Electrochemical Determination of Rivastigmine Hydrogen Tartrate at β-Cyclodextrin/Multi-Walled Carbon Nanotubes Modified Electrode

Background:

Electrochemical techniques can easily be adopted to solve many problems of pharmaceutical interest. The implementation of electroanalytical methods in the assay of pharmaceutical formulations has increased greatly. Nowadays, owing to the critical importance of electron transfer and surface properties, chemically modified electrodes have been employed in electrochemical sensors. The chemically modified electrode is one of the most popular electroanalytical sensors and used in several applications.

Methods:

In this work, a β-cyclodextrine/multi-walled carbon nanotubes (β-CD/MWCNTs) composite modified glassy carbon electrode (GCE) was produced and applied to the detection of Rivastigmine hydrogen tartrate (RVT) in pharmaceutical formulations. The voltammetric feature of RVT at this β- CD/MWCNTs modified electrode was evaluated using cyclic voltammetry and square wave voltammetry.

Results:

The β-cyclodextrin and multi-walled carbon nanotubes modified glassy carbon electrode displayed good electrocatalytic activity in the oxidation of rivastigmine hydrogen tartrate with relatively high sensitivity, stability and lifetime. The calibration graph of the analyte was linear over the range 10- 1500 µM with two linear segments and the detection limit was obtained as 2.0 µM (S/N=3). The results showed that the electrochemical sensor has good sensitivity and selectivity.

Conclusion:

The β-CD/MWCNTs modified electrode displayed a high electrochemical activity and good sensitivity toward the oxidation of RVT. Compared with the bare MWCNTs coated sensor, the response of analyte increased soundly and the response potential of target analyte shifted negatively. The results indicated that the β-CD/MWCNTs film coated electrode had good catalysis to the voltammetric oxidation of RVT. The prepared sensor was applied to determine RVT in pharmaceutical samples with satisfactory yields. The outcomes indicate that β-CD/MWCNTs coated electrode is a safe choice for the detection of RVT.

Electrosteric stealth Rivastigmine loaded liposomes for brain targeting: preparation, characterization, ex vivo, bio-distribution and in vivo pharmacokinetic studies

Being one of the highly effective drugs in treatment of Alzheimer's disease, Rivastigmine brain targeting is highly demandable, therefore liposomal dispersion of Rivastigmine was prepared containing 2 mol% PEG-DSPE added to Lecithin, Didecyldimethyl ammonium bromide (DDAB), Tween 80 in 1:0.02:0.25 molar ratio. A major challenge during the preparation of liposomes is maintaining a stable formulation, therefore the aim of our study was to increase liposomal stability by addition of DDAB to give an electrostatic stability and PEG-DSPE to increase stability by steric hindrance, yielding what we called an electrosteric stealth (ESS) liposomes. A medium nano-sized liposome (478 ± 4.94 nm) with a nearly neutral zeta potential (ZP, -8 ± 0.2 mV) and an entrapment efficiency percentage of 48 ± 6.22 was prepared. Stability studies showed no major alteration after three months storage period concerning particle size, polydispersity index, ZP, entrapment efficiency and in vitro release study confirming the successful formation of a stable liposomes. No histopathological alteration was recorded for ESS liposomes of the sheep nasal mucosa. While ESS liposomes showed higher % of drug permeating through the sheep nasal mucosa (48.6%) than the drug solution (28.7%). On completing the in vivo pharmacokinetic studies of 36 rabbits showed 424.2% relative bioavailability of the mean plasma levels of the formula ESS compared to that of RHT intranasal solution and 486% relative bioavailability of the mean brain levels.

Spectrophotometric and spectrodensitometric methods for the determination of rivastigmine hydrogen tartrate in presence of its degradation product

Three sensitive, selective and precise stability-indicating methods for the determination of the anti-Alzheimer's drug, rivastigmine hydrogen tartrate (RIV) in the presence of its alkaline degradation product (major metabolite, NAP 226-90) and in pharmaceutical formulation were developed and validated. The first method is a second derivative (D(2)) spectrophotometric one, which allows the determination of RIV in the presence of its degradate at 262 nm (corresponding to zero crossing of the degradate) over a concentration range of 50-500 microg/ml with mean percentage recovery 100.18 +/- 0.628. The second method is the first derivative of the ratio spectra (DD(1)) by measuring the peak amplitude at 272 nm over the same concentration range as (D(2)) spectrophotometric method, with mean percentage recovery 99.97 +/- 0.641. The third method is a TLC-densitometric one, where RIV was separated from its degradate on silica gel plates using methanol:butanol:H(2)O:ammonia (5:4:1:0.01 v:v:v) as a developing system. This method depends on the quantitative densitometric evaluation of thin layer chromatogram of RIV at 263 nm over a concentration range of 20-160 microg/spot, with mean percentage recovery 100.19 +/- 1.344. The selectivity of the proposed methods was tested using laboratory-prepared mixtures. The proposed methods have been successfully applied to the analysis of RIV in pharmaceutical dosage forms without interference from other dosage form additives and the results were statistically compared with reference method.