Tacrine treatment of Alzheimer's disease: many expectations, few certainties

Quality of life and behavioral functions are severely reduced in patients affected by Alzheimer's disease (AD). Among the drugs employed in the treatment of this invalidating degenerative dementia, tacrine (THA) seemed to play a possible therapeutic role. Our study was aimed to evaluate the efficacy of THA in the treatment of AD, performing a comparison with lecithin and/or placebo treatment. Five randomized controlled trials on tacrine versus lecithin and/or placebo treatment were randomly selected. Mantel-Haenszel-Peto method was applied. Patients treated with tacrine achieved better results than control subjects (overall OR = 2.34; 95% CI 1.42-3.85); but long-term treatment with tacrine was not significantly more efficacious than placebo. Statistical significance in favor of THA versus other drugs employed was obtained in MMSE and ADAS-Cog tests in the studies carried out by Eagger et al. and Knapp et al. Moreover, Fitten et al. administered the highest tolerated THA dose to only a few patients enrolled in the study. The presence of broad CIs observed in the 5 meta-analytic studies infer non homogeneity of effects of treatment. Solely few patients improved, whereas the clinical conditions of the majority remained stationary. Between 5 and 10% of the outpatients in each single study presented reversible side effects calling for suspension of THA treatment. The optimal dose ranged between 80 and 160 mg THA, but often produced side effects. Comparative trials revealed the reduced efficacy and elevated toxicity of THA treatment, dampening the initial enthusiasm concerning the usefulness of this drug in AD. Furtermore, tacrine-induced side effects provoked many dropouts in all studies investigated. The effectiveness of tacrine treatment in AD disease was not fully confirmed. Other studies are required to identify doses and modalities of administration of this drug in AD.