The treatment of B. hominis infections remains controversial, particularly in light of its uncertain pathogenicity. Strong opinions have been expressed regarding the use of potentially dangerous chemotherapeutic agents to treat B. hominis, particularly without a thorough investigation of other possible causes of symptoms (Markell and Udkow, 1990; Markell, 1995). Additionally, there is some evidence that infection may be self-limiting in some cases, and intervention may not be required (Sun et al., 1989; Doyle et al., 1990; Albrecht et al., 1995). However, in the presence of chronic or acute debilitating symptoms for which no other cause is obvious, treatment by some means is warranted (LeBar et al., 1985; Vanatta et al., 1985; Lambert et al., 1992).
Conventional chemotherapeutic treatments tend to be largely empirical, using general anti-protozoal drugs, particularly 5-nitroimidazoles (Stenzel and Boreham, 1996). Variable success in treatment, either for reduction of symptoms or removal of organisms from the faeces, has been reported (Stenzel and Boreham, 1996). Antibacterial compounds, such as ampicillin, penicillin, streptomycin, gentamicin, colistin, ceftizoxime and vancomycin, and the antifungal compound amphotericin B do not appear to be effective against B. hominis and do not inhibit growth of the organism in vitro (Zierdt and Williams, 1974; Dunn and Boreham, 1991; Zierdt, 1991).
Efficacy of drugs used clinically to treat B. hominis has not been experimentally verified, with only two studies testing in vitro responses of B. hominis to various drugs. Zierdt et al. (1983) investigated the effects of 10 antiprotozoal drugs on the growth of four isolates, and Dunn and Boreham (1991) used one isolate to compare the efficacy of 42 drugs. Variability in response to drugs was noted among isolates and between the two studies. The drugs most commonly used to treat B. hominis infections in the clinical situation (metronidazole and iodoquinol) showed in vitro activity against the isolates used in these two studies. However, iodoquinol is no longer available in many parts of the world, due to its toxicity.
Recommended doses for metronidazole in the treatment of B. hominis infections in adults are in the range 200-750 mg three times per day, over a 5-10 day period (Stenzel and Boreham, 1996). Treatment failures have been reported at all dosage levels. Co-trimoxazole has been suggested as an alternative (Schwartz and Houston, 1992), particularly if symptoms persist after treatment with metronidazole (Zaki et al., 1991). Furazo-lidone has also been suggested to be effective and has been used as a treatment for B. hominis infections in AIDS patients (Narkewicz et al., 1989).
Traditional Chinese medicinal herbs have been examined in one in vitro study (Yang et al., 1996). From 20 crude extracts, two extracts (Brucea javanica and Coptis chinensis) were considered highly inhibitory to the growth of three isolates of B. hominis, although inhibition was not as great as with similar concentrations of metro-nidazole used for comparison in this study. However, the herbs were used as crude extracts and the active components may be far more efficacious if identified and purified prior to use.
Further in vitro testing of a wider range of B. hominis isolates is necessary to determine the variability in response to drugs and whether drug resistance occurs. Additional chemotherapeutic reagents, particularly those with minimal potential toxicity to the patient, need to be assessed. However, it must be recognised that in vitro testing cannot completely mimic the in vivo situation, and in vitro responses cannot necessarily be extrapolated to drug efficacies in humans or other hosts.
Other Management Strategies
Dietary management has been suggested to reduce symptoms or numbers of B. hominis found in patients' faeces (Swellengrebel, 1917;
Kain et al, 1987). In the most recent study (Kain et al., 1987), dietary management, including the introduction of a high fibre and/or lactose-free diet, resulted in a higher proportion of patients showing clinical improvement than those treated with metronidazole. However, dietary management of B. hominis infections has not been well assessed, and it is possible that B. hominis was not the primary cause of symptoms in the six patients responding to dietary change in this study.
It has been suggested that physiological changes in the intestine, such as changes in nutrient availability, redox potential or bacterial flora, may influence the growth of B. hominis (Miller and Minshew, 1988). Thus, dietary changes which influence such factors may be of potential benefit to patients. However, intestinal factors that are detrimental to B. hominis have not so far been identified, so efficacious dietary recommendations cannot yet be made.
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