp which causes efflux of the absorbed drug back into the intestinal lumen and 3) substrate to cyp3A mediated metabolism resulting into inactive metabolite [3]. Its bioavailability can be increased to 82% by combining with ritonavir, which is a potent cyp3A inhibitor. In current therapeutic treatment, the DRV/ Ritonavir combination is taken as 800mg/100mg q.d. regimen in antiretroviral- naïve patients, and as a 600mg/100mg b.i.d. or 400mg/100mg q.d. regimen in antiretroviral-experienced individuals infected with HIV [4].

Any formulation strategy which can increase solubility and inhibit the other two reasons mentioned earlier and most importantly target lymphatic system have a chance to increase the bioavailability of DRV. The lymphatic system can be a target for treatment of other diseases such as AIDS and cancer. HIV, which causes AIDS, colonizes lymphoid organs such as the spleen, thymus and lymph nodes. In the early stage of infection and throughout the latent stage, the virus replicates vigorously in lymphoid organs, meaning that lymphatic drug delivery can be advantageous in the treatment of AIDS [5]. Drug absorbed into lymphatic system empty into systemic circulation thereby surpassing cyp3A metabolism. SMEDDS have been proved to increase solubility of poor soluble drugs and its ability to target lymphatic system has been well reported in past years. Myers et al. [6] reported 3% lymphatic uptake of the absorbed dose Penclomedine when formulated as an emulsion using soybean oil. Hauss et al. [7] reported 9% increased in bioavailability of Ontazolast when administered as a 20% soybean oil-in-water emulsion when compared to suspension formulation which had bioavailability less than 1%.

Gao et al. [8] investigated the impact of different amount of oil or surfactant included in self-micro emulsifying drug delivery systems on the intestinal lymphatic transport of Sirolimus. They reported absorption from oil-free formulation was mostly via the portal blood, in contrast to the SMEDDS formulations containing =25% MCT in which the lymphatic transport of sirolimus was a major contributor to oral bioavailability.

Most studies investigating lymphatic uptake using lipid, emphasizes on use of lipids having long chain fatty acids as compared to medium or short chain fatty acids. Also triglycerides are more favored as compared to mono or di-glycerides. Kiyasu et al. [9] reported that short- and medium-chain fatty acids (with a carbon chain length shorter than 12 carbon atoms) are transported to the systemic circulation by the portal blood and are not incorporated to a great extent in chylomicrons. Long-chain fatty acids and monoglycerides are re-esterified to triglycerides within the intestinal cell, incorporated into chylomicrons and secreted from the intestinal cell by exocytosis into the lymph vessels. They demonstrated cholesterol uptake by lymphatic system when cholesterol was dissolved in triglycerides with different fatty acid chain length. They reported that uptake increased as chain length of the fatty acid increased from C2 to C18. Holm et al. [10] reported lymphatic transport of halofantrine (43.3%) when dosed in SMEDDS formulated with structured triglyceride having mixture of fatty acid chain length (C8, C18) on same glycerol backbone.

Though the above findings are impressive, there are major concerns while formulating self-emulsifying/ self-micro emulsifying/ self-nano-emulsifying drug delivery using long chain fatty acids or triglycerides with long chain fatty acids as oil phase is their less solubilization capacity for drug. Secondly, they are difficult to selfemulsify and form less stable emulsion/microemulsion/nanoemulsion as compared to oils having small or medium chain fatty acids. Thus the aim of this study was to use structured lipid (Imwitor 988, having mixture of mono and diglyceride with fatty acids having chain length C8; Caprylic acid and C10; Capric acid) as oil phase to formulating self-micro emulsifying drug delivery system and evaluate its potential for lymphatic targeting of anti-retroviral drug DRV.

Materials and Methods


DRV was received as a kind gift from Lupin Research Park, Pune, India. Imwitor 988 was supplied as a gift sample from Cremer, Germany. Tween 20 & Span 20 was purchased from Lobachemie, Mumbai, India. Neusilin US2 was gifted by Fuji Chemicals, Mumbai, India and all other chemicals were procured from the local sources.

Saturation solubility studies

Saturation solubility of DRV in various oils, surfactants, co surfactants was determined by shake flask method. In this study, DRV was added in 25mg increments to 2gm of each vehicle and the mixture was mixed using cyclo mixer. The samples were equilibrated for 24 hours. Further they were centrifuged at 2,000rpm for 20 min. to separate the supernatant. Aliquots of supernatant were taken and were suitably diluted with chloroform and drug content was quantified by measuring absorbance at 263.5nm using UV spectrophotometer (Lab India 3000).

Construction of pseudoternary phase diagram

Microemulsion area was estimated by constructing pseudoternary phase diagram for specific Surfactant mix (Smix) at various ratios to oils by water titration method. Briefly surfactants were mixed in specific ratio like 1:1, 2:1, 3:1. Each of the Smix was added to oil in following ratios by weight: 1:9, 2:8, 3:7, 4:6, 5:5, 6:4, 7:3, 8:2 and 9:1. These mixtures were then mixed using cyclomixer for 5 min and placed at 40°C for 1 hr so that an isotropic mixture was obtained. Milli-Q Water was added to each of the mixture under continuous stirring. After each increment of water, the mixtures were observed for their appearance (turbid or clear). Turbidity of the samples would indicate formation of a coarse emulsion, whereas a clear isotropic solution would indicate the formation of a micro emulsion [11]. The phase boundary was determined by observing the changes in the sample appearance from turbid to transparent to turbid. Percentage of oil, Smix and water at which clear mixture was formed were selected and the values were used to prepare phase diagram. The data were processed by CHEMIX 3.51™ software (Arne Standnes, Norway) to construct a pseudoternary phase diagram.

Preparation of liquid DRV loaded self micro-emulsifying drug delivery system

From the solubility study data and microemulsion area depicted by construction of ternary phase diagrams, oil to surfactant ratio and their concentration ranges were selected for further formulations of DRV loaded SMEDDS (Table 1). The Surfactant system (Smix) was prepared separately by mixing the selected surfactants in their chosen ratios from the microemulsion region of the phase diagram. Oil phase containing DRV (200mg) was added into the surfactant system with continuous stirring till the homogenous mixture was formed. The resulting microemulsion preconcentrate were stored for a day and inspected for any possible physical instability characterized by phase separation and drug precipitation.