Can I treat constipation caused by antipsychotics in a patient with partial response to magnesium citrate with Miralax (polyethylene glycol 3350) and docusate/sennosides?

Treatment of Antipsychotic-Induced Constipation with Miralax and Docusate/Sennosides

Yes, you can use Miralax (polyethylene glycol 3350) twice daily for antipsychotic-induced constipation, but you should skip the docusate and use sennosides alone instead of the combination product. The evidence clearly shows that adding docusate to sennosides provides no additional benefit and may actually be less effective than sennosides alone. 1

Recommended Regimen

Primary Treatment Approach

• Polyethylene glycol 3350 (Miralax): 17 grams (one heaping tablespoon) dissolved in 8 oz of water twice daily 1
• Sennosides alone: 2-3 tablets twice to three times daily, titrated to effect 1
• Goal: One non-forced bowel movement every 1-2 days 1

Why This Combination Works

Polyethylene glycol is strongly supported by guidelines and research:

• The AGA-ACG guidelines give PEG a strong recommendation with moderate certainty of evidence for chronic constipation 1
• PEG increases complete spontaneous bowel movements by 2.90 per week compared to placebo 1
• It demonstrates sustained efficacy over 6-12 months with no evidence of tachyphylaxis 2
• The twice-daily dosing you're proposing is explicitly recommended in NCCN guidelines 1

Sennosides provide the stimulant laxative component needed for drug-induced constipation:

• NCCN guidelines specifically recommend stimulant laxatives for constipation caused by anticholinergic drugs (which includes many antipsychotics) 1
• Sennosides work by stimulating colonic motility and reducing colonic water absorption 1

Why to Avoid Docusate

The evidence against docusate is remarkably consistent across multiple high-quality guidelines:

• A study comparing senna alone versus senna-docusate combination demonstrated that adding docusate was not necessary and was actually less effective than sennosides alone 1
• An RCT in hospice patients confirmed no benefit in adding docusate to sennosides 1
• The 2019 NCCN Adult Cancer Pain guidelines explicitly state: "Based on the available literature, docusate has not shown benefit and is, therefore, not recommended" 1

Implementation Strategy

Starting the Regimen

1. Discontinue any non-essential constipating medications if possible 1
2. Begin PEG 3350: 17 grams twice daily with 8 oz water each dose 1
3. Add sennosides: Start with 2 tablets twice daily 1
4. Ensure adequate fluid intake throughout the day 1

Titration and Monitoring

• Titrate sennosides up to 8-12 tablets per day maximum if needed 1
• Assess response after 2-4 days (typical time to first bowel movement with PEG) 3
• Adjust doses based on stool frequency and consistency, aiming for one non-forced bowel movement every 1-2 days 1

If Constipation Persists

Second-Line Options

If the PEG and sennosides combination is insufficient after appropriate titration:

1. Rule out complications: Check for impaction, obstruction, or metabolic causes (hypercalcemia, hypokalemia, hypothyroidism) 1
2. Add bisacodyl: 10-15 mg orally 2-3 times daily or as a rectal suppository 1
3. Consider magnesium-based products: Magnesium hydroxide 30-60 mL daily or magnesium citrate 8 oz daily 1
4. Lactulose or sorbitol: 30-60 mL twice to four times daily 1

When to Consider Prokinetic Agents

If gastroparesis is suspected (common with some antipsychotics), consider adding metoclopramide 10-20 mg orally four times daily 1

Common Pitfalls to Avoid

Side Effects of PEG

• Gastrointestinal symptoms (abdominal distension, loose stool, flatulence, nausea) are common but generally mild 1
• These effects typically decrease markedly after the first week of treatment 4
• If diarrhea occurs, reduce the PEG dose rather than discontinuing entirely 3

Fiber Supplementation

• Do not add psyllium or other fiber supplements for antipsychotic-induced constipation 1
• Supplemental medicinal fiber is ineffective for drug-induced constipation and may worsen symptoms 1
• Adequate dietary fiber from food is appropriate only if the patient has adequate fluid intake 1

Long-Term Safety

• PEG is safe for chronic use up to 12 months with no clinically significant electrolyte changes 2
• No evidence of tachyphylaxis (tolerance) develops with continued PEG use 2
• Patients do not develop tolerance to constipation from antipsychotics, so ongoing prophylactic treatment is necessary 1

Duration of Therapy

Unlike opioid-induced constipation where prophylaxis is standard, antipsychotic-induced constipation requires ongoing treatment as long as the patient remains on the constipating medication 1. The partial response to magnesium citrate suggests your patient will likely need continuous therapy with the PEG and sennosides regimen.