Alosetron

INTRODUCTION

Indications

Treatment of severe diarrhea-predominant irritable bowel syndrome (IBS) in women who have chronic symptoms (≥6 mo), no other GI pathology, and have had no response to conventional therapy.

Action

5-HT₃ receptors are nonselective cation channels responsible for regulation of visceral pain, colonic transit, and GI secretions. Alosetron inhibits the activation of these channels. Therapeutic Effects: Increased colonic transit time without affecting orocecal transit time resulting in decreased pain/discomfort and diarrhea associated with IBS.

Adverse Reactions/Side Effects

GI: ACUTE ISCHEMIC COLITIS, TOXIC MEGACOLON, constipation, abdominal discomfort, abdominal distention, flatulence, nausea, GI viral infections, hemorrhoids, regurgitation or reflux.

PHYSICAL THERAPY IMPLICATIONS

Examination and Evaluation

• Be alert for signs of severe GI reactions such as acute ischemic colitis or toxic megacolon. Signs include sudden abdominal pain, abdominal distention, bloody diarrhea, fever, vomiting, tachycardia, and shock. See immediate medical assistance if these signs occur.

• Monitor GI symptoms (diarrhea, abdominal pain, cramps) to help document whether drug therapy is successful in reducing these symptoms.

Patient/Client-Related Instruction

• Advise patient to avoid alcohol and foods that may increase GI irritation and diarrhea.

• Instruct patient to report other bothersome GI side effects such as constipation, nausea, flatulence, hemorrhoids, heartburn, indigestion, and abdominal pain and distension.

Pharmacokinetics

Absorption: 50–60% absorbed following oral administration.

Distribution: 65–95 L.

Protein Binding: 82% bound to plasma proteins.

Metabolism and Excretion: Extensively metabolized by the liver; 13% excreted unchanged in urine.

Half-life: 1.5 hr.

Contraindications/Precautions

Contraindicated in: Hypersensitivity; Constipation; History of chronic/severe constipation or complications due to constipation; History of GI obstruction, stricture, toxic megacolon, perforation, and/or adhesions; History of ischemic colitis, decreased intestinal circulation, thrombophlebitis, or coagulation defects; History of Crohn's disease/ulcerative colitis/diverticulitis; Severe hepatic impairment; Patients taking fluvoxamine.

Use Cautiously in: Men—safety not established; Mild-to-moderate hepatic impairment; Patients who are elderly, debilitated, or taking medications that decrease GI motility; OB/Lactation/Pedi: Safety not established.

Interactions

Drug-Drug: Blood levels of alosetron can be increased by fluvoxamine (concomitant use is contraindicated). Blood levels of alosetron can be increased by amiodarone, cimetidine, ciprofloxacin, clarithromycin, itraconazole, ketoconazole, ofloxacin, protease inhibitors, telithromycin, and voriconazole (use concomitantly with caution).

Route/Dosage

PO (Adults): Women—0.5 mg ...