Predictive value of early improvement in bipolar depression trials: a post-hoc pooled analysis of two 8-week aripiprazole studies.

OBJECTIVE: To evaluate the value of early improvement to predict treatment outcome in patients with bipolar depression. METHODS: Data were pooled from two aripiprazole, 8-week, randomized, double-blind, placebo-controlled trials in patients with bipolar depression without psychotic features to determine whether early improvement (≥20% reduction in Montgomery-Åsberg Depression Rating Scale (MADRS) Total score at Week 2 or 3) predicts later response (≥50% MADRS Total score reduction at Week 8) or remission (MADRS Total ≤10 at Week 8). Sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) were calculated (LOCF). Univariate and multivariate logistic regression models were used to evaluate early improvement and baseline demographic/clinical characteristics as predictors of response/remission. RESULTS: In total, 311 patients were randomized to placebo and 306 to aripiprazole. Predictive values of early improvement (≥20% MADRS Total score reduction) for remission with aripiprazole at Week 2/3, respectively, were: sensitivity 83%/94%; specificity 41%/33%; PPV 44%/45%; NPV 81%/91%. The corresponding values with placebo were as follows: sensitivity 70%/84%; specificity 60%/51%; PPV 50%/51%; NPV 77%/84%. Univariate linear regression showed that early improvement (≥15%, ≥20%, ≥25%, ≥30% at Week 3) was a significant potential predictor of remission. CONCLUSION: Absence of early improvement after 3 weeks of treatment reliably predicted non-response/non-remission at study endpoint with high sensitivity and NPV. In patients with <20% improvement after 21 days of aripiprazole monotherapy, treatment should be modified, as continued use is unlikely to result in response/remission. Clinical decision-making to optimize treatment course in bipolar I depression may be appropriate after as little as 2 weeks and certainly within the first 3 weeks of treatment.

Effect of aripiprazole versus haloperidol on PANSS Prosocial items in early-episode patients with schizophrenia.

BACKGROUND AND AIM: Improving social functioning is critically important in early-episode schizophrenia, if patients are to achieve functional recovery. This post-hoc, pooled analysis of two studies compared the effect of aripiprazole versus haloperidol on social functioning in early-episode schizophrenia. METHODS: Data were pooled from two 52 week, randomized (2:1), double-blind, multicenter studies involving 1294 patients with chronic schizophrenia who were in an acute psychotic episode and had a history of positive antipsychotic response during previous episodes. The early-episode group was defined as patients who are

Switching to aripiprazole in outpatients with schizophrenia experiencing insufficient efficacy and/or safety/tolerability issues with risperidone: a randomized, multicentre, open-label study.

INTRODUCTION: This study evaluated the safety/tolerability and effectiveness of aripiprazole titrated-dose versus fixed-dose switching strategies from risperidone in patients with schizophrenia experiencing insufficient efficacy and/or safety/tolerability issues. METHODS: Patients were randomized to an aripiprazole titrated-dose (starting dose 5 mg/day) or fixed-dose (dose 15 mg/day) switching strategy with risperidone down-tapering. Primary endpoint was rate of discontinuation due to adverse events (AEs) during the 12-week study. Secondary endpoints included positive and negative syndrome scale (PANSS), clinical global impressions - improvement of illness scale (CGI-I), preference of medication (POM), subjective well-being under neuroleptics (SWN-K) and GEOPTE (Grupo Español para la Optimización del Tratamiento de la Esquizofrenia) scales. RESULTS: Rates of discontinuations due to AEs were similar between titrated-dose and fixed-dose strategies (3.5% vs. 5.0%; p=0.448). Improvements in mean PANSS total scores were similar between aripiprazole titrated-dose and fixed-dose strategies (-14.8 vs. -17.2; LOCF), as were mean CGI-I scores (2.9 vs. 2.8; p=0.425; LOCF) and SWN-K scores (+8.6 vs.+10.3; OC,+7.8 vs.+9.8; LOCF). CONCLUSION: Switching can be effectively and safely achieved through a titrated-dose or fixed-dose switching strategy for aripiprazole, with down-titration of risperidone.

Aripiprazole monotherapy in the treatment of acute bipolar I mania: a randomized, double-blind, placebo- and lithium-controlled study.

OBJECTIVES: To evaluate the efficacy and safety of aripiprazole as acute and maintenance of effect monotherapy for acute bipolar mania. METHODS: Patients with acute bipolar I mania (DSM-IV-TR: YMRS > or =20), manic or mixed (with or without psychotic features) were randomized to double-blind aripiprazole (15-30 mg/day; n=155), placebo (n=165) or lithium (900-1500 mg/day; n=160) (1:1:1) for 3 weeks. Aripiprazole- and lithium-treated patients remained on blinded treatment for 9 additional weeks. The primary outcome was the mean change from baseline in YMRS Total score (LOCF) to Week 3. Secondary outcomes included the mean change from baseline in YMRS Total score (LOCF) at all other timepoints up to Week 12. RESULTS: Aripiprazole demonstrated significantly greater improvement than placebo in mean YMRS Total score from baseline to Day 2 (-4.3 vs.-2.8; p=0.003), and up to Week 3 (-12.6 vs. -9.0; p<0.001). Significant improvement in YMRS Total score was also seen with lithium versus placebo at Week 3 (-12.0 vs. -9.0; p=0.005). Improvements in YMRS Total score were maintained to Week 12 for aripiprazole (-14.5) and lithium (-12.7). Response rates at Week 3 were significantly higher with aripiprazole (46.8%) and lithium (45.8%) than placebo (34.4%; both p<0.05, LOCF); increasing to Week 12 with aripiprazole (56.5%) and lithium (49.0%). Most common adverse events with aripiprazole were headache, nausea, akathisia, sedation, and constipation; with lithium were nausea, headache, constipation, and tremor. CONCLUSIONS: Aripiprazole provided statistically significant improvement of acute mania within 2 days, continuing over 3 weeks and sustained over 12 weeks. The magnitude of improvement to Week 12 was similar with aripiprazole and lithium.

Aripiprazole monotherapy in patients with rapid-cycling bipolar I disorder: an analysis from a long-term, double-blind, placebo-controlled study.

AIMS: Rapid-cycling bipolar disorder is difficult to treat and associated with greater morbidity than non-rapid-cycling disease. This post hoc analysis evaluated 28 patients with rapid-cycling bipolar I disorder from a 100-week, double-blind, placebo-controlled study assessing long-term efficacy, safety and tolerability of aripiprazole in patients with bipolar I disorder (most recently manic/mixed). METHODS: Following >or= 6 consecutive weeks' stabilisation with open-label aripiprazole, patients were randomised (1 : 1) to aripiprazole or placebo. Patients completing 26 weeks treatment without relapse could continue for a further 74 weeks. Primary end-point was time to relapse for manic, mixed or depressive symptoms, defined as discontinuation due to lack of efficacy. Safety assessments included adverse event (AE) monitoring and changes in weight and lipid, glucose and prolactin levels. RESULTS: Of the 28 patients (aripiprazole, n = 14; placebo, n = 14) with rapid-cycling bipolar disorder, 12 (aripiprazole, n = 7; placebo, n = 5) completed the initial 26-week treatment period and three (all aripiprazole treated) completed the 100-week, double-blind period. Time to relapse was significantly longer with aripiprazole vs. placebo at week 26 [log-rank p = 0.033; 26-week hazard ratio = 0.21 (95% CI: 0.04, 1.03)] and week 100 [log-rank p = 0.017; 100-week hazard ratio = 0.18 (95% CI: 0.04, 0.88)]. The most commonly reported AEs with aripiprazole during the 100 weeks (>or= 10% incidence and twice placebo) were anxiety (n = 4), sinusitis (n = 4), depression (n = 3) and upper respiratory infection (n = 3). One aripiprazole-treated patient discontinued due to an AE (akathisia). There were no significant between-group differences in mean changes in weight or metabolic parameters. CONCLUSION: In this small, post hoc subanalysis, aripiprazole maintained efficacy and was generally well tolerated in the long-term treatment of rapid-cycling bipolar disorder. Further research with prospectively designed and adequately powered trials is warranted.

Intramuscular aripiprazole or haloperidol and transition to oral therapy in patients with agitation associated with schizophrenia: sub-analysis of a double-blind study.

OBJECTIVE: A sub-population analysis of 325 patients with agitation (Positive and Negative Syndrome Scale Excited Component [PEC] score > or = 15 and < or = 32; score of > or = 4 on > or = 2 items) associated with schizophrenia in a randomized, double-blind study investigating the efficacy and tolerability of intramuscular (IM) aripiprazole 9.75 mg, IM haloperidol 6.5 mg, or IM placebo and the transition to oral therapy. RESEARCH DESIGN AND METHODS: Over 24 h, patients could receive up to three IM injections; the second and third administered > or = 2 and > or = 4 h, respectively, after the first, if deemed clinically necessary. Following IM treatment, oral aripiprazole or haloperidol was administered for 4 days. The primary efficacy measure was the mean change in PEC score from baseline at 2 h. RESULTS: At 2 h, mean improvements in PEC scores with IM aripiprazole (-8.0) were significantly greater versus IM placebo (-5.7; p < or = 0.01), and similar versus IM haloperidol (-8.3). Secondary efficacy measures also significantly improved with active IM treatment versus IM placebo. Continuation with oral treatment provided continued efficacy with both active treatments. The safety profiles of IM and oral aripiprazole were similar. The incidence of extrapyramidal symptom-related adverse events was 0% with IM aripiprazole, 1.6% with IM placebo and 16.5% with IM haloperidol. CONCLUSION: Intramuscular aripiprazole is effective in patients with acute agitation associated with schizophrenia, comparable to IM haloperidol, and enables convenient transfer to oral aripiprazole therapy.

Reemergence of sexual dysfunction in patients with major depressive disorder: double-blind comparison of nefazodone and sertraline.

BACKGROUND: Several different classes of antidepressants have been associated with sexual adverse effects. This double-blind, randomized trial compared the effects of nefazodone and sertraline on reemergence of sexual dysfunction in depressed patients who had experienced sexual dysfunction as a result of sertraline treatment. Depressive symptoms were also monitored. METHOD: One hundred five patients with DSM-III-R major depressive episode who were experiencing sexual dysfunction attributable to sertraline (100 mg/day) were screened for entry. Eligible patients entered a 1-week washout period that was followed by a 7- to 10-day single-blind placebo phase. Patients without symptoms of sexual dysfunction at the end of the single-blind placebo phase were randomly assigned to receive double-blind treatment with either nefazodone (400 mg/day) or sertraline (100 mg/day) for 8 weeks. RESULTS: Nearly 3 times more sertraline-treated patients (76%; 25/33) experienced reemergence of sexual dysfunction (ejaculatory and/or orgasmic difficulty) than did nefazodone-treated patients (26%; 10/39) (p < .001). In addition, patients treated with nefazodone were more satisfied with their sexual functioning than were patients treated with sertraline. Both treatment groups demonstrated a similar and sustained improvement in depressive symptoms. Both drugs were well tolerated, and the overall incidence of adverse reactions was similar for both treatment groups; however, 9 sertraline-treated patients (26%) discontinued because of adverse events compared with 5 nefazodone-treated patients (12%). Of the patients discontinuing therapy for adverse events, 5 of the sertraline-treated patients did so because of sexual dysfunction reported as an adverse event, whereas only 1 of the nefazodone-treated patients discontinued therapy secondary to sexual dysfunction. CONCLUSION: In this sample of patients with major depression who had recovered from sexual dysfunction induced by treatment with sertraline, nefazodone treatment resulted in significantly less reemergence of sexual dysfunction than did renewed treatment with sertraline and provided continued antidepressant activity.

In vivo autoradiography of [3H]SCH 39166 in rat brain: selective displacement by D1/D5 antagonists.

The purpose of this study was to examine the receptor occupancy of D1/D5 antagonists for D1-like dopamine receptors in rat brain using [3H]SCH 39166, a highly selective D1/D5 antagonist with low affinity for 5HT2 receptors. A single concentration of triated SCH 39166 was administered to rats, with or without competing doses of the Dl/D5 antagonist SCH 23390 and unlabeled SCH 39166. the D2-like antagonists haloperidol or the 5-HT, antagonist ketanserin. The bound radioactivity in the cortex, striatum, nucleus accumbens and olfactory tubercle was then quantified using an in vivo autoradiographic procedure. The results indicated that [3H]SCH 39166 was dose dependently displaced by the Dl/D5 antagonists in regions associated with both the nigro-striatal pathway and the mesolimbic dopamine pathway, particularly the nucleus accumbens. Neither haloperidol nor ketanserin displaced [3H]SCH 39166 in any of the regions examined. The data were compared with previously published data examining the in vivo binding of [3H]SCH 39166 in rat brain homogenates. The relative values obtained were comparable to values detected in rat brain homogenates after in vivo binding of [3H]SCH 39166.

Double-blind, placebo-substitution study of nefazodone in the prevention of relapse during continuation treatment of outpatients with major depression.

The efficacy of nefazodone in prevention of relapse of depression was evaluated in a 36-week double-blind, placebo-substitution, continuation treatment trial. After 16 weeks of acute, single-blind treatment with nefazodone, 131 patients responding to treatment and in stable remission were randomized in a 36-week double-blind trial to either nefazodone (n = 65) or placebo (n = 66). Patients were defined as having relapsed if they had a total score > or = 18 on the 17-item Hamilton Depression Scale on two consecutive visits or if they discontinued treatment for lack of efficacy. Relapse rates were significantly lower for patients randomized to continued nefazodone treatment than for patients switched to placebo. Kaplan-Meier estimates of relapse rates 9 months (36 weeks) after the end of acute treatment were 1.8% for nefazodone versus 18.3% for placebo (P = 0.009) by the Hamilton Depression Scale and 17.3% versus 32.8% (P = 0.028) by discontinuation for lack of efficacy. The mean modal dose of nefazodone was 412 mg/day at study endpoint. These results demonstrate the clinical effectiveness of up to 1 year's treatment (16 weeks acute and 36 weeks continuation) with nefazodone in depressed patients. Long-term efficacy of nefazodone was accompanied by a good safety profile without any weight gain and with minimal symptoms of withdrawal upon abrupt discontinuation of treatment.

Comparative effects of nefazodone and fluoxetine on sleep in outpatients with major depressive disorder.

BACKGROUND: Sleep disturbances are common in major depressive disorder. In previous open-label trials, nefazodone improved sleep continuity and increased rapid eye movement (REM) sleep, while not affecting stage 3/4 sleep or REM latency: in contrast, fluoxetine suppressed REM sleep. This study compared the objective and subjective effects of nefazodone and fluoxetine on sleep. METHODS: This paper reports combined results of three identical, multisite, randomized, double-blind, 8-week, acute-phase trials comparing nefazodone (n = 64) with fluoxetine (n = 61) in outpatients with nonpsychotic major depressive disorder and insomnia. Sleep electroencephalographic (EEG) recordings were gathered at baseline and weeks 2, 4, and 8. Clinical ratings were obtained at weeks 1-4, 6, and 8. RESULTS: Nefazodone and fluoxetine were equally effective in reducing depressive symptoms; however, nefazodone differentially and progressively increased (while fluoxetine reduced) sleep efficiency and reduced (while fluoxetine increased) the number of awakenings in a linear fashion over the 8-week trial. Fluoxetine, but not nefazodone, prolonged REM latency and suppressed REM sleep. Nefazodone significantly increased total REM sleep time. Clinical evaluations of sleep quality were significantly improved with nefazodone compared with fluoxetine. CONCLUSIONS: Nefazodone and fluoxetine were equally effective antidepressants. Nefazodone was associated with normal objective, and clinician- and patient-rated assessments of sleep when compared with fluoxetine. These differential sleep EEG effects are consistent with the notion that nefazodone and fluoxetine may have somewhat different modes and spectra of action.

Distribution of muscarinic receptor subtypes in rat brain from postnatal to old age.

In an effort to understand the developmental changes in the distribution of muscarinic receptor subtypes (m1-m5), specific brain regions from juvenile (16-day-old), young (21-day-old) and adult (90-day-old) rats were analyzed using subtype-selective antibodies. These studies revealed significant age-dependent changes in the four brain regions examined. In cortex, an area associated with higher cognitive functions, significant increases of m2 and m4 receptors occurred between juvenile and adult rats. In the striatum, the level of m4 receptor increased with age whereas the m1, m2 and m3 receptors had reached mature levels within the first 16 days. Small but significant changes occurred in the cerebellum with a decrease in m1, m3 and m4 receptor subtypes. In contrast to other brain regions, the hippocampus displayed consistent expression levels of muscarinic receptor subtypes. Suggesting that this brain region, which is involved in the foundation of numerous neural networks, requires a full complement of muscarinic receptors at a very early age. Muscarinic receptors have been shown to be important in a number of behavioral activities, including learning and memory. The changes observed in the age-dependent expression of these receptors most likely play an important role in how acetylcholine produces its effects in vivo.

Identification of the primary muscarinic autoreceptor subtype in rat striatum as m2 through a correlation of in vivo microdialysis and in vitro receptor binding data.

Muscarinic autoreceptors located on cholinergic nerve terminals are involved in the inhibitory feedback regulation of acetylcholine (ACh) release. Establishing the subtype identity of such sites provides a more complete understanding of both normal receptor function and the functional significance of receptor changes associated with various neurodegenerative diseases. In this study, a novel approach was used to identify the muscarinic autoreceptor in rat striatum. It involved the correlation of data from two different sources--in vivo microdialysis and in vitro receptor binding. Four standard muscarinic antagonists with varying binding profiles (scopolamine, pirenzepine, AF-DX116 and himbacine) were infused directly through a microdialysis probe into the striatum of conscious, freely moving rats. The objectives were to find the minimal concentration of each antagonist capable of manifesting a functional autoreceptor response (i.e., increased ACh release) and to compare the relative ability of the antagonists to bring about this effect with their relative abilities to bind to each of the cloned muscarinic receptor subtypes. The conclusion is that the muscarinic receptor mediating ACh release in rat striatum exhibits a pharmacological profile clearly consistent with it being of the m2 subtype.

Felbamate, a novel antiepileptic drug, reverses N-methyl-D-aspartate/glycine-stimulated increases in intracellular Ca2+ concentration.

Felbamate, 2-phenyl-1,3-propanediol dicarbamate, is a novel, orally active anticonvulsant that has recently been approved for the treatment of Lennox-Gastaut syndrome and partial onset seizures in the United States. Felbamate is active in a broad range of animal anticonvulsant tests. Although its mechanism of action has yet to be fully elucidated, felbamate appears to act by inhibiting the spread of seizures and elevating seizure threshold. One proposed mechanism of action for felbamate is via the NMDA receptor complex. Previous studies have demonstrated the ability of felbamate to inhibit glycine binding at the NMDA receptor complex. The present study examined the effects of felbamate on NMDA/glycine-stimulated increases in intracellular calcium (Ca2+) using cultured rat hippocampal neurons. The results of these experiments demonstrate that felbamate inhibits NMDA/glycine-stimulated increases in intracellular Ca2+ with a minimal effective concentration of 100 microM.

Characterization of the binding of SCH 39166 to the five cloned dopamine receptor subtypes.

Characterization studies were conducted on the five cloned dopamine receptor subtypes (D1-D5) using the novel D1-selective antagonist, SCH 39166, as well as other related benzazepines and dopaminergic agents. The results demonstrate that SCH 39166 exhibits saturable, high-affinity binding to the D1 and D5 receptors, but binds with low affinity to the D2, D3, and D4 receptors. In contrast, the D2 antagonist haloperidol showed low affinity for the "D1-like" receptors and high affinity for the "D2-like" receptors. A series of agonists was also evaluated and the D5 receptor subtype displayed a two-site fit for the endogenous agonist dopamine, as well as for the agonist apomorphine. Differences in agonist binding among the D1-like receptors reflect the importance of the nonconserved amino acid substitutions.

Studies on the glucuronidation of dopamine D-1 receptor antagonists, SCH 39166 and SCH 23390, by human liver microsomes.

Dopamine D-1 receptor antagonists are currently under investigation for use as antipsychotic agents. Two potent and selective D-1 receptor antagonists, SCH 39166 and SCH 23390, have been studied extensively in various experimental animal models. SCH 39166 has a more prolonged duration of action in primates in vivo and a lower rate of in vitro glucuronidation by microsomes from squirrel monkey liver. Because the rate of glucuronidation seems to govern the duration of action and may limit the use of these agents in humans, the glucuronidation of SCH 39166 and SCH 23390 by microsomes isolated from human liver was studied. The rates of glucuronide formation (Vmax) for SCH 39166 were much lower than those of SCH 23390, yet the KM values were similar. Therefore, the average efficiency (Vmax/KM) of SCH 39166 glucuronidation was only 14% that of SCH 23390. These results agree with previous studies in hepatic microsomes from squirrel monkeys. Marked inhibition of SCH 39166 glucuronidation by SCH 23390 and its pharmacologically inactive stereoisomer, SCH 23388, was observed. The inactive stereoisomer of SCH 39166, SCH 39165, was a weak inhibitor. In contrast, substrates for morphine UDP-glucuronosyltransferase (UGT), and p-nitrophenol, an alternative substrate for numerous human hepatic UGTs, did not inhibit SCH 39166 glucuronidation. Further separation of human hepatic UGTs activities using chromatofocusing chromatography indicated that SCH 39166 UGT activity was distinct from human hepatic UGT2B15 and human hepatic pI 6.2 UGT activity. Thus, a unique human hepatic UGT may be involved in SCH 39166 glucuronidation.(ABSTRACT TRUNCATED AT 250 WORDS)

Determination of plasma and brain concentrations of SCH 39166 and their correlation to conditioned avoidance behavior in rats.

Plasma and brain concentrations of the dopamine D1 receptor antagonist, SCH 39166, were measured and compared to behavioral activity in the conditioned avoidance response paradigm (CAR). SCH 39166 was administered at two behaviorally active doses (1 mg/kg, SC and 10 mg/kg, PO) and the time course for CAR activity was compared with the plasma and brain concentrations of unconjugated SCH 39166. Conjugation and N-demethylation of SCH 39166 after oral administration were also determined and first pass metabolism examined. Results from these studies demonstrated a similar time-dependent disappearance of unconjugated SCH 39166 from both the plasma and brain, independent of route of administration. Brain concentrations of SCH 39166 were approximately 5-fold higher than corresponding plasma concentrations, regardless of route. However, plasma and brain concentrations of unconjugated SCH 39166 were higher after SC administration of 1.0 mg/kg, than after PO administration of 10 mg/kg, suggesting a substantial first pass metabolism of SCH 39166. In addition, total (conjugated and unconjugated) plasma concentrations of SCH 39166 were at least 10-fold higher than unconjugated concentrations of SCH 39166 after PO administration of 10 mg/kg, demonstrating that a high proportion of drug was conjugated. Metabolism to the N-desmethyl analog, SCH 40853, was observed after PO administration of 10 mg/kg SCH 39166 and a high proportion of conjugation of the desmethyl analog was also seen. Finally, plasma concentrations of unconjugated SCH 39166 exhibited a high positive correlation (r = 0.934, P < 0.001) with brain concentrations of unconjugated SCH 39166.(ABSTRACT TRUNCATED AT 250 WORDS)

D1-receptor antagonists: comparison of [3H]SCH39166 to [3H]SCH23390.

A radiolabeled form of the benzonaphthazephine, SCH39166 was used to characterize the binding of this D1 antagonist in cortex, and an autoradiographic comparison of the localization of [3H]SCH39166 to [3H]SCH23390 (D1 antagonist and forerunner of SCH39166) binding was performed. The Kd for [3H]SCH39166, calculated from dissociation and association rate constants (1.09 nM), was comparable to the Kd value derived from Scatchard analyses of saturation data (1.74 nM). [3H]SCH39166 binds to brain tissue in a saturable manner with high affinity and low non-specific binding. Inhibition of [3H]SCH39166 binding by dopaminergic and serotonergic agents supports the hypothesis that this is indeed a D1-specific compound with little overlap onto serotonin (5-HT) receptors. The affinity of [3H]SCH39166 for 5-HT2 and 5-HT1c receptors is at least an order of magnitude lower than the affinity of [3H]SCH23390 for these same receptor sites. Quantitative autoradiographic analysis of [3H]SCH39166 and [3H]SCH23390 binding indicates high D1-receptor density in the caudate-putamen, nucleus accumbens, olfactory tubercle, substantia nigra and entopeduncular nucleus. Low levels of binding (not significantly above background) were detected with [3H]SCH39166 in lamina IV of the cortex and in choroid plexus; areas which had significant [3H]SCH23390 binding and are known to have a high density of 5-HT (5-HT2 and 5-HT1c respectively) receptors.

In vivo binding to dopamine receptors: a correlate of potential antipsychotic activity.

Antagonists of dopamine receptors (especially those of the D2 subtype) have long been recognized as effective antipsychotics. SCH 39166, a dopamine D1 selective antagonist, is now also being evaluated for its clinical antipsychotic properties. The studies described herein determine the binding affinity of a variety of dopamine receptor antagonists (both dopamine D1 and D2 selective compounds) for the dopamine D1 and D2 receptors, in vivo, and correlate this affinity with their behavioral activity in the rat conditioned avoidance response (CAR) test. The in vivo binding affinities of the D1 selective compounds at the dopamine D1 site exhibited a high correlation (r = 0.97) with their activities in the rat CAR test. Likewise, D2 selective compounds' inhibition of in vivo binding to dopamine D2 receptors correlated with their behavioral potencies (r = 0.98). Conversely, any binding of selective agents to their non-targeted receptor did not correlate with their behavioral activity. These data suggest that in vivo binding to either dopamine D1 and/or D2 receptors is predictive of potential antipsychotic efficacy.

Highlights of D1 dopamine receptor antagonist research.

SCH 39166 is now undergoing clinical trials in schizophrenics as a selective D1 dopamine receptor antagonist. It differs from SCH 23390, the prototype D1 receptor antagonist, by having reduced affinity for serotonin receptors and a longer duration of action in primates, as measured in the squirrel monkey conditioned avoidance paradigm. Further studies on this difference in primates indicates that it may be attributable to reduced affinity of SCH 39166 compared to SCH 23390 for the hepatic glucuronosyltransferase system. Their affinities are similar in rats, a species in which both have similar duration of action. These and other studies presented are consistent with the novel profile of SCH 39166.