Is it safe to use Miralax (polyethylene glycol) with Linzess (linaclotide)?

Miralax and Linzess Combination Therapy

It is safe to use Miralax (polyethylene glycol) with Linzess (linaclotide) as they work through different mechanisms and can be complementary for patients with inadequate response to monotherapy. 1

Mechanism of Action and Rationale

• Miralax (polyethylene glycol): Works as an osmotic laxative by increasing water in the stool to induce bowel movements 1
• Linzess (linaclotide): Functions as a guanylate cyclase-C agonist that increases intestinal fluid secretion and accelerates transit 1

The complementary mechanisms make this combination potentially beneficial for patients with chronic idiopathic constipation or irritable bowel syndrome with constipation (IBS-C) who have inadequate response to either agent alone.

Administration Guidelines

• Linzess: Should be taken on an empty stomach at least 30 minutes before the first meal of the day 1
• Miralax: Typically taken at a dose of 17g daily dissolved in 4-8 oz of water or other liquid 1
• Dosing for Linzess:
  • IBS-C (Adults): 290 mcg once daily
  • Chronic Idiopathic Constipation (Adults): 72 mcg or 145 mcg once daily
  • Functional constipation (Children 6-17 years): 72 mcg once daily 1

Monitoring Considerations

When using this combination, patients should be monitored for:

1. Diarrhea: The most common adverse effect of Linzess (occurring in up to 20% of patients), which could potentially be exacerbated by adding Miralax 2
2. Dehydration: Watch for decreased urination, dry mouth, dizziness, and increased thirst 1
3. Electrolyte disturbances: Particularly important with prolonged diarrhea 1

Important Precautions

• Contraindications: Neither medication should be used in patients with known or suspected mechanical gastrointestinal obstruction 1
• Age restrictions: Linzess is contraindicated in children under 6 years, and not recommended for IBS-C patients under 18 years (except for functional constipation in ages 6-17) 1
• Severe dehydration risk: The combination should be used cautiously in patients at risk for dehydration 1

Practical Approach to Combination Therapy

1. Start with monotherapy: Consider trying either agent alone before combining
2. Sequential addition: If response to monotherapy is inadequate, add the second agent
3. Dose adjustment: If excessive diarrhea occurs, consider reducing the Miralax dose while maintaining the Linzess dose 1

Alternative Options

If the combination proves problematic:

• Consider alternative agents such as plecanatide, lubiprostone, or prucalopride 1
• Adjust Linzess dosing (72 mcg, 145 mcg, or 290 mcg depending on indication) 1

Clinical Efficacy Context

Linaclotide has demonstrated significant efficacy in clinical trials:

• Increases complete spontaneous bowel movements per week (mean difference 1.37,95% CI 1.07-1.95) 1
• Improves abdominal pain, with 48.9% of patients reporting ≥30% reduction vs. 34.5% with placebo 1
• Improves stool consistency (mean difference 1.25,95% CI 1.1-1.39 higher) 1

The addition of Miralax may further enhance these outcomes in patients with inadequate response to Linzess alone.