L. reuteri DSM 17938 for Infant Colic: The Strongest Probiotic Evidence in Pediatrics

If pediatric probiotics have a poster child, it is Lactobacillus reuteri DSM 17938 for infant colic. Multiple randomized controlled trials, individual patient data meta-analyses, and a 2018 Cochrane review now support its use specifically in breastfed infants with colic, and the European Society for Paediatric Gastroenterology, Hepatology and Nutrition (ESPGHAN) Working Group on Probiotics has issued a conditional recommendation in support. The evidence is unusual in pediatric supplements: well-defined strain, consistent dose, replicated benefit, and a tractable safety profile.

What Counts as Colic

The Wessel "rule of threes" defines colic as crying for >3 hours/day, >3 days/week, for >3 weeks in an otherwise healthy infant. Roman IV criteria simplify to "rule of fives" for diagnostic purposes. Colic affects 10–25% of infants and resolves spontaneously by 3–4 months in nearly all cases — meaning any colic intervention has a high placebo response and a built-in regression to the mean.

The Pivotal Trials

The first signal came from Savino 2007 (Pediatrics): 90 breastfed colicky infants randomized to L. reuteri DSM 17938 (10^8 CFU/day) or simethicone for 28 days; the probiotic group had reductions in daily crying time of 95 minutes vs 7 minutes for simethicone. Replication came from Indrio 2014 (JAMA Pediatrics) and Savino 2018, both showing similar effect sizes in breastfed infants. Sung 2014 (BMJ), an Australian trial, did not replicate the benefit and crucially included formula-fed infants. The 2018 Sung individual-patient-data meta-analysis pooled 345 infants from four RCTs and found a clear benefit in breastfed infants (mean reduction 25 minutes/day, NNT ~8) and no clear benefit in formula-fed infants.

Why Breastfed Only

The reasons for the breastfed-vs-formula difference remain debated. Possibilities include differences in infant gut microbiome composition that allow L. reuteri to colonize more effectively in breastfed infants; the natural presence of L. reuteri in breastmilk; or an interaction with milk fat globule membrane components. ESPGHAN's recommendation is therefore restricted to breastfed colicky infants.

Dosing

The trial dose is 10^8 CFU/day (5 drops of the most common commercial product) given once daily for at least 21 days. Effect, if any, is typically apparent by 3 weeks. Don't add it to hot bottles — lactobacilli are heat-sensitive. Most commercial preparations require refrigeration after opening.

Other Pediatric Indications

Beyond colic, L. reuteri DSM 17938 has been studied in functional constipation (mixed results), infant regurgitation (some benefit on episodes per day), and prevention of necrotizing enterocolitis in preterm infants (the Cochrane review for NEC prevention favors a different strain combination). For the average breastfed colicky infant, this is the clearest pediatric probiotic indication on the books.

Safety

L. reuteri DSM 17938 has a long safety record in trials of preterm and term infants. Bacteremia from L. reuteri has been reported in immunocompromised neonates; the strain is not recommended in central-line patients, severely immunocompromised infants, or those with short-bowel syndrome. For healthy term breastfed infants with colic, the safety profile is excellent.