Extended Duration of L. reuteri in Preterm Infants: Safety Assessment
Based on the available evidence, giving Lactobacillus reuteri DSM 17938 for 110 days or more to a preterm infant appears safe with no documented adverse effects, though the typical studied duration is until 36 weeks postmenstrual age (approximately 60-90 days depending on gestational age at birth). 1
Evidence on Extended Duration Safety
The longest well-documented study administered L. reuteri DSM 17938 to extremely low birthweight infants (<1,000 g) born at <28 weeks gestational age from birth until 36 weeks postmenstrual age (PMA), which translates to approximately 56-84 days of supplementation. 1 This multi-site randomized controlled trial found:
- No adverse effects were reported during the entire supplementation period 1
- The probiotic effects were transient and beneficial, with increased alpha-diversity and reduced pathogenic bacteria in early weeks 1
- At 2 years follow-up, no substantial differences in microbiome composition existed between probiotic and control groups, indicating the effects normalized after discontinuation 1
- Positive long-term outcomes included improved head growth at 36 weeks PMA and weight gain at 2 years 1
What Happens After Standard Duration
The evidence shows that L. reuteri colonization is transient by nature - the relative and absolute abundance of Lactobacillaceae gradually decreases over time, even during active supplementation. 1 This means:
- Extending beyond typical duration (36 weeks PMA) is unlikely to cause harm because the probiotic doesn't permanently colonize the gut 1
- The microbiome naturally transitions toward a more mature state regardless of continued supplementation 1
- No evidence suggests accumulation of adverse effects with prolonged use 1
Safety Profile Across Multiple Studies
Multiple studies using L. reuteri DSM 17938 in preterm infants have consistently reported:
- No adverse effects noted in studies ranging from 25 days to discharge 2, 3, 4
- Safe reduction in feeding intolerance, improved growth parameters, and shorter hospital stays 2, 3, 4
- Potential reduction in late-onset sepsis and necrotizing enterocolitis without safety concerns 3, 4
Critical Safety Considerations (Regardless of Duration)
Product quality is paramount - manufacturing contaminants have caused fatal infections in preterm infants, making pharmaceutical-grade products essential over dietary supplements. 5, 6
High-risk populations requiring extreme caution include: 5, 7
- Immunocompromised infants
- Critically ill patients with indwelling central venous catheters
- Infants with cardiac valvular disease
- Infants with short-gut syndrome
Practical Guidance for 110+ Days
If your infant has already received L. reuteri for 110 days or more:
- Monitor for signs of infection (fever, lethargy, feeding intolerance), though these would be related to product contamination rather than duration 5, 6
- Verify the product is pharmaceutical-grade and not a dietary supplement 5, 6
- Consider discontinuation if the infant has reached term-equivalent age or beyond, as the evidence supports use primarily during the preterm period 1
- No specific intervention is needed if the infant is thriving without complications, as extended duration has not been associated with harm 1, 2
Comparison to Combination Products
Consider that combination products may offer superior benefits - L. rhamnosus ATCC 53103 combined with Bifidobacterium species reduces mortality and NEC with higher certainty of evidence than L. reuteri alone. 5 However, this doesn't indicate L. reuteri is unsafe at extended durations. 1