In a first‑trimester pregnant woman with constipation that started after initiating ondansetron and did not improve with a single nighttime dose of Dulcoflex (psyllium fiber), which is the safest and most effective next laxative: lactulose (Notalact), polyethylene glycol 3350 (Picofit), or sorbitol (Cadilose)?

Polyethylene Glycol (Picofit) is the Best Next Step

Switch to polyethylene glycol (PEG) 17 g daily as your next-line therapy for this first-trimester pregnant woman with ondansetron-induced constipation that failed to respond to psyllium (Dulcoflex). PEG is the preferred osmotic laxative during pregnancy because it produces bowel movements within 1–3 days and causes significantly less abdominal bloating and distension compared to lactulose 1, 2, 3.

Why PEG Over Lactulose or Sorbitol

PEG demonstrates superior tolerability and faster onset:

• PEG achieves therapeutic effect more rapidly than lactulose, with significantly better Wexner constipation scores at weeks 1 and 2 of treatment (P=0.029) 4
• Lactulose (Notalact) causes substantially more maternal abdominal distension, bloating, and flatulence—symptoms that may worsen nausea in a first-trimester patient already taking ondansetron 1, 2, 3, 5
• Sorbitol (Cadilose) lacks robust safety data in pregnancy and is not recommended by major gastroenterology guidelines 1, 3

Both PEG and lactulose are considered safe in pregnancy, but the American Gastroenterological Association specifically identifies PEG as the preferred first-line osmotic agent 1, 2, 3.

Treatment Algorithm for First-Trimester Constipation

Week 1: Dietary fiber 30 g/day (fruits, vegetables, whole grains, legumes) plus adequate hydration 1, 3

Week 2: Add bulk-forming agent (psyllium or methylcellulose) if dietary measures fail 1, 2, 3

Week 3–4 (Current Step): Switch to PEG 17 g daily when bulk-forming agents are ineffective 1, 2, 3

Refractory cases only: Consider short-term stimulant laxatives (bisacodyl, sodium picosulfate) with extreme caution—these should be avoided in the first trimester due to conflicting safety data and theoretical risk of tenesmus-associated preterm labor 2, 3, 5

Specific Dosing Recommendations

• PEG (Picofit): 17 g (one sachet) dissolved in 240 mL water, taken once daily 1, 2, 3
• Alternative if PEG unavailable: Lactulose 15 mL twice daily, though expect more bloating 2, 3, 6
• Duration: Continue until bowel movements normalize to soft, formed stools every 1–2 days 3, 7

Critical Clinical Considerations Before Escalating Therapy

Screen for secondary causes that may be contributing:

• Iron supplementation (common in pregnancy and highly constipating) 1, 3
• Hypothyroidism or hypercalcemia 2, 3
• Hemorrhoids (present in ~80% of pregnant women, though more common in third trimester) 1, 3

Assess symptom severity:

• Frequency and consistency of bowel movements 3
• Presence of pain or rectal bleeding with defecation 3
• Impact on quality of life 3

Common Pitfalls to Avoid

• Do not use stimulant laxatives routinely in the first trimester due to uncertain safety profile and potential for electrolyte disturbances 2, 3, 5, 8
• Avoid prolonged use of osmotic laxatives without reassessment, as this can lead to dehydration or electrolyte imbalances 3, 8
• Counsel about bloating risk if using lactulose, especially when combined with fiber—this can worsen patient discomfort 2, 3
• Ensure adequate hydration when increasing any laxative therapy to prevent dehydration 1, 3, 8

Why Dulcoflex (Psyllium) Failed

Bulk-forming agents like psyllium require 1–2 weeks to achieve full effect and depend on adequate fluid intake 3, 9. A single nighttime dose is insufficient—psyllium should be given consistently for at least one week before declaring treatment failure 3. However, since you've already attempted this step, moving to osmotic laxatives is appropriate 1, 2, 3.

Addressing the Ondansetron Issue

Consider whether ondansetron is still necessary:

• Ondansetron should be used cautiously in the first trimester due to some reports of congenital heart defects, and ACOG recommends case-by-case use before 10 weeks gestation 1
• If nausea/vomiting persists, consider switching to metoclopramide, which has similar efficacy but may have fewer constipating effects 1
• Metoclopramide carries no increased risk of congenital defects and has a more favorable side-effect profile than ondansetron 1

If ondansetron must be continued, PEG remains the optimal choice to counteract its constipating effects 1, 2, 3.