Comparative effects of pharmacotherapy on the maintenance of cognitive function

A meta-analysis and critical review of the effects of conventional neuroleptic treatment on cognition in schizophrenia: opening a closed book

BACKGROUND

In recent years, numerous studies have examined whether new-generation antipsychotic agents impact cognitive impairment in patients with schizophrenia when compared with conventional antipsychotic treatment. The working assumption of such studies, supported by narrative reviews, is that the conventional antipsychotic medications have little or no effect on cognition. The studies concerning the effects of conventional neuroleptics on cognition, however, have never been analyzed quantitatively. In this meta-analysis, we revisit the question of whether typical agents might have enhancing effects on cognition.

METHODS

The meta-analysis included studies that 1) compared the effects of typical neuroleptic agents with those of placebo or no medication on cognition; 2) examined adult patients identified as having schizophrenia; and 3) produced adequate data to estimate an effect size. Studies were identified by searches of computerized literature databases and by cross-referencing included studies. The effect size calculated was d, the difference between the means in cognitive measures of patients with schizophrenia taking and not taking conventional neuroleptic medication, divided by the pooled SD. Critically, when multiple measures were reported in a single article, effect sizes were combined so as to minimize the possibility that one study had undue weight simply because of the number of cognitive outcome variables that it contained. These results were corrected for bias due to sample size, with each of the effect sizes weighted by the reciprocal of its variance. The final sample after exclusion of outliers comprised 208 effect sizes from 34 studies.

RESULTS

With a random-effects model, effect sizes from the primary studies were weighted according to sample size and averaged. The resulting mean effect size was.22 (95% confidence interval =.10,.34). The result is positive, in that the range did not include zero and was of low moderate size. No moderating effects of study design or patient qualities were found to be significant. With the same procedures, effect sizes for individual neurocognitive domains were computed. Effect sizes were generally in the.13-.29 range for the majority of cognitive functions, whereas motor function was impacted negatively (-.11). Unexpectedly, medication dose did not correlate with effect size.

CONCLUSIONS

Typical antipsychotic medication provides modest-to-moderate gains in multiple cognitive domains. Given unavoidable methodologic limitations of the primary studies, current findings suggest that the impact of conventional medication on cognitive function should be re-evaluated.

Drug therapy of frontotemporal dementia

Frontal lobe dementia, or more generally frontotemporal dementia (FTD), includes several clinical entities and, although highly prevalent, lacks any codified therapeutic strategy. The present review is an attempt to depict the main neurochemical correlates of FTD and, as a consequence, to propose the most sound targets for symptomatic drugs. Large scale double-blind controlled clinical trials should be carried out to test any hypothesis: serotonergic agents, glutamate neurotransmission enhancers, monoamine oxidase inhibitors. The recent discovery of tau gene mutations in FTD with Parkinsonism linked to chromosome 17 has reinforced the direct role attributed to abnormal tau proteins (hyperphosphorylation) and thus raised the possibility to target specifically these processes by drugs (aetiopathogenic compounds).

Psychomotor and cognitive effects of piribedil, a dopamine agonist, in young healthy volunteers

Piribedil is a dopamine agonist acting on D2 and D3 central nervous system dopamine receptors. This drug has been administered to 12 young healthy male volunteers (age 22 +/- 2 years) according to a single center randomized, double-blind, two ways cross-over, placebo controlled trial, including a washout period of one week. Placebo and piribedil were administered by a single intravenous infusion over 2 h (3 mg). Psychomotor performance and cognitive functions were assessed through a standardized and computerized psychometric tests battery and a continuous electroencephalogram (EEG) mapping. Piribedil improved simple reaction time (P=0.02), immediate (P=0.045 and 0.004), and delayed free recall (P=0.05), dual coding test (P=0.02) and increased theta and fast beta waves on the EEG (P < 0.05 and 0.001, respectively). No deleterious effect was observed on the tests exploring attention and concentration via the other procedures. It is concluded that a single intravenous perfusion of piribedil 3 mg improves alertness and the information processing speed within the central nervous system, in healthy volunteers.

The preclinical pharmacologic profile of tiapride

Tiapride is a benzamide derivative that has been used successfully in the clinic for a number of years for the treatment of agitation and aggressiveness in elderly patients. Like many substituted benzamides, tiapride specifically blocks dopamine receptors in the brain. It has affinity for dopamine D(2) (IC(50) = 110-320 nM) and D(3) (IC(50) = 180 nM) receptors in vitro but lacks affinity for dopamine D(1) and D(4) receptors and for non-dopaminergic receptors including H(1), alpha(1), alpha(2)-adrenergic and serotonergic receptors. Tiapride also shows dose-related inhibition of [3H]-raclopride binding in limbic areas and in the striatum of the rat in vivo (ED(50) approximately 20 mg/kg, ip). In microdialysis experiments, tiapride (over the range 10-30 mg/kg, ip) increased extracellular levels of dopamine in the nucleus accumbens and striatum, a reflection of its blockade of postsynaptic dopamine receptors in these brain areas. In behavioral experiments in rats, lower doses of tiapride (ED(50) = 10 mg/kg, ip) antagonised dopamine agonist-induced hyperactivity while higher doses (ED(50) = 60 mg/kg, ip) were required to block stereotyped movements. In addition, doses of tiapride up to 200 mg/kg, ip failed to induce catalepsy, an effect observed with many other drugs which block dopamine receptors. In tests of conditioned behavior in rats, tiapride was found to give rise to an interoceptive stimulus associated with dopamine receptor blockade at doses (ED(50) = 2.2 mg/kg, ip) much lower than those producing motor disturbances or sedation (ED(50) = 40 mg/kg, ip), in striking contrast to a range of conventional or atypical neuroleptics that produced interoceptive stimulus and sedation at similar doses. Furthermore, the acquisition by rats of a place-learning task in a water maze was not affected by tiapride (over the range 3-30 mg/kg, ip), whereas haloperidol (MED = 0.25 mg/kg, ip) and risperidone (MED = 0.03 mg/kg, ip) impaired performance. The preclinical pharmacologic and behavioral profile of tiapride suggests that its clinical activity may be due to a selective blockade of dopamine D(2) and D(3) receptors in limbic brain regions. The results are also consistent with a lack of motor or cognitive side effects.