Clozapine drug administration

To date, clozapine remains the only drug with proven and superior efficacy in treatment-resistant patients, and it is currently the only drug approved for the treatment-resistant schizophrenic. Studies have shown a response of approximately 30% to 50% in these well-defined treatment-resistant patients. Clinical trials have consistently found clozapine to be superior to traditional antipsychotics for treatment-refractory patients, and it is efficacious even after nonresponse to other SGAs and in partially responsive patients. It is often rapidly effective even in those who have had a poor response to other medication for years. Recent studies have demonstrated that it has a beneficial effect for aggression and suicidality, which led to the Food and Drug Administration (FDA) approval for the treatment of suicidal behavior in people with psychosis.41... 

Pharmacotherapy is the cornerstone of acute and maintenance treatment of bipolar disorder. Mood-stabilizing drugs are the usual first-choice treatments and include lithium, divalproex, carbamazepine, and lamotrigine. Atypical antipsychotics other than clozapine are also approved for treatment of acute mania. Lithium, lamotrigine, olanzapine, and aripiprazole are approved for maintenance therapy. Drugs used with less research support and without Food and Drug Administration (FDA) approval include topiramate and oxcarbazepine. Benzodiazepines are used adjunctively for mania. 

Risperdal was first marketed in 1994 as an atypical neuroleptic. The clinical trials, most of which lasted a few weeks, were too short to determine the rate of tardive dyskinesia and many other adverse effects. Indeed, the brief controlled clinical trials used for the approval of both clozapine and risperidone do not provide sufficient information to determine either efficacy or safety since the drugs would be used for months and years in individual patients, rather than for a few weeks (see chapter 13). Patients taking the medications over the coming years will provide the experimental data. However, since Risperdal is a potent dopamine blocker, it should have been anticipated that it would cause similar adverse reactions as the older neuroleptics. In my own experience, I have evaluated many cases of tardive dyskinesia caused by Risperdal, Zyprexa, and Geodon. Meanwhile, the Food and Drug Administration (FDA) has required the same tardive dyskinesia and neuroleptic malignant syndrome warnings on the labels of clozapine and risperidone as on the labels of the older neuroleptics. 

US Food and Drug Administration http www.fda.gov/cder/drug/infopage/clozapine.htm(3/8/01) [NB this webpage no longer exists].. 

Hypotension is the most commonly observed cardiovascular adverse effect of neuroleptic drugs, particularly after administration of those that are also potent alpha-adrenoceptor antagonists, such as chlorpromazine, thioridazine, and clozapine (34). A central mechanism involving the vasomotor regulatory center may also contribute to the lowering of blood pressure. 

Lane HY, Chiu CC, Kazmi Y, Desai H, Lam YW, Jann MW, Chang WH. Lack of CYP3A4 inhibition by grapefruit juice and ketoconazole upon clozapine administration in vivo. Drug Metabol Drug Interact 2001 18(3— 4) 263—78. 

Because of the frequency of co-administration of benzodiazepines with neuroleptic drugs, it is important to consider possible adverse effects that can result from such combinations. In a brief review, emphasis has been placed on pharmacokinetic interactions between neuroleptic drugs and benzodiazepines, as much information on their metabolic pathways is emerging (166). Thus, the enzyme CYP3A4, which plays a dominant role in the metabolism of benzodiazepines, also contributes to the metabolism of clozapine, haloperidol, and quetiapine, and neuroleptic drug plasma concentrations can rise. Intramuscular levomepromazine in combination with an intravenous benzodiazepine has been said to increase the risk of airways obstruction, on the basis of five cases of respiratory impairment the doses of levomepromazine were higher in the five cases that had accompanying airways obstruction than in another 95 patients who did not (167). 

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