Sathyan G et al (1995) studied the effect of solvents such as water, propylene glycol and ethanol and their mixtures for transdermal drug delivery on in vitro permeation of tacrine through rat and human skin. Largest flux and permeability were observed from ethanol-propylene glycol and water-ethanol binary mixtures, respectively. Excellent correlation between the rat and human skin data was observed. The formulations were found to be devoid of skin irritancy property. Ethanol-propylene glycol (1:1) mixture with a flux of 98 µg/cm2 through rat skin was found to be a promising solvent system for the transdermal delivery of Tacrine.
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Yanq Q et al (2001) formulated microparticles of tacrine using poly (D,L-lactide-co-glycolide) (PLG) by solvent evaporation technique. Effect of formulation variables on Encapsulation efficiency and release was studied. Results showed an increase in encapsulation efficiency by 10 times and decrease in rate of release when molecular weight of polymer was changed from 8,000to 59,000 and 155,000 The study indicated that tacrine microparticles have a strong potential for long term treatment of Alzheimer’s disease.
Kankkunen T et al (2002) investigated the iontophoretic delivery of Tacrine on 10 healthy adult volunteers by comparing a commercial LOGEL electrode with an ion exchange fibre formulation. Clinically significant plasma concentrations 21.3+5.9 ng/ml was achieved by commercial system whereas 14.9+2.6 ng/ml was achieved through ion exchange fibre system. The study showed that iontophoretic delivery of Tacrine is safe .Serum alanine transferase levels <50 U/l indicated that transdermal delivery resulted in reduction in hepatotoxic effect. Iontophoresis combination with ion-exchange fibers gave better controlled release and fairly constant drug levels than commercially available system.
Jogani VV et al (2008) prepared and characterized mucoadhesive microemulsion of tacrine by the titration method for brain targeting for the treatment of Alzheimer’s disease. Selective nose to brain transport was confirmed by lower Tmax values (60 min) with intranasal administration than 120 min with intravenous administration. The brain bioavailability of tacrine after giving optimized formulation was 2 times more than obtained with intranasal tacrine solution Scintigraphy study in rabbits showed more uptake of Tacrine in brain after intranasal administration. The results indicated better, quicker transport of tacrine in scopolamine-induced amnesic mice brain and rapid regain of memory loss after intranasal administration. Hence, results suggested that intranasal tacrine delivery hold promising in treating Alzheimer’s disease.
Wilson B et al (2010) prepared Tacrine-loaded chitosan nanoparticles by spontaneous emulsification method. The particles were characterized for size, zeta potential, drug-loading capacity and in vitro release. Mean particle size for drug-to-polymer ratio 1:1 was found to be 41 ± 7 nm with average zeta potential of +34.7 ± 1.5 mV. The release of tacrine from nanoparticles ranged from 83.04% ± 1.41% to 94.64% ± 0.84% for 12 hours depending on the drug-to-polymer ratio. In vitro release studies showed an initial burst of 30 minutes followed by continuous and slow release of the drug. The release of drug from nanoparticles was diffusion-controlled, following Fickian mechanism. Controlled release characteristics suggested prolonged residence time which could improve the bioavailability of tacrine in the brain.
Luppi B et al (2011) prepared albumin nanoparticles of Tacrine hydrochloride with beta cyclodextrin, hydroxypropyl beta cyclodextrin and sulphobutylether beta cyclodextrin using coacervation method and thermal cross-linking. Prepared nanoparticles were then soaked in solutions of tacrine hydrochloride and lyophilized for effective drug loading. Evaluation results showed that nanoparticles had a spherical shape with negative charge and mean size < 300 nm with polydispersity of 0.33 nm. Further the study indicated that use of beta cyclodextrins in the polymeric network could be related to drug loading and affected mucoadhesiveness and permeation behavior of drug. The study showed that delivery of Tacrine hydrochloride by nasal route has strong potential in future for the treating Alzheimer’s patients.
.Dixit S et al (2013) formulated mouth dissolving tablets of Tacrine hydrochloride by direct compression using different superdisintegrants. Results indicated that mouth dissolving tablets showed acceptable hardness, friability, mechanical strength and weight uniformity. The optimized formulation disintegrated in less than 1 minute in mouth and released >98% of Tacrine within 14 minutes. The study reflected the potential of mouth dissolving tablet of Tacrine for quick absorption, improvement in bioavailability, increased patient compliance especially in patients with difficulty in swallowing.
Corace G et al (2014) developed liposomes delivery of tacrine hydrochloride by nasal route using cholesterol, phosphatidylcholine, a-tocopherol and/or Omega3 fatty acids by reverse phase evaporation technique followed by membrane filter extrusion. Results reflected that prepare d liposome formulations had a mean diameter varying from 175nm to 219nm with polydispersity index <0.22 and excellent encapsulation efficiency. Liposomes exhibited good mucoadhesive properties and increased tacrine permeability across phospholipid vesicle-based barrier as well as sheep nasal mucosa. Furthermore, a-tocopherol was found to enhance the neuroprotective activity and antioxidant properties of the formulation.
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Haughey DB et al(1994) developed a reversed-phase high-performance liquid chromatographic method(RPHPLC) with fluorescence detection for the analysis of Tacrine and 1-hydroxy-, 2-hydroxy-, and 4-hydroxytacrine (metabolites of Tacrine) in human plasma. The alkalinized samples of human plasma were extracted with a mixture of 90:10%v/v of chloroform and l-propanol. Calibration curves were constructed for clinically significant concentrations(5 to 30 ng/ml) for all the analytes. The method was found to be precise and accurate. The developed method was sensitive enough for the determination of tacrine and its metabolites after Cognex (40 mg single dose) was administered orally to normal volunteers.
Hansen LL et al (1998) developed and validated a method for simultaneous estimation of tacrine and its metabolites, 1-hydroxytacrine , 2-hydroxytacrine and 4-hydroxytacrine in human plasma and urine .The method involved one-step liquid–liquid extraction with ethyl acetate. Determination was done by isocratic, reversed-phase high-performance liquid chromatography using fluorescence detection (excitation: 330 nm and emission: 365 nm).The developed method demonstrated simplicity , precision, accuracy and sensitivity with limit of detection as 0.5 nM for 2-hydroxytacrine and 4-hydroxytacrine, 2 nM for 1-hydroxytacrine and tacrine in plasma. Mean recovery ranged from 84 to 105% for tacrine and its metabolites in plasma.
Aparico I et al (1998) developed a spectrofluorimetric method to estimate tacrine in human serum and pharmaceuticals. The fluorimetric method allowed the determination of Tacrine in the range of 1–70 ng /ml in aqueous solutions of acetic acid–sodium acetate buffer (pH 5.6) with (excitation wavelength of 242 nm and emission wavelength of 362 nm.
Chollet DF et al (2000) developed a high-performance liquid chromatography (HPLC) assay method for therapeutic monitoring of Tacrine. The method was based on simple protein precipitation by acetonitrile or cold methanol followed by isocratic separation on a CN column eluted in reversed-phase mode. Developed method was found to be precise, robust, accurate and suitable which was demonstrated by analyzing more than 1,000 plasma samples from patients with Alzheimer disease .
Ortuño JA et al (2007) developed a flow-injection pulse amperometric method for estimation of Tacrine on the basis of ion transfer through a plasticized poly(vinyl chloride) (PVC) membrane using a four-electrode potentiostat with ohmic drop compensation. Lnear relationship between peak height and concentration of tacrine was found up to 4×10-5M .Limit of detection was found to be 1×10-7M. The method was found to be linear, reproducible, specific and repeatable.
Qian S et al (2012) developed an assay for simultaneous determination of Tacrine and its metabolites in rat plasma and brain tissue. The analytes along with internal standard were extracted from plasma of rat or tissue homogenate of brain by liquid-liquid extraction with the help of ethyl acetate. The separation was done on Thermo Hypersil BDS C18 column using mobile phase of acetonitrile and ammonium formate-triethylamine (pH 4.0) with fluorescence detection. Percentage recovery varied from 82.1% to 93.2% in h rat plasmas and brain tissue. The developed method was found to be simple, sensitive and reproducible procedure for the estimation of Tacrine and its metabolites in rats after oral administration.
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