Effects of carbamazepine and valproate on haloperidol plasma levels and on psychopathologic outcome in schizophrenic patients

Allopurinol augmentation for poorly responsive schizophrenia

Adenosine has been proposed to contribute to the pathophysiology of schizoprenia and as a target for therapeutic intervention. In the lack of direct adenosine agonists, allopurinol may indirectly elevate adenosine levels by inhibiting degradation of purines. We report two cases of poorly responsive schizophrenic patients who improved considerably with add-on allopurinol 300 mg/day. Their clear clinical improvement warrant further investigation of allopurinol, as well as other purinergic strategies, for the treatment of schizophrenia.

Valproate as an adjunct to neuroleptic medication for the treatment of acute episodes of mania: a prospective, randomized, double-blind, placebo-controlled, multicenter study. European Valproate Mania Study Group

To compare the efficacy of sodium valproate administered as adjunct to neuroleptic medication for patients with acute mania with the efficacy of neuroleptics alone, the authors conducted a 21-day, randomized, double-blind, parallel-group, placebo-controlled trial. The study design closely reflected a clinical psychiatric setting in Europe where patients with acute mania commonly receive neuroleptic medication. In this trial, 136 hospitalized patients met the ICD-10 criteria for acute manic episodes; these patients received a fixed dose of 20 mg/kg of body weight of sodium valproate (Orfiril, Desitin Arzneimittel GmbH, Hamburg, Germany) orally, in addition to basic neuroleptic medication, preferably haloperidol and/or perazine. The primary outcome measure was the mean dose of neuroleptic medication (after conversion into haloperidol-equivalents) for the 21-day study period. Severity of symptoms was measured using the Young Mania Rating Scale (YMRS), the Global Assessment Scale, and the Clinical Global Impression Scale. Intent-to-treat analysis was based on 69 patients treated with valproate and 67 patients who received placebo. Groups were comparable with regard to demographic and clinical baseline data. Premature discontinuations occurred in only 13% of the patients. The mean neuroleptic dose declined continuously in the valproate group, whereas only slight variations were observed in the placebo group; the difference was statistically significant (p = 0.0007) for study weeks 2 and 3. The combination of neuroleptic and valproate proved superior to neuroleptics in attempts to alleviate manic symptoms. The proportion of responders (a 50% improvement rate shown on the YMRS) was higher for the combination with valproate than for the group receiving only neuroleptics (70% vs. 46%; p = 0.005). Adverse events consisted of those known for valproate or neuroleptics; the only adverse event was asthenia, which occurred more frequently with the combination therapy. Valproate represents a useful adjunct medication for the treatment of acute manic symptoms. Valproate is beneficial because it allows the administration of fewer neuroleptic medications and produces improved and quicker remission of manic symptoms.

Pharmacokinetics of haloperidol: an update

Haloperidol is commonly used in the therapy of patients with acute and chronic schizophrenia. The enzymes involved in the biotransformation of haloperidol include cytochrome P450 (CYP), carbonyl reductase and uridine diphosphoglucose glucuronosyltransferase. The greatest proportion of the intrinsic hepatic clearance of haloperidol is by glucuronidation, followed by the reduction of haloperidol to reduced haloperidol and by CYP-mediated oxidation. In studies of CYP-mediated disposition in vitro, CYP3A4 appears to be the major isoform responsible for the metabolism of haloperidol in humans. The intrinsic clearances of the back-oxidation of reduced haloperidol to the parent compound, oxidative N-dealkylation and pyridinium formation are of the same order of magnitude, suggesting that the same enzyme system is responsible for the 3 reactions. Large variation in the catalytic activity was observed in the CYP-mediated reactions, whereas there appeared to be only small variations in the glucuronidation and carbonyl reduction pathways. Haloperidol is a substrate of CYP3A4 and an inhibitor, as well as a stimulator, of CYP2D6. Reduced haloperidol is also a substrate of CYP3A4 and inhibitor of CYP2D6. Pharmacokinetic interactions occur between haloperidol and various drugs given concomitantly, for example, carbamazepine, phenytoin, phenobarbital, fluoxetine, fluvoxamine, nefazodone, venlafaxine, buspirone, alprazolam, rifampicin (rifampin), quinidine and carteolol. Overall, drug interaction studies have suggested that CYP3A4 is involved in the biotransformation of haloperidol in humans. Interactions of haloperidol with most drugs lead to only small changes in plasma haloperidol concentrations, suggesting that the interactions have little clinical significance. On the other hand, the coadministration of carbamazepine, phenytoin, phenobarbital, rifampicin or quinidine affects the pharmacokinetics of haloperidol to an extent that alterations in clinical consequences would be expected. In vivo pharmacogenetic studies have indicated that the metabolism and disposition of haloperidol may be regulated by genetically determined polymorphic CYP2D6 activity. However, these findings appear to contradict those from studies in vitro with human liver microsomes and from studies of drug interactions in vivo. Interethnic and pharmacogenetic differences in haloperidol metabolism may explain these observations.