Spectrum of antibiotic-associated diarrhoea

Systematic review: Clostridium difficile and inflammatory bowel disease

BACKGROUND

There is increasing concern about the apparently rising incidence and worsening outcome of Clostridium difficile infection (CDI) associated with inflammatory bowel disease (IBD). We have systematically reviewed the literature to evaluate the incidence, risk factors, endoscopic features, treatment and outcome of CDI complicating IBD.

AIM

To systematically review: clostridium difficile & inflammatory bowel disease.

METHODS

Structured searches of Pubmed up to September 2010 for original, cross-sectional, cohort and case-controlled studies were undertaken.

RESULTS

Of 407 studies, 42 met the inclusion criteria: their heterogeneity precluded formal meta-analysis. CDI is commoner in active IBD, particularly ulcerative colitis, than in controls. Certainty about a temporal trend to its increasing incidence in IBD is compromised by possible detection bias and miscoding. Risk factors include immunosuppressants and antibiotics, the latter less commonly than in controls. Endoscopy rarely shows pseudomembranes and is unhelpful for diagnosing CDI in IBD. There are no controlled therapeutic trials of CDI in IBD. In large studies, outcome of CDI in hospitalised IBD patients appears worse than in controls.

CONCLUSIONS

The complication of IBD by Clostridium difficile infection has received increasing attention in the past decade, but whether its incidence is really increasing or its outcome worsening remains unproven. Therapeutic trials of Clostridium difficile infection in IBD are lacking and are needed urgently.

Successful treatment with rifampin for fulminant antibiotics-associated colitis in a patient with non-Hodgkin’s lymphoma

A 74-year-old man was admitted to the hospital because of chemotherapy for relapsed non-Hodgkin’s lymphoma (NHL). The patient became febrile and experienced diarrhea after chemotherapy. Although ceftazidime and amikacin sulfate were administered as empiric therapy, diarrhea was continued. After several days, stool cytotoxin assay for clostridium difficile (C. difficile) was positive and he was diagnosed as having antibiotics-associated colitis (AAC). Although antibiotics were discontinued and both oral vancomycin and metronidazole were administrated, disease was not improved. To rule out the presence of an additional cause of diarrhea, colon fiberoscopic examination was performed. It revealed multiple deep ulcerative lesions at right side colon, surface erosive and minute erosive lesions in all continuous colon. Pseudomembranes were not seen. These findings are compatible with AAC without pseudomembranes. There are no reports that the rifampin is effective on refractory AAC. However, we administered oral rifampin for the current patient. The reasons are 1) conventional antibiotics were not effective, 2) rifampin has excellent in vitro activity against C. difficile, and 3) the efficacy of rifampin on relapsing colitis due to C. difficile is established. After administration of rifampin, fever alleviated and diarrhea was improved. Because AAC may result in significant mortality, patients with refractory or fulminant AAC should be treated with oral rifampin from outset.

Meta-analysis: the effect of probiotic administration on antibiotic-associated diarrhoea

BACKGROUND

Antibiotic-associated diarrhoea can be attributed in part to imbalances in intestinal microflora. Therefore, probiotic preparations are used to prevent this diarrhoea. However, although several trials have been conducted, no conclusive evidence has been found of the efficacy of different preparations, e.g. Lactobacillus spp. and Saccharomyces spp.

AIM

To conduct a meta-analysis of the data in the literature on the efficacy of probiotics in the prevention of antibiotic-associated diarrhoea.

METHODS

A literature search was performed of electronic databases, Abstract Books and single paper references. Data were also obtained from the authors. Only placebo-controlled studies were included in the search. The Mantel-Haenszel test was used to estimate the relative risk for single studies and an overall combined relative risk, each study being submitted to the Mantel-Haenszel test for homogeneity.

RESULTS

Twenty-two studies matched the inclusion criteria. Only seven studies (881 patients) were homogeneous. The combined relative risk was 0.3966 (95% confidence interval, 0.27-0.57).

CONCLUSIONS

The results suggest a strong benefit of probiotic administration on antibiotic-associated diarrhoea, but further data are needed. The evidence for beneficial effects is still not definitive. Published studies are flawed by the lack of a placebo design and by peculiar population features.

Pseudomembranous panenteritis and septicaemia in a patient with ulcerative colitis

Pseudomembranous colitis may occur in the immunocompromised chronic colitic patient without a prior history of antibiotic use. The entire gastrointestinal tract can be involved and the presentation can be that of a severe systemic infection that warrants prompt recognition and aggressive management.

Antibiotic-associated diarrhoea, Clostridium difficile, and short-chain fatty acids

BACKGROUND

It has been hypothesized that Clostridium difficile and decreased colonic production of short-chain fatty acids (SCFAs) cause the development of antibiotic-associated diarrhoea. We therefore wanted to investigate the effects of an intensive and uniform antibiotic therapy on faecal SCFAs concentrations. C. difficile, and extent of diarrhoea.

METHODS

Fifteen liver-transplanted patients who received oral bowel flora suppression therapy (6.3 g cefuroxime, 0.6 g tobramycin, and 0.5 g nystatin three times daily) were studied for 12 days before and 12 days after discontinuation of therapy.

RESULTS

Thirteen of the 15 patients (87%) developed diarrhoea. Colonic fermentation was negligible in all patients, judged by very low levels of faecal SCFAs (< 10 mmol/l). Diarrhoea lessened as suppression therapy proceeded despite continuous low levels of SCFAs. Initial stool frequency of 4.1 +/- 0.6 and viscosity of 2.5 +/- 0.2 per day (on a scale of 1-3; mean +/- SE) decreased to 2.2 +/- 0.5 (p = 0.0009) and 1.6 +/- 0.2 (p = 0.003) per day, respectively, just before cessation of suppression therapy. Both SCFAs and stool habits normalized within days after discontinuation of antibiotics. Only a few samples from 2 patients were culture-positive for C. difficile during therapy, whereas 9 of the 15 patients (60%) became culture-positive (6 cytotoxin-positive) after cessation of suppression therapy at a time when none had diarrhoea.

CONCLUSIONS

Intensive treatment with antibiotics directed against the colonic flora resulted in diarrhoea in the vast majority of patients, but the diarrhoea was self-limiting despite continual antibiotic treatment and very low faecal concentrations of SCFAs. C. difficile was not associated with antibiotic-associated diarrhoea but was a common finding after treatment with antibiotics was stopped at the time when diarrhoea had ceased.

Patterns and prognosis of Clostridium difficile colitis

The incidence of Clostridium difficile colitis has increased during recent years, presumably because of liberal use of broad-spectrum antibiotic regimens.

METHODS

A retrospective review to determine patterns of C. difficile colitis development, morbidity, and treatment results was undertaken. During an 18-month period, 90 patients were diagnosed with C. difficile colitis by fecal toxin assays. Patient demographics, symptoms, previously administered antibiotic regimens, diagnostic evaluations, treatment modalities, morbidity, and mortality were identified, entered into a computer data base, and analyzed.

RESULTS

The mean age was 58 years; males outnumbered females 1.2:1. Among 90 patients, 41 (46 percent) developed C. difficile colitis after surgical procedures. Eighty (89 percent) patients received antibiotic therapy before developing C. difficile colitis: 35 (44 percent) for documented infections and 45 (56 percent) as empiric or prophylactic therapy. Cephalosporins, penicillins, quinolones, vancomycin, and aminoglycosides were the most frequently administered antibiotic classes prior to C. difficile colitis diagnosis. Ten (11 percent) patients developed C. difficile colitis without previous antibiotic therapy. Eighty-two (91 percent) patients presented with diarrhea, while eight (9 percent) had fever only. Primary C. difficile colitis treatment for both groups included vancomycin (66 percent), metronidazole (24 percent), or both drugs (10 percent). Ten (11 percent) patients received no treatment. No patient developed toxic colitis or megacolon. Colonoscopy was performed in four (4 percent) patients; pseudomembranes were identified in one (25 percent) patient. There was one C. difficile colitis recurrence after treatment, but no C. difficile colitis-associated morbidity. Mortality (14 patients, 16 percent) was not related to C. difficile colitis, but to underlying illness. No difference in patient age, sex, previous antibiotic administration, serum albumin, total days hospitalized, duration of C. difficile colitis antibiotic therapy, C. difficile colitis treatment regimens, or mortality was identified between nonsurgical and surgical patients. The white blood cell count was significantly lower in the nonsurgical group however. Clostridium difficile colitis developed most commonly after antibiotic administration with symptoms of diarrhea, but did occur without previous antibiotic administration or diarrhea.

CONCLUSION

Despite the clinical setting, C. difficile colitis had no associated morbidity and treatment was highly effective. Mortality was related to underlying medical illness, not C. difficile colitis.

Antibiotic associated colitis

It is a prospective study based on 100 consecutive cases of diarrhea following antibiotic therapy admitted to the pediatric services of J.N. Medical College, A.M.U., Aligarh between January to December 1987. They had C. penicillin (50), chloramphenicol (34), ampicillin (34), gentamicin (34), cephalosporin (4) and cotrimoxazole (4) for 3 days to 3 weeks prior to the onset of diarrhea. Apart from routine and special investigations, naked eye and microscopic examination of stool, its culture for pathogens including Cl. difficile were carried out in all cases. Presence of Cl. difficile cytotoxin was demonstrated by observing the cytopathic. Effect on veru cell culture, 18 grew Cl. difficile (14 cyto toxin positive). Frequency of fever, vomiting, abdominal distension, dehydration and duration of diarrhea was not different (p > 0.05) in the two groups. Purge rate and presence of mucus and blood in Cl. difficile positive patients was significantly higher (p < 0.05). Eight Cl. difficile positive (7 cytotoxin+ve) were subjected to endoscopy. Three of them showed P.M. colitis and 2 non specific colitis. Chloromycetin, gentamicin and penicillin were the main culprits responsible for AAC. None of the patients given ampicillin alone suffered from AAC. The mortality was 5%.

Prevalence of Clostridium difficile on a mixed-function ward for the elderly

We studied the prevalence of Clostridium difficile over a period of 2 months on a mixed-function geriatric ward. Seven (14%) of the 49 patients were long-stay but the remainder were in hospital for acute illness or required a short period of active rehabilitation. Although 69% patients had recently received antibiotics, from only two (4%) was C. difficile isolated from their faeces. Our results show that C. difficile is not endemic in patients on all geriatric wards as has been previously suggested.

Prevention of antibiotic-associated diarrhea by Saccharomyces boulardii: a prospective study

Saccharomyces boulardii, a nonpathogenic yeast, has been widely used in Europe to prevent antibiotic-associated diarrhea (AAD). We performed a prospective double-blind controlled study to investigate AAD in hospitalized patients and to evaluate the effect of S. boulardii, a living yeast, given in capsule form concurrently with antibiotics. Over 23 mo, 180 patients completed the study. Of the patients receiving placebo, 22% experienced diarrhea compared with 9.5% of patients receiving S. boulardii (p = 0.038). Risk factors found to be associated with AAD were multiple antibiotic combinations (containing clindamycin, cephalosporins, or trimethoprim-sulfamethoxazole) and tube feeding. Clostridium difficile, an anaerobe found in the stools of most patients with pseudomembranous colitis, was variably associated with AAD. We evaluated the role of C. difficile in AAD in the study population and found no significant association between the presence of C. difficile or cytotoxin with AAD. Approximately 33% of the patients without diarrhea harbored at least one C. difficile-positive stool and nearly 50% of these patients had detectable cytotoxin. Similar values were obtained in patients with diarrhea. Of C. difficile-positive patients, 31% (5/16) on placebo developed diarrhea compared with 9.4% (3/32) on S. boulardii; this difference was not statistically significant (p = 0.07). There were no discernable adverse effects of yeast administration. We conclude that S. boulardii reduces the incidence of antibiotic-associated diarrhea in hospitalized patients.

A prospective randomized trial to compare triple dose mezlocillin with triple dose cefuroxime plus metronidazole as prophylaxis in colorectal surgery

The results of a prospective randomized clinical trial to compare three dose regimens of mezlocillin with cefuroxime plus metronidazole for prophylaxis in emergency and elective colorectal surgery are reported. Severe wound infection occurred in five patients (10%) receiving mezlocillin and in four patients (7%) receiving cefuroxime and metronidazole. There were two episodes of septicaemia, each in the mezlocillin group. The total number of surgically related infections was less with cefuroxime plus metronidazole (n = 10) compared with mezlocillin (n = 17), but this was not statistically significant (P greater than 0.1).

Nosocomial diarrhoeas in a surgical division hyperendemic for Clostridium difficile: epidemiologic aspects emerging from an analysis of clinical records

Having previously shown that Clostridium difficile was responsible for an intense and protracted endemic of nosocomial diarrhoeas in the surgical division of a Tuscan hospital, we started a retrospective analysis on all records from the affected division, to cover a period of 15 months. A statistical description is given of a large series of nosocomial diarrhoeas, as well as direct estimates of their incidence rates in selected high risk subgroups. The situation described is epidemiologically unique, and its study tells how an endemic may reach a steady state of high nosocomial morbidity.

Diagnosis of Clostridium difficile-associated intestinal disease

Toxigenic Clostridium difficile is the major cause of antimicrobial agent-associated pseudomembranous colitis and is the etiological agent of approximately 30% of cases of nonspecific colitis and diarrhea (without colitis) induced by antimicrobial agents. In addition, C. difficile has been implicated in certain intestinal diseases not related to prior antimicrobial administration. C. difficile has been reported to be one of the most common enteropathogens isolated from stool specimens submitted to hospital laboratories. Thus, diagnosis of C. difficile-associated intestinal disease should now be routinely performed in diagnostic clinical laboratories. The diagnosis of C. difficile-associated intestinal disease relies on the demonstration of either the organism or the toxin(s) in stool specimens or antibody response in serum to the toxin(s). Several selective medium are available for the recovery of C. difficile from stool specimens. The toxin(s) of C. difficile can be demonstrated using a variety of techniques, including biological assays as well as immunological assays. This article will review the techniques currently available to aid in the diagnosis of C. difficile-associated intestinal disease.

Effect of a lactobacillus preparation on the absorption of oral ampicillin

Lactobacillus preparations have been demonstrated to be beneficial in the prevention of antibiotic-associated diarrhea resulting from ampicillin. Since the bioavailability of oral ampicillin is known to be affected by food and fluid volume, a study to evaluate the influence of a lactobacillus product on ampicillin bioavailability was performed. Twelve healthy volunteers, male and female, were studied in a randomized three-way cross-over study. Each received ampicillin alone, ampicillin with a lactobacillus preparation, and ampicillin followed 1 h later by the lactobacillus preparation. Blood was sampled over a 6-h time period. Ampicillin content was determined by high-pressure liquid chromatography. Area under the concentration-time curve, area under the first moment of the concentration-time curve, maximum concentration of drug in plasma, time to maximum concentration of drug in plasma, and mean residence time were determined for each study interval. No differences in maximum concentration of drug in plasma, time to maximum concentration of drug in plasma, area under the concentration-time curve, or mean residence time were seen for either males or females or the combined group. The lactobacillus preparation as used in this study did not appear to interfere with the bioavailability of oral ampicillin.

The significance of quantitative results of C. difficile cultures and toxin assays in patients with diarrhea

The clinical courses of 114 patients with positive Clostridium difficile cultures or toxin assays performed between 1981 and 1984 were reviewed to determine the relationship between outcome of treatment and quantitative bacteriologic test results. C. difficile culture was positive in 60 of 91 patients while toxin assay was positive in 99 of 114. One third of the patients received supportive therapy only, and 30 percent of these failed to resolve their symptoms. Ninety-one percent of the patients treated with vancomycin resolved, although 11 percent of these suffered relapse. Patients with high toxin titers receiving supportive treatment alone showed a lower response rate than patients with lower toxin titers. This effect was not seen in patients treated with specific therapy nor with different culture quantities. C. difficile colitis has a range of clinical and microbiologic manifestations. Endoscopy is not always diagnostic, both culture and toxin assays are needed for diagnosis, and toxin titer may help in planning treatment. Patients with low toxin titers may be treated supportively, but high toxin titers are an indication for specific therapy. Quantitative culture results have little diagnostic or therapeutic value.

Antibiotic-associated colitis due to Clostridium difficile: double-blind comparison of vancomycin with bacitracin

A randomized double-blind study was carried out in patients with unresolving antibiotic-associated colitis due to Clostridium difficile, to compare the effect of bacitracin (80,000 U/day) with vancomycin (500 mg/day) on the resolution of symptoms, clearance of organism, and prevention of relapse. Forty-two patients with colitis, 9 of whom had a pseudomembrane, were randomized, 21 patients to each treatment group. The two groups were comparable in age, disease severity, and antibiotic exposure. For a 50% reduction in stool frequency the mean times (+/- SE) were 4.1 +/- 0.4 days for bacitracin and 4.2 +/- 0.4 days for vancomycin. Sixteen patients (76%) had symptom resolution after 7 days of treatment with bacitracin, compared with 18 patients (86%) given vancomycin. Patients who failed to respond were crossed over (blind) to the alternative antibiotic, but tended to be refractory to the alternative medication as well. Vancomycin-treated patients had negative toxin (83% vs. 53%, p = 0.04) and negative stool cultures (81% vs. 52%, p = 0.02) more frequently than did those patients given bacitracin. Similar numbers of patients in each group had symptomatic relapse during 1 mo of follow-up, but most of them relapsed yet again after blinded crossover therapy. Although bacitracin was significantly less effective than vancomycin in clearing C. difficile from the stools, both were of similar value in the control of symptoms in a group of patients with predominantly nonpseudomembranous colitis. In view of its low cost, bacitracin is a reasonable first-line alternative to vancomycin in the treatment of antibiotic-associated colitis.

Asymptomatic neonatal colonisation by Clostridium difficile

In a prospective survey of infants born in a single maternity unit, asymptomatic faecal colonisation by Clostridium difficile occurred in 31 (47%) of 66 babies who provided a faecal sample during week one of life and at age 14 and 28 days, and in 46 (30.7%) of the total of 150 babies for whom at least one faecal sample was obtained during the month of study. There was no evidence for acquisition of the organism from the mother during delivery and colonisation was unrelated to the means of delivery, infant sex, means of feeding, duration of hospital stay, or antibiotic treatment. New colonisation occurred throughout the month of the study and further evidence for environmental acquisition was obtained by the finding of a similar strain of C difficile in 7 babies from one ward together with positive environmental cultures. Colonisation was frequently transient and occasionally intermittent; most infants kept the same strain during their period of carriage. Twenty two (47.8%) babies colonised by C difficile had low titres of cytopathic faecal toxin but none had symptomatic diarrhoea or features of necrotizing enterocolitis. The in vitro toxigenic potential of 57 toxigenic isolates from 36 babies was low and 12 babies carried non-toxigenic strains. Transient colonisation by C difficile in early life is almost certainly more common than is generally recognized and the neonate provides an important reservoir of potential infection.

Clostridium difficile in young children. Association with antibiotic usage

Clostridium difficile was isolated from the stools of 11/52 (21%) of children aged 0 to 2 years hospitalized with diarrhoea, and from 17/52 (33%) of a control group of hospitalized children with no diarrhoea; this difference was not significant. Direct demonstration of C. difficile toxin from the stools was positive in 1 case with diarrhoea and in 5 control cases. The children with positive stool culture for C. difficile had had significantly more treatments with antibiotics or chemotherapeutics than those with negative C. difficile culture (3.3 +/- 2.7 vs. 1.6 +/- 1.8, p less than 0.001), but there was no significant difference in the incidence of diarrhoea in the past. During a 4-6-month follow-up, C. difficile disappeared from the stools of 24 out of 28 initially culture-positive children; 3 of the 4 children with persistent C. difficile had received antibiotics during the follow-up period. We conclude that the presence of C. difficile is common in the stools of young children up to the age of 2 years, and that C. difficile is more frequently found in children who have received antimicrobial therapy. Most cases of C. difficile carriage state are symptomless at this age.

Incidence and origin of Clostridium difficile in neonates

The stools of 65 of 92 (71%) infants in a special care nursery yielded Clostridium difficile on culture. Ninety percent of stools collected after 6 to 35 days in the unit were positive, and 36% of these also contained toxin. When tested in vitro, 94% of the isolates produced toxin. Of 110 swabs collected from the environment of the unit, 9% were positive for C. difficile, but the stools of 12 nurses working on the unit were negative. Thirty-five vaginal swabs collected from mothers just before delivery were negative for C. difficile on culture, but 16 of their infants had C. difficile in their stools. It was concluded that there is a high carriage rate in the stools of neonates of C. difficile acquired progressively during the course of their stay in the special care unit. Infection is mainly from environmental sources rather than maternal transmission.

A prospective randomized trial to compare mezlocillin and metronidazole with cefuroxime and metronidazole as prophylaxis in elective colorectal operations

A prospective randomized trial has compared a broad spectrum ureidopenicillin with a broad spectrum cephalosporin for prophylaxis against the aerobic organisms encountered during elective colonic surgery. Even though only two doses of antibiotics were administered the incidence of severe sepsis was low. Severe wound infection occurred in three of the patients receiving mezlocillin and metronidazole (6 per cent) compared with six in the group receiving cefuroxime and metronidazole (13 per cent). Minor wound sepsis was recorded in 24 per cent of patients receiving mezlocillin and metronidazole compared with only 11 per cent after cefuroxime and metronidazole. There were two episodes of septicaemia, one in each group, and three abscesses, all of which occurred in patients receiving metronidazole and mezlocillin. The total number of surgically related infections was, however, significantly less with cefuroxime and metronidazole (N = 13) compared with mezlocillin and metronidazole (N = 23; P less than 0.03). Escherichia coli was the principal organism responsible for surgically-related postoperative sepsis: (22 isolates: 14 mezlocillin and eight cefuroxime) all of which sensitive to the agents used. Pseudomonas aeruginosa was recovered from 10 patients (three mezlocillin and seven cefuroxime), all of the isolates were resistant to both antibiotics and were associated with severe morbidity. There were 11 isolates of Staphylococcus spp. (nine mezlocillin and two cefuroxime: P less than 0.03). Postoperative diarrhoea occurred in six patients, all were in the group receiving cefuroxime and metronidazole. (Clostridium difficile was recovered from the stool in three of which one was associated with Cl. difficile cytotoxin.)

Clostridium difficile and inflammatory bowel disease

Stools from 109 patients with inflammatory bowel disease (13.4%) contained Clostridium difficile or its toxin, an incidence similar to the stools of 99 control patients with diarrhoea (11.9%), but significantly higher than the stools of 77 control patients with a normal bowel habit (1.4%). Sixty-six per cent of the diarrhoea controls, but only 11% of the inflammatory bowel disease patients, reported recent antibiotic use: however, 67% of inflammatory bowel disease patients were taking sulphasalazine. The presence of Cl difficile in the stool was not related to the clinical assessment of inflammatory bowel disease relapse, but it was related to hospital admission. During the one year study, 31 of the 109 patients (28%) with inflammatory bowel disease had one or more stool samples that were positive for Cl difficile.

Infectious diarrhea. Which culprit? What strategy?

The patient with diarrhea is generally looking for prompt relief, not a prolonged diagnostic workup. In many cases effective treatment can be initiated after careful review of the clinical symptoms and of the patient's recent travel or other activities. Stool examination, sigmoidoscopy, or other studies may be necessary for definitive diagnosis or in refractory cases. Drugs are useful to combat many of the causative organisms, but in mild, self-limited infections, supportive therapy may suffice. Indeed, antimotility agents are contraindicated in some types of infectious diarrhea.

Nosocomial spread of Clostridium difficile

Environmental transmission of Clostridium difficile, the causative agent of antibiotic-associated pseudomembranous colitis (PMC), has been supported by animal studies and implicated in spread of C. difficile among leukemic children receiving non-absorbable antibiotics. We report antibiotic-associated C. difficile-related colitis in two adults who shared a commode chair during hospitalization.

Clostridium difficile toxin in acute diarrhoea complicating inflammatory bowel disease

The incidence of Clostridium difficile cytotoxin has been studied in 69 consecutive patients with inflammatory bowel disease complicated by severe diarrhoea or ileostomy flux during 74 admissions to hospital. The cytotoxin was identified in only four patients, all of whom had received antimicrobials. Clostridium difficle, but not cytotoxin, was identified in 10 of 43 admissions. This followed antimicrobial prophylaxis to cover a recent operation in two patients, and five were on long-term sulphasalazine. Only three patients with Clostridium difficile had not received an antimicrobial within one month of the study. Isolation of Clostridium difficile alone is of doubtful pathological significance, as it spontaneously disappeared without treatment in all patients.

Medical management of antimicrobial-associated diarrhea and colitis

Gastrointestinal complications, including diarrhea, may occur with virtually all antimicrobial agents. Such diarrhea may represent either a common, nonspecific adverse effect, or it may be one of the manifestations of antimicrobial-associated colitis (AAC), a potentially fatal complication. Clostridium difficile and a cytotoxin neutralized by Clostridium sordellii antitoxin has been isolated from the stools of nearly all patients with antibiotic-associated pseudomembranous colitis, many patients with AAC, and approximately 20% of those with antimicrobial-induced diarrhea. Demonstration that C. difficile is responsible for cytotoxin production has allowed for specific therapy for these disorders. General treatment measures include discontinuation of the causative antimicrobial agent(s), bowel rest, and supportive care with fluids, electrolytes and colloids, if necessary. Antiperistaltic agents and corticosteroids are not recommended. Various antimicrobials demonstrate potential efficacy in treating AAC in humans. Oral vancomycin is the most widely tested and is currently the treatment of choice. It achieves high concentrations in the feces and is very active against C. difficile in doses of 125-500 mg by mouth every six hours. Other potentially useful but inadequately tested antimicrobials include metronidazole (500 mg by mouth every eight hours) and bacitracin (25,000 units by mouth every six hours). Tetracycline has been employed with some success in nonspecific antibiotic-associated diarrhea, although it is as yet untested in humans with AAC and may induce diarrhea itself. Both miconazole and rifampin are highly effective against C. difficile in vitro but have not been evaluated in AAC. Anion-exchange resins bind the cytotoxin found in stools of patients with AAC. Cholestyramine has been used with variable response in oral doses of 4 g every six to eight hours. Since these resins may also bind vancomycin, resulting in lowered vancomycin concentrations in the stool, combination therapy should be used cautiously. With specific therapy directed against the toxin and aggressive supportive therapy, surgical intervention is rarely necessary. More recently, investigations have been directed at using bacterial preparations to suppress C. difficile by restoring the normal flora. The development of immunological agents (i.e., vaccines, toxoids, antitoxins) for the prevention or treatment of AAC would be a significant advance in therapy.