Disposition of oxfendazole in goats and efficacy compared with sheep

Researchin VeterinaryScience1991,51, 258-263

Disposition of oxfendazole in goats and efficacy compared with sheep N. C. SANGSTER, J. M. RICKARD, Department o f Veterinary Pathology, University o f Sydney, New South Wales 2006, Australia, D. R. HENNESSY, J. W. STEEL, CSIRO Division of Animal Health, McMaster Laboratory, Private Bag No 1, PO Glebe, New South Wales 2037, Australia, G. H. COLLINS, Department o f Veterinary Pathology, University of Sydney, New South Wales 2006, Australia

The disposition of intraruminally administered oxfendazole (orz) in goats was studied at 5, 10 and 20 mg kg-1. The area under the plasma concentration with time curve (AUC) increased with increasing dose but at a declining rate. AUC was lower after intraabomasal compared with intraruminal administration. OFZ was less effective against drug resistant Trichostrongylus colubriformis in goats than in sheep but was of similar efficacy against drug resistant Haemonchus contortus in both host species. In the same experiment peak plasma levels of OFZ in goats were about half those in sheep given the same dose. Of 70 goats tested in the field, total rumen bypass occurred in 12 per cent and partial bypass in 67 per cent. Lower systemic availability due to bypass would be expected to reduce further anthelmintic efficacy in goats. From the results of these experiments a dose rate of 10 mg k g - ~ is recommended for goats. When given at this rate as a divided dose at 12 hourly intervals over 24 hours, OFZ was significantly more effective than a single dose in reducing egg counts.

O X F E N D A Z O L E (OFZ) at 5"0 mg kg-1 has been effective in the treatment of the economically important gastrointestinal nematodes in goats (Elliott 1987, McKenna and Watson 1987). However, several reports indicate that OFZ has variable field efficacy (McKenna 1984). It is possible that lower drug levels in goats compared with sheep contributed to their reduced efficacy. After oral dosing, some OFZ is reduced to fenbendazole (FBZ), predominantly in the rumen (D. R. Hennessy and R. W. Steel, unpublished observations), and both compounds are absorbed from the gastrointestinal tract, and then metabolised in the liver to the sulphone (FBZ.SO2). All three compounds reach peak concentrations in the plasma of goats between 16 and 36 hours after dosing with OFZ (Delatour 1984, Bogan et al 1987). When goats were compared with sheep under pen conditions, the area under the plasma concentration with time curve (AUC) for OFZ in goats was about 80 per cent of that in

sheep (Delatour 1984, Bogan et al 1987). Activation of the oesophageal groove reflex, which permits drugs to bypass the rumen, is another possible reason for apparent failure of treatment in goats. In 42 per cent of 60 sheep orally dosed with OFZ, some of the drug passed directly into the abomasum resulting in rapid absorption and clearance with a concomitant reduction in efficacy against benzimidazole-resistant parasites (Prichard and Hennessy 1981). Lower systemic availability of the drug, from whatever cause, is unlikely to have noticeably reduced the efficacy of OFZ or other benzimidazole anthelmintics against gastrointestinal species of drug-susceptible parasites but may have increased selection for resistant strains and contributed to the rapid appearance of benzimidazole resistance in the trichostrongylid nematodes of goats (McKenna 1984). The aims of the present study were to measure the disposition of OFZ over a range of doses in goats and to measure the efficacy of OFZ against benzimidazoleresistant parasites in goats. The incidence of rumen bypass and the effectiveness of divided doses of OFZ in goats at pasture was also assessed.

Materials and methods

Experiment 1 Two male and two female dairy goats of mixed breed, weighing between 12 and 17 kg, were purchased from commercial producers. They had low faecal egg counts and were treated with ivermectin at 0.2 mg kg -~ (Ivomec; Merck, Sharp & Dohme, Australia) which reduced all faecal egg counts to zero. They were later surgically fitted with a cannula in the pyloric region of the abomasum. The presence of a cannula has not been associated with alterations in the kinetics of OFZ in sheep and it is assumed they caused no kinetic alterations in goats. The goats were individually penned and provided with a mixture of equal parts by weight of oats, wheat and lucerne chaff and 258

259

Oxfendazole in goats TABLE 1: Efficacy of oxfendazole (OFZ) against benzimidazole-resistant Haemonchus contortus and Trichostrongylus colubriformis in goats and sheep. Values are geometric means (with range), n = 5 Goats Worm count

Dose (mg OFZ kg - 1)

Sheep Worm count

% reduction

% reduction

Haemonchus contortus 0 2- 5 5 10 20

1015 143 83 25 12

(633-1500) (25-375) (50-100) (0-100) (0-100)

0 85" 9 91 -8 97-5 98 " 8

(3450-6200) (350-1425) (800-1450) (300-1300) (125-525)

0 82,6 77' 8 87.8 94.5*

384 77 16 21 0

(75-3525) (25-200) (0-133) (9-25) (0)

0 79.9 95"8 94'5 1O0

Trichostrongylus colubriformis 0 2.5 5 10 20

4499 782 997 548 247

3418 798 310 211 46

(2700-4350) (600-1100) (250-700) (100-500) (0-250)

0 76.7 90" 9 93 ~8 98- 7

* OFZ was significantly less effective in reducing worm burdens at 20 mg k g - 1 in goats than in sheep (P
water ad libitum. OFZ (Synanthic; Syntex Animal Health, Australia) was administered, sequentially at two-week intervals, at 5, 10 and 20 mg oEz kg -~ by intraruminal injection and at 10 mg kg -1 into the abomasum via the cannula. Blood was collected from a jugular vein into evacuated heparinised tubes at zero, two and four hours after administration, then every four hours to 36 hours, then every 12 hours until 96 hours.

Experiment 2 Twenty-eight Merino sheep and 28 goats of mixed breed, purchased from commercial producers, were maintained as described above. Two weeks before the start of the experiment faecal egg counts were performed and the three sheep and three goats with the highest counts discarded from the experiment. The remainder were treated orally with 7.6 mg kg l of albendazole (Valbazen; SmithKline Animal Health Products, Australia) and 16 mg kg -1 of levamisole (Ripercol; SmithKline Animal Health Products, Australia). Seven days later faecal egg counts of all animals were zero. The 25 goats were infected by intraruminal injection with 7500 infective larvae of Haemonchus contortus which was the 3 IVM strain of Waller et al (1989) (22 mg kg-1 thiabendazole was 95 per cent effective) and 15,000 infective larvae of Trichostrongylus colubriformis from Armidale (Dash 1986) (4"5 mg ovz kg -~ was 69 to 74 per cent effective). Twenty-five sheep were similarly infected with 5000 H contortus and 10,000 T colubriformis infective larvae. On day 28, }'aecal egg counts were ranked for each host species. For the goats the first five animals were randomly allocated into five'groups and the process repeated until there were five animals in each group. The same procedure was followed for the sheep. On day 29, the groups were treated with OFZ by intraruminal injection, at the rates shown in

Table 1. Samples of jugular blood were taken from all animals at 16, 20 and 24 hours after treatment. The animals were killed on either day 35 or 36, and the numbers of worms in the abomasum and small intestine were estimated using standard parasitological techniques.

Experiment 3 Five Angora goats, fitted with abomasal cannulae and maintained as above, were given 0.3 mg kg- 1 of glucose (30 per cent solution in water), by intraruminal injection, intra-abomasally and orally, on three successive days. Jugular blood was collected by syringe just before and 75 minutes after dosing, and the glucose concentration measured immediately using AmeS-BG reagent strips and Ames Dextrometer reflectometer (Miles Laboratories, Australia). This method gave results less than 5 per cent different from those measured spectrophotometrically with the hexokinase reaction (Mira/Cobas, Roche, Australia). The percentage increase in blood glucose concentration over the 75 minutes was calculated for each animal and for each route of administration. Seventy Angora goats of both sexes, aged one month to three years, were brought in from pasture, and dosed orally with glucose. The dosing procedure was designed to approximate drenching in the method, site of delivery and volume of the dose. The dosing and analysis protocol was the same as above.

Experiment 4 Two field experiments were performed with 36 and 24, one-year-old, male Cashmere goats. They were naturally infected with parasites and run on pasture (near Robertson, New South Wales). In both experiments the animals were allocated into groups in a fashion similar to experiment 2 except that groups

260

N. C. Sangster, J. M. Rickard, D. R. Hennessy, 3". W. Steel G. H. Collins

TABLE 2: Faecal egg count reduction in goats at pasture given various oral doses of OFZ. Values are geometric means of eggs per gram (epg). Reductions were calculated by comparing mean (n = 6) after treatment (day 1O) epg with controls (0 dose). Where multiple dosing was used, 24 hours (A) or 12 hours (B) elapsed between doses Dose r a t e (mg OFZ k g - 1)

Pre-treatment Post treatment epg epg

Experiment A 0 10 10+ 5 + 5 20 20 + 10 + 10 40

% reduction

O - - - - O FBZ

Intraruminal

1 "0"

--

~. OFZ

Faz.S02

0.80.6-

o

8

0.40.2-

2533 2420 2531 3020 2493 2553

Experiment B 0 10 5+2.5+2.5 10+5+5

1473 a 660 ab 97 c 600 ab 167 c 280 bc

0 53 93 66 89 81

0 10

1.0843 843 797 787

804 a 366 b 47 d 0c

0 54 94 100

-

20

~

30

40

50

60

Intra-ab0masal

70

90

100

o---o FBZ -.

~"

80

0"8-

~. OFZ

~

FBz.S0 2

E 0.6=o

Within each experiment after treatment epg with the same superscripts are not significantly different at P < 0 - 0 5

8

0.40'20"

/

10

were of six animals. Treatment groups were given single doses of OFZ at either 24 or 12 hour intervals (Table 2). One group in each experiment remained as untreated controls. The egg count 10 days after treatment was used to calculate the percentage reduction in faecal egg output compared with controls (Presidente 1985). Eggs recovered 10 days after treatment with 10 mg kg- 10FZ (experiment 4A only) were cultured for identification of infective larvae.

Drug concentrations Blood collected in experiments 1 and 2 was examined for OFZ and its metabolites by high performance liquid chromatography using the method described by Hennessy et al (1985).

Analysis of data The concentrations of oFz in experiment 1 were used to calculate its maximum concentration (Cmax), time of Cmax (Tmax), AUC, and the half-life in plasma 03T,/2) with a computer program for pharmacokinetic modelling (PCNONLIN, Statistical Consultants, Kentucky) in two compartments. AUGwas also calculated for the metabolites. Peak drug levels in experiment 2 were taken as the highest mean concentration at either 16, 20 or 24 hours after administration. These were subject to analysis in SAS (SAS Institute, Cary). The angular transformation was used when comparing ratios. Worm counts in experiment 2 and faecal egg counts in experiment 4 were log-transformed (count + 20) in order to stabilise variances, and subjected to analysis of variance. Further comparisons between

!

20

i- ~

30

I

40

~l

~

60

I

80

edit

70

I-

i

80

90

m

i

100

Time(h) FIG 1: Mean plasma concentrations in goats (n =4) of oxfendazole (OFZ), fenbendazole (FBZ) and fenbendazole sulphone (FBZ.S02) after intraruminal or intra-abomasal administration, of OFZat l O m g k g -1

groups were made by the method of Donald et al (1980). Results

Experiment 1 Plasma concentration profiles (Fig 1) following intraruminal administration of orz showed the presence of parent drug and its metabolites FBZ and FBz.SO2; OFZ was the predominant compound at each of the three dose rates. A curvilinear increase in AU¢ and Cmax occurred with increasing dose of OFZ (Table 3). Tmax was significantly earlier and /3T½ significantly shorter with 5 mg OFZ kg-1 than at 20 mg kg -1. Except for the relatively high level of FBZ with 5 mg kg-l, changes in the AUG of the metabolites at different dose rates paralleled those of ovz (see ratios in Table 3). FBZ was virtually absent after intra-abomasal administration but oFz had an earlier Tmax, an elevated Cmax and the AUC tended to be lower, but not significantly, compared with intraruminal administration at the same dose rate (Table 3, Fig 1).

Experiment 2 The relationship between dose rate and peak con-

261

Oxfendazole in goats TABLE 3: Pharmacokinetic parameters for OFZ in the plasma of goats given 0FZ intraruminally or intraabomasally. Ratios of AUC values for 0FZ and its metabolites are also given. Means of four animals (SEM)

Intraruminal Parameter

5

AUC (/xg m l - 1 h) Cmax(#gml-1) Tmax (h) /3T½ (h) FBZ:OFZ:FBz.SO2

12.7a (2-11) 0.35a(0-07) 12.0b (1 .8) 6.5a (1.0) 28:48:24

Dose rate (rag 0FZ kg - 1) Intra-abomasa[ 10 20 10

2 6 ' 7 b (1"90) 0 ' 5 5 b (0"04) 15.5bc (0.6) 8-5ab (0"4) 11:53:36

3 5 ' 8c (3"09) 0"61b(0"07) 17.6c (3-5) 9" lb (0"9) 15:46:39

18"3ab (3"41) 0 . 9 0 c (0-84) 4-1 a (1"5) NC 3:57:40

NC Not calculated; AUC Area under the concentration with time curve; Cmax Maximum concentration; Tma x Time of maximum concentration;/3T,/2 Half-life of elimination Means with different subscripts are significantly different at P < 0 ' 05

centration of OFZ metabolites in blood was curvilinear in both species. The concentrations of OFZ and its metabolites in goats were significantly (P < 0.01) lower at corresponding dose rates and consistently about half those in sheep (Table 4). The ratio of FBz.SO 2 to total metabolites (including orz) was significantly (P <0.01) higher in sheep. At all dose rates OFZ significantly reduced the counts of both worm species compared with the controls (P < 0.05) (Table 1). There was no difference in the efficacy of OFZ against H contortus between goats and sheep, but ovz at 20 mg k g - 1 was significantly less efficient against T colubriformis in goats than in sheep (P <0-05) (Table 1).

1614- --7

12-

I

=~ 10=o

I

F'-3 NObypass I I N Partialbypass I Complete bypass I

I

if-

64200

6

12 18 24 30 36 42 Percentage increase in plasma (glucose)

48

FIG 2: Frequency distribution of percentage increases in blood glucose concentrations in 70 goats after oral administration of O' 3 mg kg - 1 of glucose

Experiment 3 After intraruminal glucose administration no significant increase in blood glucose occurred; the upper limit of the 95 per cent confidence interval was a 3 per cent increase. When glucose was given into the abomasum, blood glucose concentrations increased 35 to 40 per cent. Results of the field experiment were therefore classified on the basis of: less than 3 per cent increase=no rumen bypass; 3 to 35 per cent increase=partial bypass; more than 35 per cent increase = total bypass. Total rumen bypass occurred in 12 per cent, partial bypass in 67 per cent and no bypass in 21 per cent of goats (Fig 2). All ages showed a similar distribution.

Experiment 4 A level of OFZ resistance was indicated by the poor efficacy of 10 and 20 mg kg -I of OFZ and the only marginal improvement at 40 mg kg-1 (Table 2A). Divided doses given at 12 or 24 hour intervals were significantly more effective than the same quantity of OFZ given as a single dose (Table 2A and B). The best efficacy was achieved with 12 hour intervals but it is difficult to judge whether 12 hour intervals were superior to 24 hour intervals as the groups were in

TABLE 4: Peak mean plasma concentrations (/~g m l - 1) of OFZ and its metabolites, FBZ and FBZ.SO 2, between 16 and 24 hours after OFZ administration in goats and sheep. Values are means, n = 4 (SEM)

Dose rate (mg kg - 1) 2'5 5 10 20

FBZ

Goats OFZ

FBZ.SO2

FBZ

Sheep OFZ

FBz.SO 2

0 " 0 1 8 (0-007) 0-066(0"026) 0 - 1 0 1 (0"025) 0-220(0'046)

0"085(0"011) 0-210(0"065) 0-350(0'033) O" 559 (0"086)

0 ' 0 2 6 (0'005) 0 " 0 4 2 (0 ' 004) 0-126(0"017) 0-198(0'025)

0-051 (0-004) 0"155(0"039) 0-259(0"051) O" 510 (0-057)

0-168(0"010) 0"412(0-100) 0'707(O'118) 1"284(O'118)

0-064(0'009) O" 180 (0'047) 0"307(0"098) O'588(0-125)

262

N. C. Sangster, J. M. Rickard, D. R. Hennessy, J. W. Steel, G. H. Collins

colubriformis as in sheep and that there is a positive relationship between peak plasma OFZ concentration (Table 4) and efficacy. However, despite the difference in plasma concentrations between sheep and goats, the efficacy against H contortus was similar in the two hosts. This is difficult to explain, especially as H contortus ingests blood and, in goats, presumably would take in significantly less drug than in sheep. The duration as well as concentration of drug in Discussion plasma and abomasal fluid may be important in The rectilinear relationship between the same dose efficacy although information on the relative levels of rates and AUC in goats reported by Bogan et al (1987) the drug in these two compartments in goats is was not seen in this study. For example, in the present lacking. A contemporaneous study of the pharmacostudy a fourfold increase in dose rate produced a kinetics of OFZ in sheep and goats including measurethreefold increase in AU¢ and a doubling of Cmax. ment of abomasal drug levels has since been perThe curvilinearity reported here suggests that the bio- formed in this laboratory and the results will be availability of OFZ in goats is limited at higher dose published later. The low systemic availability of OFZ in goats, rates. Furthermore, the later Tmax and longer /3Tv2 after 20 mg OFZ k g - 1compared with 5 mg k g - 1could especially infected goats, could be exacerbated by be due to prolonged absorption of the larger dose of rumen bypass after oral dosing. As some degree of drug delivered. Increasing the dose rate above 10 mg bypass of glucose occurred in 80 per cent of goats in k g - 1 provided only a marginal increase in AUC. This this study and as Prichard and Hennessy (1981) is supported by the generally lower activity of OFZ observed an inverse correlation between blood against T colubriformis in goats compared with sheep glucose concentration and AUC of OFZ in sheep when (Table 1) and the results of experiment 4A where a glucose and OFZ were coadministered orally, it is single dose of 40 mg k g - 1 was not significantly more likely that OFZ could bypass the rumen in a significant effective in reducing egg counts than 10 or 20 mg proportion of goats. As intra-abomasal dosing results in a 30 per cent lower AUC (Table 3), the effect of kg - l . Compared with sheep, goats had consistently lower ruminal bypass on plasma concentrations could be plasma concentrations of OFZ and its metabolites, at profound. The 80 per cent incidence in goats of mixed dose rates between 2.5 and 20 mg k g - I (Table 4). ages compares with only 42 per cent in six-month-old Similar differences were reported previously by sheep (Prichard and Hennessy 1981). In sheep, FBZ Delatour (1984) who showed that after giving 7.5 mg given into the abomasum was less effective in OFZ k g - 1 orally, the peak concentration in plasma of removing drug-resistant H contortus and T colubrigoats was 80 per cent of that in sheep. Bogan et al formis than when given into the rumen (Kelly et al 1977). A similar effect would be expected in goats. (1987) reported that after giving 10 mg OFZ k g - 1 the The anthelmintic efficiency of OFZ in goats may AUC in sheep was about 2.5 times that in goats, but the comparison is open to question as the two species therefore be limited by a number of factors and were examined at different times. The higher pro- increasing the dose rate beyond twofold, as is widely portion of F B z . S O 2 in sheep plasma suggests a more practised in the field, would provide little additional effective oxidation or less efficient removal of the benefit. Prolonging plasma OFZ concentrations may sulfone in this species. The presence of Ostertagia provide a better Option. In goats, daily dosing of OFZ circumcincta infection reduced the AUG of OFZ by 33 caused an apparent increase in AUG compared with per cent compared with uninfected goats (Bogan et al the same quantity of drug administered as a single 1987). In the present study, although the comparison dose suggesting that clearance of successive doses is is not direct, it is noteworthy that at each dose rate the delayed (Bogan et al 1987). Experiment 4 clearly Cma x values for OFZ from infected goats in showed that multiple dosing was superior, in terms of experiment 2 (Table 4) tended to be lower than in un- egg count reduction, to giving the same amount of drug as a single dose. Furthermore, when the dosing infected goats in experiment 1 (Table 3). The efficacy of OFZ against T colubriformis in interval was reduced to 12 hours, which is closer to the goats appeared to be lower than in sheep at 5, 10 and half-life of OFZ in goats (Table 3), a total dose of 10 20 mg kg -~, but the difference was statistically mg kg-~ eliminated egg counts of benzimidazolesignificant ( P < 0 - 0 5 ) only at 20 mg kg - l . This is resistant worms. Multiple dosing with OFZ may be the further evidence of the impact of lower drug con- most appropriate approach to the control of resistant centrations in goats. The results in Table 1 suggest goat parasites; however, dosing would be more that twice the dose may be needed in goats to achieve practical with a device or formulation which released the same efficacy against benzimidazole resistant T anthelmintic over a day or two.

different experiments. After a single dose of 10 m g kg - 1 0 F Z larvae derived from surviving eggs comprised 32 per cent Hcontortus, 49 per cent Ostertagia species and 19 per cent Trichostrongylus species which indicates that resistant strains of all three genera were present on this property.

O x f e n d a z o l e in g o a t s

Acknowledgements The authors thank Jane McCormack, Karen Parsons and Sally Pope for their technical support, a n d D r I. C. A . M a r t i n f o r t h e SAS a n a l y s i s . C o o p e r s Animal Health and Syntex Animal Health financially supported this work. N.C.S. was supported by the Wellcome Trust.

References BOGAN, J., BENOIT, E. & DELATOUR, P. (1987) Pharmacokinetics of oxfendazole in goats: a comparison with sheep. Journal of Veterinary Pharmacology and Therapeutics 10, 305-309 DASH, K. M. (1986) Multiple anthelmintic resistance in Triehostrongylus colubriformis. Australian Veterinary Journal 63, 45 -47 DELATOUR, P. (1984) Pharmacocinetique compar6e de l'oxfendazole chez la ehevre et le mouton. Les Colloqnes de l'Inra (Institut National de la Researche Agronomique [France]) No 28. pp 513-516 DONALD, A. D., WALLER, P. J., DOBSON, R. J. & AXELSEN, A. (1980) The effect of selection with levamisole on benzimidazole resistance in Ostertagia spp of sheep. International Journal for Parasitology 10, 381-389 ELLIOTT, D. C. (1987) Removal of Haemonchus eontortus, Ostertagia circumcincta and Trichostrongylus spp from goats, by morantel citrate, levamisole hydrochloride, fenbendazole, and oxfendazole. New Zealand Veterinary Journal 35,208-210 HENNESSY, D. R., LACEY, E., PRICHARD, R. K. & STEEL,

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J .W. (1985) Potentiation of the anthelmintic activity of oxfendazole by parbendazole. Journal of Veterinary Pharmacology and Therapeutics 8, 270-275 KELLY, J. D., HALL, C. A., WHITLOCK, H. V., THOMPSON, H. G., CAMPBELL, N. J. & MARTIN, I. C. A. (1977) The effect of route of administration on the anthelmintic efficacy of benzimidazole anthelmintics in sheep infected with strains of Haemonchus contortus and Triehostrongylus colubriformis resistant or susceptible to thiabendazole. Research in Veterinary Science 22, 161- 168 McKENNA, P. B. (1984) Gastrointestinal parasitism and 'anthelmintic resistance' in goats. Surveillance 11, 2-4 MeKENNA, P. B. & WATSON, T. G. (1987) The comparative efficacy of four broad spectrum anthelminties against some experimentally induced trichostrongylid infections in sheep and goats. New Zealand Veterinary Journal 35, 192-195 PRESIDENTE, P. J. A. (1985) Methods of detection of resistance to anthelmintics. In Resistance in Nematodes to Anthelmintic Drugs. Eds N. Anderson and P. J. Waller. CSIRO. pp 13-27 PRICHARD, R. K. & HENNESSY, D. R. (1981) Effect of oesophageat groove closure on the pharmacokinetic behaviour and efficacy of oxfendazole in sheep. Research in Veterinary Science 30, 22-27 WALLER, P. J., DONALD, A. D., DOBSON, R. J., LACEY, E., HENNESSY, D. R., ALLERTON, G. R. & PRICHARD, R. K. (1989) Changes in anthelmintic resistance status of Haemonchus contortus and Trichostrongylus eolubriformis exposed to different anthelmintic selection pressures in grazing sheep. International Journal for Parasitology 19, 99- 110

Received January 22, 1991 Accepted May 28, 1991