الفهرس 
Physiological factors
Scope of WorkOnly 14 pages are availabe for public view
 |  | from | 276 |  |  |
| | | from | 276 | | |
Abstract
Tropisetron is one of the 5-HT3 receptor antagonists, reported to be effective
in the prophylaxis of acute chemotherapy-induced nausea and vomiting (CINV).
Tropisetron as the hydrochloride salt (TRO) is available in the pharmaceutical
market, under the trade name Navoban® produced by Novartis Pharmaceuticals
Ltd, in the form of hard gelatin capsules containing drug dose equivalent to 5 mg
of the base as well as ampoules (2 or 5 mL) containing doses equivalent
respectively to 2 or 5 mg of the base.
Due to first-pass metabolism in the liver, the absolute bioavailability of TRO
is about 60%. However, it suffers from phenotypic variability in hepatic
metabolism due to genetic polymorphism of the cytochrome P450 enzyme, thus
generating population of either poor or extensive TRO metabolizers. Headache and
constipation with abdominal pain are the main adverse effects associated with
recurrent TRO administration.
Therefore, it could be assumed that the transdermal route would be
advantageous to deliver TRO over the oral and parenteral ones; by avoiding drug
first pass effect, reducing gastrointestinal side effects, improving drug
bioavailability as well as patient convenience and compliance.
Hence, the purpose of work in this thesis was to formulate, optimize, and in
vitro/in vivo evaluate TRO-loaded ethosomes and flexosomes (Flex), considered as
novel ultra-deformable vesicular systems for enhanced transdermal delivery.
Firstly, TRO-loaded ethosomes were prepared by the “hot” technique. The
effect of different formulation variables, phospholipid (A) and ethanol
concentrations (B), and exclusively the type of phospholipid (C) either egg
phosphatidylcholine (EPC) or soybean phosphatidylcholine (SPC) were prepared using 3×22 full factorial design and then optimized using the desirability function.
The entrapment efficiency (EE%, Y1), vesicle size (VS, Y2), polydispersity index
(PDI, Y3), and zeta potential (ZP, Y4) were the responses studied. Predictive
modelling of such responses was generated and confirmed. The ex-vivo drug
permeation across rat skin from the selected formulations was investigated
associated with the determination of various permeation parameters (Q24, Jss, Kp,
and D) as well as permeation kinetics. Particle morphology using HR-TEM, drug–
excipient interactions, and vesicle stability were also explored.
The results proved the critical contributions of all formulation variables on the
ethosomal characteristics. The suggested equation models for EE%, VS, and PDI
responses showed good predictability. Only the concentration of phospholipid,
irrespective to PC type, had a significant effect on the transdermal flux (p<0.01).
All formulations followed zero order permeation kinetics. The ethosomal vesicles
were nearly spherical in shape. Drug amorphization and compatibility with
phospholipids were confirmed by DSC and FT-IR, respectively. EPC-based
ethosomes proved good stability. The ethanolic vesicular formula (E-4), composed
of 3 and 40% of EPC and ethanol, respectively, was chosen considered as a novel
potential nanocarrier for accentuated transdermal TRO delivery.
Aiming to ameliorate the transdermal permeation of TRO through the skin,
the novel ultra-deformable vesicular system (Flex) was developed, based on the
composition of the selected ethosomal formula. Flex were prepared by the
previously applied ‘hot’ method with some modifications. A systematic
optimization process was adopted where the edge activator (EA) type, PC:EA
molar ratio, and cholesterol concentration were the variables studied. Various EA
types, such as the cationic cetyl trimethylammonium bromide (CTAB), the anionic sodium cholate (NaC) and sodium deoxycholate (SDC), and the non-ionic tween
80 (T80), D-α-Tocopherol polyethylene glycol 1000 succinate (TPGS), cremophor
RH 40 (CREM) and Span 85 were all tried at different PC:EA molar ratios (5:1,
2:1, 1:1), without and with the inclusion of various cholesterol concentrations (0.1,
0.2, 0.3%w/v). The prepared formulations were subjected to visual inspection
aiming to describe and anticipate the formed systems, further confirmed with
turbidity measurements. Moreover, the particle size (PS), PDI, and ZP were
determined. The drug EE%, ex-vivo permeation study across rat skin and
permeation kinetics were performed on the selected Flex. Besides, the permeation
enhancing mechanisms of the selected ethanolic vesicles were assessed on isolated
stratum corneum (SC) from rat skin applying the DSC technique on the dried
treated SC samples. The morphologies of the selected Flex based on TPGS and
CREM were determined using HR-TEM. Drug-excipient interaction studies were
also executed using DSC and FT-IR. Finally, the selected Flex were stored under
refrigeration (5 ±3◦C) for a period of 6 months for physical stability testing. The
effect of storage on PS, PDI, ZP, and EE% of TPGS-Flex, CREM-Flex as well as
E-4 was assessed at different time intervals.
The results revealed that all variables strongly affected the studied responses.
CTAB, T80, TPGS, and CREM-based Flex, all prepared at 2:1 PC:EA molar ratio
and 0.1 %w/v cholesterol, were the optimized Flex formulae. Both TPGS and
CREM-based Flex showed the highest EE% and the prominent enhancement of exvivo
transdermal TRO permeation through rat skin. DSC analysis of treated SC
samples showed the additive effect of EAs in ethosomes for enhanced skin
permeation via lipid solubilization and denaturation of keratin filaments
mechanisms. TEM images for the selected formulations showed multi-lamellar
lipid stacked vesicles with almost spherical shape and defined edges. DSC results
for each Flex constituents and their physical mixtures proved the dissolution and amorphization of drug crystals in the molten lipid. FTIR spectra confirmed the
chemical compatibility of TRO with the vesicular constituents. Stability studies
showed the increase in the diameter of CREM-based Flex, while the drug EE%
showed a decline in both EA-based vesicles.
Additionally and for better evaluation, in vivo assessments of the selected
ethanolic vesicles were accomplished. The tracking of the selected vesicles; E-4,
TPGS-Flex, and CREM-Flex, through the different layers of rat skin was executed
with the aid of confocal laser scanning microscope (CLSM) after being labelled
with Nile Red as a fluorescent dye. Additionally, a pharmacokinetic study was
adopted aiming to test the efficacy of the prepared formulations in transdermal
TRO delivery. The selected vesicles as well as an aqueous drug solution (TS) were
applied topically onto rat skin and compared to a control oral solution (OS). The
various pharmacokinetic parameters (Cmax, Tmax, AUC, Frel) were determined.
Furthermore, a dermato-histopathological examination was performed on rat skin
treated with the selected formulations (E-4, TPGS-Flex, and CREM-Flex) as well
as an aqueous drug solution as a control, and the prepared histology slide images
were then captured using an optical microscope.
Confocal laser scanning micrographs showed that the fluorescent dye was
observed deeper and higher in intensity in case of both Flex formulae rather than
the ethosomal one. The pharmacokinetics study confirmed the superiority of the
ethanolic vesicles, particularly Flex, in enhancing transdermal TRO delivery and
hence improving its BAV compared with the oral and topical aqueous solutions.
The dermato-histopathologic examinations of the rat skin showed SC detachment
in case of all applied vesicles with no alterations in the underlying dermis.