A 68-year-old woman with a history of colorectal cancer presents with acute left-sided colonic obstruction due to a stenosing tumour. She is haemodynamically stable but has abdominal distension and altered bowel habits. After initial resuscitation, what is the drug of choice for preoperative management to reduce intraluminal pressure and prevent perforation?

Explanation

## Pharmacological Management of Malignant Colonic Obstruction ### Role of Somatostatin Analogues in Obstructive Ileus **Key Point:** Octreotide is the drug of choice for reducing secretions and intraluminal fluid accumulation in malignant colonic obstruction, thereby reducing the risk of perforation and managing symptoms preoperatively. ### Mechanism of Octreotide Octreotide is a somatostatin analogue that: 1. Inhibits secretion of water and electrolytes into the GI lumen 2. Reduces pancreatic and biliary secretions 3. Decreases splanchnic blood flow 4. Reduces intraluminal pressure and bowel distension 5. Decreases vomiting and abdominal discomfort ### Clinical Application in Malignant Obstruction **High-Yield:** Octreotide dosing in obstruction: - Dose: 100–600 μg/day in divided doses (SC or IV) - Typical: 100–200 μg three times daily - Reduces fluid accumulation by 30–50% - Improves symptom control in 60–70% of cases - Allows time for preoperative optimization ### Comparison of Agents in Colonic Obstruction | Agent | Mechanism | Role in Obstruction | Efficacy | |-------|-----------|-------------------|----------| | **Octreotide** | Somatostatin analogue → ↓ secretion | Reduces intraluminal fluid | High (60–70%) | | **Ondansetron** | 5-HT3 antagonist | Antiemetic only | Symptomatic relief only | | **Metoclopramide** | D2 antagonist | Contraindicated (↑ pressure) | Harmful | | **Hyoscine butylbromide** | Anticholinergic | Reduces spasm only | Limited benefit | ### Clinical Pearl **Warning:** Metoclopramide is contraindicated in mechanical obstruction because it increases intraluminal pressure, worsening distension and perforation risk. ### Advantages of Octreotide in Malignant Obstruction - Reduces the "vicious cycle" of obstruction: distension → increased secretion → further distension - Improves quality of life by reducing vomiting and abdominal pain - Allows time for staging and surgical planning - Reduces the need for nasogastric tube in some cases - Safe in both partial and complete obstruction **Clinical Pearl:** Octreotide is particularly valuable in **inoperable malignant obstruction** (palliative care) where it can provide symptom control without surgery. ### Adjunctive Measures - Nasogastric decompression (initial management) - IV fluid and electrolyte replacement - Antiemetics (ondansetron) for symptom control - Surgical resection or bypass (definitive treatment when feasible) [cite:Harrison Principles of Internal Medicine 21e Ch 297]