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Probiotics: panacea or simply a placebo?

Probiotics are widely hailed by patients as a harmless natural treatment ­ Professor Stephen Gillespie and

Dr Janet Gillespie discuss their efficacy and safety

robiotics are portrayed as a natural alternative treatment not requiring medical supervision. Evidence suggests they have a probable value in treating specific infection but studies are notoriously difficult to perform. A probiotic is defined as a formulation of living micro-organisms that exerts health benefits beyond their inherent nutritional value when ingested in significant numbers. They are classified as foods and sold in health food shops, supermarkets and pharmacies. Live yoghurt is the most common form.

More expensive tablet and capsule formulations are available offering specific organisms and dosages. However, some manufacturing processes may affect the ultimate viability of organisms in tablets.

Probiotics are not new. A century ago, it was suggested a lifelong intake of bacteria-laden yoghurt could be responsible for differences in longevity between ethnic groups.

Do probiotics work?

Claims for the efficacy of probiotics are based on the theory that there is a balance within the body's normal flora. Conventional medicine recognises that when either disease or antibiotics disturb this balance, one particular organism,

for example candidial vaginosis or pseudomembranous colitis, may become predominant.

Probiotics are difficult to assess by conventional scientific studies and trials. They are not a single entity ­ there may be any number of completely different organisms present in a formulation.

As each organism may only benefit a particular condition, it makes assessing their efficacy even more complicated.

An absence of standardised dosage regimens raises questions about the concentration of micro-organisms. Probable modes of action include:

- competing with pathogens for attachment sites

- competing with pathogens for nutrients

- releasing antibacterial substances

- stimulating host immunity.

How should they be given?

Enteric-coated tablet formulations can deliver probiotic organisms at a high enough dose for gut applications (enteric coating protects bacteria against digestion in the stomach). The milky formulation of live yoghurt offers similar protection against digestion in the stomach.

In the urogenital tract, local applications using live yoghurt administered vaginally using syringes or by dipping tampons is thought to be of some benefit, although neither means of delivery has been evaluated.

Treating the gut with probiotics has been shown to reduce infections of the urogenital tract.

Commercially available products generally have accurate labelling for their strains. The body will eradicate the bacteria fairly quickly, so it is necessary to keep using the probiotic to get any effect.

Are they dangerous?

Many anecdotal reports tell of patients developing septicaemia or endocarditis after receiving probiotic therapy. However, a Finnish study shows no associated rise in the number of cases of Lactobacillus bacteraemia, despite the increasing use of lactobacilli by the general population. It is probably safe to say that there may be a low risk.

Replacing like for like

It is relatively easy to argue for 'replacing' the vagina's indigenous lactobacilli if 'depleted' by competitive infection or following the use of antibiotics.

Ecessive growth of Gardnerella vaginalis, Prevotella bivia and Peptostreptococcus anaerobius will reduce the lactobacilli population. Gardnerella produces a toxin that acts directly on the lactobacilli of the vaginal flora.

In addition to restoring the normal bacterial balance of the urogenital tract, there is some evidence that lactobacilli have a prophylactic action in the vagina and may reduce the risk of further infection.

Probiotics and bowel infections

Gut flora is a complex ecosystem with more than 100 species of bacterium. How new organisms enter the system and establish themselves is not well understood.

 · Stomach Lactobacilli (Lactobacillus salivarius, Lactobacillus acidophilus and Lactobacillus casei subspecies rhamnosus) can inhibit growth of Helicobacter pylori, possibly by producing lactic acid or secreting an autolysin. Clinical studies have shown administration of Lactobacillus acidophilus La1 improves eradication of H. pylori in patients given standard triple therapy (antibiotics and proton pump inhibitors).

Lactobacillus has been shown to ameliorate the adverse effects of triple therapy: in one clinical trial that investigated prevention of side-effects, all the probiotic regimens were superior to placebo. Use of probiotics was not associated with better compliance of the triple therapy.

 · Intestine Probiotics may have a role in developing and maintaining the gut barrier. As such, they have a place in treatment of acute infectious diarrhoea.

Well-controlled clinical studies show probiotics, such as Lactobacillus rhamnosus GG, L. reuteri,

L. casei Shirota and Bifidobacterium lactis Bb12, shorten the duration of acute rotavirus diarrhoea. A multicentre study of probiotics in infectious diarrhoea showed significant curtailment of symptoms in patients with rotavirus infection but, paradoxically, not in cases caused by bacteria. With inflammatory bowel disease, the scope for probiotics to restore balance, and how they could do this, are less easy to understand.

Can probiotics help in

the urinary tract?

Probiotics are often promoted in prevention of recurrent urinary tract infection. Treatment is based on the rationale that changing the colonisation of the gut ­ which is the usual source for ascending UTI ­ reduces the risk of recurrent urinary infection.

Lactobacilli may have a role in achieving this by competing for receptors and by producing hydrogen peroxide and lactic acid.

Clinical trials are few and some results have been contradictory.

Evidence for use before or after conventional treatment

 · Before A clinical trial that used probiotics (Lactobacillus plantarum 299v) as prophylaxis against infection and sepsis in elective surgical patients found no significant difference between the two groups (in terms of bacterial translocation, gastric colonisation with enteric organisms or septic morbidity). By contrast, some investigators have shown considerable success in preventing surgical sepsis by combining probiotics with fibre.

 · After A minority of patients develop diarrhoea following antibiotic therapy. A review of a number of clinical studies demonstrates that when probiotics are given with antibiotics, there appears to be a decrease in the incidence of antibiotic-associated diarrhoea. Lactobacillus GG and Saccharomyces boulardii seem to provide the most benefit. The probiotic organisms administered, the dosages, and duration of administration differed between studies. Such variability has not promoted the cause of probiotics in this area of medicine.

In some patients disturbance to the gut flora following antibiotic therapy is more severe and they develop pseudomembranous colitis caused by the overgrowth of Clostridium difficile .

A combination of S. boulardii with the standard treatment of pseudomembranous colitis has shown to reduce the risk of relapse, although a subsequent study suggested the effect was limited to patients given probiotics and a high treatment dose of vancomycin.

Recommending probiotics

Evidence for using probiotics is increasing, and there is more to do in designing robust clinical trials. Lack of interest may slow this progress.

With the increasing problem of resistance, probiotic therapy may well prove to be a valuable ally in the future.

Our current knowledge supports their use as adjunctive therapy in bacterial vaginosis, vaginal thrush and recurrent urinary tract infection and they are of probable value in the management of viral and post-antibiotic diarrhoea.

Key points

 · Conventional scientific trials to assess the efficacy of probiotics are difficult to carry out

 · There is no statistical evidence that they are dangerous

 · Probiotics may be used as adjunctive treatment in bacterial and/or candidial vaginosis and in prevention of urinary tract infections

 · They have probable value in the treatment of viral diarrhoea and

post-antibiotic diarrhoea

Probiotics: panacea

or simply a placebo?

Useful websites

Further reading

Cremonini F et al. Effect of different probiotic preparations on anti-Helicobacter pylori therapy-related side-effects: a parallel group, triple blind, placebo-controlled study. Am J Gastroenterol. 2002;97:2744-9

D'Souza AL et al. Probiotics in prevention of antibiotic-associated diarrhoea: meta-analysis. BMJ 2002;324:1361

Guarner F, Malagelada JR. Gut flora in health and disease. Lancet 2003;361:512-9

Isolauri E. Probiotics for infectious diarrhoea. Gut 2003;52:436-7

McNaught CE et al. A prospective randomised study of the probiotic Lactobacillus plantarum 299V on indices of gut barrier function in elective surgical patients. Gut 2002;51:827-31

Rayes N et al. Influence of probiotics and fibre on the incidence of bacterial infections following major abdominal surgery ­ results of a prospective trial.

Z Gastroenterol. 2002;40:869-76

Salminen MK et al. Lactobacillus bacteremia during a rapid increase in probiotic use of Lactobacillus rhamnosus GG in Finland.

Clin Infect Dis. 2002;35:1155-60

Sheu BS et al. Impact of supplement with Lactobacillus- and Bifidobacterium-containing yogurt on triple therapy for Helicobacter pylori eradication.

Aliment Pharmacol Ther. 2002;16:1669-75

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