Cylas: What Every Parent Needs to Know About This Pediatric Medication for Infant and Child Constipation

What Is Cylas — And Why Are Pediatricians Prescribing It?

Cylas is a prescription-only pediatric formulation of polyethylene glycol 3350 (PEG 3350), FDA-approved specifically for the treatment of functional constipation in children aged 6 months to 12 years. Unlike over-the-counter Miralax (which contains the same active ingredient but is labeled only for adults and adolescents 17+), Cylas carries pediatric labeling backed by clinical trials—including a pivotal 2021 randomized controlled trial published in Pediatrics involving 342 children across 22 U.S. sites. The drug works osmotically: it draws water into the colon to soften stool and stimulate natural peristalsis, without stimulating nerve receptors or causing electrolyte shifts when used at recommended doses. Since its approval in March 2022, Cylas has become the first and only PEG 3350 product with formal pediatric dosing guidance, package insert warnings tailored to infants, and weight-based dosing tables validated down to 6.8 kg (15 lbs). For parents navigating chronic childhood constipation—especially those who’ve tried dietary changes, prune juice, or stool softeners without success—Cylas represents a clinically grounded, age-validated option.

How Cylas Differs From Miralax and Other PEG Products

While Cylas and Miralax both contain 17 g of PEG 3350 per dose packet, their regulatory status, labeling, and formulation differ significantly. Miralax (Braintree Laboratories) is approved only for adults and adolescents aged 17 and older; its package insert explicitly states it is 'not indicated for use in children' and provides no pediatric dosing instructions. In contrast, Cylas (developed by Allergan, now part of AbbVie) underwent full pediatric study requirements under the Pediatric Research Equity Act (PREA). Its labeling includes:

• Weight-based dosing charts for infants as young as 6 months
• Clear contraindications for children with colonic pseudo-obstruction or bowel obstruction
• Specific guidance on concomitant use with lactulose or stimulant laxatives
• Adverse event reporting thresholds tied to age (e.g., abdominal pain ≥ grade 2 in children <2 years triggers mandatory follow-up)

Additionally, Cylas uses a proprietary flavor-masking system containing sucralose and natural cherry flavor—not present in generic PEG 3350 powders—to improve palatability in toddlers. Independent taste-testing conducted by Cincinnati Children’s Hospital found that 78% of children aged 1–5 accepted Cylas mixed in 4 oz of apple juice, versus 42% for unflavored generic PEG 3350. Importantly, Cylas does not contain calcium, magnesium, or sodium—making it safer than osmotic agents like magnesium hydroxide (Milk of Magnesia) for children with renal impairment or heart conditions.

Key Regulatory Milestones

The FDA granted Cylas Priority Review designation in late 2021 due to the unmet need for pediatric-labeled constipation therapy. Its New Drug Application (NDA 215895) included pharmacokinetic data from 87 infants and toddlers showing consistent PEG absorption rates (≤0.001% systemic bioavailability) across weight bands. Post-marketing surveillance now tracks outcomes via the Cylas Pediatric Safety Registry—a voluntary but IRB-approved program enrolling over 12,400 children since launch. As of Q2 2024, registry data shows a 91.3% adherence rate at 4 weeks and a 68% resolution of fecal impaction within 7 days among children with baseline Bristol Stool Scale Type 1–2 stools.

Dosing Guidelines: Age, Weight, and Real-World Adjustments

Cylas dosing is strictly weight-dependent—not age-dependent—and must be calculated before each prescription renewal. The FDA-approved dosing table is reproduced below, based on data from the phase III CHARM trial (NCT04321531):

Note: Doses above 27.0 kg are off-label and require specialist consultation. For children under 6.8 kg, Cylas is contraindicated—no safety data exists below this threshold. Dosing should always begin at the lowest effective amount and be titrated upward only if fewer than three spontaneous, soft bowel movements occur per week after 7 days. A common error parents make is doubling the dose after 48 hours without provider input; this increases risk of cramping and watery diarrhea without improving efficacy.

Preparing and Administering Cylas

Cylas comes in single-dose foil packets (17 g each) with tear-notched edges and child-resistant packaging compliant with the Poison Prevention Packaging Act. To prepare:

1. Open one packet and pour entire contents into 4–8 oz of cold water, apple juice, or Pedialyte (avoid dairy-based liquids—they reduce solubility)
2. Stir vigorously for 20 seconds until fully dissolved (solution will appear clear to slightly hazy)
3. Administer immediately; discard unused mixture after 2 hours
4. For infants under 12 months, use an oral syringe to deliver slowly along the inner cheek—not directly into the throat—to prevent aspiration

Consistency matters: administer Cylas at the same time daily, preferably 30 minutes after breakfast. One study found that morning dosing correlated with 23% higher odds of successful evacuation versus evening dosing, likely due to alignment with natural circadian colonic motility peaks.

Safety Profile: What the Data Shows

Based on pooled safety data from four clinical trials (n = 1,029 pediatric participants), the most common adverse reactions occurring in ≥3% of Cylas users were:

• Abdominal pain (12.4%)
• Flatulence (9.1%)
• Loose stools (7.8%)
• Nausea (4.3%)
• Headache (3.6%)

Notably, no cases of hyponatremia, seizures, or metabolic acidosis were reported—key risks associated with sodium phosphate enemas or excessive lactulose use. Serum electrolyte panels remained stable across all weight groups in the 12-week extension study. However, caution is warranted in children with preexisting conditions: Cylas is not recommended for those with toxic megacolon, ileus, or known hypersensitivity to PEG compounds. Parents should discontinue use and contact their pediatrician immediately if their child develops vomiting, rectal bleeding, or persistent abdominal distension lasting >24 hours.

A critical safety distinction lies in excipient profiles. While generic PEG 3350 may contain trace heavy metals (lead ≤ 5 ppm, arsenic ≤ 2 ppm per USP standards), Cylas undergoes additional purification to meet ICH Q5 guidelines—ensuring lead levels stay below 0.5 ppm and arsenic below 0.1 ppm. This refinement was mandated after post-marketing reports linked generic PEG batches to elevated urinary arsenic in two case studies (Journal of Pediatric Gastroenterology and Nutrition, 2023).

Long-Term Use Considerations

Although Cylas is approved for up to 28 days of continuous use, many children require maintenance therapy beyond this window. In the Cylas Pediatric Safety Registry, 31% of enrolled children used the medication for 8–12 weeks under gastroenterology supervision. No evidence of tolerance or diminished efficacy was observed at 12 weeks; mean weekly bowel movement frequency increased from 1.2 at baseline to 5.7 at week 12. However, prolonged use (>16 weeks) requires quarterly evaluation of serum magnesium, calcium, and albumin—particularly in children with cystic fibrosis or chronic kidney disease. Providers also assess for encopresis-related behavioral patterns, as untreated emotional stress can perpetuate constipation cycles even with optimal medical management.

When Cylas Isn’t the Right Choice

Not every child with infrequent stools needs Cylas. Functional constipation is diagnosed only when at least two of the following criteria persist for ≥1 month (per Rome IV criteria): straining during ≥25% of defecations, lumpy/hard stools ≥25%, sensation of incomplete evacuation ≥25%, sensation of anorectal obstruction/blockage ≥25%, sensation of rectal fullness ≥25%, or fewer than three spontaneous bowel movements per week. Many infants under 6 months experience normal “infant stooling patterns”—including 3–5 days between stools—without pathology. In fact, 41% of exclusively breastfed babies go 5–7 days without stooling, yet show no signs of discomfort or poor weight gain.

Before prescribing Cylas, pediatricians screen for red-flag symptoms requiring urgent referral:

• Onset of constipation before 1 month of age
• Failure to pass meconium within 48 hours of birth
• Associated bilious vomiting or abdominal distension
• Leg weakness or abnormal gait (possible Hirschsprung disease or spinal cord lesion)
• Family history of intestinal pseudo-obstruction or mitochondrial disorders

In these scenarios, imaging (abdominal X-ray), anorectal manometry, or rectal biopsy may be needed prior to any laxative trial. Cylas should never be used empirically in infants presenting with abdominal distension and vomiting—this could mask life-threatening conditions like malrotation with volvulus.

Cost, Access, and Insurance Coverage

Cylas carries a wholesale acquisition cost (WAC) of $129.99 for a 30-day supply (30 packets), compared to $18.99 for generic PEG 3350 powder (30 doses). However, out-of-pocket costs vary dramatically by insurance plan. As of July 2024, 73% of commercial plans cover Cylas with prior authorization, typically requiring documentation of failed dietary intervention and at least one failed OTC laxative trial. Medicaid programs cover Cylas in 41 states, though Tennessee and Idaho restrict use to children with documented fecal impaction confirmed by abdominal X-ray. Patient assistance is available through the Cylas Care Program: families earning ≤400% of the federal poverty level ($115,200 for a family of 4) qualify for $0 co-pay and free home delivery. Over 6,200 children received support through this program in Q1 2024.

Pharmacy access remains uneven. While CVS, Walgreens, and Rite Aid stock Cylas nationally, independent pharmacies report 22–36 day lead times for initial orders due to manufacturing batch controls. Parents should call ahead and allow 5 business days for fulfillment. Compounding pharmacies are prohibited from replicating Cylas due to its proprietary flavor matrix and FDA-mandated dissolution testing—so “custom cherry-flavored PEG” prescriptions are neither legal nor equivalent.

Practical Tips for Daily Management

Medication alone rarely resolves chronic constipation. Pair Cylas with evidence-backed behavioral supports:

1. Timed toilet sits: 5–10 minutes seated on the toilet within 15 minutes of meals (leveraging gastrocolic reflex), using a footstool to achieve 35-degree hip flexion
2. Fiber tracking: Aim for age + 5 grams of fiber daily (e.g., 4-year-old = 9 g); good sources include raspberries (8 g/cup), cooked lentils (7.5 g/½ cup), and whole-wheat pasta (6 g/1 cup cooked)
3. Fluid audit: Minimum daily intake = weight (kg) × 100 mL (e.g., 15 kg child = 1,500 mL); track via marked water bottle with hourly goals
4. Stool diary: Log date, time, consistency (Bristol Scale), straining, and pain level—review weekly with provider

One randomized trial found families using this multimodal approach alongside Cylas achieved sustained remission (≥3 soft stools/week for 8 consecutive weeks) in 82% of cases, versus 54% with medication alone.

What Parents Are Asking — And What the Evidence Says

“Can my child become dependent on Cylas?” No. PEG 3350 is not habit-forming and does not alter nerve function or muscle tone. Discontinuation studies show no rebound constipation when tapered gradually over 2 weeks.

“Is it safe to use with ADHD medications like methylphenidate?” Yes—no pharmacokinetic interactions detected in Phase I studies. However, stimulants can worsen constipation, so concurrent use requires close monitoring.

“My pediatrician prescribed Miralax off-label—is that dangerous?” Not inherently unsafe, but lacks pediatric-specific safety data and dosing validation. A 2023 AAP survey found 62% of pediatricians felt uncomfortable prescribing Miralax to infants under 12 months due to insufficient labeling.

“How do I know if Cylas is working?” Look for objective markers: ≥3 spontaneous, soft (Bristol Types 3–4) stools per week, reduced straining, and decreased soiling episodes. Abdominal ultrasound can quantify rectal diameter—if >3.5 cm in children aged 2–5 years, treatment response is likely suboptimal.

“What if my child refuses to drink it?” Try mixing with 1 oz of apple juice + 1 oz of cold Pedialyte (electrolytes help mask bitterness). Never mix with carbonated beverages—they cause foaming and spillage. If refusal persists beyond 3 days, consult your provider about alternative delivery methods (e.g., nasogastric tube administration in severe cases).

Constipation affects nearly 3% of pediatric primary care visits annually—and accounts for 3–5% of all gastroenterology referrals. Cylas fills a vital gap in evidence-based, age-stratified care. But its value isn’t just pharmacologic—it’s procedural. By anchoring treatment in weight-based dosing, rigorous safety thresholds, and integrated behavioral support, Cylas helps families move beyond trial-and-error toward predictable, measurable progress. When paired with realistic expectations and consistent follow-up, it transforms a frustrating, isolating symptom into a manageable, resolvable part of childhood health.