Efficacy of high-dose glycine in the treatment of enduring negative symptoms of schizophrenia. Double-blind, placebo-controlled, crossover trial of D-cycloserine adjuvant therapy for treatment-resistant schizophrenia. D-serine added to antipsychotics for the treatment of schizophrenia. Lamotrigine in treatment-resistant schizophrenia: a randomized placebo-controlled crossover trial. Effect of clozapine and adjunctive high-dose glycine in treatment-resistant schizophrenia. Adjunctive high-dose glycine in the treatment of schizophrenia. Placebo-controlled trial of lamotrigine added to conventional and atypical antipsychotics in schizophrenia. Placebo-controlled trial of glycine added to clozapine in schizophrenia. D-serine added to clozapine for the treatment of schizophrenia.
Disturbances of N-methyl-D-aspartate (NMDA) receptor-mediated glutamatergic neurotransmission may play an important role in the pathophysiology of negative symptoms of schizophrenia. Glycine, a small nonessential amino acid, functions as an obligatory coagonist at NMDA receptors through its action at a strychnine-insensitive binding site on the NMDA receptor complex. Glycine-induced augmentation of NMDA receptor-mediated neurotransmission may thus offer a potentially safe and feasible approach for ameliorating persistent negative symptoms of schizophrenia.
                Twenty-two treatment-resistant schizophrenic patients participated in a double-blind, placebo-controlled, 6-week, crossover treatment trial with 0.8 g/kg per day of glycine added to their ongoing antipsychotic medication. Clinical assessments, including the Brief Psychiatric Rating Scale (BPRS), the Positive and Negative Syndrome Scale (PANSS), the Simpson-Angus Scale for Extrapyramidal Symptoms, and the Abnormal Involuntary Movement Scale, were performed biweekly throughout the study. Clinical laboratory values and amino acid serum levels were monitored.
                Glycine treatment was well tolerated and induced increased glycine (P=.001) and serine (P=.001) serum levels. Glycine administration resulted in (1) a significant (P<.001) 30%+/-16% reduction in negative symptoms, as measured by the PANSS, and (2) a significant (P<.001) 30%+/-18% improvement in the BPRS total scores. The improvement in negative symptoms was unrelated to alterations in extrapyramidal effects or symptoms of depression. Low pretreatment glycine serum levels significantly predicted (r= 0.80) clinical response.
                These findings support hypoglutamatergic hypotheses of schizophrenia and suggest a novel approach for the pharmacotherapy of negative symptoms associated with this illness. Dysfunction of N-methyl-D-aspartate (NMDA) receptor-mediated glutamatergic neurotransmission may be relevant to the pathogenesis of negative symptoms in schizophrenia. The tuberculostatic compound D-cycloserine (DCS) acts as a partial agonist at the strychnine-insensitive glycine regulatory site on the NMDA receptor complex. Dose-finding trials suggest that DCS doses of 50-100 mg/d may be beneficial in the treatment of negative symptoms in schizophrenia. Nine treatment-resistant chronic schizophrenic patients participated in a double-blind, placebo-controlled, adjuvant treatment trial with 50 mg/d DCS. Between treatment-groups differences in symptom changes were not significant. However, a significant (p<0.05) reduction in negative symptoms was registered during treatment with DCS but not placebo. Greater reductions were registered in patients with lower baseline serum glycine levels (p<0.008). No side effects were registered. These preliminary findings indicate a potential role of DCS in the treatment of negative symptoms in schizophrenia. However, the degree of symptom reduction may be modest, at least among treatment-resistant inpatients. Hypofunction of N-methyl-D-aspartate (NMDA) subtype glutamate receptor has been implicated in the pathophysiology of schizophrenia. D-serine is a full agonist of the glycine site of NMDA receptor, an endogenous cotransmitter enriched in corticolimbic regions and distributed in parallel with NMDA receptor. Supplementation of D-serine may improve the symptoms of schizophrenia.
                Thirty-one Taiwanese schizophrenic patients enrolled in a 6-week double-blind, placebo-controlled trial of D-serine (30 mg/kg/day), which was added to their stable antipsychotic regimens. Of these, 28 completed the trial. Measures of clinical efficacy, side effects, and serum levels of amino acids and D-serine were determined every other week. Wisconsin Card Sorting Test (WCST) was performed at the beginning and end of the trial.
                Patients who received D-serine treatment revealed significant improvements in their positive, negative, and cognitive symptoms as well as some performance in WCST. D-serine levels at week 4 and 6 significantly predicted the improvements. D-serine was well tolerated and no significant side effects were noted.
                The significant improvement with the D-serine further supports the hypothesis of NMDA receptor hypofunction in schizophrenia. Given the effects of D-serine on positive symptoms, a trial of D-serine alone in schizophrenia should be considered. There is no evidence from randomized, controlled trials that demonstrate effectiveness for any pharmacological treatment in clozapine-resistant schizophrenia. Since the introduction of chlorpromazine, all antipsychotics with proven efficacy on positive symptoms have been dopamine antagonists, but recent experimental data suggest that ketamine-induced positive schizophreniform symptoms in healthy subjects can be controlled by a glutamate antagonist lamotrigine. The hypothesis tested was that lamotrigine is more effective than placebo in the treatment of positive schizophrenic symptoms when combined with clozapine.
                Thirty-four hospitalized treatment-resistant patients having chronic schizophrenia participated in a double-blind, placebo-controlled, 14-week, crossover trial where 200 mg/day lamotrigine was gradually added to their ongoing clozapine treatment. Clinical assessments were made by the Positive and Negative Syndrome Scale at the beginning and end of each treatment period.
                In intention-to-treat analysis, lamotrigine treatment was more effective in reducing positive (effect size.7, p =.009) and general psychopathological (effect size.6, p =.030) symptoms, whereas no improvement was observed in negative symptoms.
                These results provide the first evidence from a randomized controlled trial of an effective pharmacological treatment with an anticonvulsant agent in treatment-resistant schizophrenia and indicate that both positive and general psychopathological symptoms in patients with schizophrenia can be controlled by a drug that is not a dopamine antagonist. The results are in line with previous experimental data suggesting that excessive glutamate neurotransmission contributes to the positive symptoms of schizophrenia. The focus of this study was the systematic evaluation of the clinical effects of glycine as an adjunct to the atypical antipsychotic clozapine in the treatment of schizophrenia.
                In a double-blind, placebo-controlled study, 19 patients with chronic, treatment-resistant schizophrenia who were maintained on optimal doses of clozapine (400-1200 mg/day) were administered either 30 g/day of glycine (N=9) or placebo (N=10) for 12 weeks. Clinical evaluations with the Brief Psychiatric Rating Scale, the Scale for the Assessment of Negative Symptoms, and the Simpson-Angus movement scale were completed biweekly.
                The use of glycine as an adjunct to clozapine was not effective in decreasing positive or negative symptoms. In contrast, the patients treated with clozapine without glycine had a 35% reduction in positive symptoms.
                These preliminary data suggest that glycine may interfere with the antipsychotic efficacy of atypical neuroleptics such as clozapine. Glycine is an agonist at brain N-methyl-D-aspartate receptors and crosses the blood-brain barrier following high-dose oral administration. In a previous study, significant improvements in negative and cognitive symptoms were observed in a group of 21 schizophrenic patients receiving high-dose glycine in addition to antipsychotic treatment. This study evaluated the degree to which symptom improvements might be related to alterations in antipsychotic drug levels in an additional group of 12 subjects. Glycine treatment was associated with an 8-fold increase in serum glycine levels, similar to that observed previously. A significant 34% reduction in negative symptoms was observed during glycine treatment. Serum antipsychotic levels were not significantly altered. Significant clinical effects were observed despite the fact that the majority of subjects were receiving atypical antipsychotics (clozapine or olanzapine). As in earlier studies, improvement persisted following glycine discontinuation. Lamotrigine, a novel anticonvulsant drug having modulatory effects on glutamatergic neurotransmission, improves mood and cognition parameters in bipolar disorder. Recent studies suggest that when added to clozapine, lamotrigine treatment may result in significant positive symptoms reductions in schizophrenia. Similar effects were not observed in an open trial in which lamotrigine was used as adjuvant to nonclozapine antipsychotics.
                Thirty-eight treatment-resistant schizophrenia inpatients receiving conventional and atypical antipsychotics enrolled in a 10-week, double-blind, placebo-controlled study, in which they were randomized in a 2:1 ratio to receive adjuvant treatment with lamotrigine, gradually titrated to a 400 mg/day dose, or placebo. Of these, 31 completed the trial. Measures of clinical efficacy and side effects were determined every other week. Serum levels of amino acids were assessed at the beginning and end of the study.
                In primary last observation carried forward analysis, no statistically significant between-group differences were observed; however, the completers' analyses revealed that lamotrigine treatment resulted in significant (p < or = .05) reductions in positive and general psychopathology symptoms, as measured by the Positive and Negative Syndrome Scale. No significant differences in lamotrigine effects were noted between conventional versus atypical antipsychotics. Lamotrigine treatment was well tolerated, and glutamate serum levels remained stable throughout the study.
                These preliminary findings 1) support the hypothesis that lamotrigine adjuvant treatment may improve positive symptoms and general psychopathology in schizophrenia, 2) suggest that beneficial effects may be achieved when lamotrigine is added to both conventional and atypical antipsychotics, and 3) warrant additional, larger scale trials. The purpose of this study was to evaluate the effects of high-dose oral glycine on positive and negative symptoms and cognitive function when added to clozapine in adults with schizophrenia.
                The authors conducted a double-blind, placebo-controlled, parallel-group trial of 60 g/day of glycine added to clozapine for 8 weeks in 30 adults with schizophrenia. Clinical ratings were performed every 2 weeks.
                Twenty-seven patients completed the trial. Glycine augmentation of clozapine produced no statistically significant change in positive or negative symptoms or cognitive functioning. No subjects showed clinically significant worsening of clinical ratings.
                These data, combined with data from previous trials with D-cycloserine and glycine, suggest that agonists at the glycine site may be less effective when combined with clozapine than they are when combined with conventional antipsychotics. D-Serine is a full agonist at the glycine site on the N-methyl-D-aspartate (NMDA) receptor. Previous administration of D-serine to schizophrenic patients taking nonclozapine antipsychotics improved positive, negative, and cognitive symptoms, whereas the partial agonist D-cycloserine improved negative symptoms of patients taking conventional antipsychotics but worsened symptoms in clozapine-treated patients. To study the difference between full and partial agonists at the NMDA receptor glycine site, the clinical effects of adding D-serine to clozapine were assessed.
                In a 6-week double-blind trial, 20 schizophrenic patients received placebo or D-serine (30 mg/kg per day) in addition to clozapine. Clinical efficacy, side effects, and serum levels of D-serine were determined every other week.
                The patients exhibited no improvement with D-serine, nor did their symptoms worsen, as previously reported with D-cycloserine.
                The results suggest either that clozapine may have an agonistic effect on the NMDA system or that clozapine-treated patients do not respond to D-serine.
In general, all glutamatergic drugs appeared to be ineffective in further reducing positive symptoms of the disease when added to the existing antipsychotic treatment. Glycine and D-serine may somewhat improve negative symptoms when added to regular antipsychotic medication, but the results were not fully consistent and data are too few to allow any firm conclusions. Many participants in the included trials were treatment-resistant which may have reduced treatment response. Additional research on glutamatergic mechanisms of schizophrenia is needed.