5HT-3 Antagonists in Obstetrics/Gynecology Patients


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5HT-3 Antagonists in Obstetrics/Gynecology Patients

Background

Nausea and vomiting (N/V) is a common problem in pregnancy, with the majority of causes being mild in nature and not requiring treatment with an antiemetic. However, some women can experience persistent vomiting which can cause harm to the fetus if not controlled. In these cases, treatment with an antiemetic agent is necessary. Antiemetics traditionally used in pregnancy include doxylamine plus pyridoxine, promethazine, prochlorperazine, droperidol, and metoclompramide. In refractory cases of N/V that do not respond to the traditional treatment, physicians have recently begun using the 5HT-3 antagonists (particularly Zofran^Ž). There is relatively little experience with these agents in pregnancy, but they have shown effectiveness in other patient populations with refractory N/V and their pregnancy category B status gives them a favorable benefit versus risk profile. Again, these agents should not be used as first line therapy in this population, but they do provide a viable alternative in cases that do not respond to traditional therapy.

Cost Implications

The following table includes a cost comparison of equivalent doses of the 5HT-3 antagonists. Assuming a usage rate of 8 doses per month (approximately 96 doses per year), the annual cost implications would be as follows.

5HT-3 Antagonist	Cost Per Dose ($)	Resulting Annual Cost ($)
Granisetron 1 mg IV	92.07	8838.72
Ondansetron 4 mg IV	16.17	1552.32
Dolasetron 12.5 mg IV	9.63	924.48

Guidelines

1. OB/GYN has been added to the list of approved services for prescribing 5HT-3
    antagonists. These drugs may be used for management of patients who have nausea/
    vomiting refractory to traditional agents. Agents to be used before Anzemet (dolasetron)
    should be:

              Phenergan (promethazine)
              Compazine (prochlorperazine)
              Inapsine (droperidol)
              Diclectin(doxylamine plus pyridoxine)

(If all of these agents are used and are ineffective, dolasetron can be used at 12.5mg IV)

2. Dolasetron is the 5HT-3 antagonist of choice for OB/GYN patients via the IV route at a
dose of 12.5mg.

References:

1. Briggs GG, Freeman RK, Yaffe SJ, ed. Drugs in Pregnancy and Lactation, 5^th ed.
    Baltimore, MD: Williams and Wilkins, 1998.

2. Koren G, Pastuszak A, Ito S. Drugs in Pregnancy. N Engl J Med 1998;338(16):1128-37.

3. Nelson-Piercy C. Treatment of nausea and vomiting in pregnancy. When should it be
    treated and what can be safely taken? Drug Saf 1998 Aug;19(2):155-64.

4. DiPalma JR. Drugs for nausea and vomiting of pregnancy. Am Fam Physician 1983
    Oct;28(4):272-4.

_________________________________________________________________________________________________________
Approved by P&T Committee | Posted on: 8/02 | For Internal University of Kentucky Chandler Medical Center Use Only

Comments to Kelly Smith, Pharm.D., Last Modified: August 13, 2006
Copyright Š 2002, University of Kentucky Chandler Medical Center
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