Preparation of Calibration Curve and Estimation of Drug Concentration
The in vivo
pharmacokinetic and tissue distribution studies were performed in male Wistar rats and the plasma and tissue concentrations of indinavir at different time points following IV administration of indinavir solution, SLE control, SLE-A3 and SLE-G3 were determined by using HPLC method. The amount of indinavir in serum and other tissue homogenates viz
., brain, heart, liver, kidney, and spleen at different time intervals were calculated by using the individual calibration curves y
0.995), and y
0.990) respectively. The concentration vs
. time profiles of different formulations in serum, brain, kidney, liver, heart and spleen are plotted as shown in Figs. , , , , , and . There was no significant difference in the serum levels of indinavir from SLE-A3 and SLE-G3 (Fig. ) and the control formulations at all time points. The brain levels (Fig. ) of indinavir from SLE-A3 and SLE-G3 were significantly higher than control formulations at all time points. This resulted in higher availability of indinavir from SLE-A3 and SLE-G3.
In this study, the indinavir drug solution and SLE were used as controls to study the effect of incorporating the LAAs in SLEs. The mean cmax
, AUC(0–6 h)
, and TA of indinavir from various SLEs following administration in rats (n
3) were calculated for different tissues (Table ). The cmax
values of SLE, SLE-A3, and SLE-G3 were higher than that of the drug solution in all the tissues. The cmax
values of SLE-A3 and SLE-G3 in comparison to control SLE was significant in brain and spleen but insignificant in other tissues. However, there were some changes observed in case of tmax
values for all control and test formulations. The difference in AUC is significant (P
0.05) for SLE, SLE-A3, and SLE-G3 formulations for all tissues in comparison to drug solution, however, insignificant in heart and spleen in case of SLE-G3 formulation. The difference in AUC(0–6 h)
value is significant in brain and kidney tissues for SLE-A3 and SLE-G3 in comparison to control SLE. Here, the design of submicron lipid emulsion of indinavir clearly improved the brain-specific delivery, when compared with drug solution.
The TA is a parameter to assess drug-targeting potential of drug carrier system (26
). It shows the extent of localization of a drug in the tissue. The SLE-A3 and SLE-G3 systems were found to have greater therapeutic availability than drug solution and SLE (control formulations) indicating the localization of indinavir in brain tissue. Furthermore, using of LAAs of glutamic acid and aspartic acid as specific ligands significantly improved by 2–3-fold, respectively, in the brain localization of indinavir when compared with control SLE. In kidney, the indinavir levels due to SLE-A3 and SLE-G3 were significantly higher than control formulation at all time points after 1 h. However, in between 0 and 1 h the levels were fluctuating. The TA values of SLE, SLE-A3, and SLE-G3 were significant (P
0.05) in comparison to drug solution. In heart, there is no significant difference in the indinavir levels in case of SLE—A3 and SLE—G3 in comparison to drug solution and SLE. In general, in case of liver and spleen the indinavir levels from SLE were higher than that of drug solution, SLE-A3 and SLE-G3 at almost all the time points, where as the serum drug levels were low in case of drug solution in comparison to SLE-A3 and SLE-G3.Tissue to serum drug concentration ratio (T/S) is commonly employed as an index of targeting (27
). If the ratio is more than one, it indicates the drug targeting to that tissue. The ratios of brain to serum concentrations of indinavir at different time points following IV administration of indinavir solution, SLE, SLE-A3, and SLE-G3 in rats are shown in Fig. . From this histogram, it was found that for SLE-A3 formulations, tissue to serum drug concentration ratio (T/S) for brain tissue was consistently greater than one after 1 h interval indicating the preferential localization of indinavir in brain for SLEs prepared with LAAs. However, for SLE-G3 the ratio was slightly less than one at 1st-, 4th-, and 6th-hour intervals. These results indicate that the system L present in brain can be utilized for improving the brain-specific delivery of drug and confirms the previous findings of others (15
Based on the above results, it is concluded that the indinavir levels due to emulsions containing lipoamino acids are significantly higher than control formulations at all time points in brain and also in case of kidney. However, the extent of difference in indinavir levels in brain tissue is 2.5–3.3-fold, but in case of kidney, it is around 1.2–1.5-fold. The slightly higher levels in kidney are possibly achieved due to the presence of LAT system (5
) apart from in brain tissue.In conclusion, using a commercially viable manufacturing process stable submicron emulsions of indinavir containing lipoamino acids as specific ligands were prepared, characterized and the in vitro
and in vivo
behavior was studied in Wistar rats. The tissue distribution studies clearly indicated that the lipoamino acid containing SLE-A3 and SLE-G3 emulsions improved the brain-specific delivery of indinavir in comparison to drug solution and control SLE.