PH6.4 | PH6.4 | Constipation Pharmacotherapy — SDL Guide — Summary & Reflection

KEY TAKEAWAYS

Constipation Pharmacotherapy — Key Points:

Classification by mechanism (critical for safe selection):
- Bulk-forming (ispaghula, methylcellulose): safe long-term; must take with water.
- Osmotic (PEG: preferred long-term; lactulose: gas/bloating, hepatic encephalopathy use; Mg salts: rapid-acting, avoid in renal failure).
- Stimulant (senna: anthraquinone, bacterial activation, 6–12 h; bisacodyl: diphenylmethane, oral + suppository; avoid bisacodyl within 1 h of milk/antacids — enteric coating dissolves).
- Softeners (docusate: modest effect, useful adjunct; liquid paraffin: avoid — aspiration + vitamin malabsorption).
- Newer secretagogues (lubiprostone: ClC-2 → Cl-/water into lumen; linaclotide: GC-C → cGMP → CFTR + pain ↓; both for refractory or IBS-C).
- Prokinetic (prucalopride: 5-HT4, colonic; for refractory chronic constipation).

OIC (opioid-induced): PEG + docusate backbone; add PAMORA (methylnaltrexone SC or naloxegol oral) if inadequate — blocks gut mu-opioid receptors without reversing analgesia.

Pregnancy: Ispaghula + lactulose safe. Avoid castor oil (uterotonic), high-dose stimulants, liquid paraffin.

IBS-C: Linaclotide (constipation + pain) or lubiprostone (constipation).

REFLECT

A 55-year-old patient has been taking senna tablets every night for the past 5 years. He tells you that without them, he 'cannot go at all.' He has melanosis coli on recent colonoscopy (polyp surveillance). He asks whether he needs to keep taking senna indefinitely. Think through: (a) what is melanosis coli and what does it tell you about his laxative use? (b) What is the concern about long-term stimulant laxative use and the concept of 'cathartic colon'? (c) How would you counsel him — acknowledging his dependence experience while explaining the evidence? (d) What would you substitute for senna, and over what timeframe would you transition him? This scenario tests your ability to convert pharmacological knowledge into a patient-centred management conversation that respects the patient's experience while directing care towards evidence-based practice.