dromlakhani Chronic Constipation — Cascade Laxative Selector
Before using this skill: Alarm symptoms must be excluded, secondary causes ruled out, and constipation type classified. If defecatory disorder is the primary problem → use the Defecatory Disorder Management Pathway instead.
STEP 1 — Confirm Constipation Type
| Type | Key Features |
|---|---|
| Normal-transit / IBS-C | Normal exam, pain + bloating, incomplete evacuation |
| Slow-transit (STC) | Infrequent stools, confirmed slow transit, normal pelvic floor |
| Defecatory disorder | Straining even with soft stools, manual manoeuvres → stop, use Defecatory Disorder skill |
| Secondary | Medication-induced or metabolic → address cause first |
STEP 2 — Assess Resource Level
| Level | Setting |
|---|---|
| Level 1 | Primary care / limited resources / OTC medications |
| Level 2 | Access to psychologist + prescription drugs |
| Level 3 | Specialist centre + advanced pharmaceuticals |
STEP 3 — Select Treatment
🟢 LEVEL 1 — Start here for ALL patients
A. Lifestyle first (always — regardless of other treatments):
- Dietary fibre: target 20–30 g/day — increase gradually over weeks, not days
- Psyllium (soluble fibre): 14 g/1000 kcal/day — NNT 2.6 for global symptoms
- Fluid intake ↑, regular exercise (walking, jogging, cycling, swimming)
- Adopt squatting posture; respond promptly to urge; regular toilet habits
- Review and stop constipating medications (see Table 4 of WGO guideline)
⚠️ Avoid fibre supplementation in defecatory disorders or obstructive intestinal disease
B. If lifestyle insufficient → Osmotic laxative (first-line pharmacologic):
| Drug | Starting Dose | Max Dose | Notes |
|---|---|---|---|
| PEG (polyethylene glycol) | 17 g daily | No clear maximum | Preferred — fewer GI side effects |
| Magnesium oxide | 400–500 mg daily | ~1000–1500 mg daily | Alternative in some regions |
| Lactulose | 15 g daily | No precise max | Effective; more bloating/flatulence than PEG |
C. Rescue / short-term symptom relief → Stimulant laxative:
| Drug | Starting Dose | Max Dose | Notes |
|---|---|---|---|
| Bisacodyl | 5 mg daily | 10 mg daily | Intermittent use only |
| Senna | 8.6–17.2 mg daily | ~4 tablets BD | Cramping common |
⚠️ Stimulants: limit to intermittent/rescue use — theoretical risk of colonic neuromuscular dysfunction with long-term continuous use
🟡 LEVEL 2 — If Level 1 fails after 4–8 weeks
- Psychological therapy (CBT or gut-directed hypnotherapy) — particularly effective for IBS-C, patients with comorbid anxiety/depression, or maladaptive illness behaviours
- Continue and optimise Level 1 medications; consider combining osmotic + stimulant
- Neuromodulators (if pain/visceral hypersensitivity prominent): use secondary-amine TCAs (nortriptyline, desipramine) or SNRIs — avoid amitriptyline (worsens constipation)
🔴 LEVEL 3 — Specialist setting; Level 1+2 failed
Choose based on predominant problem:
| Agent | Class | Dose | Best For | NNT |
|---|---|---|---|---|
| Prucalopride | 5HT4 agonist | 1–2 mg daily (max 2 mg) | STC, infrequent stools | 6 |
| Linaclotide | GC-C agonist | 72–145 µg daily (max 290 µg) | IBS-C, bloating + constipation | 10–12 |
| Lubiprostone | Chloride channel activator | 24 µg BID | General chronic constipation | 4 |
| Plecanatide | GC-C agonist | 3 mg daily | IBS-C (similar to linaclotide) | 11–12 |
| Elobixibat | Bile acid inhibitor | 10 mg daily (max 15 mg) | STC, post-meal symptoms | 3 |
| PAMORA (e.g. naloxegol) | µ-opioid receptor antagonist | Per formulary | Opioid-induced constipation only | — |
STEP 4 — When to Escalate to Investigations
Refer for physiologic testing if:
- Failed adequate trial of Level 1 laxatives (4–8 weeks)
- Suspicion of slow-transit constipation or evacuation disorder
- No alarm features but persistent severe symptoms
Investigation cascade (resource-dependent):
- Level 1: Medical history + anorectal exam + 1-week bowel diary + radiopaque marker transit study + balloon expulsion test
- Level 2: Defecography
- Level 3: MR proctography + anorectal manometry + sphincter EMG
Clinical Guardrails
- Don't escalate to advanced agents without excluding defecatory disorder — secretagogues and prokinetics won't work if there is outlet obstruction
- Prefer PEG over lactulose when available — better tolerability
- Never use long-term stimulant laxatives as sole therapy — rescue only
- Fibre can worsen symptoms in defecatory disorders and obstruction — always classify first
- Opioid-induced constipation requires a PAMORA — osmotic laxatives alone are insufficient
- Avoid amitriptyline in constipation-predominant patients — use secondary amine TCAs instead
Source: WGO Global Guideline — A Global Cascade Approach to Diagnosis and Management of Chronic Constipation. World Gastroenterology Organisation, 2025.