sou · GLB3132d3 · 1998-01-01 00:00:00 — When olaquindox-resistant strains were used as challenge, the disease was not prevented, but morbidity was lower than in the non-medicated control group. and Libke (1976) prevented clinical signs of swine dysentery in experimentally infected pigs by dosages of olaquindox higher than what is permitted for growth promotion. These experimental results have been confirmed by various field studies. In a study from (Anonymous, 1980), carbadox at the maximum growth promoting dosage totally prevented occurrence of swine dysentery. Hunneman (1980) reported a notable decrease in outbreaks of swine dysentery in an area when carbadox was introduced as a feed additive in local swine herds. Molnar (1987) reported an attempt to eradicate swine dysentery from swine herds by the aid of carbadox at growth promoting levels. The eradication program failed, but on an individual basis, medication was successful both as a preventive and therapeutic measure. No carbadox-resistant 3ERPULINA spp. Colibacillosis and salmonellosis were also successfully prevented in the medicated herds. (1986) reported successful eradication of swine dysentery with in-feed carbadox at 5 ppm above the maximum growth promoting level. (1987) also reported successful eradication of swine dysentery on a farm with in-feed carbadox. The dosage used in this case was not reported. Some information is also available concerning the preventive effect of quinoxalines for other diarrhoeal conditions of pigs. Bertschinger (1976) found that olaquindox at low dosages (50 ppm) in feed was effective for prevention of experimentally induced % COLI-diarrhoea in piglets. (1994) found that prophylactic treatment with 122 ppm or 173 ppm olaquindox in commercial swine herds significantly (p<0.01) reduced the incidence of post-weaning diarrhoea in all but one of the herds investigated. From the herd where olaquindox had no prophylactic effect, % COLI resistant to olaquindox were isolated. Troutt and co-workers (1974) found that carbadox at the maximum growth promoting concentration reduced clinical signs and intestinal lesions in pigs experimentally infected with 3ALMONELLA Cholerasuis Winkelman and (1996) evaluated carbadox for the control of proliferative enteropathy in swine. Carbadox at growth promoting levels was found to reduce clinical signs and pathological lesions in pigs experimentally infected with ,AWSONIA INTRACELLULARIS (the causative agent of porcine proliferative enteritis). Stutz and co-workers (1984) showed that carbadox at 55 ppm significantly (p<0.05) reduced the amount of # PERFRINGENS (associated with necrotic enteritis) in the intestines of chickens. Carbadox is not used in poultry, so this may be of limited interest, but it is clear that carbadox is effective against clostridia, both IN VIVO and in . F.6 Impact of resistance on animal and human health Carbadox, and to some extent olaquindox, are used for prevention or therapy in veterinary medicine. Neither of those, nor related substances, are used in human medicine. As no information on possible cross-resistance to the modern quinolones, which are valuable drugs in human and animal medicine, is available, the impact of an emergence of resistance cannot be fully assessed. Quinoxalines are valuable for prevention of swine dysentery and weaning diarrhoea. Development of resistance in 3ERPULINA spp. olaquindox would entail reduced effectiveness of strategies employing quinoxalines for prevention of this disease. Few drugs are available for this purpose. However, available data indicate that the development of resistance to quinoxalines is slow. F.7 Other effects on the microflora The influence of carbadox treatment on salmonellosis was investigated by Troutt (1974). When fed at 55 ppm to pigs experimentally infected with 3ALMONELLA Choleraesuis, carbadox diminished the clinical signs and reduced the extent and severity of lesions. Development of resistance in salmonella towards carbadox has been documented (Mills and , 1986). investigations concerning possible effects of quinoxalines on infections with resistant strains of 3ALMONELLA spp. have been found. No information on the influence of quinoxalines on other food-borne pathogens such as #AMPYLOBACTER spp. or 9ERSINIA ENTEROCOLITICA has been A series of investigations concerning adrenal toxicity of quinoxalines, particularly carbadox, has been published. Field observations of intoxications in pigs fed high doses of carbadox (up to 150 ppm) were confirmed by an experimental study where 150 ppm carbadox was given to weaned pigs for up to 10 weeks (van der Molen ET AL , 1985). Clinical signs of dehydration and impaired growth were observed from 3 weeks and onwards. Histopathological examination revealed atrophy of the glomerular zone of the adrenal glands. In a subsequent experiment, pigs fed carbadox at doses between 25 and 200 ppm were investigated (van der Molen ET AL , 1986). The results confirmed the observation of adrenal damage as lowered plasma-aldosterone concentrations and corresponding changes in sodium and potassium in blood samples were observed for all doses. The magnitude of the effects were dose dependent. Further investigations into the pathomorphological changes showed that after 10 weeks of carbadox at 25 ppm or more, damage to the cells of the zona glomerulosa of the adrenal gland could be observed histologically (van der Molen, 1988). Again, the effects were dose and time dependent. Only two animals per dosage group were examined histologically. The hormonal changes induced by carbadox were further investigated (van der Molen ET AL , 1989). After 9 weeks, the levels of plasma renin were higher in all groups fed carbadox than in the control group. Taken together, these experiments show that carbadox supresses the mineral-corticoid secretion from the adrenal gland, inducing secondary hormonal changes in the renin-angiotensin system. These observations explain the clinical picture observed. The dose-dependent inhibition of the aldosterone production of porcine adrenal cells was confirmed by IN experiments (Spierenburg ET AL , 1988a; Spierenburg ET AL , 1988b; Jager ET AL , 1994). In a study comparing the effects of carbadox, cyadox and olaquindox similar toxic effects were noted. For olaquindox, adrenal toxcicity was observed, although less pronounced, at dosages of 100 ppm or more (Nabuurs ET AL , 1990). Again, the effects were dose- and time dependent. The clinical signs observed were also dose-related, ranging from mild to severe. At 50 ppm of carbadox or 100 ppm of olaquindox, mild effects in the form of increased faecal dryness were observed. Other signs included dehydration (urine drinking), decreased abdominal volume and lowered haematocrit values. Further, changes in hair quality, with hair becoming longer and withered, irritable behaviour and a decrease in feed intake and weight gain could sometimes be observed. It should be noted that also in other respects, there is a difference in activity between the substances, and carbadox is permitted in feed at a concentration of 50 ppm, whereas olaquindox is used at 100 ppm. In the IN VIVO studies cited above, the growth-rate of the medicated animals was either equal to or reduced compared to the control group. This is in conflict with the reported growth promoting effect of these substances. It is possible that in a field situation, the preventive effects of the quinoxalines against common enteric diseases act as confounders, i.e. if the (sub)clinical diseases negatively affect the growth-rate. Accidental overdosing of olaquindox (Köfer ET AL , 1990; Stockhofe- Zurwieden ET AL , 1991) and carbadox (ET AL , 1989) has been reported to cause death and severe adrenal damage in piglets. As the main early sign of intoxication with quinoxalines, i.e. dry faeces, may be mistaken for recovery from enteric disease, mild intoxications are expected to be overlooked by farmers and farm workers. Further, as the symptoms are diffuse, a definite diagnosis might be difficult to reach. F.8.2 Adverse effects in humans In a study where radiolabelled carbadox was fed to swine at 55 ppm for 5 consecutive days, total residues 30 days after withdrawal were around 5, 74 and /kg in muscle, liver and kidney, respectively. After 70 days, the measured concentrations in liver were 13µg/kg (FAO/WHO, 1990). Carbadox is rapidly metabolised to, among other metabolites, quinoxaline- 2-carboxylic acid (QCA) and desoxycarbadox. In a pig study on residues of carbadox and its metabolites, feeding of 50 ppm carbadox did not result in any detectable residues after a withdrawal time of one day (Baars ET AL , 1991). Desoxycarbadox was measurable in liver for 14 days (detection limit 1µg/kg). samples yielded residues of QCA above /kg in liver and kidney for 4 to 5 weeks. In an experiment by Rutalj (1996), QCA was still present at around /kg at 62 days after cessation of feeding of carbadox at 50 ppm. Detection of QCA is dependent on the extraction method used, and it has been suggested that this is due to other unknown intermediate metabolites in the pathway of carbadox to QCA (Baars ET AL , 1991). QCA, being the major residual metabolite, has been suggested as a marker substance for residue studies (FAO/WHO, 1990). Long term toxcicity studies on carbadox in rats have shown dose-related increases of benign and malignant liver tumors. Positive results were reported in 14 out of 15 mammalian and non- mammalian genotoxicity studies (FAO/WHO, 1990), clearly indicating a genotoxic potential of carbadox. Chronic administration of the meatabolite desoxycarbadox to rats has resulted in an increase of liver tumour incidence in all dosage groups (FAO/WHO, 1990; FAO/WHO, 1991). Most tests for genotoxicity have produced negative results, but positive findings were recorded in the cell transformation test and in Ames test using liver cells pre-treated with polychlorinated biphenyls. With respect to QCA, no studies indicate reasons to suspect carcinogenic or genotoxic properties (FAO/WHO, 1990; FAO/WHO, 1991) In the 36th report of JECFA (FAO/WHO, 1990) it was concluded that an could not be established, due to the carcinogenic and genotoxic nature of carbadox and some of its metabolites. MRLs set in 1990 (FAO/WHO, 1990) for QCA as marker substance were apparently based on the detection limit of the analytical method. Olaquindox is rapidly absorbed from the gut and mainly excreted via urine. No bound residues appear to be present in tissue (FAO/WHO, 1995). In a study where radiolabelled olaquindox was given to pigs as a single oral dose of /kg body weight, <1, 2 and /kg of total residues were detected in muscle, liver and kidney, respectively after 28 days. (FAO/WHO, 1990). At doses corresponding to recommended feed inclusion doses (/kg body weight) and a 28 days withdrawal period, olaquindox residues were below 5µg/kg in muscle and below 10µg/kg in kidney (FAO/WHO, 1995). The substance is extensively metabolised the animal. The metabolites found vary between tissues and between animal species (FAO/WHO, 1995). In pigs given 60 ppm olaquindox in the feed up to 16 weeks of age, and with a withdrawal period of 28 days, olaquindox residues were below 0.005 ppm in muscle and below 0.01 ppm in kidney (FAO/WHO, 1995). One of the metabolites, 3-methylquinoxaline-2-carboxylic acid (MQCA) has been chosen as a marker compound (FAO/WHO, 1995). Radiolabel studies indicate that the MQCA accounts for approximately of the total residues. In long-term toxicity studies in mice, an increase in the incidence of benign adrenal cortical adenomas and benign proliferative lesions in the lungs were noted at the highest dose level (/kg). There was no effect on the incidence of malignant tumours (FAO/WHO, 1990). In another long term study in rats, no increase in the incidence of tumours was noted. The genotoxicity of olaquindox has been investigated in a range of IN studies. Both positive and negative findings were reported in assays using various mammal and non-mammal systems (Nunoshiba and Nishioka, 1989; FAO/WHO, 1990). The marker substance, MQCA, is known to be responsible for the bacterial mutagenecity of other quinoxaline derivatives (FAO/WHO, 1995). No studies specific for olaquindox are available. An could not be allocated by JECFA 1995, because of the genotoxic potential of the parent compound and the absence of specific toxicity studies on the metabolites. No MRL has been set. Carbadox, olaquindox and other quinoxalines induce both photoxicic and photoallergic mechanisms through formation of a reactive oxaziridine reacting with proteins upon exposure to light (de Vries ET AL , 1990b). The photoallergic properties of olaquindox has been confirmed in studies on rats (de Vries ET AL , 1990a). Olaquindox-induced photoallergy has been described in pig breeders following airborne exposure (Schauder, 1989; Hochsattel ET AL , 1991; Schauder ET AL , 1996). In a report by Schauder (1996), twelve out of 15 patients habitually mixed feed containing 1000 ppm olaquindox on the farm, two of the patients only handled pellets. The average interval of exposure at onset of clinical signs for the patients who mixed feed was 2.5 years. The clinical symptoms are characterised by eczema worsened by sunny weather. At worst, the affected persons have to stay during daytime. The reaction may be persistent and can be severely disabling (Schauder ET AL , 1996). In spite of the experimental findings indicating similar properties of carbadox, no clinical reports have been found. Nonetheless, carbadox should be regarded as a potential photoallergen (de Vries ET AL , 1990b). Some comments on toxicological aspects The quinoxalines are suspected of having carcinogenic and genotoxic properties (Cihák and Srb, 1983; Nunoshiba and Nishioka, 1989). Carcinogenic and genotoxic effects are not acceptable since the effect could occur at very low intake levels, especially if the substance in question is ingested regularly over a number of years. Farm and feedmill workers are a special risk group, frequently exposed to when handling animal feed. If appropriate protection cannot be ensured, the handling of animal feed containing quinoxalines and other with potentially genotoxic effects must be regarded as an occupational hazard both due to potential genotoxicity and to photoallergenicity. Althogh the precise exposure cannot be determined, a conservative approach is often recommended for genotoxic substances in order to prevent underestimation of the risks. No information on the environmental fate of quinoxalines has been found. The quinoxalines are mainly excreted via urine (FAO/WHO, 1990; FAO/WHO, 1995). They are sensitive to photodegradation. Considering the potential genotoxicity of some of these substances, not only the fate of the parent substance but also of relevant metabolites should be investigated. Although transferable resistance to carbadox and olaquindox has been reported, the mechanisms and molecular biology of this or other resistance phenomena are still unclear. The precise target in the bacterium of the quinoxalines or their metabolites is still unknown. The development of resistance in important animal pathogens such as 3ERPULINA spp. No information is available concerning cross-resistance to the most modern class of antibacterials, the quinolones. Therefore, the impact of a possible emergence of resistance in enteric bacteria cannot be fully assessed. The preventive effects of carbadox and olaquindox against enteric diseases of pigs is well documented. Olaquindox and carbadox have several unwanted properties related to toxicology. Both substances have toxic effects on the adrenal glands of exposed animals at the dosages used for growth promotion. Profound disturbances in the stereoid balance of the animals, resulting in clinical signs of dehydration has been reported. The quinoxalines and some of their metabolites are, or are suspected to be, genotoxic. Olaquindox is a well known photoallergen and according to IN data, carbadox shares this property. Therefore, exposure to quinoxalines must be regarded as an occupational hazard. !NONYMOUS, 1980. Carbadox vs lincomycin in swine dysentery control. -ODERN 6ETERINARY 0RACTICE 152-153. !NONYMOUS, 1995. Scientific conference on growth promotion in meat production - report and conclusions. European Commission, . * *, 0 3PIERENBERG 4 * DE 'RAAF ' * AND 3EINHORST * 7 , 1991. 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