Do probiotics or prebiotics alone or in combination reduce the incidence of NEC in very low birth weight (<1500 grams) infants?

MANUSCRIPT CITATION

Dilli D, Aydin B, Fettah ND, Özyazıcı E, Beken S, Zenciroğlu A, Okumuş N, Özyurt BM, İpek MŞ, Akdağ A, Turan Ö, Bozdağ Ş. The propre-save study: effects of probiotics and prebiotics alone or combined on necrotizing enterocolitis in very low birth weight infants. J Pediatr. 2015 Mar;166(3):545-51.e1. doi: 10.1016/j.jpeds.2014.12.004. Epub 2015 Jan 13. PMID 25596096

REVIEWED BY

Dr Janet Berrington
Consultant Neonatal Paediatrician
Newcastle Neonatal Service
Newcastle upon Tyne Hospitals NHS Foundation Trust

Dr Thomas Skeath
Research Fellow
Newcastle Neonatal Service
Newcastle upon Tyne Hospitals NHS Foundation Trust

TYPE OF INVESTIGATION

Prevention. Randomized placebo-controlled trial

QUESTION

In infants <1500g and <32 weeks receiving some enteral feeding on day 7, does the Bifidobacterium lactis (probiotic), inulin (prebiotic), or combined (synbiotic) reduce the incidence of necrotizing enterocolitis (NEC) compared to placebo in infants ?

METHODS

  • Design: Double blinded RCT
  • Allocation: Allocation in balanced blocks by sealed envelope. It is unclear whether the allocation was stratified by site, or how infants from multiple pregnancies were allocated to groups.
  • Blinding: Pro- and prebiotic products and placebo are described as similar in color, odor and texture. A feeding team (distinguished from those caring for the baby) added the product to the milk. Parents were blinded to the intervention. ‘Investigators’ were aware of allocation and it is unclear whether they were involved in clinical care or determining of primary or secondary outcomes.
  • Follow-up period: Until discharge from the nursery.
  • Setting: 5 tertiary neonatal units in Turkey.
  • Patients: Infants with both a gestational age of <32 weeks and a birth weight of <1500g, without congenital abnormalities affecting the gastrointestinal tract were described as eligible if they were enterally fed at least 1ml every 4 hours and had survived until postnatal day 7. However, the quoted age at enrollment in the article is not compatible with the stated entry criteria of survival to seven days being necessary for enrollment (median ages at enrollment for the four groups were between 2 and 3 days).
  • Intervention: Infants received either probiotic (Bifidobacterium lactis, 5×109 colony-forming units), prebiotic (inulin, 900 mg), or both (synbiotic), or placebo (maltodextrin, dose unknown). Infants received the intervention once minimal enteral feed was tolerated until either 8 weeks of treatment, death or discharge whichever occurred first.
  • Outcomes:
    • Primary outcome: Necrotizing enterocolitis defined as modified Bells criterion stage II – III
    • Secondary outcomes: Multiple secondary outcomes are reported: time to reach full enteral feed (>100 and >150mls/kg/day), days of parenteral nutrition, late onset sepsis (beyond 72 hours, culture proven and clinically suspected), feed intolerance (complex definition), cholestasis (undefined), length of NICU stay, and death.
  • Analysis and Sample Size: Over the study period, 677 VLBW infants were admitted to the participating centers, of which 277 were excluded. There were 81 exclusions due to parents declining consent, the other 196 are described as not meeting eligibility criteria but not further detailed. A total of 398 infants (~100 per arm) was necessary to detect an absolute reduction in the incidence of NEC by 50%, providing an error of 0.05 (two-sided) and power of 85%. Expected baseline rates of NEC are not given. No mention is made of siblings from multiple pregnancies and how/if they were accounted for in the analysis. Although groups were randomized, multivariate analysis was undertaken accounting for gestational age, birthweight, antenatal steroid use, maternal antibiotic exposure, UVC duration, feed type, transfusion, ventilation and centre. Analysis is done in several ways: all treatment groups combined against placebo, each individual group against each other, and any probiotic containing group against no probiotic (placebo and prebiotic).
  • Patient follow-up: 100% of allocated infants were included in the analysis.

MAIN RESULTS

Comparison of each individual group to the placebo group are given in the table below. As 100 are in each trial group, n also equals %.

Outcome n (p value vs placebo) Probiotic Prebiotic Synbiotic Placebo
NEC 2 (0.001) 12 (0.23) 4 (0.002) 18
Clinical Sepsis 29 (0.02) 23 (0.001) 26 (0.06) 49
Proven sepsis 8 (0.24) 10(0.50) 8(0.26) 13
NICU Stay (Days) 37 (0.001) 38 (0.004) 42(0.01) 50
Death 3 (0.01) 2(0.06) 3(0.01) 12

Rates of NEC were significantly lower among infants that received probiotic alone or in combination with prebiotic, while prebiotic alone had no effect (Table).

Time to full feeds was statistically significantly shortened by 7 days in the probiotic group compared to placebo, and by 8 days in the prebiotic group, but did not reach significance (p=0.05) in the synbiotic group. Mortality rates were reduced when all active treatment groups were compared to placebo (p=0.003), and when separate analysis was performed, mortality was significantly lower in synbiotic and probiotic groups compared to placebo. Secondary outcome measures where the synbiotic group had advantage over the prebiotic group alone were restricted to growth defined by length gain per week and discharge weight.

The further analysis of any probiotic receipt (combined pro or synbiotic groups) against none (pre or placebo groups), showed that NEC rates were significantly lower in the probiotic group, and mortality rates were on the borderline of significance between the two groups (p=0.05). No other assessed outcomes were significantly different in this analysis. 

CONCLUSION:

The authors conclude that the administration of the probiotic Bifidobacterium lactis alone or in combination with the prebiotic inulin has a positive health benefit in VLBW infants in the reduction of NEC. The prebiotic inulin alone did not exert this effect.

 

COMMENTARY:

NEC is recognized as one of the major challenges in neonatal care. Alongside improvements in survival in the very preterm, mortality attributable to NEC has risen.1 Rates of NEC identified by different groups are very variable due to differences in diagnostic criteria, gestations included, additional risk factors within individual populations, feed practices and other variables. The latest Cochrane review identified rates of NEC in control populations all <1500g that vary between 0% and 16%.2 Around 30% of babies with NEC will either die or require surgery3 and long term neurocognitive outcome in survivors of NEC is worse than in those surviving meningitis.4 Costs to family and health care providers are substantial.

It is therefore not surprising that efforts have been focused on trials of the most promising intervention in NEC to date – probiotics. This paper adds value to the current (extensive) probiotic literature including the recent Cochrane review2 which is strongly supportive of the use of probiotics, by exploring the potential benefit of prebiotic both separately and when given with a probiotic. In terms of trial design, the inclusion of a placebo group is also of value. The choice of placebo (maltodextrin) is of interest given the data in piglets that this increases NEC.5 Doses of maltodextrin are not given, but we can probably assume the dose was very small, in comparison to that given to the piglet model. Equally the choice of Bifidobacterium lactis is of interest and not justified by the authors. Of the studies included in the recent Cochrane review only two6,7 use Bifidobacterium lactis alone, and neither study showed a significant reduction in NEC. Jacobs (2013) did report a significant reduction in NEC with Bifidobacterium lactis in combination with Bifidobacterium infantis and Streptococcus thermophilus.8 A further study using Bifidobacterium lactis alone is currently only available in abstract form.9 It reports trial discontinuation for futility reasons after enrolling 318 infants, and identifying NEC in 8.9% of infants receiving Bifidobacterium lactis and 8.6% receiving placebo, but may well still have been underpowered for NEC as the primary outcome. Choosing this particular probiotic species where less data already exist means that the authors then risked not being able to explore their primary question (is probiotic plus prebiotic better than probiotic) had the probiotic alone not been effective.

The trial design appears sensible, although timing of recruitment in relation to stated inclusion criteria are not compatible. The decision to only recruit surviving infants that tolerated milk by day 7 (had that been followed) potentially excludes the highest risk infants, and needs to be taken into account when assessing generalizability. However the median ages of recruitment given in Table II suggest that these criteria were not enrollment criteria, and this perhaps make the data more generalizable.

When considering study effect, NEC rate of 18% in the placebo group is higher than in many units, and in all the currently included studies in the Cochrane review reporting NEC as outcome. For units considering whether and how their own babies may benefit from probiotic use this is highly relevant. The number of infants that are exposed to an intervention for one infant to gain benefit (the number needed to treat) is dependent on the background rate of the disease that is being modulated. Thus, units with a very much lower incidence of NEC would see many more infants treated before benefit was gained. This affects how units with lower background rates of NEC could expect a similar approach to impact on their own units.

The presentation and analysis of the data is slightly complex but justified given the four groups in the study. All treated infants are together compared to placebo, and then individual groups are both compared to placebo and other groups. This allows potentially ‘hidden’ effects from the initial combined approach in one group to be explored, and allows more precision about the prebiotic and probiotic effects. In the subgroup analyses it is evident that for the primary outcome (NEC), probiotic receipt is the key factor, and that addition of prebiotics does not affect this in any direction. However there are potential growth benefits seen with the synbiotic group over the probiotic group alone. Although the authors do not emphasize this point given the association between growth and longer-term outcomes, this is a potentially important finding unless the association is explained by chance.10

The final analysis is of any probiotic receipt against none. This is a pragmatic analysis that acknowledges that the majority of the effect appears to be due to probiotic receipt (since prebiotic alone does not reach significance for NEC), and that this study then adds important data to the probiotic question alone. However, the prebiotic element of this study is what separates it from most other probiotic studies. This specific prebiotic (inulin) alone does not reduce NEC or proven late onset sepsis, nor do infants receiving it as symbiotic treatment with Bifidobacterium lactis gain additional reduction in these outcomes.

This study adds further support to those who argue for the administration of probiotics to reduce NEC but does not support inulin supplementation as an additional strategy for this purpose. Given the strength of support in the current Cochrane review, it is surprising that more units have not already started to use them. Important regulatory issues remain in many countries and these coupled with ongoing and perhaps unanswerable questions around which specific combination in which dose is ‘best’ remain reasons why individual babies and families are still not uniformly able to access probiotics. The lack of long term data on infants exposed to probiotics (or prebiotics) and the possible effects on growth (as alluded to by this data), allergy or other potentially micriobiomically modulated areas of health remain relatively poorly explored. Given the prophylactic nature of this treatment, many individuals are exposed to it who would never have developed the disease, making long term follow up of these cohorts important.

REFERENCES

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