Evaluation of new anti-infective drugs for the treatment of acute infectious diarrhea. Infectious Diseases Society of America and the Food and Drug Administration

Pharmacokinetics and Safety of Rifamycin SV after Single and Multiple Doses of MMX® Modified Release Tablets in Healthy Male and Female Volunteers

The primary objective of this single- and multiple-dose pharmacokinetic study was the investigation of rifamycin SV’s pharmacokinetic profile in plasma and urine. All the 18 enrolled healthy men and post-menopausal women received modified release tablets containing 600 mg of the oral non-absorbable antibiotic, rifamycin SV, according to a multiple dose regimen: one tablet three times a day (daily intake: 1800 mg) for 14 consecutive days. Blood sampling and urine collection were performed up to 24 h post-dose after the first dose on Days 1 and 7. On average, on Day 1, C_max,0–24 was 5.79 ± 4.24 ng/mL and was attained in a median time of 9 h. On Day 7, all the subjects had quantifiable levels of rifamycin SV in plasma at each sampling time. After a peak concentration attained 2 h post-dose (mean ± SD concentration: 10.94 ± 16.41 ng/mL), rifamycin SV decreased in plasma to levels similar to those of Day 1. The amounts of rifamycin SV excreted in urine paralleled the plasma concentration at the corresponding times. On Day 1, the total amount excreted in urine was 0.0013%, and was 0.0029% on Day 7. The study results confirmed those of the previous Phase I study: the systemic absorption of rifamycin SV was also proved negligible after 7 days of the 600 mg t.i.d. dose regimen of the newly formulated tablets, currently under development for the treatment of several small and large intestinal pathologies, including diarrhea-predominant irritable bowel syndrome, hepatic encephalopathy, and others. Registered at ClinicalTrials.gov with the identifier NCT02969252, last updated on 26JAN18.

ACG Clinical Guideline: Diagnosis, Treatment, and Prevention of Acute Diarrheal Infections in Adults

Acute diarrheal infections are a common health problem globally and among both individuals in the United States and traveling to developing world countries. Multiple modalities including antibiotic and non-antibiotic therapies have been used to address these common infections. Information on treatment, prevention, diagnostics, and the consequences of acute diarrhea infection has emerged and helps to inform clinical management. In this ACG Clinical Guideline, the authors present an evidence-based approach to diagnosis, prevention, and treatment of acute diarrhea infection in both US-based and travel settings.

A systematic review of experimental infections with enterotoxigenic Escherichia coli (ETEC)

Volunteer challenge with enterotoxigenic Escherichia coli (ETEC) has been used for four decades to elucidate the pathogenesis and immune responses and assess efficacy of various interventions. We performed a systematic review of these studies and a meta-analysis of individual patient-level data (IPD) from a subset of studies using standard methodology. We identified 27 studies of 11 ETEC strains administered to 443 naive subjects at doses from 1×10(6) to 1×10(10) colony forming units (cfu). Diarrhea attack rates varied by strain, dose and enterotoxin. Similar rates were seen at doses of 5×10(8) to 1×10(10)cfu with the three most commonly used strains B7A, E24377A, H10407. In IPD analysis, the highest diarrhea attack rates were seen with strains B7A, H10407 and E24377A. The H10407 induced significantly higher stool output than the other strains. Additionally, the rate of output was different across strains. The risk of diarrhea, abdominal cramps, nausea and headaches differed significantly by ETEC strain. An increased risk of nausea, abdominal cramps and headaches was seen for females. Baseline anti-LT IgG titers appeared to be associated with a decrease risk of diarrhea outcomes, a trend not seen with anti-LT IgA or seen consistently with anti-colonization factor antibodies. Neither early antibiotic treatment nor diarrhea duration significantly affected the frequency or magnitude of serologic responses. These studies have served as an invaluable tool in understanding disease course, pathogenicity, innate immune responses and an early assessment of product efficacy. When designing and planning experimental ETEC infection studies in this age of increased ethical scrutiny and growing appreciation of post-infectious sequelae, better understanding of available data is essential.

Systemic absorption of rifamycin SV MMX administered as modified-release tablets in healthy volunteers

The new oral 200-mg rifamycin SV MMX modified-release tablets, designed to deliver rifamycin SV directly into the colonic lumen, offer considerable advantages over the existing immediate-release antidiarrheic formulations. In two pharmacokinetics studies of healthy volunteers, the absorption, urinary excretion, and fecal elimination of rifamycin SV after single- and multiple-dose regimens of the new formulation were investigated. Concentrations in plasma of >2 ng/ml were infrequently and randomly quantifiable after single and multiple oral doses. The systemic exposure to rifamycin SV after single and multiple oral doses of MMX tablets under fasting and fed conditions or following a four-times-a-day (q.i.d.) or a twice-a-day (b.i.d.) regimen could be considered negligible. With both oral regimens, the drug was confirmed to be very poorly absorbable systemically. The amount of systemically absorbed antibiotic excreted by the renal route is far lower than 0.01% of the administered dose after both the single- and multiple-dose regimens. The absolute bioavailability, calculated as the mean percent ratio between total urinary excretion amounts (ΣXu) after a single intravenous injection and after a single oral dose under fasting conditions, was 0.0410±0.0617. The total elimination of the unchanged rifamycin SV with feces was 87% of the administered oral dose. No significant effect of rifamycin SV on vital signs, electrocardiograms, or laboratory parameters was observed.

Antimotility agents for chronic diarrhoea in people with HIV/AIDS

BACKGROUND

AIDS-related diarrhoea is a common cause of morbidity and mortality in HIV positive individuals, especially in the sub-Saharan Africa where 70% of deaths from HIV occur. It often compromises quality of life both in those receiving antiretroviral therapy (ART) and the ART naive. Empirical antidiarrhoeal treatment may be required in about 50% of cases which are non-pathogenic or idiopathic and in cases resulting from antiretroviral therapy. Antimotility agents (Loperamide, Diphenoxylate, Codeine) and adsorbents (Bismuth Subsalicylate, Kaolin/Pectin, Attapulgite) are readily available, and have been found to be useful in this condition and so, are often used. Antimotilitics are opioids, decreasing stool output by reducing bowel activity thereby increasing fecal transit time in the gut, promoting fluid and electrolyte retention while adsorbents act by binding to fluids, toxins and other substances to improve stool consistency and eliminate the toxins. Due to its potential impact on the management of chronic diarrhoea in persons with HIV/AIDS, we reviewed the effectiveness of antimotility agents in controlling chronic diarrhoea in immunocompromised states caused by HIV/AIDS.

OBJECTIVES

To assess the effectiveness of antimotility agents in controlling chronic diarrhoea in people with HIV/AIDS.

SEARCH STRATEGY

We searched Medline, EMBASE, the Cochrane Controlled Trials Register, the Cochrane HIV/AIDS Register and AIDSearch databases in November 2006. We also contacted WHO, CDC, pharmaceutical companies and experts in the field for information on previous or on-going trials and checked reference list from retrieved studies, irrespective of language and publication status.

SELECTION CRITERIA

Randomised controlled trials comparing an antimotility agent or an adsorbent with another antimotility agent, placebo, an adsorbent or no treatment in children and adults diagnosed with HIV and presenting with diarrhoea of three or more weeks duration.

DATA COLLECTION AND ANALYSIS

Two authors independently undertook study selection and examined full articles of potentially eligible studies.

MAIN RESULTS

One trial was found assessing the use of an adsorbent (attapulgite) compared to a placebo for chronic diarrhoea in people with HIV/AIDS. It included 91 adults (Aged 18 to 60), diagnosed with AIDS and experiencing diarrhoea for at least 7 days. There was no evidence that attapulgite is superior to placebo in controlling diarrhoea by reducing stool frequency and normalising stool consistency on days 1 (0.34 (95% CI 0.01 - 8.15)), 3 (1.35 (95% CI 0.51 - 3.62)) and 5 (1.74 (95% CI 0.89 - 3.38)). This was a small trial and may not have had enough power to show evidence of effects. Five deaths were reported which was not classified according to the arms of the study.Studies assessing the use of antimotility agents were not found.

AUTHORS' CONCLUSIONS

This review highlights the absence of evidence for the use of antimotility agents and adsorbents in controlling diarrhoea in people with HIV/AIDS. While no trials assessing the use of Antimotilitics were found, the retrieved study showed that attapulgite was not better than placebo in controlling diarrhoea in HIV/AIDS patients . For optimum patient care, these agents can still be used, with greater emphasis placed on adjunct therapies like massive fluid replacement while evidence for practice is awaited from further studies and reviews.

Rifaximin treatment of pathogen-negative travelers' diarrhea

BACKGROUND

Antibacterial drugs appear to be effective in shortening the illness of a majority of cases of travelers' diarrhea.

METHODS

This was a subanalysis from two randomized, double-blind, placebo-controlled trials in adult travelers with acute diarrhea treated with rifaximin 200 mg three times a day or placebo for 3 days. Efficacy was assessed by the interval beginning with the first dose of medication and ending with the last unformed stool passed after becoming well [time to last unformed stool (TLUS)]; number of unformed stools passed; percent with clinical improvement; and incidence of wellness achieved.

RESULTS

Stool pathogens were not identified in pretreatment samples in 122 of 322 (38%) patients and 106 of 230 (46%) randomized to rifaximin and placebo, respectively. Among pathogen-negative patients, rifaximin was more effective than placebo for median TLUS (33 vs 68 h, p < 0.005), mean number of unformed stools passed (6.5 vs 8.6, p < 0.0001), and clinical wellness (77% vs 61%, p = 0.01). The adverse-event profiles between rifaximin and placebo were similar.

CONCLUSIONS

More than one third of patients with travelers' diarrhea had pathogen-negative illness. Rifaximin was effective in treating the illness without associated side effects. These results are consistent with the hypothesis that undetected bacterial pathogens are the most likely cause of travelers' diarrhea without definable cause.

Traveler's diarrhea in Thailand: randomized, double-blind trial comparing single-dose and 3-day azithromycin-based regimens with a 3-day levofloxacin regimen

BACKGROUND

Traveler's diarrhea in Thailand is frequently caused by Campylobacter jejuni. Rates of fluoroquinolone (FQ) resistance in Campylobacter organisms have exceeded 85% in recent years, and reduced fluoroquinolone efficacy has been observed.

METHODS

Azithromycin regimens were evaluated in a randomized, double-blind trial of azithromycin, given as a single 1-g dose or a 3-day regimen (500 mg daily), versus a 3-day regimen of levofloxacin (500 mg daily) in military field clinics in Thailand. Outcomes included clinical end points (time to the last unformed stool [TLUS] and cure rates) and microbiological end points (pathogen eradication).

RESULTS

A total of 156 patients with acute diarrhea were enrolled in the trial. Campylobacter organisms predominated (in 64% of patients), with levofloxacin resistance noted in 50% of Campylobacter organisms and with no azithromycin resistance noted. The cure rate at 72 h after treatment initiation was highest (96%) with single-dose azithromycin, compared with the cure rates of 85% noted with 3-day azithromycin and 71% noted with levofloxacin (P=.002). Single-dose azithromycin was also associated with the shortest median TLUS (35 h; P=.03, by log-rank test). Levofloxacin's efficacy was inferior to azithromycin's efficacy, except in patients with no pathogen identified during the first 24 h of treatment or in patients with levofloxacin-susceptible Campylobacter isolates, in whom it appeared to be equal to azithromycin. The rate of microbiological eradication was significantly better with azithromycin-based regimens (96%-100%), compared with levofloxacin (38%) (P=.001); however, this finding was poorly correlated with clinical outcome. A higher rate of posttreatment nausea in the 30 min after receipt of the first dose (14% vs. <6%; P=.06) was observed as a mild, self-limited complaint associated with single-dose azithromycin.

CONCLUSIONS

Single-dose azithromycin is recommended for empirical therapy of traveler's diarrhea acquired in Thailand and is a reasonable first-line option for empirical management in general.

Antibacterial Chemoprophylaxis in the Prevention of Traveler's Diarrhea: Evaluation of Poorly Absorbed Oral Rifaximin

The use of antibacterial drugs was first shown to effectively reduce the occurrence of traveler's diarrhea nearly 50 years ago. The approach was not encouraged for general use by a Consensus Development Conference in 1985 because of concerns about adverse effects of the drugs and the possible development of resistance against systemically absorbed drugs. When therapy with poorly absorbed rifaximin was shown to be as effective as therapy with systemically absorbed drugs in shortening the duration of traveler's diarrhea, without the development of resistant coliform flora, the use of rifaximin for the prevention of traveler's diarrhea was studied. In the present study, rifaximin provided 72% protection against the development of diarrhea and 77% protection against active or treated diarrhea during 2 weeks of drug administration to United States students in Mexico. Rifaximin offers a potentially useful approach for preventing traveler's diarrhea. Potential areas of future study include use of the drug to prevent diarrhea due to mucosally invasive bacteria, including ciprofloxacin-resistant Campylobacter species, and to reduce the occurrence of postinfectious irritable bowel syndrome.

Rifaximin--a novel antimicrobial for enteric infections

Rifaximin is a poorly absorbed rifamycin antimicrobial drug with in vitro activity against Gram-positive, Gram-negative and anaerobic bacteria. The minimal concentration that inhibits 90% of strains of bacterial pathogens (MIC90) ranges between 32 and 64 microg/ml. Less than 1% of the drug is absorbed after oral administration. After three days of therapy, the average fecal level of this drug is 8000 microg/g of stool. Selection of resistant mutants, a problem with the related rifampin, appears to be unusual with rifaximin. Rifaximin shortens the duration of travelers' diarrhea and non-dysenteric diarrheal illness due to enterotoxigenic, enteroaggregative E. coli and Shigella sonnei without major alteration of aerobic fecal flora and without important side effects. The drug has been successfully used in preliminary studies of small bowel bacterial overgrowth syndrome and hepatic encephalopathy. To explain the beneficial effect of the drug on bacterial diarrhea without change in colonic flora or high rates of pathogen eradication, rifaximin may be more active against pathogens in the small bowel rather than the colon and/or the drug may alter the virulence of enteric pathogens in addition to organism inhibition.

Rifaximin in the Treatment of Infectious Diarrhea

Rifaximin matches the criteria for an ideal agent for the treatment of infectious diarrhea. It has excellent activity against a broad range of enteropathogens. It is nonabsorbable, which may help explain its excellent side effect profile and lack of emergence of resistance because of high stool levels that are not likely to reach subinhibitory levels before the target Gram-negative bacilli are killed. It has shown excellent efficacy in numerous clinical trials of bacterial diarrhea. Because of the lack of systemic absorption and minimal adverse reactions, rifaximin should be useful in treating hosts such as pregnant women in whom the currently favored fluoroquinolones are contraindicated. Uses limited to enteric indications and its inherently low propensity to induce sustainable resistance among Gram-negative flora favor the sustained usefulness of rifaximin in the treatment of enteric infectious syndromes.

Travelers' diarrhea: antimicrobial therapy and chemoprevention

The use of preventive measures and self-treatment for travelers' diarrhea is routine in regions where the occurrence of diarrhea is predictably high. People traveling to these areas who do not exercise care in their selection of consumed foods and beverages will suffer high rates of illness. Such diarrhea normally affects the traveler for a day, although it can result in chronic postinfectious irritable bowel syndrome. Although systemic antibacterial drugs are effective in preventing diarrhea, their use is not routinely recommended because of side effects and their importance as a therapy for extra-intestinal infections. This review focuses on current and future uses of antibacterial drugs in the prevention and therapy of travelers' diarrhea. Minimally absorbed (< 0.4%) rifaximin can effectively reduce the occurrence of travelers' diarrhea without side effects. Bismuth subsalicylate is a useful alternative, although it is less effective than rifaximin for the prevention of travelers' diarrhea and the required doses are less convenient. All people who travel to high-risk areas should take curative antimicrobial agents with them for self-treatment of illness: rifaximin 200 mg three times a day for 3 days, or an absorbable agent such as a fluoroquinolone or azithromycin taken in a single dose initially, with the need for a second or third dose determined by clinical response. Loperamide (up to 8 mg per day for < or = 2 days) can be given with the antibiotic to offer rapid symptomatic improvement. In the future, the ability to evaluate the genetic risk of illness acquisition might allow person-specific recommendations to be made.

The Role of Diet in the Treatment of Travelers' Diarrhea: A Pilot Study

A pilot study was performed to compare the effects of a restricted physiologic diet in 48 subjects with those of an unrestricted diet in 57 subjects on the duration and symptoms of acute travelers' diarrhea among US adults being treated with an antimicrobial agent in Mexico. Restricted physiologic diet was defined as the avoidance of certain foods during diarrheal illness, as specified in limited published literature. The mean duration of diarrhea (37 vs. 33 h) and clinical symptoms were similar between those practicing the restricted diet and those practicing unrestricted diets. These results suggest that restricting diet during treatment of travelers' diarrhea with an antimicrobial agent is not associated with improvement of clinical symptoms or with decreased duration of diarrhea. However, a much higher number of subjects would need to be studied to prove this point statistically.

Enteroaggregative Escherichia coli diarrhea in travelers: response to rifaximin therapy

BACKGROUND AND AIMS

We have recently shown that enteroaggregative Escherichia coli (EAEC) strains commonly cause travelers' diarrhea. The study was designed to determine whether U.S. travelers with EAEC diarrhea responded to rifaximin therapy.

METHODS

In a multicenter placebo-controlled clinical trial of travelers' diarrhea without non-EAEC pathogens we evaluated 2 doses of rifaximin. EAEC was sought in stool samples in enrolled subjects by HEp-2 cell assay. Response to rifaximin (both groups combined) and placebo were evaluated in EAEC-positive and EAEC-negative patient groups.

RESULTS

Compared with placebo, rifaximin shortened the postenrollment illness in travelers with EAEC diarrhea (median, 22 vs. 72 hours; P = 0.03). In subjects with EAEC-negative diarrhea, the median duration of post-treatment diarrhea was shorter with rifaximin (33 hours) than with placebo (52 hours), but this difference was not significantly different (P = 0.14).

CONCLUSIONS

Improvement of EAEC-mediated diarrhea with antibiotic treatment supports the pathogenicity of this organism in travelers to developing countries. The study provides information on the value of the poorly absorbed drug rifaximin in therapy of travelers' diarrhea.

Therapy of travelers' diarrhea with rifaximin on various continents

OBJECTIVE

Our aim was to compare the efficacy and safety of rifaximin, a virtually nonabsorbed antibiotic, 600 and 1200 mg per day, with placebo in patients with travelers' diarrhea.

METHODS

This was a multicenter, 1:1:1 randomized, parallel-group, double-blind study, conducted in Antigua, Guatemala; Guadalajara and Morelia, Mexico; and the coast of Kenya north and south of Mombasa. Adult patients with acute travelers' diarrhea were recruited; exclusion criteria included primarily medication that could influence the outcome. Subjects were treated for 3 days, three times daily; follow-up lasted 5 days. For each 24-h period, the subjects completed a diary card. Pre- and posttreatment stool, blood, and urine samples were assessed.

RESULTS

Among the 380 volunteers, median time to the last unformed stool was 32.5 and 32.9 h in both rifaximin groups, compared with 60.0 h with placebo (p = 0.0001). Also, secondary clinical outcome measures were favorably influenced by the active agent. No relevant side effects were reported.

CONCLUSION

Rifaximin is efficacious and safe for treatment of travelers' diarrhea at daily doses of 600 mg or higher.

A double blind, randomized, placebo-controlled study of SP-303 (Provir) in the symptomatic treatment of acute diarrhea among travelers to Jamaica and Mexico

OBJECTIVE

The study was designed to evaluate the effectiveness of SP-303 (Provir), a plant-derived product with novel antisecretory properties, in the treatment of travelers' diarrhea.

METHODS

A total of 184 persons from the United States who acquired diarrhea in Jamaica or Mexico were enrolled in a double-blind, placebo-controlled study examining the effectiveness of three doses of SP-303 in reducing illness. Subjects were treated with 125 mg, 250 mg, or 500 mg SP-303 or a matching placebo four times a day for 2 days. Subjects kept daily diaries of symptoms and were seen each day for 3 days. Of the subjects, 169 (92%) were included in the efficacy analysis.

RESULTS

The most common etiological agent identified was enterotoxigenic Escherichia coli, found in 19% of subjects. The mean time interval from taking the first dose of medication until passage of the last unformed stool during 48 h therapy (TLUS48) was 38.7 h for the placebo group. TLUS48 was shortened by SP-303: 30.6 h for the 125-mg dose group (p = 0.005); 30.3 h for the 250-mg group; and 32.6 h for the 500-mg group (p = 0.01). Treatment failures were seen in 29.3% in the placebo group compared with 7.3% (p = 0.01), 4.3 (p = 0.002), and 9.8 (p = 0.026) in the three treatment groups. SP-303 was well tolerated at all doses.

CONCLUSIONS

SP-303 was effective in shortening the duration of travelers' diarrhea by 21%. This antisecretory approach works directly against the pathophysiology of travelers' diarrhea and is not likely to potentiate invasive forms of diarrhea or to produce posttreatment constipation.

Susceptibility and serologic response of healthy adults to reinfection with Cryptosporidium parvum

Healthy adults are susceptible to infection with small numbers of Cryptosporidium parvum oocysts, resulting in self-limited infection. We investigated if infection of humans with C. parvum is protective 1 year after primary exposure. At 1 year after a primary challenge with 30 to 10(6) oocysts, 19 healthy immunocompetent adults were rechallenged with 500 oocysts and monitored for the development of infection and/or illness. Oocyst excretion was quantitated by direct immunofluorescence with a C. parvum-specific monoclonal antibody, and anti-C. parvum antibodies in serum were detected by an enzyme-linked immunosorbent assay. Fewer subjects shed oocysts after the second exposure (3 of 19; 16%) than after the first exposure (12 of 19; 63%) (P < 0.005). Although the rates of diarrhea were comparable after each of the two exposures, the clinical severity as determined by the mean number of unformed stools passed was lower after reexposure (11.25 versus 8.62; P < 0.05). The number of anti-Cryptosporidium immunoglobulin G and A seroconversions increased after secondary exposure. However, the C. parvum serum antibody response did not correlate with the presence or absence of infection.

Prognostic Factors Related to Recovery from Diarrhea among U.S. Students with Diarrhea in Mexico

Background: Medical charts of subjects treated with placebo from five double-blinded placebo-controlled clinical trials were reviewed to determine pre-enrollment prognostic factors related to later recovery from diarrhea. Method: Recovery or time from initiation of a placebo until passage of the last unformed stool after being declared well was calculated for each subject. Results: A longer duration of diarrhea was associated with presence of fever (rate ratio = 0.34; 95% CI = 0.2-0.9), presence of an invasive pathogen in the stool (rate ratio = 0.35; 95% CI = 0.2-0.7) or a noninvasive pathogen in stool (rate ratio = 0.7; 95% CI = 0.6-1.0), severe abdominal pain or cramps (rate ratio = 0.5; 95% CI = 0.3-0.9), passage of more than five watery stools per 24 hours (rate ratio = 0.58; 95% CI = 0.4-0.8). Severe vomiting predicted a shorter duration of post-enrollment diarrhea (rate ratio = 2.43; 95% CI = 1.1-5.6). Conclusion: A number of clinical and microbiologic factors found in travelers with diarrhea in the present study predicted duration of untreated diarrhea. The authors suggest the use of antimicrobial therapy in travelers with predictors of a long duration of diarrhea. Data developed in the present study may be used to create a historical control for clinical trials of antidiarrheal compounds using the same study criteria.

An open, controlled study of two non-absorbable antibiotics for the oral treatment of paediatric infectious diarrhoea

Forty-nine children in need of antibacterial treatment for a severe episode of bacterial diarrhoea were consecutively treated with either an oral paediatric suspension of rifaximin (100 mg every six hours for an average of four days: 24 patients), or paromomycin (125 mg every six hours for an average of four days: 25 patients). Stools (number and form), enteritis symptoms and signs, and intolerance manifestations were all monitored on each day of treatment. A stool culture was performed on the first available stool after enrolment and after the end of treatment to monitor the drugs' antibacterial activity. A similar rate of bacteriological cure, with normalisation of stools and elimination of the clinical symptomatology, was attained by the two antibiotics, with statistical significance of changes vs. baseline being apparent on the second treatment day, in both treatment groups. Rifaximin results were quicker (treatment lasted three days in several cases) and on the whole slightly better (though without statistical significance) than those of paromomycin: 21/24 vs. 20/25 children were completely cured, with a failure rate of three and five cases, respectively. Systemic and local tolerance of both treatments were very good in all children.

The infectivity of Cryptosporidium parvum in healthy volunteers

BACKGROUND

Small numbers of Cryptosporidium parvum oocysts can contaminate even treated drinking water, and ingestion of oocysts can cause diarrheal disease in normal as well as immunocompromised hosts. Since the number of organisms necessary to cause infection in humans is unknown, we performed a study to determine the infective dose of the parasite in healthy adults.

METHODS

After providing informed consent, 29 healthy volunteers without evidence of previous C. parvum infection, as determined by the absence of anti-cryptosporidium-specific antibodies, were given a single dose of 30 to 1 million C. parvum oocysts obtained from a calf. They were then monitored for oocyst excretion and clinical illness for eight weeks. Household contacts were monitored for secondary spread.

RESULTS

Of the 16 subjects who received an intended dose of 300 or more oocysts, 14 (88 percent) became infected. After a dose of 30 oocysts, one of five subjects (20 percent) became infected, whereas at a dose of 1000 or more oocysts, seven of seven became infected. The median infective dose, calculated by linear regression, was 132 oocysts. Of the 18 subjects who excreted oocysts after the challenge dose, 11 had enteric symptoms and 7 (39 percent) had clinical cryptosporidiosis, consisting of diarrhea plus at least one other enteric symptom. All recovered, and there were no secondary cases of diarrhea among household contacts.

CONCLUSIONS

In healthy adults with no serologic evidence of past infection with C. parvum, a low dose of C. parvum oocysts is sufficient to cause infection.

Rifaximin. A review of its antibacterial activity, pharmacokinetic properties and therapeutic potential in conditions mediated by gastrointestinal bacteria

Rifaximin is a derivative of rifamycin which acts by inhibiting bacterial ribonucleic acid (RNA) synthesis. It is virtually unabsorbed after oral administration; thus it is used primarily to treat local conditions within the gastrointestinal tract. In vitro data indicate rifaximin possesses good activity against species of Staphylococcus, Streptococcus and Enterococcus but lesser activity against species of Enterobacteriaceae. Bacterial resistance during exposure to rifaximin has been reported but its clinical importance remains to be fully defined. Results of comparative trials demonstrate that rifaximin is similar in efficacy to neomycin and lactulose in patients with hepatic encephalopathy and appears to be better tolerated. In 1 study, cyclical administration of rifaximin for 15 days per month was associated with progressive improvement over a 3-month period. In patients with infectious diarrhoea, rifaximin induces more rapid improvement in stool consistency and decreased frequency of faecal evacuations when compared with placebo, and is similar in efficacy to neomycin. Available data suggest rifaximin may be of some use in acute diverticulitis, but its use for the prevention of inflammatory complications or for control of common symptoms of diverticulosis requires further study. Preoperative treatment with rifaximin as antibacterial prophylaxis in colorectal surgery shows some potential but should be further investigated. Overall, rifaximin may be useful as an alternative therapy in hepatic encephalopathy but more data are needed to better define its clinical potential in infectious diarrhoea, diverticular disease and as antibacterial prophylaxis prior to colorectal surgery.

Zaldaride maleate, an intestinal calmodulin inhibitor, in the therapy of travelers' diarrhea

BACKGROUND

The therapeutic value of zaldaride maleate (Zm), an intestinal calmodulin inhibitor, was examined in patients with travelers' diarrhea, known to be caused by enterotoxigenic Escherichia coli (ETEC) and other bacterial agents.

METHODS

One hundred seventy-six American students acquiring diarrhea in Mexico during the summer of 1991 were given Zm in doses of 5 mg, 10 mg, or 20 mg, or a matching placebo, four times a day for 48 hours.

RESULTS

The duration of diarrhea was reduced by 53% in the group given the 20-mg Zm dose (overall P < 0.01). Curative antibiotics were required post-treatment only in the placebo and 5-mg Zm groups (P < 0.01). The number of unformed stools passed during 0-48 hours of therapy with the highest Zm dose was reduced compared with placebo by 36% for all subjects (P < 0.05), by 39% for ETEC diarrhea (NS), by 45% for those with any bacterial agents (NS), and by 38% for those without an identifiable bacterial agent (NS).

CONCLUSIONS

The fact that a calmodulin inhibitor decreases the severity and duration of travelers' diarrhea has therapeutic implications and suggests that calmodulin and intracellular calcium may serve as mediators of diarrhea in bacterial enteric infection.