Enhancement of the anticoccidial activity of polyether antibiotics in chickens by tiamulin

Ionophore Toxicity in Animals: A Review of Clinical and Molecular Aspects

For many years, ionophores have been used to control coccidiosis in poultry. However, misuse of ionophores can cause toxicity with significant clinical symptoms. The most critical factors influencing ionophores' toxicity are administration dose, species, and animal age. Although clinical signs of ionophore intoxication are well studied, the toxicity mechanisms of the ionophores at the molecular level still are not fully elucidated. This review summarizes the studies focused on polyether ionophores toxicity mechanisms in animals at the clinical and molecular levels. Studies show that ionophore toxicity mainly affects myocardial and skeletal muscle cells. The molecular mechanism of the toxication could be explained by the inhibition of oxidative phosphorylation via dysregulation of ion concentration. Tiamulin-ionophore interaction and the synergetic effect of tiamulin in ionophore biotransformation are discussed. Furthermore, in recent years ionophores were candidates for reprofiling as antibacterial and anti-cancer drugs. Identifying ionophores' toxicity mechanisms at the cellular level will likely help develop novel therapies in veterinary and human medicine.

The In Vitro Cytotoxic Effects of Ionophore Exposure on Selected Cytoskeletal Proteins of C2C12 Myoblasts

Carboxylic ionophores, such as monensin, salinomycin and lasalocid, are polyether antibiotics used widely in production animals for the control of coccidiosis, as well as for the promotion of growth and feed efficiency. Although the benefits of using ionophores are undisputed, cases of ionophore toxicosis do occur, primarily targeting the cardiac and skeletal muscles of affected animals. The 3-[4,5-dimethylthiazol-2yl]-2,5-diphenyl tetrazolium bromide (MTT) viability assay was used to determine the cytotoxicity of monensin, salinomycin and lasalocid on mouse skeletal myoblasts (C2C12). Immunocytochemistry and immunofluorescent techniques were, in turn, performed to investigate the effects of the ionophores on the microfilament, microtubule and intermediate filament, i.e., desmin and synemin networks of the myoblasts. Monensin was the most cytotoxic of the three ionophores, followed by salinomycin and finally lasalocid. Monensin and salinomycin exposure resulted in the aggregation of desmin around the nuclei of affected myoblasts. The synemin, microtubule and microfilament networks were less affected; however, vesicles throughout the myoblast’s cytoplasm produced gaps within the microtubule and, to a limited extent, the synemin and microfilament networks. In conclusion, ionophore exposure disrupted desmin filaments, which could contribute to the myofibrillar degeneration and necrosis seen in the skeletal muscles of animals suffering from ionophore toxicosis.

Maximum levels of cross-contamination for 24 antimicrobial active substances in non-target feed. Part 8: Pleuromutilins: tiamulin and valnemulin

The specific concentrations of tiamulin and valnemulin in non-target feed for food-producing animals, below which there would not be an effect on the emergence of, and/or selection for, resistance in bacteria relevant for human and animal health, as well as the specific antimicrobial concentrations in feed which have an effect in terms of growth promotion/increased yield were assessed by EFSA in collaboration with EMA. Details of the methodology used for this assessment, associated data gaps and uncertainties, are presented in a separate document. To address antimicrobial resistance, the Feed Antimicrobial Resistance Selection Concentration (FARSC) model developed specifically for the assessment was applied. However, due to the lack of data on the parameters required to calculate the FARSC, it was not possible to conclude the assessment until further experimental data become available. To address growth promotion, data from scientific publications obtained from an extensive literature review were used. Levels in feed that showed to have an effect on growth promotion/increased yield were reported for tiamulin, while for valnemulin no suitable data for the assessment were available. It was recommended to carry out studies to generate the data that are required to fill the gaps which prevented the calculation of the FARSC for these two antimicrobials.

Compatibility of a combination of tiamulin and chlortetracycline with salinomycin in feed during a pulsed medication program coadministration in broilers

In an earlier study, the continuous medication of broiler feed with a combination of tiamulin (TIA; 20 mg/kg), chlortetracycline (CTC; 60 mg/kg), and the ionophore anticoccidial salinomycin (SAL; 60 mg/kg) caused an initial increase in BW and feed efficiency (FE; g of weight gain/kg of feed intake). However, as doses increased to combinations of 30 mg/kg of TIA and 90 mg/kg of CTC or 50 mg/kg of TIA and 150 mg/kg of CTC, there was a dose-related reduction in growth rate and FE. This was thought to be due to the interaction between TIA and SAL. In this study, using a protocol similar to the previous trial, broiler chicks were administered SAL at 60 mg/kg via the feed and the same inclusion rates of TIA + CTC. However, instead of feeding the birds continuously, considering the cost of TIA and possibly to compensate for the depressed growth attributable to the interaction with SAL, they were pulse-dosed for 1 to 10 d and again at 21 to 27 d, and the whole trial lasted 35 d to see if the intermittent pulses might reduce production losses. A total of 200 straight-run 1-d-old broiler chicks (Hubbard classic) were randomly distributed into 4 groups, with each group consisting of 5 cages containing 10 birds. The 20 cages were allocated to the 4 treatment groups on a random basis. The control diet, containing only SAL at 60 mg/kg, was fed to all birds throughout the 35-d trial, including the period during the gaps between dosing (i.e., d 11 to 20 and d 28 to 35). Feed and water were available for the whole trial period. Several serum enzymes (creatine kinase, lactate dehydrogenase, and aspartate aminotransferase) were determined from blood samples taken on d 35. Blood samples were also collected at 1, 19, and 35 d of age and were examined for antibody titers to Mycoplasma gallisepticum and Mycoplasma synoviae. Necropsy and histopathology of the birds (n = >or=4) were conducted during weekly intervals. There was no significant difference in weight gain, feed intake, and FE when the groups treated with TIA + CTC were compared with the control group (P > 0.05). There was no relationship between mortality and inclusion rates of the medication. No clinical signs of an interaction were exhibited during the trial, which was supported by necropsy and serum enzyme results. Maternally derived antibodies against M. gallisepticum were identified at the start of the trial but disappeared within 19 d, and infection with M. gallisepticum or M. synoviae was found neither serologically nor clinically during the trial. The results demonstrated that intermittent pulse administration of TIA at 50 mg/kg + CTC at 150 mg/kg from d 1 to 10 and d 21 to 27, along with continuous feeding of SAL (60 mg/kg), would be possible without altering performance and while maintaining the health status of the broilers. However, further research is required on the presence of artificial infections with Mycoplasma pathogens to determine the efficacy of the combination of TIA +CTC.

Tiamulin and semduramicin: effects of simultaneous administration on performance and health of growing broiler chickens

The pleuromutilin antibiotic tiamulin (TIA) is known to produce a variety of negative interactive effects when it is administered in combination with several anticoccidial ionophores. A 35-d growth study was performed in cages to evaluate the compatibility of TIA when it was administered concurrently with the poly-ether ionophore anticoccidial semduramicin (SEM). Tiamulin and SEM, both alone and in combination, were administered to 10 replicates of female broilers arranged in a completely randomized block design. Tiamulin was administered in drinking water (250 mg of TIA/kg of water) from d 15 through 19 of the study, whereas SEM was incorporated in feed (25 mg/kg) from placement to the conclusion of the test. Water consumption was determined during the period of concurrent administration of the drugs and weekly measurements of feed intake and bird performance were recorded. In addition, hematocrit, blood cell counts, serum protein, albumin, glucose, uric acid, electrolytes, and activities of several enzymes were determined from blood samples taken at d 35. Results indicated that simultaneous administration of TIA and SEM during the third week of the trial reduced water and feed intake resulting in a temporary growth depression. Feed efficiency was transiently affected during the period of coadministration. However, during the fourth week of the test, negative effects in body weight were not observed for any treatment and feed conversion improved for birds concurrently receiving TIA + SEM. By the termination of the experiment, no adverse effects were observed in final performance for any treatment. Histopathological and hematological parameters were unaffected by treatment at d 35 of the test. These results demonstrated that simultaneous administration of TIA and SEM produced only temporary impairments of water and feed consumption that transiently influenced performance. Neither mortality nor long-term effects on performance variables occurred in broilers.

Interaction of monensin and sulfadimethoxine in broilers, as mediated by hepatic microsomal cytochrome P-450 monooxygenases

The influence of monensin + sulfadimethoxine on cytochrome P-450 monooxygenase activity in broilers, and the possible consequences of modification of this system, including changes in blood levels of sulfadimethoxine, influence on the duration of xylazine-ketamine anesthesia, total antioxidant status and superoxide dismutase activity were studied. The results indicate that the combination of monensin + sulfadimethoxine gave a short-term inhibition of microsomal cytochrome P-450 monooxygenase activity but apparently did not influence the metabolism of other (exogenic) substances (ketamine, xylazine), and did not change the state of antioxidant systems or the relative liver weight. There was a rise in blood sulfadimethoxine levels.

Macrolide antibiotics, drug interactions and microsomal enzymes: implications for veterinary medicine

The macrolide group of antibiotics includes natural members, pro-drugs and semi-synthetic derivatives, thus named because they are composed of a large aglycone ring (from 14 to 16 carbon atoms), to which are attached several sugars. Some of them are amino-sugars, containing a diethylamino, tertiary amine function. A number of antibiotics, including erythromycin, oleandomycin, triacetyl-oleandomycin (troleandomycin), carbomycin, spiramycin, tylosin, rosamicin, azithromycin, clarithromycin, dirithromycin and others, are members of this group. On a comparative basis, erythromycin and oleandomycin are similar, with the same basic 14-carbon lactone ring and side chain sugars. The remaining compounds contain a basic 15- or 16-carbon lactone ring and one or two side-chain sugars. Most of the macrolides are produced by Streptomyces spp bacteria. An exception is rosamicin, which is produced by Micromonospora. Clarithromycin and azithromycin are new semi-synthetic derivatives of erythromycin.

Toxicosis in cattle from concurrent feeding of monensin and dried distiller's grains contaminated with macrolide antibiotics

Consumption of monensin-containing feed contaminated with macrolide antibiotic residues resulted in the death of cattle from multiple feedlots in south-central Kansas. Cattle were fed milo dried distiller's grains (DDG) with solubles from a common source in conjunction with the ionophore antibiotic, monensin. Deaths occurred as early as 72-96 hours after feeding and were preceded by either no premonitory signs or 1 or more of the following: anorexia, depression, dyspnea, locomotor deficits, and recumbency. Significant gross lesions were pulmonary and mesenteric edema, hepatomegaly, and generalized myocardial and skeletal muscle pallor that was confirmed histologically as acute myodegeneration and necrosis. Other significant histologic lesions included centrolobular hepatocellular necrosis, congestion, and pulmonary interstitial and alveolar edema with fibrin exudation. Animals that survived beyond 6 weeks had poor weight gain and coalescing foci of myocardial fibrosis with residual myocardial degeneration. Analysis of trace mineral supplements for monensin were within the manufacturer's label range. The DDG samples from affected feedlots had 50-1,500 ppm of erythromycin, clarithromycin, and related macrolide antibiotic analogues, which originated in the alcohol residue. In a preliminary feeding trial, cattle fed this contaminated DDG in combination with monensin had clinical signs and died with gross and histologic findings comparable to those of the field cases. Even though rations supplemented with the contaminated DDG contained approved levels of monensin, the clinical and postmortem findings were consistent with those expected for monensin toxicosis. The presence of macrolide antibiotic residues in the contaminated feed appeared to affect the biotransformation of otherwise nontoxic levels of monensin, leading to clinical ionophore toxicosis.

Effect of betaine on the growth performance of chicks inoculated with mixed cultures of avian Eimeria species and on invasion and development of Eimeria tenella and Eimeria acervulina in vitro and in vivo

At 7 d postinoculation (DPI) with a mixed culture of avian Eimeria species, 21-d-old chicks maintained in batteries and floor pens on a diet containing 0.15% (3 lb/ton) betaine plus 66 ppm (60 g/ton) salinomycin were significantly heavier and had significantly lower feed conversion ratios and mortality than chicks fed diets containing 0.15% betaine or 66 ppm salinomycin alone, or the control diet. At 31 DPI, when the chicks were 45 d old, the differences between the diet groups were not as great as at 7 DPI. In vitro, except at high concentrations, betaine was nontoxic to sporozoites of Eimeria tenella or Eimeria acervulina and had little effect on their invasion and development in cultured cells. In vivo, invasion by E. tenella and E. acervulina sporozoites was significantly reduced in all chicks fed diets containing betaine or salinomycin compared with that in control chicks. There was a significant interaction between betaine and salinomycin that impacted on invasion by both species. Overall development of E. tenella did not appear to be adversely affected by addition of betaine to diets containing salinomycin. Conversely, development of E. acervulina was reduced in chicks fed diets containing 0.075% (1.5 lb/ton) betaine plus 66 ppm salinomycin as compared with that in chicks fed salinomycin alone.

Tiamulin selectively inhibits oxidative hepatic steroid and drug metabolism in vitro in the pig

The simultaneous use of the antibiotic tiamulin with certain ionophoric antibiotics (monensin, salinomycin) may give rise to a toxic interaction in pigs and poultry. In the present study, effects of tiamulin on hepatic cytochrome P450 activities in vitro were studied using pig liver microsomes. When tiamulin was added to the incubation medium the N-demethylation rate of ethylmorphine and the hydroxylation of testosterone at the 6 beta- and 11 alpha-positions was strongly inhibited. Tiamulin inhibited these activities more than SKF525A or cimetidine, but less than ketoconazole. The microsomal N-demethylation rate of erythromycin and the hydroxylation of testosterone at the 2 beta-position were inhibited to a lesser degree, whereas the ethoxyresorufin-O-deethylation, aniline hydroxylation and testosterone hydroxylations at the 15 alpha- and 15 beta-positions were not affected by tiamulin. No in vitro complexation by tiamulin of cytochrome P450 resulting in a loss of CO-binding capacity could be demonstrated. Results from the present study suggest a selective inhibition of cytochrome P450 enzymes in pigs, probably belonging to the P4503A subfamily. The mechanism of this interaction is still unclear. However, interactions between tiamulin and those veterinary drugs or endogenous compounds which undergo oxidative metabolism by P450 enzymes must be considered. More research is needed to reveal which of the P450 enzymes are affected by tiamulin in order to improve the understanding and probably the predictability of this interaction.

Potentiation of ionophorous anticoccidials with dihydroquinolines: battery trials against Eimeria tenella in chickens

Seven battery tests, employing a total of 1344 Hybro cockerels, were conducted in order to study the interaction between ionophorous anticoccidials and a new dihydroquinoline-type antioxidant known as duokvin. A significant, non-selective, toxic interaction was established, resulting in growth depression and improved anticoccidal efficacy against Eimeria tenella and E. mitis in these chickens. The duokvin itself showed no appreciable activity against the coccidia. The adverse effects of the interaction were eliminated, and the anticoccidial efficacy of the approved levels of ionophores was maintained, when the dietary levels of monovalent cation ionophorous monensin, salinomycin and narasin were reduced to approximately 12% in the presence of 120 p.p.m. duokvin. No adverse effects on the growth of chickens appeared in the combination with maduramicin, yet the enhancement of anticoccidial activity allowed an approx. 50% reduction of this ionophore as well.

Anticoccidial efficacy of semduramicin in battery studies with laboratory isolates of coccidia

The anticoccidial activity of semduramicin against laboratory isolates of five species of poultry Eimeria was investigated. In laboratory scale battery trials, semduramicin at 20 to 30 ppm demonstrated broad-spectrum anticoccidial efficacy equivalent to salinomycin at 60 ppm. Also, semduramicin at 25 ppm was fed to uninfected cockerels in batteries for 21 days, and growth rate and feed efficiency were found to be equivalent to birds fed salinomycin at 60 ppm. Semduramicin was well tolerated when coadministered with tiamulin. Semduramicin demonstrated the same activity whether produced by semisynthesis or by direct fermentation.

Enhanced myotoxicity and involvement of both type I and II fibers in monensin-tiamulin toxicosis in pigs

Simultaneous administration of monensin and tiamulin to pigs resulted in enhanced myotoxicity. Skeletal muscles of tongue, diaphragm and legs were preferentially affected, whereas the masseter, longissimus thoracis and cardiac muscles, including the left auricle, were spared. Histochemical examination revealed an involvement of both type I and II fibers of skeletal muscles.

The effect of tiamulin administered by different routes and at different ages to turkeys receiving monensin in their feed

Healthy turkeys receiving 80 ppm monensin in their feed were injected at 26, 40 and 61 days of age with tiamulin at dosages of 12.5 and 25 mg/kg body weight. The aim of the study was to develop a regime for medicating with tiamulin turkeys receiving monensin in their feed, and which would circumvent the known toxicity created by the simultaneous administration of the two drugs. One injection of 12.5 mg/kg tiamulin up to the age of 61 days or 2 injections of 12.5 mg/kg tiamulin up to 40 days of age caused no mortality or adverse reaction.

Effect of dietary ingredients on monensin toxicity in chicks

A corn-soybean (CS) diet and diets containing medium or high levels of animal protein (AP) calculated to contain the same concentrations of the main nutrients promoted essentially the same growth rate and feed utilization in 20-day-old chicks. Supplementation with monensin sodium (100 or 120 mg/kg) depressed growth rate of the chicks fed all three diets. However, effect of the drug was much more severe in chicks fed the diets containing AP. This interaction resulted in significant (P < .05) differences in body weights between chicks fed the CS diet and PA diets. Moreover, feed-to-gain ratio was significantly (P < .05) adversely affected by monensin only in chicks fed the AP diets. Supplementation of the high AP diet with extra vitamin E, a mixture of arginine and tryptophan, or a mixture of silicon, chromium, and molybdenum failed to prevent the growth depression caused by monensin. These studies demonstrate that ingredient composition of diets for broiler chicks affects the magnitude of growth depression caused by monensin supplementation.