Ziprasidone metabolism, aldehyde oxidase, and clinical implications

An in vitro approach to detect metabolite toxicity due to CYP3A4-dependent bioactivation of xenobiotics

Many adverse drug reactions are caused by the cytochrome P450 (CYP) dependent activation of drugs into reactive metabolites. In order to reduce attrition due to metabolism-mediated toxicity and to improve safety of drug candidates, we developed two in vitro cell-based assays by combining an activating system (human CYP3A4) with target cells (HepG2 cells): in the first method we incubated microsomes containing cDNA-expressed CYP3A4 together with HepG2 cells; in the second approach HepG2 cells were transiently transfected with CYP3A4. In both assay systems, CYP3A4 catalyzed metabolism was found to be comparable to the high levels reported in hepatocytes. Both assay systems were used to study ten CYP3A4 substrates known for their potential to form metabolites that exhibit higher toxicity than the parent compounds. Several endpoints of toxicity were evaluated, and the measurement of MTT reduction and intracellular ATP levels were selected to assess cell viability. Results demonstrated that both assay systems are capable to metabolize the test compounds leading to increased toxicity, compared to their respective control systems. The co-incubation with the CYP3A4 inhibitor ketoconazole confirmed that the formation of reactive metabolites was CYP3A4 dependent. To further validate the functionality of the two assay systems, they were also used as a "detoxification system" using selected compounds that can be metabolized by CYP3A4 to metabolites less toxic than their parent compounds. These results show that both assay systems can be used to screen for metabolic activation, or de-activation, which may be useful as a rapid and relatively inexpensive in vitro assay for the prediction of CYP3A4 metabolism-mediated toxicity.

Best clinical practice with ziprasidone IM: update after 2 years of experience

Acute agitation is a common psychiatric emergency often treated with intramuscular (i.m.) medication when rapid control is necessary or the patient refuses to take an oral agent. Conventional i.m. antipsychotics are associated with side effects, particularly movement disorders, that may alarm patients and render them unreceptive to taking these medications again. Ziprasidone (Geodon) is the first second-generation, or atypical, antipsychotic to become available in an i.m. formulation. Ziprasidone IM was approved by the Food and Drug Administration in 2002 for the treatment of agitation in patients with schizophrenia. In October 2004, a roundtable panel of physicians with extensive experience in the management of acutely agitated patients met to review the first 2 years of experience with this agent. This monograph, a product of that meeting, discusses clinical experience to date with ziprasidone IM and offers recommendations on its use in various settings. In clinical trials, patients treated with ziprasidone IM demonstrated significant and rapid (within 15-30 minutes) reduction in agitation and improvement in psychotic symptoms, agitation, and hostility to an extent greater than or equal to that attained with haloperidol i.m. Tolerability of ziprasidone IM was superior to that of haloperidol IM, with a lower burden of movement disorders. Clinical trials have also shown that ziprasidone IM can be administered with benzodiazepines without adverse consequences. Transition from i.m. to oral ziprasidone has been well tolerated, with maintenance of symptom control. The most common adverse events associated with ziprasidone IM were insomnia, headache, and dizziness in fixed-dose trials and insomnia and hypertension in flexible-dose trials. No consistent pattern of escalating incidence of adverse events with escalating ziprasidone doses has been observed. Changes in QTc interval associated with ziprasidone at peak serum concentrations are modest and comparable to those seen with haloperidol IM. Results of randomized clinical trials of ziprasidone IM have been corroborated in studies in real-world treatment settings involving patients with extreme agitation or a recent history of alcohol or substance abuse. In these circumstances, clinically significant improvement was seen within 30 minutes of ziprasidone IM administration, without regard to the suspected underlying etiology of agitation. Agents with a good safety/tolerability profile, such as ziprasidone IM, may be more cost effective long term than older agents, due to reduced incidence of acute adverse effects (eg, acute dystonia) that often require extended periods of observation. Additional trials of ziprasidone IM in agitated patients in a variety of clinical setting are warranted to generate comparative risk/benefit data with conventional agents and other second-generation antipsychotics.

The dosing of atypical antipsychotics

Drug-drug interactions or genetic variability may require using doses different from those recommended for atypical antipsychotics. Dosage alterations of olanzapine and clozapine, dependent on cytochrome P450 1A2 (CYP1A2) for clearance, and quetiapine, dependent on cytochrome P450 3A (CYP3A), may be necessary when used with other drugs that inhibit or induce their metabolic enzymes. Smoking cessation can significantly increase clozapine, and perhaps olanzapine, levels. Ziprasidone pharmacokinetic drug-drug interactions are not likely to be important. Genetic variations of cytochrome P450 2D6 (CYP2D6) and drug-drug interactions causing inhibition (CYP2D6 and/or CYP3A) or induction (CYP3A) may be important for risperidone, and perhaps for aripiprazole, dosing. Adding inhibitors may cause side effects more easily in drugs with a narrow therapeutic window, such as clozapine or risperidone, than in those with a wide therapeutic window, such as olanzapine or aripiprazole. Adding inducers may be associated with a gradual development of lost efficacy.

Expert Canadian consensus suggestions on the rational, clinical use of ziprasidone in the treatment of schizophrenia and related psychotic disorders

Many atypical antipsychotic medications are becoming available for clinical use. Ziprasidone is a recent addition to this group and is expected to become available for clinical use in Canada in 2005. Ziprasidone has some significant differences compared with other atypicals currently available in Canada. Clinicians need to understand the benefits and risks associated with each of the antipsychotic medications available for the treatment of schizophrenia and related psychotic disorders to ensure their most appropriate utilization. At the suggestion of Professor Stan Kutcher (chair) and as part of an ongoing commitment to provide independent education pertaining to the utility of new psychotropic compounds to health professionals, a panel of Canadian experts in the treatment of schizophrenia spectrum disorders was convened to provide consensus suggestions for the appropriate clinical use of ziprasidone. The consultations regarding the development of these recommendations were organized by Brainworks International (BWI) with arms-length funding from Pfizer Canada. This paper describes the experts' consensus views on the efficacy and safety of ziprasidone, their suggestions on which patients may be suitable for ziprasidone treatment, and how to initiate treatment (including how to switch from other antipsychotic medications), manage side effects, and monitor patients in long-term therapy. These suggestions are those of the authors only and are not endorsed by or necessarily reflect the opinions of BWI or Pfizer Canada.

Switching atypical antipsychotics: a review

BACKGROUND

Atypical antipsychotics are increasingly used in the treatment of diverse psychiatric disorders; however, there is little information on the 'why, when, and how' of switching between the different atypical antipsychotics currently available.

OBJECTIVE

To review the data on switching and atypical antipsychotics.

METHODS

A literature search was initially conducted using the key words followed by a search of relevant articles including conference abstracts; relevant pharmaceutical companies were also contacted.

RESULTS

Clinical trial data are limited in terms of parameters measured, and case reports describe specific problems. Few studies are based on real world populations of psychiatric patients over the long-term. Careful patient and drug selections matched to a carefully supervised and appropriate cross titration based upon the pharmacodynamic and pharmacokinetic properties of all of the drugs involved is important to avoid potential complications such as re-emergence or worsening of psychosis and withdrawal, rebound, and emergent phenomena including new or uncovered side-effects. Psychoeducation and involvement of patients and caregivers in the process are also necessary for a successful switch.

CONCLUSION

Despite the prevalence of switching in real world clinical practice, there is a paucity of data to guide clinicians with respect to effective and safe strategies. There are no criteria defining a successful switch. With the increasing range and formulations of atypical antipsychotics available, there is a rationale for their early use to avoid the practical problems associated with switching from conventional antipsychotics as well as the opportunity to maintain patients on an optimal atypical antipsychotic monotherapy.

A randomized evaluation of the effects of six antipsychotic agents on QTc, in the absence and presence of metabolic inhibition

Many drugs have been associated with QTc prolongation and, in some cases, this is augmented by concomitant administration with metabolic inhibitors. The effects of 6 antipsychotics on the QTc interval at and around the time of estimated peak plasma/serum concentrations in the absence and presence of metabolic inhibition were characterized in a prospective, randomized study in which patients with psychotic disorders reached steady-state on either haloperidol 15 mg/d (n = 27), thioridazine 300 mg/d (n = 30), ziprasidone 160 mg/d (n = 31), quetiapine 750 mg/d (n = 27), olanzapine 20 mg/d (n = 24), or risperidone 6-8 mg/d increased to 16 mg/d (n = 25/20). Electrocardiograms (ECGs) were done at estimated Cmax at steady-state on both antipsychotic monotherapy and after concomitant administration of appropriate cytochrome P-450 (CYP450) inhibitor(s). Mean QTc intervals did not exceed 500 milliseconds in any patient taking any of the antipsychotics studied, in the absence or presence of metabolic inhibition. The mean QTc interval change was greatest in the thioridazine group, both in the presence and absence of metabolic inhibition. The presence of metabolic inhibition did not significantly augment QTc prolongation associated with any agent. Each of the antipsychotics studied was associated with measurable QTc prolongation at steady-state peak plasma concentrations, which was not augmented by metabolic inhibition. The theoretical risk of cardiotoxicity associated with QTc prolongation should be balanced against the substantial clinical benefits associated with atypical antipsychotics and the likelihood of other toxicities.