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Nutrition in Clinical Practice
Volume 31 Number 4
August 2016 502 –513
© 2016 American Society
for Parenteral and Enteral Nutrition
DOI: 10.1177/0884533616639399
ncp.sagepub.com
hosted at
online.sagepub.com
Review
Antibiotic-associated diarrhea (AAD) refers to diarrhea fol-
lowing antibiotic administration.1 AAD can be mild or serious
and may occur with progressive diseases,2 which is a common
problem in hospitalized adults and elderly patients, due to the
widespread use of antibiotics and the concurrent illnesses pres-
ent in this population. The definitions of AAD are diverse, but
one of the most accepted definitions is the onset of diarrhea
after receiving antibiotics within the previous 2 months.1 The
elderly population is at increased risk of AAD. The incidence
of AAD varies between 5%–39% of adult patients and 15%–
20% of elderly people, which is higher in hospitalized patients,
as the incidence has been reported as <0.1% in the outpatient
setting in comparison to 39% for inpatients.3 AAD increases
costs, mortality, morbidity, and length of hospital stay.1,4-6
A probiotic is defined as a live or microbial mixture admin-
istered in adequate amounts to confer a health benefit to the
host. The main reason for the use of probiotics in AAD is based
on the favorable outcome of specific probiotic strains that will
normalize the unbalanced indigenous microflora.6 This is
based on the assumption that antibiotics represent one of the
most common agents associated with diarrhea, which is the
result of alteration in the normal microflora. Thus, the use of
probiotics may be especially suited for AAD.6
There are multiple pathophysiologic determinants of
AAD.7,8 Treatment of systemic infections by antimicrobial
drugs leads to the disturbance of the gastrointestinal microflora
and is responsible for reducing concentrations of the normal gut
bacteria. It will result in pathogenic bacterial overgrowth or the
lack of the nutrient competition. This gastrointestinal micro-
flora acts as a barrier against colonization by facultative and
obligative enteropathogens altering the bacterial breakdown of
carbohydrates and the concentration of conjugated and uncon-
jugated bile acids in the gut, which may result in alteration in
the bowel habits from osmotic and motor mechanisms.9 The
639399NCPXXX10.1177/0884533616639399Nutrition in Clinical PracticeJafarnejad et al
research-article2016
From the 1Department of Clinical Nutrition, School of Nutritional
Sciences and Dietetics, Tehran University of Medical Sciences, Tehran,
Iran; 2Department of Community Nutrition, School of Nutritional
Sciences and Dietetics, Tehran University of Medical Sciences, Tehran,
Iran; 3Institute of Biological and Environmental Sciences, University
of Aberdeen, Aberdeen, Scotland; and 4Department of Cellular and
Molecular Nutrition, School of Nutritional Sciences and Dietetics, Tehran
University of Medical Sciences, Tehran, Iran.
Financial disclosure: None declared.
Conflict of interest: None declared.
This article originally appeared online on April 29, 2016.
Corresponding Author:
Kurosh Djafarian, PhD, Department of Clinical Nutrition, School
of Nutritional Sciences and Dietetics, Tehran University of Medical
Sciences, No 44, Hojjat-dost Alley, Naderi St, Keshavarz Blvd, Tehran
1416-643931, Iran.
Email: kdjafarian@tums.ac.ir
Probiotics Reduce the Risk of Antibiotic-Associated
Diarrhea in Adults (18–64 Years) but Not the Elderly
(>65 Years): A Meta-Analysis
Sadegh Jafarnejad, DVM1; Sakineh Shab-Bidar, PhD2; John R. Speakman, DSc, PhD3;
Karim Parastui, MS4; Milad Daneshi-Maskooni, MS2; and Kurosh Djafarian, PhD1
Abstract
Background: Antibiotic-associated diarrhea (AAD) is a common problem in adults and elderly patients due to the widespread use of
antibiotics in this population. Multiple previous systematic reviews have demonstrated an association between specific probiotics and
decrease of AAD, especially in children. As there is no specific analysis concerning the elderly patients, we decided to focus on adults,
especially elderly people. Methods: We performed a systematic review of the literature regarding the use of probiotics in the treatment
of AAD in adults (18–64 years old) and elderly subjects (≥65 years old). We identified 436 articles that met the search criteria. Thirty
randomized controlled trials met the predefined inclusion criteria and were included in the meta-analysis. Results: There was considerable
heterogeneity among the trials (P < .001); thus, subgroup analyses were performed. The meta-analysis resulted in a pooled relative risk
(RR) of AAD of 0.69 (95% confidence interval [95% CI]: 0.62–0.76) in a fixed effects model and 0.58 (95% CI: 0.48–0.71) in a random
effects model, as compared with placebo. The positive association between intake of probiotic and reduced risk of AAD was observed in
adults (RR, 0.47; 95% CI: 0.4–0.56). In contrast, in elderly patients, there was no positive effect (RR, 0.94; 95% CI: 0.76–1.15) of probiotic
use and AAD. Conclusion: In summary, the results emerging from our meta-analysis suggested that adjunct probiotic administration is
associated with a reduced risk of AAD in adults but not in elderly people. (Nutr Clin Pract. 2016;31:502-513)
Keywords
probiotics; antibiotic-associated diarrhea; diarrhea; elderly; adults; aged
Jafarnejad et al 503
unveiling of toxin receptors or the attachment sites caused by
the disappearing of the normal flora is another theory of the
etiology of AAD. Allergic, toxic, and direct pharmacologic
motility effects on the gut can also be factors.9 Clostridium dif-
ficile diarrhea (CD), which is linked to AAD, may be responsi-
ble for a inflammatory diarrhea, which is not because of
antibiotics.10 However, antimicrobial exposure is one of the risk
factors for CD development. This may lead to severe condi-
tions, such as toxic megacolon and pseudomembranous coli-
tis.10,11 Therefore, we decided to exclude participants with CD
from the meta-analysis.
As recent epidemiologic studies show a significant increase
in the occurrence of AAD among healthy people or patients
who are most vulnerable to the complications, especially
elderly people, there should be an immediate action for finding
an innovative and applicable method for prevention.11
There are systemic infections associated with specific
strains of probiotics that have been shown in some studies.
These include sepsis or endocarditis with lactobacilli, funge-
mia with Saccharomyces boulardii, and liver abscess caused
by LGG.12 Pneumonia and meningitis are also among the
infections associated with lactobacilli. However, bacteremia
due to lactobacilli rarely occurs.13
Multiple systematic reviews have shown that some probiot-
ics are associated with reduced risk of AAD and hence favor
probiotic coadministration with antibiotics.11,14-18 Although
several studies describe the effect of probiotics on AAD in
children, to the best of our knowledge, there is no comprehen-
sive meta-analysis assessing the effects of probiotics on AAD
in the outpatient and inpatient elderly (aged >65 years) com-
pared with adults (aged 18–64 years). It is not clear whether
similar benefits arise in adults and/or elderly people with dif-
ferent characteristics and in different settings.16,17 Therefore,
the present review was performed to address the effectiveness
of probiotics used in randomized controlled trials (RCTs) for
the treatment of AAD in adults and the elderly based on the
currently available peer-reviewed RCTs.
Materials and Methods
Data Source and Strategy of Search
The meta-analysis was performed on the available data based
on PRISMA guideline.19 Relevant articles were identified by a
systematic search of PubMed, SCOPUS, and Google Scholar
up to October 2014, with the following search terms (in title,
abstract, and keywords with no restriction imposed): probiotic,
diarrhea or diarrhoea, AAD, antibiotic-associated, probiotic*,
common probiotic species as Lactobacillus, Saccaromyces and
Bifidobacter*, adult, elderly, antibiotic therapy, and randomised
controlled trials (RCTs). The PubMed search text example was
as follows: [(probiotic* OR Lactobacillus OR saccharomyces
OR Bifidobacter*) AND (antibiotic AND diarrhea OR diar-
rhoea AAD OR antibiotic-associated)] AND (Elderly OR adult)
AND (Clinical Trial[ptyp] AND English[lang]).
Additional papers were found through a manual search of
reference lists of review articles.
Study Selection
Studies were eligible for inclusion if they fulfilled the fol-
lowing criteria: (1) the study design was an RCT; (2) the
exposure of interest was oral probiotic intake (in either sup-
plements or foods); (3) the outcome of interest was AAD;
and (4) the population of interest was individuals aged >18.
We considered only RCTs published in English. The control
group may have included groups with the use of placebo or
active control or no treatment. Interventions with any dura-
tion and dose were included. We included studies with con-
current administration of antibiotics and probiotics. These
studies should consider the incidence of diarrhea as a pri-
mary or secondary aim with the time range of during or after
antibiotic administration in both control and placebo groups.
The primary outcomes of the study were the incidence of
AAD (except for CD), as defined by the researchers, in adults
and the elderly.
The studies were excluded if they were animal and observa-
tional studies. Also excluded were preclinical studies, dupli-
cate studies, and case reports or case series; studies with
diarrhea of just C difficile source; and studies related to some
strains of probiotics that are rare and for which there is insuf-
ficient scientific evidence regarding their safety or efficiency.
Also, if studies were conducted on pregnant and lactating
females, they were excluded.
We performed a systematic review of the literature regarding
the use of probiotics in the treatment of AAD in adults (18–64
years) and the elderly (>65 years). Titles and abstracts of full-
text articles were independently reviewed. Two trained mem-
bers of the team screened inclusion and exclusion based on the
eligibility criteria described above.
Extraction of Data and Assessment of
Quality
Data were extracted independently by 2 investigators (K.P. and
S.J.) with a predefined data collection form. Disagreements were
resolved by consensus. The following information was extracted:
sample size of each group, population study, geographic location,
year of publication, mean age of participants, sex, dose of probi-
otics, different species of probiotics duration of study, and odds
ratio (with corresponding 95% confidence interval [95% CI]) of
AAD. Authors were contacted in case extra data were required.
To assess the quality of the trials, standard criteria were
used, such as concealment of the allocation, intention-to-treat
analysis, loss to follow-up of individuals, and blinding. Trial
quality was assessed per the risk of bias (low, high, or unclear).
We assigned risk-of-bias categories based on the number of
items judged inadequate in each study: low risk of bias (≤2
inadequate items), high risk of bias (>2 inadequate items), and
unclear (undefined characteristics).
504 Nutrition in Clinical Practice 31(4)
Statistical Analysis
We pooled odds ratio estimates from each study, separately for
each outcome, with a random effects meta-analysis. We calcu-
lated the relative risks (RRs) and heterogeneity in outcomes
within studies with 95% CIs according to both random and
fixed effects models within RevMan 5.2 based on case analy-
sis. Subgroup analyses were based on the probiotic genus, par-
ticipants’ age, clinical condition, and setting. To assess
heterogeneity, we computed the I2 statistic. For identifying and
exploring the reasons of heterogeneity, we analyzed the sub-
groups and examined characteristics of included trials. For
assessing the publication bias, we evaluated the asymmetry of
the funnel plot with Egger regression.
Results
Study Selection
Out of the 436 studies retrieved the primary literature search,
348 studies were excluded. Of these, 28 were removed because
they were duplicate references; 62 were excluded because they
were reviews; 241 were excluded because they were not rele-
vant; and 17 were excluded because they were not available as
full texts in English. A further 58 were excluded during screen-
ing of titles and abstracts because they were case series, case
reports, or preclinical studies or they had inadequate character-
ization of the probiotic, with insufficient reporting of data. The
flow diagram of this meta-analysis is shown in Figure 1. In
total, 30 double-blinded placebo-controlled RCTs (Table 1)
involving 3805 individuals and 3455 individuals in the inter-
vention and control groups, respectively (total, 7260 partici-
pants), met the predefined inclusion criteria and thus were
included in the meta-analysis.20-49
Study Characteristics
Characteristics of the included studies are shown in Table 1.
Mean age of participants in trials was 54 years. The type of
probiotics that were used in the meta-analysis were as follows
(alone or in combination with one another): Lactobacilli (aci-
dophilus, casei, reuteri, bulgaricus, paracasei, plantarum,
rhamnosus, salivarius), Bifidobacteria (bifdum, lactis, longum,
breve, clausii, infantis), Enterococci (faecium), Streptococci
(thermophiles), and the yeast S boulardii.
Duration of intervention varied between 5–21 days. The
dosage of interventions ranged from minimal (7 × 106 CFU
[colony-forming units] / mL) to high (6 × 1010 CFU/mL). Ten
RCTs were high quality, while 11 RCTs were low (Table 1).
The 30 selected studies with a total of 7260 individuals com-
pleted the follow-up interval. A considerable heterogeneity
was observed among the studies (P < .001); thus, subgroup
analyses were performed to assess the effect of different
factors on heterogeneity. Furthermore, there was variability in
the definition of the main outcome measure. The definition of
diarrhea varied from stool consistency to bowel frequency.
However, the most common definition of diarrhea was the
abrupt onset of ≥3 loose or watery stools.
Meta-Analysis
The meta-analysis resulted in a pooled RR of AAD of 0.69
(95% CI: 0.62–0.76) in the fixed effects model and 0.58 (95%
CI: 0.48–0.71) in the random effects model, compared with
placebo (Figure 2). The pooled RR among the 22 inpatient
studies was 0.67 (95% CI: 0.58–0.77, random effects), which
was similar to the pooled RR of 0.67 (95% CI: 0.49–0.92) from
the 5 outpatient studies (Figure 3). The positive association
between intake of probiotics and reduced risk of AAD was
confirmed when the analysis was restricted to studies of adults
(25 RCTs, 3826 individuals; RR, 0.47; 95% CI: 0.4–0.56;
Figure 4a). In contrast, in elderly patients, there was no
Figure 1. Meta-analysis flow diagram.
505
Table 1. Characteristics of Included Trials.
Incidence of AAD n (N)
Trial N Probiotic Placebo
Population,
Setting
Age,
y
Antibiotic /
Indication Probiotics Dose per Day
Duration of
Intervention
Risk of
Bias
Allen
(2013)20
2888 159 (1417) 153 (1471) Adults, inpatient 77.1 Various L acidophilus, B bifdum, and B B
lactis
6 × 1010 CFU 21 d High
Armuzzi
(2001)21
60 1 (30) 8 (30) Adults,
asymptomatic
40 H pylori
eradication
L GG 6 × 109 CFU twice a day 14 d Low
Beausoleil
(2007)49
89 7 (44) 16 (45) Adults, inpatient 70.9 Various L acidophilus and L casei 5 × 1010 CFU (both strains) 8–10 d
(antibiotic use)
Unclear
Can
(2006)22
151 1 (73) 7 (78) Adults, inpatient 23.9 Various Sboulardii Twice a day Unclear Unclear
Chatterjee
(2013)23
343 19 (176) 26 (167) Adults,
outpatient
37.8 Cefadroxil or
amoxicillin
L acidophilus LA-5 and B BB-12 Twice a day 14 d Low
Cimperman
(2011)24
23 1 (13) 5 (10) Adults, inpatient 51 Various L reuteri 108 CFU/tablet, twice a day 28 d High
Cindoruk
(2007)25
124 9 (62) 19 (62) Adults,
outpatient
48 H pylori
eradication
Sboulardii 500 mg, twice a day 2 wk Low
Cremonini
(2002)26
83 3 (63) 6 (20) Adults,
asymptomatic
39.5 H pylori
eradication
3 probiotic groups: L GG, S boulardii,
Bifidobacteria / Lactobacilli
2 sachets/day (twice a day) 14 d Low
Gao
(2010)27
255 37 (171) 37 (84) Adults, inpatient 60 Various L acidophilus, L casei 5 × 1010 CFU (both strains );
twice a day
5 d after last
antibiotic dose
High
Gotz
(1979)28
79 3 (36) 9 (43) Adult, inpatient 64.5 Ampicillin L acidophilus and L bulgaricus 108 CFU/sachet; 4 times a day 5 d Unclear
Hickson
(2007)29
113 7 (57) 19 (56) Adults, inpatient 73.8 Various L bulgaricus, L casei, S thermophilus L casei and S thermophilus 108
CFU/mL; L bulgaricus 107;
twice a day
Unclear Unclear
Koning
(2008)47
38 9 (19) 15 (19) Adults, healthy
volunteers
26.9 Amoxicillin Ecologic (B bifidum, B lactis, B
longum, E faecium, L acidophilus,
L paracasei, L plantarum, L
rhamnosus, L salivarius)
5 g (109 CFU/g); twice a day 14 d Unclear
Koning
(2010)30
30 13 (17) 9 (13) Adults with
COPD,
inpatient
pulmonary,
rehabilitation
61.4 Various (COPD
exacerbation)
B bifidum, B lactis, E faecium,
L acidophilus, L paracasei,
L plantarum, L rhamnosus, L
salivarius
5 g (109 CFU/g); twice a day 14 d High
Lonnermark
(2010)31
163 6 (80) 5 (83) Adults,
inpatient,
outpatient
45 Various L plantarum 1010 CFU per drink; a drink
daily
21 d Low
McFarland
(1995)32
193 7 (97) 14 (96) Adults, inpatient 41.5 Beta-lactams S boulardii 3 × 1010 CFU/g, 500 mg, twice
a day
Unclear Low
Myllyluoma
(2005)33
47 4 (23) 2 (24) Adults, healthy
volunteers
55.6 H pylori
eradication
L GG, L rhamnosus, P freudenreichii
ssp shermanii, B breve
L rhamnosus, 6 × 108 CFU/
mL (combined strains); L
rhamnosus and B breve, 7 ×
106 CFU/mL; 65 mL, twice a
day (7 d) and 1/d (3 wk)
28 d Low
(continued)
506
Incidence of AAD n (N)
Trial N Probiotic Placebo
Population,
Setting
Age,
y
Antibiotic /
Indication Probiotics Dose per Day
Duration of
Intervention
Risk of
Bias
Nista
(2004)34
100 5 (50) 15 (50) Adults,
asymptomatic
44.5 H pylori
eradication
B clausii 2 × 109 CFU, 3 times a day 14 d Unclear
Orrhage
(1994)35
30 6 (20) 7 (10) Adults, healthy
volunteers
37 Clindamycin B longum 5 × 107 to 2 × 108 CFU/mL of
B longum BB 536 and 2 ×
108 to 3 × 108 CFU/mL of L
acidophilus NCFB 1748; twice
a day
21 d Unclear
Ouwehand
(2014)36
450 48 (304) 36 (146) Adults, inpatient 50 Various L acidophilus, L paracasei and B
lactis
1.70 × 1010 (high dose); 4.17 ×
109 CFU (low dose); daily
17–28 d Low
Pozzoni
(2012)37
204 16 (106) 13 (98) Adults, inpatient 79.3 Various S boulardii 5 × 109 CFU; twice a day Antibiotic
treatment
period plus 7 d
Low
Psaradellis
(2010)48
437 47 (216) 65 (221) Adults, inpatient
outpatient
58.8 Various L acidophilus, L casei High
Safdar
(2008)38
39 4 (23) 6 (16) Adults, inpatient 69.1 Various Florajen (L acidophilus) 2 × 1010 CFU, 1 capsule, 3 times
a day
14 d Low
Selinger
(2013)39
229 5 (117) 10 (112) Adults, inpatient 57.5 Various B breve, B longum, B infantis,
L acidophilus, L plantarum, L
paracasei, L delbrueckii subsp
bulgaricus, S thermophilus
1 sachet, twice a day Antibiotic
treatment
period
Low
Song
(2010)40
214 4 (103) 8 (111) Adults, inpatient 60.5 Various L rhamnosus, L acidophilus L rhamnosus, 2 × 109 CFU (both
strains) and L acidophilus, 1
capsule twice a day
14 d High
Souza
(2012)41
70 4 (35) 10 (35) Adults, inpatient 55 Various L casei and B breve 1 sachet (1 g), contained 2 × 107
to 109 L casei and 5 × 107 to
109 B breve
Unclear High
Surawicz
(1989)42
180 11 (116) 14 (64) Adults, inpatient 47.5 Various S boulardii S boulardii, 250 mg (0.5 g
lyophilized), twice a day
Unclear High
Thomas
(2001)43
267 39 (133) 40 (134) Adults, inpatient 55.8 Various L GG 1010 CFU/capsule, 1 capsule
twice a day
14 d High
Wenus
(2008)44
63 2 (34) 8 (29) Adults, inpatient 57.5 Various L GG, L acidophilus, Bifidobacterium
Bb-12
108 CFU/mL of LGG and Bb-12
and 107 CFU/mL of La-5; 250
mL/d
14 d Unclear
Wong
(2014)45
158 13 (76) 45 (82) Adults, inpatient 51.8 Various L casei Shirota Once daily Duration of
antibiotic
therapy + 7 d
High
Wright
(2015)46
87 5 (41) 4 (46) Adults,
inpatient,
outpatient
85.8 Various L casei Shirota Twice a day Duration of
antibiotic
therapy
Unclear
AAD, antibiotic-associated diarrhea; CFU, colony-forming units; COPD, chronic obstructive pulmonary disease.
Table 1. (continued)
Jafarnejad et al 507
Figure 2. Forest plot showing the association between probiotics (all strains) and antibiotic-associated diarrhea. M-H, Mantel–Haenszel
method.
Figure 3. Forest plot showing the association between probiotics and antibiotic-associated diarrhea in 2 clinical conditions: (a)
inpatient, (b) outpatient. M-H, Mantel–Haenszel method.
508 Nutrition in Clinical Practice 31(4)
significant relationship (5 RCTs, 3434 individuals; RR, 0.94;
95% CI: 0.76–1.15) between the risk reduction of the AAD and
probiotic use (Figure 4b).
Subgroup Analysis
The heterogeneity testing showed a statistically significant
result (χ2 = 69.12, P < .001, I2 = 58%). Because significant
heterogeneity might be attributable to the studies with high risk
of bias (no definition of diarrhea, lack of description of meth-
ods, incomplete follow-up), these trials were excluded as a
subgroup. Thus, both “high risk of bias” and “low risk of bias”
subgroups were extracted, which were as follows: high risk of
bias with 10 trials (χ2 = 35.42, P < .0001, I2 = 75%) and low
risk of bias with 11 trials (χ2 = 14.91, P = .14, I2 = 33%). The
latter (low risk of bias) resulted in a homogenous group involv-
ing 1935 individuals (Figure 5). However, there are significant
differences in clinical outcome in both groups of bias.
The association between risk reduction of AAD and the use
of all species of Lactobacillus (22 RCTs, 5828 individuals;
RR, 0.66; 95% CI: 0.57–0.77), S boulardii (11 RCTs, 1832
individuals; RR, 0.5; 95% CI: 0.38–0.64), and all species of
bifidobacteria (13 RCTs, 4511 individuals; RR, 0.77; 95% CI:
0.65–0.92) was observed (Figure 6).
The estimation of publication bias was based on the funnel
plot. Figure 7 shows the funnel plot with random effects. The
symmetrical inverted funnel plot demonstrated the absence of
significant bias.
Discussion
It is well known that antibiotic therapy can disrupt the balance
of microbiota, involving overgrowth of pathogenic microbes
relative to beneficial flora. This allows pathogenic bacteria to
colonize the gut and gain access to the gastrointestinal mucosa,
precipitating diarrhea and predisposing patients to fluid and
electrolyte disturbances. However, exposure to antimicrobial
agents may contribute to CD infection. Since this infection has
a clinical spectrum ranging from mild diarrhea to fulminant,
potentially fatal colitis and severe conditions, the participants
with CD infections were excluded from the study.
Probiotics can confer health benefits in different ways: (1)
competing for binding sites by antagonistic activity against
pathogenic bacteria50; (2) increasing sIgA production following
Figure 4. Forest plot showing the association between probiotics and antibiotic-associated diarrhea in 2 target populations: (a) adults,
(b) geriatrics. M-H, Mantel–Haenszel method.
Jafarnejad et al 509
stimulation of mucosal defense at the level of epithelial and
immune function45; (3) increasing anti-inflammatory cytokine
levels and decreasing proinflammatory factors51; (4) inducing
production of protective substances by the epithelium, such as
bacteriocins (antimicrobial peptides) and hydrogen peroxide,
mucins,52 and heat shock proteins53; and (5) preventing bacterial
translocation and improving the intestinal barrier function by
competing for receptors or adhesion to endothelial cells,54 by
creating nutrient competition, by favorably altering the micro-
biota, and by reducing osmotic diarrhea. The main objective of
this study was to evaluate the scientific evidence from RCTs on
probiotic interventions for the treatment of AAD. Meta-analyses
of AAD in the literature indicated the effectiveness of probiotics
for the treatment of AAD generally, but there are issues that
remained and limited the conclusions for elderly population. For
instance, the analysis of populations, especially adults and
elderly patients, in studies has not been assessed separately.
Assessment of the efficacy of specific strains is another impor-
tant part because studies showed that the relative efficacy of pro-
biotic interventions may be strain specific.55
This meta-analysis revealed the favorable effects of probi-
otics on AAD in adults (not the elderly) treated with antibiot-
ics, regardless of the reasons for antibiotics prescription. The
principal finding of this review is that using probiotics as
adjunct therapy reduces the risk of AAD, with an RR of 0.58,
although this reduction was associated with heterogeneity.
A large number of subgroup analyses was carried out to
identify sources of statistical heterogeneity among the trials.
No systematic differences in results were identified across tri-
als with different clinical conditions, types of probiotics, and
biases. But the different levels of age groups showed different
results. As stated before, in the elderly group, there were no
significant differences in clinical outcome. However, it seems
that age (adults or elderly), next to bias level, is a potentially
important source of heterogeneity (χ2 = 35.42, P < .0001, I2 =
75%), perhaps because of limited studies of the elderly. One of
the main reasons of the unexpected results in elderly patients
was a large-scale study done by Allen et al. The trial followed
nearly 3000 inpatients aged ≥65 years. The analysis of the
study showed no evidence of a beneficial effect attributable to
the microbial preparation. The authors reported no significant
change of findings in regard to potential risk factors for AAD
and compliance with the trial interventions.20
The results of the current meta-analysis confirm the results of
prior meta-analysis.13,16 The distinctiveness and differentiation
that we found in our meta-analysis and other systematic reviews
are that they include only RCTs with a target population of
adults and especially the elderly, while other analyses include
Figure 5. Forest plot showing the association between probiotics and antibiotic-associated diarrhea in studies with 2 levels of bias: (a)
high risk of bias, (b) low risk of bias. M-H, Mantel–Haenszel method.
510 Nutrition in Clinical Practice 31(4)
children or adults in general. These analyses suggest that the use
of probiotics may have a beneficial effect in patients with AAD.
It seems that some class of antibiotics are more likely to
cause diarrhea as an adverse effect,14 but as seen in Table 1,
included studies rarely specified the antibiotics used. With a
variety of classes of antibiotics, the accurate analysis of dif-
ferential effectiveness by antibiotic taken is impaired. However,
our data do not let us draw firm conclusions about the effec-
tiveness of different strains of probiotics in prevention of diar-
rhea caused by different classes of antibiotics. According to
Figure 6. Forest plot showing the association between antibiotic-associated diarrhea and probiotics that used a product containing (a)
Lactobacillus species, (b) Bifidobacter species, (c) Saccharomyces boulardii. M-H, Mantel–Haenszel method.
Jafarnejad et al 511
existing trials, the prevention or treatment of AAD consists
primarily of Lactobacillus and Bifidobacter interventions,
which could be alone or in combination with other genera.
Although RCTs of interventions of all strains of probiotics
were eligible for inclusion in the meta-analysis, few trials with
strains including Bacillus or Enterococcus were identified
because of the limited use of these strains.
Our meta-analysis does not allow us to make a conclusion
regarding the efficacy of probiotics for the treatment of AAD
in elderly people, as the trials were limited, especially with
small sample sizes. In elderly patients, the meta-analysis of tri-
als of lactobacilli, bifidobacteria, or both showed that probiot-
ics administration for preventing development of AAD is not
firmly supported by the evidence.17 Therefore, a better under-
standing of the pathophysiology and the mechanisms of AAD
in elderly patients and the impacts of probiotics on them are
needed for guiding future studies.
The number of randomized trials assessing probiotics for
AAD has increased recently, whereas the RCTs with target pop-
ulation of elderly people are still low. Only 5 trials met the inclu-
sion criteria and are in the analysis as elderly studies, which is
low in comparison with adult or child studies. Yet, there are
some methodological limitations in the included studies, such as
inconsistent design/method and sample size. Thus, because of
the several limitations noted above, some steps are suggested for
improving the quality of research in this area. First, the efficacy
of specific genera and strains of probiotic and specific class/type
of antibiotic should be evaluated. Second, the target population
with a high risk of AAD and the best choice for probiotic therapy
should be identified. Finally, the cost-effectiveness of using pro-
biotics to prevent AAD in adults and elderly people should be
determined. So, to reach these goals, well-designed clinical stud-
ies with widely agreed outcomes are recommended.
Among the different strains of probiotics evaluated,
Lactobacillus casei, Lactobacillus acidophilus, and S boulardii
were more frequent in various studies and showed a favorable
effect on AAD. The minimum dose varies depends on the
strain of probiotic, which is 6–60 million CFU/d. The wide
range of dosage requirement may not have any problem,
because adverse events as reported are very rare. However, it is
difficult to draw firm conclusions concerning the safety of pro-
biotic agents for elderly patients, especially those who have
immune problems. Duration of intervention with probiotics
varies between 5–28 days, but about one-third of studies (10 of
30, 33%) reported that 2 weeks may be appropriate.
Several limitations should be highlighted in our meta-anal-
ysis. The primary limitations to this review were residual het-
erogeneity. The other limitations include poor selection and
documentation of the probiotic species. In spite of the exten-
sive searching for published studies in several databases, we
could not find unpublished data. Another limitation is the data
quality and the quantity of the existing data, which is true about
this and any systematic review. A further limitation is the
diversity of the methods of the included studies. Another
potential limitation was a small size in some trials, and the use
of inconsistent definitions of diarrhea across studies may be
problematic to obtain exact conclusion. Most documented
studies used blends of species and strains, and some interven-
tions were poorly documented. Some trials did not indicate the
strains used, and other studies did not show the potency of the
products tested. Based on these limitations, it is clear that the
heterogeneity of the studies is the main problem.
In summary, the results emerging from our meta-analysis
suggested that adjunct probiotic administration is associated
with a reduced risk of AAD in adults but not in elderly people.
Future studies should assess these factors and explicitly assess
the possibility of adverse events to better refine our under-
standing of the use of probiotics to prevent AAD in adults.
However, the optimal dose of the probiotic preparation, timing,
duration of treatment, and further delineation of the groups
(outpatient, inpatient, adult vs elderly) to target the best clinical
benefits from specific strains of probiotic therapy should be
considered in future studies.
Statement of Authorship
S. Jafarnejad, S. Shab-Bidar, and J. R. Speakman equally contrib-
uted to the conception and design of the research; K. Parastui and
M. Daneshi-Maskooni contributed to the design of the research;
and S. Jafarnejad, S. Shab-Bidar, and K. Djafarian contributed to
the acquisition, analysis, and interpretation of the data. All authors
drafted the manuscript, critically revised the manuscript, agree to
be fully accountable for ensuring the integrity and accuracy of the
work, and read and approved the final manuscript.
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