Dolasetron

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