Transdermal iontophoretic delivery of tacrine hydrochloride: Correlation between in vitro permeation and in vivo performance in rats.

The aim of present investigation is to evaluate the feasibility of transdermal iontophoretic delivery of tacrine hydrochloride in Sprague Dawley (SD) rats using anodal iontophoretic patches and to correlate plasma tacrine concentration profiles to in vitro tacrine permeation flux. In vitro skin permeation studies were carried out across artificial membrane CELGRAD® 2400, freshly excised SD rat abdominal skin, freshly excised hairless rat abdominal skin, and frozen pig skin to examine the role of permeation membranes. Furthermore, plasma profiles with an application of 0.1-0.3mA current strength and tacrine concentration loading of 5-20mg/ml were obtained in SD rats. The tacrine plasma profiles were fitted to one-compartmental model using WinNonlin and in vivo transdermal absorption rates were then correlated to in vitro permeation profiles using various approaches. Tacrine permeation across membranes revealed current dependent interspecies differences at lower current strength application which diminished at higher current strength application, whereas, no significant difference in tacrine permeation was observed across fresh and frozen SD rat skin under 0.2mA current application. In vivo studies confirmed current and concentration dependent tacrine plasma profiles with possible tacrine depot formation under the skin in-line with earlier in vitro results. Correlation of in vivo transdermal absorption rates to in vitro permeation profiles revealed higher in vitro permeation fluxes compare to in vivo transdermal absorption rates at varied combination of current strength and concentrations. Present in vivo studies support the earlier published in vitro findings and tacrine plasma profiles show a potential to reach therapeutic effective concentration of tacrine hydrochloride to provide a platform for pre-programmed tacrine delivery.

An HPLC-MS method for the quantification of new acetylcholinesterase inhibitor PC 48 (7-MEOTA-donepezil like compound) in rat plasma: Application to a pharmacokinetic study.

A simple, rapid and sensitive method based on liquid chromatography-tandem mass spectrometry (LC-MS/MS) has been developed and validated for the quantitative determination in rat plasma of a new candidate for AD treatment, namely PC 48 (a 7-MEOTA-donepezil like compound) in rat plasma. Sample preparation involved pH adjustment with sodium hydroxide followed by solvent extraction with ethyl acetate:dichloromethane (80:20, v/v). The chromatographic separation was achieved on an Ascentis Express RP-Amide column (75 mm × 2.1mm, 2.7 µm) with a gradient mobile phase consisting of 0.05 M aqueous formic acid and acetonitrile. Detection was carried out using positive-ion electrospray tandem mass spectrometry on an LTQ XL system using the MS/MS CID (collision-induced dissociation) mode. The method was linear in the range 0.1-1000 ng/ml (r(2)=0.999) with a lower limit of quantitation of 0.1 ng/mL. Extraction recovery was in the range 63.5-72.1% for PC 48 and 70.5% for reserpine (internal standard, IS). Intra- and inter-day precisions measured as relative standard deviation were below 10.8% and accuracy was from -7.2% to 7.4%. The method was successfully applied to a pharmacokinetic study involving intramuscular application of 3.86 mg/kg PC 48 to rats for the first time. Pharmacokinetic parameters for PC 48 include Cmax 39.09 ± 4.45 ng/mL,Tmax 5.00 ± 3.08 min, AUC0-t 23374 ± 4045 min ng/mL and t1/2 1065 ± 246 min.

Highly Sensitive LC-MS-MS Method for the Determination of Tacrine in Rat Plasma: Application to Pharmacokinetic Studies in Rats.

A rapid and highly sensitive assay method has been developed and validated for the estimation of tacrine in rat plasma using liquid chromatography coupled to tandem mass spectrometry with electrospray ionization in the positive-ion mode. The assay procedure involves a simple liquid-liquid extraction of tacrine and phenacetin (internal standard, IS) from rat plasma using ethyl acetate. Chromatographic separation was achieved with 0.2% formic acid : acetonitrile (30 : 70, v/v) at a flow rate of 0.50 mL/min on an Atlantis dC18 column with a total run time of 3.0 min. The MS-MS ion transitions monitored were 199.10 → 171.20 for tacrine and 180.10 → 110.10 for IS. Method validation was performed as per United States Food and Drug Administration (US FDA) guidelines and the results met the acceptance criteria. The lower limit of quantification achieved was 0.008 ng/mL and linearity was observed from 0.008 to 53.4 ng/mL. The intra- and inter-day precision was in the range of 2.76-12.5 and 5.15-12.8%, respectively. This novel method has been applied to a pharmacokinetic study in rats.

Determination of tacrine-6-ferulic acid in rat plasma by LC-MS/MS and its application to pharmacokinetics study.

Tacrine, as a drug for treating Alzheimer's disease (AD), has low efficacy owing to its single function and serious side effects. However, tacrine-6-ferulic acid (T6FA), the dimer which added ferulic acid to tacrine, has been found to be a promising multifunctional drug candidate for AD and much more potent and selective on acetylcholinesterase (AChE) than tacrine. The aim of the present work was to develop and validate an LC-MS/MS method with electrospray ionization for the quantification of T6FA in rat plasma using tacrine-3-ferulic acid (T3FA) as internal standard and to examine its application for pharmacokinetic study in rats. Following a single liquid-liquid extraction with ethyl acetate, chromatographic separation was achieved at 25 °C on a BDS Hypersil C18 column with a mobile phase composed of 1% formic acid and methonal (30:70, v/v) at a flow rate of 0.2 mL/min. Quantification was achieved by monitoring the selected ions at m/z 474.2 → 298.1 for T6FA and m/z 432.2 → 199.0 for T3FA. The method was validated to be rapid, specific, accurate and precise over the concentration range of 0.5-1000.0 ng/mL in rat samples. Furthermore, it was successfully applied for the pharmacokinetic measurement of T6FA with an oral administration at 40 mg/kg to rats.

Development, characterization and application of in situ gel systems for intranasal delivery of tacrine.

The present study aimed to develop an in situ gel formulation for intranasal delivery of tacrine (THA), an anti-Alzheimer's drug. Thermosensitive polymer Pluronic F-127 was used to prepare THA in situ gels. Sol-gel transition temperature (Tsol-gel), rheological properties, in vitro release, and in vivo nasal mucociliary transport time were optimized. The pharmacokinetics and brain dispositions of in situ gel were compared with that from THA oral solution in rats. The in situ gel demonstrated a liquid state with Newtonian fluid behavior under 20 °C, while it exhibited as non-flowing gel with pseudoplastic fluid behavior beyond its Tsol-gel of 28.5 °C. Based on nasal mucociliary transport time, the in situ gel significantly prolonged its retention in nasal cavity compared to solution form. Moreover, the in situ gel achieved 2-3 fold higher peak plasma concentration (Cmax) and area under the curve (AUC) of THA in plasma and brain tissue, but lowered Cmax and AUC of the THA metabolites compared to that of oral solution. The enhanced nasal residence time, improved bioavailability, increased brain uptake of parent drug and decreased exposure of metabolites suggested that the in situ gel could be an effective intranasal formulation for THA.

Selective and sensitive determination of bis(7)-tacrine, a high erythrocyte binding acetylcholinesterase inhibitor, in rat plasma by high-performance liquid chromatography-tandem mass spectrometry.

The current study aims to develop a specific and sensitive LC-MS/MS method for determination of bis(7)-tacrine (B7T) in rat plasma. A 100 microL plasma sample was extracted with ethyl acetate. B7T and the internal standard (IS), pimozide, in the samples were then analyzed with LC-MS/MS in positive electrospray ionization condition. Chromatographic separation of B7T and IS was achieved in a C(18) reversed-phase HPLC column (150 x 2.1 mm i.d.) by isocratic elution with a mobile phase consisting of 0.05% formic acid in water and acetonitrile (1:1, v/v) at a flow rate of 0.35 mL/min. Multiple-reaction monitoring (MRM) mode was employed to measure the ion transitions: m/z 247 to 197 for B7T and m/z 462 to m/z 328 for IS, respectively. The method was linear over the studied ranges of 100-5000 and 10-100 ng/mL. The intra-day and inter-day variations of the analysis were less than 6.8% with standard errors less than 9.0%. The detection limit of B7T in rat plasma was 1 ng/mL. The developed method was successfully applied to the pharmacokinetic study of B7T after intravenous administration of 1 mg/kg B7T and further proved to be readily utilized for determination of B7T in rat plasma samples.

Development of a high performance liquid chromatography-tandem mass method for determination of bis(7)-tacrine, a promising anti-Alzheimer's dimer, in rat blood.

An analytical method using on-line high performance liquid chromatography-tandem mass spectrometry with electrospray ionization was developed and applied for the quantification of bis(7)-tacrine (B7T) in rat blood. B7T and pimozide (internal standard, IS) were extracted in a single step from 100 microl of alkalized blood with ethyl acetate. Analytes were separated using an Extend C-18 column at 25 degrees C. The elution was achieved isocratically with a mobile phase composed of 0.05% aqueous formic acid and acetonitrile (60:40, v/v) at a flow rate of 0.35 ml/min. Quantification was achieved by monitoring the selected ions at m/z 247 for B7T and m/z 462-->m/z 328 for pimozide. Retention times were 1.45 and 2.23 min for B7T and IS, respectively. Calibration curves were linear in the range from 86.4 to 2160.0 ng/ml. The established method is rapid, selective and sensitive for the identification and quantification of B7T in biological samples. The assay is accurate (bias <10%) and reproducible (intra- and inter-day variation <10%), with detection and quantification limit of 3.6 and 42.3 ng/ml, respectively. Furthermore, it was successfully applied for the pharmacokinetic measurement of B7T in rat with a single intravenous administration at 0.3mg/kg.

Consumption of charcoal-broiled meat as an experimental tool for discerning CYP1A2-mediated drug metabolism in vivo.

Cytochrome P450 1A2 (CYP1A2) is a major drug-metabolising enzyme. Polycyclic aromatic hydrocarbons, present in high concentrations in tobacco smoke and charcoal-broiled meat, are known to induce CYP1A2. The purpose of the present study was to validate enzyme induction by consumption of charcoal-broiled meat as an experimental tool for discerning CYP1A2-mediated drug metabolism in vivo. Twenty-four healthy, non-smoking men, all extensive metabolisers of sparteine (CYP2D6), participated in the study. All participants were genotyped for a putative CYP1A2-inducibility genotype. In the study diet period charcoal-broiled meat was served for lunch and dinner for five consecutive days. All participants were tested with probe reactions for CYP1A2 (caffeine) and CYP2C19 (proguanil) before and after consuming the study diet. Further, in three subgroups, they were tested with either the CYP1A2-substrate tacrine or probe reactions for CYP3A4 (quinidine) or CYP2C9 (tolbutamide). Neither probe reactions for CYP1A2, CYP2C9, CYP2C19 or CYP3A4 were affected by consumption of charcoal-broiled meat as practised in this study. No modifying role of the CYP1A2-inducibility genotype was evident. A number of experimental limitations are discussed, among them the lack of standardisation of exposure, the timing of phenotyping, and the choice of probe reactions. In conclusion, consumption of charcoal-broiled meat as practised in the present study appears not to be a useful experimental tool for discerning CYP1A2-mediated metabolism in vivo.

Saturable distribution of tacrine into the striatal extracellular fluid of the rat: evidence of involvement of multiple organic cation transporters in the transport.

The kinetics and mechanism by which tacrine is distributed in the rat brain were examined. Tacrine levels in plasma and striatal extracellular fluid were used to evaluate the pharmacokinetics of this process. The K(D,brain) was decreased with the dose for tacrine, indicating that the distribution to the brain is saturable. The uptake of organic cations such as choline, 1-methyl-4-phenylpyridinium (MPP), tetraethylammonium (TEA), and carnitine was inhibited by the addition of tacrine to cultures of mouse immortalized brain capillary endothelial cells. In addition, the apical to basal transport and basal to apical transport of tacrine were inhibited by the addition of organic cations to cultures of LLC-PK1 cells, suggesting that tacrine transport across the blood-brain barrier (BBB) is mediated by organic cation transport system(s). Consistent with the in vitro results, a standard reverse transcription-polymerase chain reaction procedure was able to amplify the message of mOCT2 and mOCTN2, but not mOCT1, in MBEC4 (mouse brain microvessel endothelial cell line 4) cells. Similarly, mRNAs for rOCT2 and rOCTN2 were present in representative rat brain samples. To determine whether OCT2 and/or OCTN2 transport tacrine, these transporters were cloned and then transfected in SK-HEP1 and HEK 293 cells. The uptake of choline, MPP, and TEA was inhibited by the presence of tacrine in rOCT2-expressing SK-HEP1 cells, whereas the uptake of carnitine was inhibited by the presence of tacrine in rOCTN2-expressing HEK 293 cells. Collectively, these observations suggest that the transport of tacrine across the BBB is mediated, at least in part, by multiple organic cation transport systems in rats.

Synthesis and characterization of 9-[P-(N, N-dipropyl sulfamide)] benzoylamino-1,2,3,4-4H-acridine--a potential prodrug for the CNS delivery of tacrine.

9-[P-(N,N-dipropylsulfamide)]benzoylamino-1,2,3,4-4H-acridine (PTHA) was synthesized as a prodrug to improve the curative effect of tacrine hydrochloride (THA), to prolong the activation time in brain, and to decrease the hepatic toxicity. The prodrug was prepared by attaching carboxyl group of probenecid to 9-amino group of THA. The structure of PTHA was confirmed by IR, HNMR, MS and UV. The physiochemical properties and stabilities of the prodrug under various conditions were investigated. Possibility of the prodrug passing through the blood-brain barrier (BBB) was evaluated in vitro by biopartition micellar chromatography (BMC). The concentrations of THA and PTHA in various tissues were determined by reversed-phase high-performance liquid chromatography after intravenous (i.v.) administration. The results showed PTHA was stable in various pHs and temperatures. It was indicated by partition coefficient in ethyl acetate/water that lipophilicity of the prodrug increased and it was predicted by BMC that the prodrug could improve the infiltration ability across BBB of THA. In-vivo experiment showed the concentrations of THA in brain and liver kept stable for about 4 h, which was beneficial for the treatment of Alzheimer's disease (AD). Compared with THA at the same time, AUC in liver decreases significantly, the overall targeting efficiency (TE) was enhanced from 10.97 to 16.11% and AUC(brain)/AUC(liver) increased from 1.52 to 2.53, which suggests the possibility to reduce the hepatic toxicity of THA by the way of the prodrug.

Spectrofluorimetric determination of velnacrine in human serum and urine.

A simple, sensitive and rapid spectrofluorimetric method to determine velnacrine, a cholinesterase inhibitor, has been developed and validated. The influence of pH, temperature, ionic strength, presence of excipients, metal ions and surfactants on the fluorescence intensity has been studied. The proposed method allows the determination of 5-100 ng ml(-1) of velnacrine in aqueous solution containing sodium acetate buffer (pH 5.6; 0.04 M) with lambda(excitation) 242 nm and lambda(emission) 359 nm. The detection and quantitation limits were 1.7 and 4.5 ng ml(-1) respectively. The method was successfully applied to the determination of velnacrine in human serum and urine.

Simultaneous determination of N-butyramide-tacrine and tacrine in mouse plasma and brain homogenate by high-performance liquid chromatography with a simple gradient solvent system.

A novel reversed-phase HPLC method was developed for the simultaneous determination of tacrine (THA) and the newly synthesized prodrug (N-butyramide-THA, BTHA) in mouse plasma and brain homogenate. The assay involves deproteinisation and subsequent detection at 240 nm with a gradient solvent system. Retention times were 18.5 and 9.3 min for BTHA and THA, respectively. Average recoveries for the analytes were 80.7% (BTHA) and 76.6% (THA) from plasma, and 75.0% (BTHA) and 68.4% (THA) from brain homogenate. Linear responses were observed over a wide range (0.25-20 microg/ml for BTHA in plasma and in brain homogenate, 0.025-20 microg/ml for THA in both matrices). Both BTHA and THA degraded from the prodrug can be detected even 12 h after intravenous administration of BTHA, indicating that BTHA is a promising prodrug for brain targeting.

[Synthesis of prodrugs of tacrine hydrochloride and evaluation of the stability and biodistribution in mice].

AIM: To synthesize acylated prodrug of tacrine hydrochloride (THA) to improve the infiltration ability across the blood brain barrier (BBB). METHODS: A series of prodrugs were prepared by acylation of the 7-amino group of THA. The degradation of prodrugs was investigated under different conditions. Biodistribution studies of N-butyramide-THA (BTHA) in mice were carried out to evaluate the function of brain targeting. RESULTS: The structures of prodrugs were confirmed by IR, 1HNMR and MS. All prodrugs were stable in different medium. Octanol-water partition coefficients indicated increased lipophlicity for various prodrugs compared to the THA. In vivo distribution studies showed that BTHA was mainly distributed in brain, blood and liver (the maximum concentrations were 17.5725, 13.1400 and 22.8279 mg.L-1, respectively), while the THA concentration were very low in lung and heart (the maximum concentrations were 4.9475 and 4.4925 mg.L-1, respectively). The BTHA concentration (2.4159 mg.L-1) was relatively high even 12 h after administration, showing that BTHA degraded more slowly in brain than in other tissues. CONCLUSION: The infiltration ability of THA across BBB was increased in the form of N-acylate-THA prodrug, indicating that this kind of prodrug is a promising brain-targeting delivery system.

Plasma levels of Abeta42 and Abeta40 in Alzheimer patients during treatment with the acetylcholinesterase inhibitor tacrine.

Deregulation of amyloid precursor protein (APP) processing with increased production of amyloid beta-peptide (Abeta) is considered to be a key pathogenic event in Alzheimer's disease (AD). It has been suggested that stimulation of the muscarinic M(1) receptor subtype affects APP processing and leads to a change in Abeta concentration. To test the hypothesis that treatment with a cholinesterase inhibitor could change the levels of Abeta in plasma, we measured Abeta42 and Abeta40 plasma levels in AD subjects before tacrine treatment and at weeks 2 and 6 of treatment. Treatment with tacrine had no statistically significant effect on plasma Abeta42 and Abeta40 either at 2 weeks or at 6 weeks of administration compared to baseline levels. Plasma Abeta42 and Abeta40 levels showed large subject-to-subject variation but small variation within the same patient over the 3-sample interval. After 2 weeks of treatment with tacrine, there was a strong negative correlation between tacrine concentration and levels of Abeta42 (r = -0.64; p = 0.01) and Abeta40 (r = -0.55; p = 0.04). However, after 6 weeks there was no correlation between plasma concentrations of tacrine and Abeta42 (r = 0.33; p = 0.34) or Abeta40 (r = -0.22; p = 0.54) levels in plasma. After 2 weeks of treatment with an acetylcholinesterase inhibitor, we found a correlation between higher drug concentrations and lower beta-amyloid levels. This might indicate an effect on APP metabolism with an increased alpha-cleavage. But after 6 weeks of drug treatment, there was no obvious drug effect on beta-amyloid concentrations. This finding may indicate that compensatory mechanisms have started at 6 weeks and that no long-term effect on key pathological features in AD is to be expected by an inhibition of acetylcholinesterase.

Therapeutic drug monitoring of tacrine: simple and fast high-performance liquid chromatography assay method for its determination in human plasma.

A new high-performance liquid chromatography (HPLC) assay method was developed for the therapeutic monitoring of tacrine. The method involved a simple protein precipitation by means of either acetonitrile or cold methanol followed by a fast isocratic separation on a CN column eluted in reversed-phase mode. The entire sample preparation took place in an HPLC vial and no further liquid transfer was required. The validation data showed that the assay method was precise, accurate, and robust. Analysis of more than 1,000 plasma samples collected from patients with Alzheimer disease demonstrates the suitability of the assay.

Plasma tacrine concentrations are significantly increased by concomitant hormone replacement therapy.

BACKGROUND: In vitro results suggest that the synthetic hormones used in postmenopausal hormone replacement therapy (HRT) may be significant inhibitors of oxidative drug metabolism. Moreover, HRT has been reported to enhance response to tacrine in postmenopausal patients with Alzheimer's disease, but the mechanism of this interaction remains unclear. OBJECTIVE: To examine the effect of HRT with 2 mg estradiol valerate and 0.25 mg levonorgestrel once daily on the pharmacokinetics of tacrine. METHODS: Ten healthy female volunteers received treatment for 10 days with once-daily HRT or placebo in a randomized, double-blind crossover study. One hour after the last HRT or placebo capsule on day 10, the subjects received a single 40-mg dose of tacrine. Plasma samples were collected for 30 hours and urine samples were collected for 24 hours after tacrine intake for the measurement of tacrine and 1-hydroxytacrine concentrations. RESULTS: HRT increased the mean plasma concentration-time curve calculated from zero to infinity (AUC) of tacrine by 60% (P = .009); the greatest individual increase in the AUC was about threefold. Similarly, the mean peak concentration in plasma of tacrine was 46% (P = .031) higher in the HRT phase compared with the placebo phase. HRT reduced the mean apparent oral clearance of tacrine by 31% (P = .014), but no significant difference was found in the elimination half-life or the renal clearance of tacrine between the HRT phase and the placebo phase. The metabolic ratio (1-hydroxytacrine AUC/tacrine AUC) was significantly (mean, 26%; P < .001) reduced in all 10 subjects. CONCLUSIONS: HRT with estradiol and levonorgestrel significantly increased plasma tacrine concentrations. This interaction between tacrine and HRT involves reduced metabolic conversion of tacrine to its main metabolite 1-hydroxytacrine by CYP1A2 during the first-pass phase. The interaction may be clinically important with regard to both enhanced efficacy and increased likelihood of concentration-dependent adverse effects of tacrine in the long-term treatment of patients with Alzheimer's disease. Accordingly, smaller doses of tacrine may be appropriate when coadministered with HRT.

Fluvoxamine is a potent inhibitor of tacrine metabolism in vivo.

OBJECTIVE: In vitro studies have shown that tacrine is metabolized by cytochrome P4501A2 (CYP1A2). One of the monohydroxy-metabolites has been incriminated with tacrine-induced hepatotoxicity. The aim of this study was to establish whether the potent CYP1A2 inhibitor fluvoxamine in clinically relevant doses could inhibit tacrine metabolism. METHODS: Eighteen healthy young men were enrolled in an open, randomized crossover study. In the first study period a single oral dose of tacrine 40 mg was given. In the second period the volunteers were randomized to maintenance doses of fluvoxamine 50 or 100 mg per day, and a single oral dose of tacrine 20 mg was given. RESULTS: Fluvoxamine was found to be a very potent inhibitor of tacrine metabolism. A fractional decrement in tacrine clearance of approximately 85% was found with both fluvoxamine doses, which was in good agreement with a prediction based on in vitro data. The medians of the steady-state concentration of fluvoxamine were 43 nM (range 25-49) and 70 nM (range 44-124) in the 50 mg per day and 100 mg per day groups, respectively. The steady-state concentration of fluvoxamine correlated with the fractional decrement in tacrine clearance (Spearman Rs = 0.53, P < 0.05). Modest, but statistically significant, reductions in the formation of the metabolites 1- and 2-hydroxytacrine were found during concomitant fluvoxamine treatment. CONCLUSION: Fluvoxamine at clinically relevant doses is a potent inhibitor of tacrine metabolism. This interaction is very likely to have clinical relevance. Whether concomitant fluvoxamine treatment reduces tacrine-induced hepatotoxicity needs further study.

Aminotransferase levels and silymarin in de novo tacrine-treated patients with Alzheimer's disease.

BACKGROUND: Silymarin is a well-known hepatoprotective agent. Tacrine, the first drug marketed for Alzheimer's disease (AD), induces an elevation of serum liver transaminase prohibiting an effective dosage in many patients. This 12-week randomised, double-blind, placebo-controlled study was undertaken to evaluate the ability of silymarin to antagonise or prevent the hepatotoxic effects of tacrine and to analyse its action on tacrine efficacy and tolerability. METHODS: Outpatients suffering from mild-to-moderate dementia of the Alzheimer type were randomly assigned to two treatment groups: tacrine + silymarin and tacrine + placebo. The study was double-blind for silymarin and open for tacrine and was conducted in 22 French neurology and geriatric centres. Silymarin (420 mg/day) was given first (1 week) and tacrine was added at 40 mg/day for 6 weeks, then increased to 80 mg/day (6 weeks). Serum ALAT was the main evaluation criterion (> upper limit of normal, ULN). Serum ASAT as well as adverse side effects and cognitive performance assessed by MMSE and the Syndrome Kurtz test (SKT) were secondary evaluation criteria. Null hypotheses were evaluated with Fisher's exact test. FINDINGS: 222 patients were recruited and received silymarin and tacrine (110 patients) or placebo and tacrine (112 patients). 28 patients dropped out; 217 were included in the intent-to-treat analysis. No statistical difference was observed between the two groups for serum ALAT (p = 0.39). Fewer patients had ALAT levels >5 ULN in the silymarin group (-33.3%). Side effects and notably gastrointestinal disorders were much less frequent in the silymarin group. Cognitive performance remained unchanged in both groups. INTERPRETATION: Silymarin does not prevent tacrine-induced ALAT elevation but does reduce the rate of gastrointestinal and cholinergic side effects without any impact on cognitive status. As a consequence, silymarin (420 mg/day) could be co-administered with tacrine to improve tolerability in the initial phases of AD treatment.

Spectrofluorimetric determination of tacrine in pharmaceuticals and spiked human serum.

A spectrofluorimetric method to determine tacrine is proposed and applied to the determination of tacrine in human serum and pharmaceuticals. The fluorimetric method allows the determination of 1-70 ng ml-1 of tacrine in aqueous solutions containing acetic acid-sodium acetate buffer (pH 5.6) with lambda exc = 242 nm and lambda em = 362 nm.