Constipation in Hospitalized Patients: Evaluation, Stepwise Laxatives, and Opioid-Induced Constipation

Conclusión

Initial workup

• Red-flag sweep: continued flatus, a soft abdomen, no vomiting, and an empty rectum argue against obstruction and impaction, but recheck the exam and bowel sounds daily. Obtain flat and upright abdominal films if distension increases, flatus stops, vomiting develops, or the exam worsens, looking for a dilated colon (a cecum beyond 9–12 cm suggests acute colonic pseudo-obstruction), air-fluid levels or ileus, or a transition point.
• Check a BMP (potassium, calcium, magnesium, creatinine) and TSH if not recent, and review every medication for additive constipating effects — anticholinergics, ondansetron, diphenhydramine, calcium-channel blockers, iron, and diuretic-induced hypokalemia.
• Document the rectal exam (impaction, stool consistency, anal tone, paradoxical contraction): an empty vault with distal loading changes therapy from oral agents to rectal disimpaction.

How the laxative classes work

• Osmotic laxatives (polyethylene glycol, lactulose) are poorly absorbed molecules that hold water in the bowel lumen by osmosis. They soften stool and add volume, which stretches the colon and helps trigger a bowel movement, but they do not directly make the gut contract. PEG is inert and not absorbed, which is why it is safe in kidney disease; lactulose is fermented by colonic bacteria, which is why it causes more gas and bloating.
• Stimulant laxatives (senna, bisacodyl) act on the enteric nerves and the colonic lining to increase propulsive contractions and fluid secretion. Opioids slow the gut by suppressing exactly that motility, so an osmotic agent alone often produces soft stool that still does not move; a stimulant supplies the push, which is why every opioid bowel regimen needs one.
• Why magnesium laxatives are avoided in chronic kidney disease: magnesium citrate and milk of magnesia work osmotically, but a fraction of the magnesium is absorbed and the kidney is the only route for clearing it. With a reduced GFR it accumulates, and hypermagnesemia causes nausea, flushing, hypotension, bradycardia, loss of deep tendon reflexes, muscle weakness, respiratory depression, and in severe cases heart block or arrest. The same renal-clearance logic applies to sodium phosphate preparations, which can also precipitate acute phosphate nephropathy.
• How suppositories and enemas work: rectal therapy acts only on stool that has already reached the rectum and distal colon, which is why it is the step for a loaded vault or for no result after oral therapy, and why it does nothing for stool still sitting in the proximal colon. A bisacodyl suppository is a stimulant delivered straight to the rectal lining, triggering contractions within about 15–60 minutes; a glycerin suppository draws water into the rectum and lubricates the stool plug. An enema works mainly by volume: the fluid distends the rectum, which fires the defecation reflex, while also softening and lubricating the stool. Tap-water and saline enemas rely on that volume effect, a mineral-oil retention enema coats and softens hard stool over 30–60 minutes before it is passed, and soap-suds enemas add mucosal irritation. Because the fluid and any additives contact a large absorptive surface, sodium phosphate enemas are avoided in older adults, CKD, and heart failure, repeated large-volume enemas can cause electrolyte shifts and mucosal injury, and rectal instrumentation is avoided in neutropenia or thrombocytopenia. Hard impacted stool is removed manually first, because neither an oral stimulant nor an enema can clear a plug that blocks the outlet.
• What a PAMORA is: a peripherally acting mu-opioid receptor antagonist (methylnaltrexone, naloxegol, naldemedine) blocks the mu-opioid receptors in the gut wall that opioids use to slow transit, but it is designed not to cross the blood–brain barrier. Unlike naloxone, it therefore relieves opioid-induced constipation without reversing pain relief or precipitating central withdrawal. Because it restores gut motility against a blocked outlet, it is contraindicated when mechanical obstruction is known or suspected.

Stepwise management

• Step 1 — osmotic: polyethylene glycol 3350 17 g in 8 oz of water orally twice daily, scheduled rather than as needed, titrated to a soft daily stool; PEG is safe in chronic kidney disease and is the preferred osmotic. Lactulose 15–30 mL twice daily is an acceptable alternative but causes more gas and bloating.
• Step 2 — stimulant: senna 8.6 mg, 2 tablets at bedtime (up to 2 tablets twice daily), or bisacodyl 5–10 mg orally daily. Opioids require a stimulant; softener-only regimens (docusate) are ineffective and should be stopped.
• Step 3 — rectal therapy if there is no bowel movement within about 24 hours of oral therapy and the rectum is loaded or distally obstructed: a bisacodyl 10 mg or glycerin suppository, then a tap-water or mineral-oil retention enema if still no result. Avoid sodium phosphate (Fleet) enemas in CKD and older adults because of acute phosphate nephropathy, hyperphosphatemia, and hypocalcemia.
• Avoid magnesium-containing laxatives (magnesium citrate, milk of magnesia) in CKD and high-sodium agents in heart failure.
• Minimize the driver: reduce the opioid to the lowest effective dose, use scheduled acetaminophen or other opioid-sparing analgesia, and mobilize the patient.

Laxative-refractory opioid-induced constipation and prophylaxis

• If constipation persists despite 48–72 hours of optimized scheduled osmotic plus stimulant therapy, treat as laxative-refractory opioid-induced constipation and add a PAMORA: naldemedine 0.2 mg orally daily; naloxegol 25 mg orally daily on an empty stomach (12.5 mg if poorly tolerated or CrCl < 60 mL/min); or methylnaltrexone 12 mg subcutaneously daily when oral intake is unreliable. Mild CKD needs no dose change for naldemedine or methylnaltrexone.
• When a PAMORA is started, hold other laxatives initially per label practice, avoid strong CYP3A4 inhibitors with naloxegol, and monitor for cramping, diarrhea, and opioid withdrawal symptoms; never use a PAMORA with known or suspected GI obstruction.
• Keep the patient on a standing bowel regimen (PEG plus senna with a defined rescue step) for the entire duration of opioid therapy rather than as-needed orders — this is the default prophylaxis for any hospitalized adult started on scheduled opioids.
• Before discharge address contributors: hydration, fiber only with adequate fluid intake and no suspicion of slow transit or obstruction, toileting after meals, and deprescribing constipating agents.

Monitoring and disposition

• Keep a daily bowel-movement record with the Bristol stool scale, abdominal exam, and flatus; reassess response 24 hours after each escalation.
• Monitor the BMP for diarrhea-related volume depletion, hypokalemia, and a rising creatinine once stooling begins; check magnesium and phosphate if any magnesium- or phosphate-containing product was used.
• The medical floor is the right level of care unless pseudo-obstruction requiring neostigmine or a surgical abdomen develops.
• Discharge once there is a documented bowel movement and a soft, non-distended abdomen, with a written standing regimen (PEG plus senna) and rescue instructions for any ongoing opioid prescription; primary care or GI follow-up in 1–2 weeks if a PAMORA was started or symptoms persist.

Escalate care if

• Flatus stops, the abdomen becomes tense or tympanitic, or vomiting develops — stop oral laxatives, make the patient NPO, obtain abdominal imaging, decompress with a nasogastric tube if obstructed, and consult surgery or GI.
• Imaging shows marked colonic dilation without mechanical obstruction (acute colonic pseudo-obstruction, Ogilvie syndrome) — supportive care, correct electrolytes, stop opioids and anticholinergics; neostigmine on monitored telemetry or colonoscopic decompression if the cecum is ≥ 12 cm or there is no improvement in 24–48 hours.
• The rectal exam shows hard impacted stool — manual disimpaction plus an enema first; do not push oral osmotics until the distal obstruction is cleared.
• Still no bowel movement after 72 hours of optimized laxatives plus a PAMORA, or bleeding, weight loss, anemia, or a new change in bowel habit — GI consult and consideration of colonoscopy or anorectal evaluation.
• Fever, leukocytosis, peritoneal signs, or hemodynamic instability — urgent imaging and surgical evaluation for perforation or stercoral colitis.

Duration

Continue the scheduled bowel regimen for as long as opioids are prescribed, including after discharge. A PAMORA continues while opioid-induced constipation persists on opioid therapy.

Advertencias

• Avoid magnesium-based laxatives in CKD (hypermagnesemia) and sodium phosphate oral solutions or enemas in CKD, older adults, or heart failure (acute phosphate nephropathy, electrolyte shifts).
• PAMORAs are contraindicated with known or suspected mechanical GI obstruction because of perforation risk; use caution with advanced structural GI disease.
• Naloxegol: avoid strong CYP3A4 inhibitors and inducers, take on an empty stomach, and reduce the dose at CrCl below 60 mL/min.
• Docusate alone is ineffective for opioid-induced constipation, and bulk-forming fiber can worsen distension in opioid-slowed transit and should not be used as monotherapy.
• This overview assumes no mechanical obstruction, prior bowel surgery or stricture, or peritoneal signs; reassess if the exam changes.

Referencias

1. Constipation — Symptoms, diagnosis and treatment. BMJ Best Practice. (2019) · Derivado de guías“Constipation is initially evaluated with a detailed history and physical exam, including a digital rectal exam.”
2. Management of constipation: A narrative review of evolving strategies and methodological challenges. (2026) · Revisión narrativa“Opioid-induced constipation (OIC) has a distinct pathophysiology rooted in peripheral μ-opioid receptor activation, which decreases propulsive motility and increases fluid absorption.”