Laxatives
Key Points
- Laxatives are classified by mechanism: bulk-forming (absorb water), osmotic (draw water into colon), stimulant (increase peristalsis), lubricant (coat stool), and stool softeners (emollients).
- Stimulant laxatives are first-line for opioid-induced constipation (OIC); stool softeners alone are insufficient for OIC.
- Adequate fluid intake (≥8 oz with bulk-forming agents) is essential to prevent bowel obstruction.
- Chronic stimulant laxative abuse causes electrolyte imbalances, dehydration, and bowel dysfunction.
Pathophysiology
Constipation results from reduced colonic motility, inadequate fluid intake, low dietary fiber, or drug-induced slowing of peristalsis (opioids, anticholinergics, antacids). Laxatives correct constipation through five distinct mechanisms:
- Bulk-forming: Increase stool bulk → stimulate peristalsis
- Osmotic: Draw water into colon → soften and increase stool volume
- Stimulant: Irritate colonic mucosa → increase peristalsis
- Lubricant: Coat stool and intestinal wall → facilitate passage
- Stool softener (emollient): Lower stool surface tension → allow water penetration
Classification
| Type | Examples | Onset |
|---|---|---|
| Bulk-forming | Psyllium (Metamucil), methylcellulose (Citrucel), calcium polycarbophil | 12–72 hours |
| Osmotic | Lactulose, polyethylene glycol (MiraLAX), magnesium hydroxide (Milk of Magnesia) | 30 min–6 hours |
| Stimulant | Bisacodyl (Dulcolax), senna (Senokot) | 6–12 hours |
| Lubricant | Mineral oil | 8–48 hours |
| Stool softener (emollient) | Docusate sodium (Colace), docusate calcium | 12–72 hours |
Nursing Assessment
NCLEX Focus
Patients on opioid analgesics should receive stimulant laxatives prophylactically — stool softeners alone do not counteract opioid-induced decreased peristalsis.
- Assess bowel elimination pattern, date of last bowel movement, stool consistency, and abdominal assessment before administration.
- Assess for signs of bowel obstruction or ileus (absent bowel sounds, severe pain, distension) — laxatives are contraindicated.
- Assess for appendicitis, perforation, or acute abdominal conditions — absolute contraindications.
- Assess current medications for opioids, anticholinergics, iron, calcium — common constipation causes.
- Assess fluid/food intake, activity level, and fiber consumption.
Nursing Interventions
- Administer bulk-forming laxatives with a full 8 oz glass of water to prevent esophageal or bowel obstruction.
- Administer bisacodyl tablets without crushing; do not give within 1 hour of antacids or dairy — enteric coating dissolves prematurely.
- Mineral oil should not be administered to bed-bound, children <6 years, or patients with dysphagia — aspiration risk causing lipid pneumonia.
- Docusate (stool softener) alone is inadequate for opioid-induced constipation; combine with stimulant laxative (bisacodyl or senna).
Bowel Obstruction Risk
Bulk-forming laxatives without adequate fluid intake can cause esophageal or intestinal obstruction, especially in patients with strictures or limited mobility.
Stimulant Laxative Abuse
Chronic misuse of stimulant laxatives causes electrolyte imbalances (hypokalemia), dehydration, and cathartic colon (loss of bowel muscle tone). Monitor for abuse in eating disorder patients.
Pharmacology
| Drug | Class | Key Nursing Considerations |
|---|---|---|
| Psyllium (Metamucil) | Bulk-forming | Drink 8 oz fluid; takes 12–72 hrs; safe for daily use; may lower cholesterol |
| Docusate (Colace) | Stool softener | Insufficient for OIC alone; onset 12–72 hrs; safe in pregnancy/postpartum |
| Bisacodyl (Dulcolax) | Stimulant | Available PO and rectal; do not crush tablets; avoid with antacids or dairy |
| Senna (Senokot) | Stimulant | Often combined with docusate for OIC prophylaxis in opioid patients |
| Lactulose | Osmotic | Also lowers ammonia in hepatic encephalopathy; target 2–3 soft stools/day |
| Polyethylene glycol (MiraLAX) | Osmotic | Low electrolyte disturbance risk; used for bowel prep |
Clinical Judgment Application
Clinical Scenario
A postoperative patient on IV morphine patient-controlled analgesia has not had a bowel movement in 3 days and reports abdominal bloating.
- Recognize Cues: Opioid-induced constipation (OIC) — reduced peristalsis; not responsive to docusate alone.
- Analyze Cues: Stimulant laxative + stool softener combination is the evidence-based approach for OIC.
- Prioritize Hypotheses: Constipation vs. paralytic ileus — bowel assessment needed first.
- Generate Solutions: Assess bowel sounds; administer bisacodyl + docusate per order if bowel sounds present.
- Take Action: Implement laxative regimen; encourage ambulation and fluid intake.
- Evaluate Outcomes: Patient passes stool within 24 hours; bowel routine established.
Related Concepts
- constipation - Clinical nursing management of constipation.
- opioids - Primary cause of opioid-induced constipation requiring prophylactic laxatives.
- antidiarrheals - Opposing class for managing loose stool.
- fluid-volume-deficit-hypovolemia-and-dehydration - Osmotic laxatives increase fluid loss risk.
- fecal-incontinence-and-bowel-retraining - Bowel regimen management context.
Self-Check
- Why is a stool softener alone insufficient for opioid-induced constipation?
- What is the critical patient education point when taking psyllium?
- What adverse effects result from chronic stimulant laxative abuse?