What is the best treatment for constipation in patients with Parkinson's disease?

Treatment of Constipation in Parkinson's Disease

Start with polyethylene glycol (PEG) 17g with 8 oz water twice daily as first-line pharmacological treatment, combined with increased water and fiber intake plus daily fermented milk containing probiotics and prebiotic fiber. 1, 2

Understanding the Problem

Constipation is the most frequent non-motor symptom in Parkinson's disease, affecting over 50% of patients and can precede motor symptoms by up to 20 years. 2, 3 The pathophysiology is multifactorial:

• Neurodegeneration of the enteric nervous system is the primary driver 2, 1
• Medication side effects, particularly from dopamine agonists and anticholinergics, worsen constipation 2, 1
• Reduced physical activity from motor impairment contributes significantly 2, 1
• Pelvic floor dyssynergia causes defecatory dysfunction in many patients, not just slow transit 2, 1

First-Line Treatment Algorithm

Non-Pharmacological Interventions (Start Immediately)

• Increase fluid intake to improve colonic transit 2, 1
• Increase dietary fiber intake through diet and supplements (psyllium is most effective) 2
• Encourage physical activity within the patient's motor limitations 1
• Add fermented milk with probiotics and prebiotic fiber daily - a large RCT (n=120) demonstrated this increases complete bowel movements, improves stool consistency, and reduces laxative requirements after 4 weeks 2, 1

First-Line Pharmacological Treatment

Polyethylene glycol (PEG) is the strongest evidence-based first-line agent:

• Dosing: 17g with 8 oz water twice daily 1
• Strong recommendation with moderate certainty of evidence from the AGA/ACG 2023 guidelines 2
• Durable response over 6 months 2
• Side effects: abdominal distension, loose stool, flatulence, nausea 2

If PEG alone is insufficient, add stimulant laxatives:

• Bisacodyl 10-15 mg daily to three times daily to achieve one non-forced bowel movement every 1-2 days 1
• Senna starting at lower doses and titrating upward as needed 1

Second-Line Options (If First-Line Fails or Is Intolerant)

• Magnesium oxide - start at lower doses and increase as necessary; avoid in renal insufficiency due to hypermagnesemia risk 2, 1
• Lactulose for patients who fail or are intolerant to over-the-counter therapies, though bloating and flatulence are common dose-dependent side effects that may limit use 2, 1

Treatment for Refractory Cases

Before escalating therapy, rule out mechanical problems:

• Perform digital rectal examination and abdominal x-ray to exclude impaction or obstruction 1

If no mechanical obstruction:

• Glycerine suppository or mineral oil retention enema for rectal impaction 1
• Methylnaltrexone 0.15 mg/kg subcutaneously every other day for severe refractory cases (contraindicated in post-operative ileus and mechanical bowel obstruction) 1
• Prokinetic agents (metoclopramide 10-20 mg PO four times daily) can be considered for severe cases, though use cautiously given potential for worsening motor symptoms 1

Critical Pitfalls to Avoid

• Do not use stool softeners alone without stimulant laxatives - they are ineffective as monotherapy 1
• Do not wait to start prophylactic treatment - begin constipation management at the start of therapy with constipation-inducing PD medications 1
• Do not rely solely on lifestyle modifications - while important, they have limited efficacy alone and must be combined with pharmacological treatment 2
• Do not overlook pelvic floor dyssynergia - if standard laxatives fail, consider that the problem may be defecatory dysfunction rather than slow transit, which may require different interventions 2, 1, 4

Special Considerations in PD

The 2018 ESPEN guidelines specifically recommend following the same treatment algorithm as for idiopathic chronic constipation in PD patients, as few PD-specific treatments have been adequately studied. 2 However, the addition of probiotics/prebiotics shows particular promise in this population with strong RCT evidence. 2