Ondansetron

INTRODUCTION

Indications

Prevention of nausea and vomiting associated with chemotherapy or radiation therapy. IM, IV: Prevention and treatment of postoperative nausea and vomiting.

Action

Blocks the effects of serotonin at 5-HT₃ receptor sites (selective antagonist) located in vagal nerve terminals and the chemoreceptor trigger zone in the CNS. Therapeutic Effects: Decreased incidence and severity of nausea and vomiting following chemotherapy or surgery.

Adverse Reactions/Side Effects

CNS: headache, dizziness, drowsiness, fatigue, weakness. GI: constipation, diarrhea, abdominal pain, dry mouth, increased liver enzymes. Neuro: extrapyramidal reactions.

PHYSICAL THERAPY IMPLICATIONS

Examination and Evaluation

• Monitor improvements in GI symptoms (decreased nausea and vomiting, increased appetite) to help document whether drug therapy is successful.

• Assess motor function, and report any extrapyramidal reactions. Common extrapyramidal symptoms include:

  • ∘ Tardive dyskinesia (uncontrolled rhythmic movement of mouth, face, and extremities, lip smacking or puckering, puffing of cheeks, uncontrolled chewing, rapid or worm-like movements of tongue).

  • ∘ Pseudoparkinsonism (shuffling gait, rigidity, tremor, pill-rolling motion, loss of balance control, difficulty speaking or swallowing, masklike face).

  • ∘ Akathisia (restlessness or desire to keep moving).

  • ∘ Other dystonias and dyskinesias (dystonic muscle spasms, twisting motions, twitching, inability to move eyes, weakness of arms or legs).

• Assess dizziness and drowsiness that might affect gait, balance, and other functional activities (see Appendix C). Report balance problems and functional limitations to the physician and nursing staff, and caution the patient and family/caregivers to guard against falls and trauma.

Patient/Client-Related Instruction

• Instruct patient to report bothersome side effects such as severe or prolonged headache, weakness, fatigue, or GI problems (diarrhea, constipation, abdominal pain, dry mouth).

Pharmacokinetics

Absorption: IV administration results in complete bioavailability; 50% absorbed following oral administration.

Distribution: Unknown.

Metabolism and Excretion: Extensively metabolized by the liver; 5% excreted unchanged by the kidneys.

Half-life: 3.5–5.5 hr.

Contraindications/Precautions

Contraindicated in: Hypersensitivity; Orally disintegrating tablets contain aspartame and should not be used in patients with phenylketonuria.

Use Cautiously in: Liver impairment (daily dose not to exceed 8 mg); Abdominal surgery (may mask ileus); OB/Pedi: Pregnancy, lactation, or children ≤3 yr (safety not established).

Interactions

Drug-Drug: May be affected by drugs altering the activity of liver enzymes.

Route/Dosage

PO (Adults ...