The residue kinetics and safety of R-salbutamol in ruminants

Prinsloo, Marlien (2019-04)

Thesis (MScAgric)--Stellenbosch University, 2019.

Thesis

ENGLISH ABSTRACT: With an increased demand to supply food to an ever-increasing world population the application of new technologies to improve animal production efficiency has become a global priority. A balance must be found however between the production benefit of these technologies, animal welfare and human safety. The purpose of the two studies undertaken was to determine the target animal tolerance of R-salbutamol when included in feed, the remaining residues in liver, kidney, muscle and fat following various withdrawal periods, and the withdrawal period at which animal tissue will be safe for human consumption. To determine the withdrawal period, the residues detected in animal tissue must be compared to the Acceptable Daily Intake (ADI) of R-salbutamol in humans. As no extensive toxicological evaluation has ever been done for R-salbutamol, a complete evaluation of available toxicological data was performed. Repeat dose studies, carcinogenicity, genotoxicity, reproductive, foetal and acute toxicity data were evaluated to determine the ADI. No carcinogenicity, genotoxicity or reproductive toxicity were noted for R-salbutamol. Long-term effects were observed with a No Adverse Effect Level (NOAEL) of 12 mg/kg BWt. Foetal toxicity (teratology) were noted at high inclusion levels in rabbits (cranioschisis at 50 mg salbutamol/kg BWt) with a NOAEL of 10.75 mg/kg derived from a rat teratology study. The Acute Reference Dose (ARfD), derived from human studies, was however the lowest safe level with a NOAEL (also referred to as the point of departure (POD)) of 1mg R-salbutamol/kg BWt, due to the possible acute effects of R-salbutamol ingestion at higher inclusion levels. An ARfD of 3 μg/kg BWt were calculated and used as the upper limit of the ADI, which was determined to be 0 - 3 μg/kg BWt in humans. The lamb feedlot study included 13 lambs; one lamb being slaughtered at the start of the trial as control. The remaining 12 lambs were treated with 21 mg R-salbutamol per day (0.5 mg/kg BWt) for 28 days. R-salbutamol was withdrawn from the feed 7 hours prior to slaughter for 6 of the lambs and withdrawn for 24 hours from the feed for the remaining 6 lambs. Liver, kidney, muscle and fat samples were collected at slaughter and analysed for parent and total salbutamol (parent + metabolites) residues. Heart rate, rectal temperature and respiratory rate were measured before the start of the medicated period (study day -1) and again on day 28 of the medicated period. Heart rate did not differ between day -1 and 28, but respiratory rate and rectal temperature were both higher at day 28 compared to day -1 (P < 0.05). The increase in rectal temperature was not clinically significant as it remained within normal parameters. The increase in respiratory rate in 7 of the 12 lambs was attributed to lower respiratory tract infection. Parent salbutamol residues in lambs were the highest in the liver (± 89% of residues detected) at 7 hours withdrawal, followed by the kidney (± 7%), fat (± 2.5%) and muscle (± 1%). The residue concentrations at 24 hours after withdrawal were less than 50% of the levels detected at 7 hours following withdrawal. Metabolism of R-salbutamol is rapid following absorption due to high pre-systemic metabolism as indicated by the high level of metabolites detected following hydrolysis of tissue samples with β-glucoronidase. At 7 hours after withdrawal, 44% of the total residues were present as parent salbutamol in the liver and 39% at 24 hours after withdrawal. In the kidney 28% and 30% of parent salbutamol were detected at 7 hours and 24 hours, respectively as a percentage of total salbutamol. Muscle had 47% parent salbutamol as a percentage of total salbutamol at 7 hours after withdrawal. The percentage reduced to 17% after 24 hours withdrawal. In fat, 11% of total salbutamol were present as parent salbutamol at 7 hours and 14% 24 hours after withdrawal. The theoretical maximum daily intake of salbutamol for humans calculated from the lamb residue data is less than 10% (16.88 μg/day) of the acceptable daily intake (ADI) (180 μg/kg BWt in adult human). Animal tissue from feedlot lambs fed R-salbutamol, according to label recommendations, with zero withdrawal in feed, will provide adequate consumer protection. In a similar study performed in beef cattle one group of four cattle received non-medicated feed as the negative control group. Three groups of six cattle each received 150 mg R-salbutamol/head/day (0.42 mg/kg BWt) in feed for 44 days. One animal from the control group was slaughtered on study day 3. The three medicated groups were slaughtered on <12-, 24- and 48-hours following withdrawal of R-salbutamol from feed respectively together with one each of the control group. The control animals were included to show that there were no residues occurring naturally within the test herd. Liver, kidney, muscle and fat samples were collected and analysed for salbutamol residues. No residues were detected for total salbutamol (LOQ = 3 μg/kg) in any of the tissues. No visual adverse events were observed in the study animals and R-salbutamol was well tolerated in feedlot cattle. From the data in this study MRL for R-salbutamol is therefore suggested to be set for liver at 300 μg/kg, muscle at 6.5 μg/kg, kidney at 40 μg/kg and fat at 13 μg/kg. At these levels the daily intake of residue will still be below 20% of the ADI. Further investigation into intravenous and oral pharmacokinetics of R-salbutamol in both lambs and cattle will be beneficial to better understand the absorption, distribution, metabolism and excretion of R-salbutamol in feedlot lambs and cattle.

AFRIKAANSE OPSOMMING: Met die toenemende vraag na voedsel vir 'n steeds toenemende wêreldbevolking, het die toepassing van nuwe tegnologie om die doeltreffendheid van diereproduksie te verbeter, 'n wêreldwye prioriteit geword. Daar moet egter ‘n balans gevind word tussen die produksie voordele van hierdie tegnologie, dierewelsyn en menslike veiligheid. Die doel van die twee studies wat onderneem is, was om die veiligheid van R-salbutamol te bepaal in die teiken diere na voer insluiting, die oorblywende residue te bepaal in lewer, niere, spier en vet na aanleiding van verskillende onttrekkingsperiodes en die onttrekkingstydperk waar dierlike weefsel veilig sal wees vir menslike gebruik. Om die onttrekkings periode te kan bepaal, moet die residue wat waargeneem is in die dierlike weefsel vergelyk word met die aanvaarbare daaglikse inname (ADI) vir R-salbutamol in mense. Geen ekstensiewe toksikologiese evaluasie is al ooit vir R-salbutamol gedoen nie. Gevolglik is ‘n volledige evaluasie hier gedoen op die beskikbare toksikologiese data. Herhaalde dosis studies, karsinogenisiteit, genotoksisiteit, reproduktiewe, fetale en akute toksisiteitsdata is geëvalueer om die ADI te bepaal. Geen karsinogeniese, genotoksiese of reproduktiewe toksisiteit is vir R-salbutamol opgemerk nie. Langtermyn effekte is waargeneem met 'n Geen Negatiewe Effek Vlak (NOAEL) van 12 mg/kg LM. Fetale toksisiteit (teratologie) is op hoë insluitingvlakke aangetoon in konyne (kranioskise teen 50 mg salbutamol/kg LM) met 'n NOAEL van 10,75 mg/kg LM, wat afgelei is van 'n rot teratologie studie. Die akute verwysingsdosis (ARfD), afgelei van menslike studies, was egter die laagste veilige vlak met ‘n NOAEL (ook verwys na as die Vertrek Punt (POD)) van 1 mg R-salbutamol/kg LM, as gevolg van die moontlike akute effekte as gevolg van inname van R-salbutamol. ‘n ArfD van 3 μg/kg LM is bereken en gebruik as die boonste limiet van die ADI, vasgestel as 0 - 3 μg/kg LM in mense. Dertien lammers is in the die eerste studie ingesluit; een lam is aan die begin van die studie as kontrole dier geslag. Die oorblywende 12 lammers is vir 28 dae behandel met 21 mg R-salbutamol per dag (0.5 mg/kg LM). R-salbutamol is 7 uur voor slag by 6 van die lammers uit die voer onttrek en onttrek vir 24 uur voor slag in die oorblywende 6 lammers. Lewer-, nier-, spier- en vet monsters is by slag ingesamel en geanaliseer vir biointakte en totale salbutamol (biointakte + metaboliete) residue. Hartklop, liggaamstemperatuur en respirasietempo is voor die aanvang van die medikasie periode (studie dag -1) en weer op dag 28 van die medikasie periode gemeet. Geen verskil is waargeneem in hartklop tempo tussen dag -1 en 28 nie, maar respirasietempo en liggaamstemperatuur was beide hoër op dag 28 in vergelyking met dag -1 (P <0.05). Die toename in rektale temperatuur was nie klinies beduidend nie, aangesien dit binne normale parameters gebly het. Die toename in respiratoriese tempo in 7 van die 12 lammers is toegeskryf aan lae respiratoriese infeksie. Biointakte salbutamol residue in lammers was die hoogste in lewer (± 89% van residue) by 7 uur onttrekking, gevolg deur nier (± 7%), vet (± 2,5%) en spier (± 1%). Die residu konsentrasies 24 uur na onttrekking was minder as 50% van die vlakke wat op 7 uur na onttrekking gemeet is. R-salbutamol metaboliseer vinnig na absorpsie as gevolg van hoë pre-sistemiese metabolisme, soos aangedui deur die hoë vlak van metaboliet wat gemeet is na die hidroliese van weefselmonsters met β-glukoronidase. Sewe ure na onttrekking was 44% van die totale residue in die lewer teenwoordig as biointakte salbutamol en 39% op 24 uur na onttrekking. In nier is 28% en 30% van ouer salbutamol as 'n persentasie van die totale salbutamol onderskeidelik by 7 uur en 24 uur na onttrekking aangetref. Spier het 47% ouer salbutamol as 'n persentasie van totale salbutamol by 7 uur na onttrekking gehad. Die persentasie het gedaal na 17% na 24 uur onttrekking. In vet was 11% van die totale salbutamol teen 7 uur as ouer salbutamol teenwoordig en 14% 24 uur na onttrekking. Die teoretiese maksimum daaglikse inname van salbutamol vir mense, bereken uit die data van die lam residu studie, is minder as 10% (16.88 μg/dag) van die aanvaarbare daaglikse inname (ADI) (180 μg/dag vir ‘n volwasse mens). Diereweefsel uit voerkraal lammers wat volgens die etiketaanbevelings R-salbutamol gevoer word, met ‘n nul onttrekking in voer, sal dus sal voldoende beskerming van verbruikers bied . In 'n soortgelyke studie wat in beeste uitgevoer is, het een groep van vier beeste nie gemedikeerde voer ontvang nie en gedien as die negatiewe kontrolegroep. Drie groepe van ses beeste elk het vir 44 dae 150 mg R-salbutamol / kop / dag (0.42 mg/kg LM) in voer ontvang. Een dier van die kontrolegroep is op studie dag 3 geslag. Die drie medikasie groepe is geslag op onderskeidelik <12, 24 en 48 uur na die onttrekking van R-salbutamol uit voer, saam met een elk van die kontrolegroep. Die kontrole diere is ingesluit om aan te toon dat daar geen residue binne die toets kudde voorkom nie. Lewer-, nier-, spier- en vet monsters is versamel en ontleed vir salbutamol residue. Geen residue is opgespoor vir totale salbutamol (LOQ = 3 μg / kg) in enige van die weefsels nie. Geen visuele newe-effekte is waargeneem in die studie diere nie, en R-salbutamol was dus goed verdra in voerkraalbeeste. Uit die data in hierdie studie word dit voorgestel dat die Maksimum Residu Vlak vir R-salbutamol ingestel word vir lewer teen 300 μg / kg, spier teen 6.5 μg / kg, nier teen 40 μg / kg en vet teen 13 μg / kg. Op hierdie vlakke sal die daaglikse inname van residu steeds onder 20% van die ADI wees. Verdere ondersoek na binneaarse en mondelingse farmakokinetika van R-salbutamol by beide beeste en lammers sal voordelig wees om die absorpsie, verspreiding, metabolisme en uitskeiding van R-salbutamol beter te verstaan in voerkraalbeeste en lammers.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/105761
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