Ziprasidone chemical structure
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Ziprasidone

Ziprasidone (Geodon®) was the fifth atypical antipsychotic to gain FDA approval. Ziprasidone is FDA approved for the treatment of schizophrenia, and the intramuscular injection form of ziprasidone is approved for acute agitation in schizophrenic patients. Clinical trials were conducted in acute cases of mania. Long-term trials have not been conducted for acute bipolar symptoms. Any "hypersensitivity to the product" -- including any of the adverse events noted during clinical trials-- should be grounds for discontinuance. It has been approved for acute episodes indicative of bipolar type I. It has not been studied in adolescents or children (under age 10). more...

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Such a trial has been ordered by the FDA as one condition during the approval process. The brand name (Geodon®) has been suggested to bring to mind the phrase 'down (don) to earth (geo)' referring to the goals of medication.

Pharmacology

Ziprasidone has a high affinity for dopamine, serotonin, and alpha-adrenergic receptors and a medium affinity for histaminic receptors. Ziprasidone is somewhat unique among the "atypicals" in that it also displays some inhibition of synaptic reuptake of serotonin and norepinephrine, although the clinical significance of this is unknown. The mechanism of action of ziprasidone is unknown. However it is theorized that its antipsychotic activity is mediated primarily by antagonism at dopamine receptors, specifically D2. Serotonin antagonism may also play a role in the effectiveness of ziprasidone, but the significance of 5-HT2A antagonism is debated among researchers. Antagonism at histaminic and alpha adrenergic receptors likely explains some of the side effects of ziprasidone, such as sedation and orthostasis.

Pharmacokinetics

The systemic bioavailability of ziprasidone administered intramuscularly is 100%, or 60%, administered orally with food. After a single dose intramuscular administration, the peak serum concentration typically occurs at about 60 minutes after the dose is administered, or earlier. Steady state plasma concentrations are achieved within one to three days. The mean half-life (T 1/2) ranges from two to five hours. Exposure increases in a dose-related manner and following three days of intramuscular dosing, little accumulation is observed.

Metabolism

Ziprasidone is hepatically metabolized by aldehyde reductase. Minor metabolism occurs via cytochrome P450 3A4. Medication that induce (e.g carbamazepine) or inhibit (e.g. ketoconazole) CYP3A4 have been shown to decrease and increase, respectively, blood levels of ziprasidone. There are no known induces or inhibitors of aldehyde reductase.

Adverse Events

Ziprasidone may increase the QTc interval in some patients and may increase the risk of a type of heart arrythmia known as torsades de pointes. Ziprasidone should be used cautiously in patients taking other medications likely to interact with ziprasidone or increase the QTc interval.

Adverse events reported for ziprasidone include sedation, insomnia, orthostasis, akathisia and other permanent extrapyramidal side-effects such as tardive dyskinesia. Rarely, temporary speech disorders may result.

The medication can cause any conceivable side effect. See the FDA label for more information.

Recently, the FDA required the manufacturers of all atypical antipsychotics to include a warning about the risk of hyperglycemia and Type II diabetes with atypical antipsychotics. Some evidence suggests that ziprasidone may not be as bad as some of the other atypical antipsychotics at causing insulin resistance and weight gain. In fact, in a trial of long term therapy with ziprasidone, overweight patients (BMI>27) actually had a mean weight loss overall. Ziprasidone, though, is not a weight loss drug. The weight loss reflected in this study on ziprsidone was really reflective of patients who had gained weight on other antipsychotics who were now trending back toward their baseline.

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Ziprasidone: Test your drug IQ
From Nursing, 11/1/03 by Gever, Marcy Portnoff

This drug for schizophrenia may help a patient who hasn't responded to other antipsychotics.

Treating schizophrenia usually requires lifelong use of an antipsychotic; once the medication is stopped, symptoms usually recur. Ziprasidone (Geodon), an atypical antipsychotic that helps to manage symptoms of schizophrenia, is given orally or via intramuscular (I.M.) injection. The injectable form is used for control of acute agitation.

Q. What's the usual dosage for ziprasidone?

A. Ziprasidone is available as capsules (20 mg, 40 mg, 60 mg, and 80 mg) for oral administration and as a 20-mg/ml solution for I.M. injection.

The initial oral dosage is 20 mg twice daily with food. The dosage may be increased at intervals of 2 days or more, up to a maximum of 80 mg twice daily (although dosages of 100 mg twice daily have been used in some cases).

The dosage for I.M. injection is 10 mg every 2 hours or 20 mg every 4 hours, up to a maximum of 40 mg/day.

Q. What are the possible adverse reactions?

A. The most common adverse reactions associated with ziprasidone are somnolence, dizziness, orthostatic hypotension, nausea, constipation, rash, rhinitis, tremor, and tardive dyskinesia (involuntary muscle movements). Unlike other atypical antipsychotics, ziprasidone usually doesn't cause weight gain.

A less common but serious adverse reaction associated with ziprasidone is torsades de pointes, a potentially fatal cardiac arrhythmia resulting from a prolonged QT interval. Because of this dangerous possibility, ziprasidone isn't a first-line treatment for patients with schizophrenia; it's reserved for patients who haven't responded to other antipsychotics.

Q. What precautions and contraindications should I know about?

A. Assess patients for any increased risk of QT prolongation before administering ziprasidone. Use ziprasidone with caution in patients with a history of hypokalemia, hypomagnesemia, or cardiac arrhythmias such as bradycardia, which may increase their risk of QT prolongation.

Ziprasidone is contraindicated in patients with a history of QT prolongation (including congenital long QT syndrome), recent acute myocardial infarction, uncompensated heart failure, and in those who are taking other medications that can prolong the QT interval. Ziprasidone also is contraindicated in patients with a known hypersensitivity to the drug.

Q. What other drugs may prolong the QT interval?

A. The following drugs prolong the QT interval and shouldn't be given with ziprasidone:

* antiarrhythmics: dofetilide, sotalol, and quinidine

* antipsychotics: mesoridazine, thioridazine, chlorpromazine, and pimozide, and the sedative droperidol.

* quinolone antibiotics: sparfloxacin, gatifloxacin, and moxifloxacin

* antimalanal drugs: halofantrine and mefloquine

* miscellaneous drugs, such as pentamidine, dolasetron, levomethadyl, probucol, tacrolimus, and arsenic trioxide.

Q. What other drug interactions should I watch out for?

A. Ziprasidone may antagonize the effects of levodopa and dopamine agonists such as pramipexole, ropinirole, bromocriptine, or pergolide. Monitor your patient for new symptoms of Parkinsons disease or symptoms that seem to be getting worse.

Ziprasidone also may enhance the effects of anti-hypertensive drugs, so monitor your patient's blood pressure and warn her to sit up or stand up slowly to avoid orthostatic hypotension.

SELECTED REFERENCES

American Hospital Formulary Service. Bethesda, Md., American Hospital Formulary Service, 2002.

Nursing 2004 Drug Handbook, 24th edition. Philadelphia, Pa., Lippincott Williams & Wilkins, 2004.

Physicians' Desk Reference, 57th edition. Montvale, N.J., Medical Economics Co., Inc., 2003.

By Marcy Portnoff Gever, RPh, MEd

Marcy Portnoff Gever is an independent pharmacist consultant and educator in Ringoes, N.J.

Copyright Springhouse Corporation Nov 2003
Provided by ProQuest Information and Learning Company. All rights Reserved

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