Constipation Laxative Selector

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name: constipation-laxative-selector
description: Selects the right pharmacologic treatment for chronic constipation using a resource-stratified cascade approach (Level 1/2/3), with doses and NNTs for each agent. Trigger when a clinician asks which laxative to use, what to prescribe for constipation, how to escalate treatment for chronic constipation, which osmotic or stimulant laxative to choose, or when first-line treatment has failed and the next step is needed.
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# 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.

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## 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** |

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## 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 |

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## 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

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### 🟡 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)

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### 🔴 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** | — |

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## 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

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## 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

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*Source: WGO Global Guideline — A Global Cascade Approach to Diagnosis and Management of Chronic Constipation. World Gastroenterology Organisation, 2025.*