Chapter 10 Albendazole in Cattle Administered via a Sustained-Release "Captec" Device Downloaded via TUFTS UNIV on July 9, 2018 at 23:43:13 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.
Pharmacokinetics and Tissue Residues M.Y.K.Ho, D. W. Gottschall, andR.Wang Department of Drug Metabolism and Developmental Pharmacokinetics, SmithKline Beecham Animal Health, 1600 Paoli Pike, West Chester, PA 19380
The tissue residue levels and plasma pharmacokinetics of albendazole in cattle administered via a new sustained release 'Captec' device were studied. The daily dosage level released by the device of 0.9 mg/kg was maintained for up to 85 days for the eighteen devices studied. Neither albendazole (ABZ) nor albendazole sulfoxide (ABZ-SO) was detected in the plasma during the entire study period. The plasma albendazole sulfone (ABZ-SO2) level was 100 fold less than that observed when ABZ is given at the normal commercial single dose of 10 mg/kg b.w. and its presence can be used to monitor the proper functioning of the device. The albendazole marker (albendazole 2-aminosulfone, ABZ-NH2) residue levels in the liver of 'Captec' cattle at 0- and 5-Day withdrawal were 651 ± 38 ppb and 317 ± 43 ppb, respectively, the majority of which was bound residue. These values are significantly lower than the levels observed at similar withdrawal times when ABZ is given as a single 10 mg/kg dose. Thus, this type of sustained release formulation of albendazole lowered both the plasma and tissue residue levels of albendazole in cattle. Although not proven in this study, it is also highly likely that the relationship between the marker and total residue (Rm) is different from that of the single dose case. This difference may present a regulatory dilemma for the drug sponsor since a uniform method and marker threshold must be applied for each individual drug regardless of the type of formulation.
Albendazole (ABZ) is one of a class of benzimidazoles used to control helminth infections in cattle. It is generally administered as a single oral dose of 10 mg/kg b.w. either by bolus or drench. The residue levels and plasma pharmacokinetic profiles resulting from a single dose of A B Z are well documented (/). Recent studies have made important progress into alternative methods of anthelmintic
0097-6156/92/0503-0148506.00/0 © 1992 American Chemical Society Hutson et al.; Xenobiotics and Food-Producing Animals ACS Symposium Series; American Chemical Society: Washington, DC, 1992.
10.
HO ET AL.
Albendazole in Cattle Administered via a "Captec" Device 149
delivery systems. It was found that efficacy can be attained if the anthelmintics are administered at a significantly lower dose but for longer periods of time. In other words, the achievement of a minimum level of parent drug and/or active metabolite(s) in plasma represents the important factor for effective anthelmintic activity rather than a high Cmax or AUC (2,3). As a result of these findings, devices for the continuous slow release of drug are becoming available. The advantages of these devices are numerous (4) and include (a) convenience in drug administration, (b) economy and cost savings due to the administration of fewer doses, (c) reduced handling stress to the animals, (d) pasture-clean resulting in reduced reinfection rates, and (e) lower milk and tissue residue levels. The 'Captec' device (manufactured by 'Captec' Ltd. in New Zealand) is one of the sustained release intra-ruminal devices currently under development for use in cattle. Its design is rather simple (Figure 1) and basically consists of a polypropylene barrel with a plunger and spring on one closed end. The spring is compressed and the barrel filled with seven tablets containing ABZ. Drug is extruded when contact is made between rumen fluid and the ABZ tablet at the orifice on the opposite end of the barrel. The primary factors governing drug release rate include the diameter of the orifice, spring strength and chemical properties of the gel which forms between the rumen fluid and the tablets at the orifice. The 'Captec' device includes a set of "wings" which are secured to the barrel with water-soluble tape prior to administration. Upon contact with the rumen, the tape dissolves, and the wings expand to a predetermined angle, preventing regurgitation of the device. The metabolism of albendazole has been well studied (7,5). The parent compound is short-lived with the major metabolites being generated by a combination of oxidative and hydrolytic processes (Figure 2). One of the major metabolites, albendazole 2-aminosulfone, has been designated as the marker metabolite for which an approved regulatory method has been established in liver, the target tissue. In the present study, three groups of six cattle (a total of eighteen) were administered the 'Captec' device intra-ruminally via a fistula. Drug release rates were determined by HPLC assay of ABZ and its major metabolites in plasma as well as by physical measurement of the plunger movement. ABZ marker residue levels were determined using the established regulatory procedure in total liver, an ethyl acetate extractable fraction as well as the remaining intractable (bound) residue on each of three cattle at 0- and 5-Day withdrawal. Experimental Materials. The albendazole tablets used in Group I and II were formulated by Captec Ltd. and Fernz Corp., respectively, while the Group III tablets were pressed in-house at SmithKline Beecham Animal Health (SBAH). The 'Captec' devices were provided by Captec Ltd. Nylon strings were attached to the devices to facilitate removal from the rumen for the measurement of plunger movement. Albendazole (SKF 62979), albendazole sulfoxide (SKF 77664), albendazole sulfone (SKF 63896), albendazole 2-aminosulfone (SKF 81038), and 5-(n-butylsulfonyl)-lH-benzimidazolyl-2-amine (internal standard, SKF 101437) were obtained in-house.
Hutson et al.; Xenobiotics and Food-Producing Animals ACS Symposium Series; American Chemical Society: Washington, DC, 1992.
150
XENOBIOTICS
AND FOOD-PRODUCING
ANIMALS
Plunger Movement Measurement (Initial value 94-96 mm; the value decreases as plunger movement increases)
7 Tablets Containing Albendazole
End View of Captec Device
Figure 1
4
Diagram of A Captec' device ο
H
Figure 2
Major Metabolic Pathway of Albendazole (Adapted from ref.5) where (1) = ABZ (2) = ABZ-SO (3) = ABZ-S02 (4) = ABZ-NH2
Hutson et al.; Xenobiotics and Food-Producing Animals ACS Symposium Series; American Chemical Society: Washington, DC, 1992.
J
10.
HO ET AL.
Albendazole in Cattle Administered via a "Captec" Device 151
Animal Husbandry and Dosing Procedures. Eighteen Holstein cattle (9 steers and 9 heifers) with an average weight of 226.8 Kg were selected for the present study. A rumen fistula was surgically implanted in selected cattle by a veterinarian and each fistula was exteriorized and fitted with a removable cap. Following a 3-6 week recovery period, the cattle were weighed and randomly assigned to three groups as shown in Table I. The devices were subsequently placed in the rumen of each animal via the fistula. Three cattle were selected for tissue residue analysis following 0-Day and 5-Day withdrawal. The 0-Day withdrawal point was defined as the day when total depletion of the 'Captec' device contents had occurred for the first of the three devices in each 0-D and 5Day withdrawal groups.
Table I. 'Captec' Cattle Group Assignments Group
Cattle ID.
Sex
#352 #350 #348 #337 #334 #341
F F F M M M
#347 #353 #354 #336 #343 #335
F F F M M M
#345 #349 #355 #342 #340 #338
F F F M M M
Withdrawal Period (Days)
0
0 5 5 0 5
Group I refers to 'Captec' devices containing 1987 commercial albendazole tablets (Lot # 021389/70304-1 A) Group II refers to 'Captec' devices containing 1989 commercial albendazole tablets (Lot # 90119-28) Group III refers to Captec' devices containing albendazole tablets prepared in-house (at SBAH, Lot # RCG 17813-92)
Hutson et al.; Xenobiotics and Food-Producing Animals ACS Symposium Series; American Chemical Society: Washington, DC, 1992.
152
XENOBIOTICS AND FOOD-PRODUCING ANIMALS
Plunger Measurement. At selected intervals, the 'Captec' devices were retrieved from the rumen through the fistula using the attached nylon string and measurements of plunger movement were taken using a pair of calipers (Figure 1). Initially, weekly measurements of plunger measurement were taken, but this frequency increased when the devices were nearing depletion in order to accurately assign the 0-Day withdrawal point. Plunger measurement required opening of the rumen to the air which affected feed consumption in some animals. Therefore, a compromise between obtaining sufficient data points and maintaining the overall animal health was required for each animal on an individual basis.
Plasma Collection. Blood samples were collected from all animals at 0, 2, 4, 6, 12, 18 and 24 hours after the devices were inserted, then once daily until Day 10. On Days 13, 18, and 21, blood samples were withdrawn again followed by weekly collections between Day 21 and Day 84. Blood samples were subsequently taken on Days 86, 88 and Day 90, and then daily until the end of the in-life study when all the devices had been depleted. Approximately 10 mL of blood was collected from all animals in VACUTAINER tubes containing heparin at each sampling point. The blood was immediately centrifuged at 2000 rpm for ten minutes and the plasma was stored frozen until extraction.
Analytical Methods Plasma. Albendazole (ABZ), albendazole-sulfone (ABZ-S02), albendazole 2aminosulfone (ABZ-NH2, marker metabolite) and albendazole-sulfoxide (ABZSO), were extracted from the plasma using a perchloric acid precipitation method followed by a solid phase extraction procedure. The residue levels were quantitated using a normal or reversed phase H P L C method with fluorescence detection. One mL of plasma was spiked with 20 of a 10 μ g / m L solution of the internal standard, vortex-mixed for approximately one minute and let stand for one hour at room temperature. The sample was protected from sunlight during the entire process. A 0.5 mL aliquot of 6% perchloric acid was then added followed by brief vortexing, centrifugation, and removal of the supernatant. One mL of deionized water was then added to the remaining residue in the centrifuge tube. Following vortexing and centrifugation at 2000 rpm for 15 minutes, the supernatant was removed and combined with the initial sample. The pH of the combined supernatants was adjusted to 9.5 with a 10% sodium carbonate solution. The entire sample along with a 1 mL wash of the supernatant container was applied to a Waters SEP-PAK CI8 cartridge which had been prewashed with 1 mL H P L C grade methanol and 1 mL deionized water. The sample was subsequently eluted with 2 ml of H P L C grade acetonitrile. The acetonitrile eluant was evaporated to dryness with a gentle stream of nitrogen and stored frozen until H P L C analysis. The plasma extract was reconstituted in 5:1 acetonitrile/acetic acid solution just prior to H P L C analysis of A B Z , A B Z - S 0 2 and ABZ-NH2. For A B Z - S O H P L C analysis, the sample extract was reconstituted in mobile phase (see below).
Hutson et al.; Xenobiotics and Food-Producing Animals ACS Symposium Series; American Chemical Society: Washington, DC, 1992.
10. HO ET AL.
Albendazole in Cattle Administered via a "Captec" Device
Reversed phase HPLC conditions for ABZ-SO2 and ABZ-NH2 were as follows. Column : Guard Column: Flow rate: Mobile phase:
25 cm χ 4.6 mm Econosphere CI8 5 μ (Alltech) 3 cm χ 4.6 mm C-18 Brownlee Inc. 2 mL/minute
Injection volume:
50μί
60% 0.01 M KH2P04 : 40% acetonitrile
Normal Phase H P L C conditions for ABZ-SO are as follows: Column: 25 cm χ 4.6 mm Econosphere Silica 5 μ (Alltech) Guard Column: 3 cm χ 4.6 mm Silica Brownlee Inc. Flow rate: 2.5 mL/minute Mobile phase: 60:25 : 15 : 0.1 Chloroform : Hexane : Acetic Acid: Ammonium Hydroxide Injection volume:
70μί
Reversed phase H P L C conditions for A B Z are as follows: Column: 25 cm χ 4.6 mm Econosphere CI8 5 μ (Alltech) Guard Column: 3 cm χ 4.6 mm C-18 Brownlee Inc. Flow rate: 1.5 mL/minute Mobile phase: 50% 0.01 M KH2P04 : 50% acetonitrile Injection volume:
50μL
All H P L C analyses employed a Perkin-Elmer LS-4 fluorescence detector operating at excitation and emission wavelengths of 296 nm and 326 nm respectively.
Tissue.
The liver homogenates were analyzed according to the procedure shown on Figure 3. Fraction (a) was used to determine the total marker residue level in liver. The amount of marker residue that was bound in liver tissue was obtained using fraction (b) while that of the extractable portion was determined using fraction (c), i.e.
Total marker residue in liver (a) = marker residue in boundtissue(b)
+ extractable marker residue (c)
The level of marker residue(ABZ-NH2) was determined using the approved regulatory method entitled "Quantification of Albendazole Marker Residue in Cattle Liver Tissue Using a Fluorescence H P L C Method" (6).
Hutson et al.; Xenobiotics and Food-Producing Animals ACS Symposium Series; American Chemical Society: Washington, DC, 1992.
153
154
XENOBIOTICS AND FOOD-PRODUCING ANIMALS
Results Plunger Movements and Daily Dosage Level. The 'Captec' devices exhibited a consistent uniform release rate. The average plunger movement up to 85 days was 0.7 mm/day for all groups which corresponds to a daily release of 0.2 g, or an average dose of 0.9 mg/kg. Figure 4 shows the results for heifer #348 which are typical of all animals in the study. Plasma Residues. Plasma samples from two cattle from each group were analyzed for levels of ABZ and ABZ-SO, however, neither compound was detected at any time point (detection limits of lOOppb and 25ppb respectively). The ABZ-NH2 levels were below 350 ppb throughout the study period and there was no obvious correlation between the plunger movement and the plasma residue level of ABZ-NH2. The concentrations of ABZ-S02 were less than 90 ppb at all time points but generally averaged between 20-40 ppb for all animals. ABZ-S02 was the only metabolite seen consistently in the plasma throughout the study duration. Its presence during the primary drug release period correlated well with the uniform plunger movement (Figure 5) and can thus be used as a monitor for proper functioning of the device when given to intact animals. Tissue Residues. Liver samples were analyzed using the approved regulatory method for the marker, albendazole 2-aminosulfone. In this method, the liver homogenate ((a), Figure 3), was subjected to vigorous acid hydrolysis conditions, 6 Ν HCL for 1 hours at 110 ° C before any clean-up procedures. Using this method, the albendazole marker residue levels in the liver of 'Captec' cattle at 0- and 5-Day withdrawal were 651 ± 3 8 ppb and 317 ± 43 ppb, respectively. When the same method was applied to an ethyl acetate tissue extract and the remaining tissue pellet (Figure 3, (c) and (b) respectively), the data clearly indicated that nearly all of the recovered marker was released from the bound residue and was not freely extractable. The results are summarized in Table II. Table II. Extractable vs. Bound Residues for 'Captec' Device Withdrawal (Days)
0 5
Extractable * Residues(%)
3 0
Bound * Residuesf %)
97 100
Marker Concentration(ppb)
651 317
* Estimates based on marker method analysis of extractable analysis Discussion When albendazole is administered as a single dose at 10 mg/kg b.w., albendazole sulfoxide ( C m a x 2-3 μg/mL; T m a x 12-16 hours) and albendazole sulfone (Cmax 1-2 μg/mL; T m a x 18-24 hours) are routinely seen in the plasma of cattle (7). When ABZ was administered via the 'Captec" sustained release device, as in this study, the plasma profiles were markedly different. Only ABZ-S02 was seen in the plasma with concentrations averaging 20-40 ppb. ABZ-SO was not observed. Thus, a reduction in the daily dose of approximately 10 fold (10mg/kg vs 0.9 mg/kg/day) led to over a 100-fold reduction in plasma metabolite levels.
Hutson et al.; Xenobiotics and Food-Producing Animals ACS Symposium Series; American Chemical Society: Washington, DC, 1992.
Albendazole in Cattle Administered via a "Captec" Device
HO ET AL.
Liver Homogenate
Regulatory Method (6 Ν HC1, 1 Hr. J sample clean-up, HPLC)
Ethvl Acetate Extraction
(a) marker residue in liver tissue PELLET Regulatory Method (6 Ν HCI, 1 Hr. sample clean-up, HPLC1| (b) marker residue in pellet
Figure 3
_
EXTRACT I Regulatorv Method (6NHCI,"lHr. I sample clean-up, HPLC) (Q
I marker residue in extract
Flow Chart Showing the Extraction Scheme
100 η
60
20 20
40
60
80
100
Davs
Figure 4
Plunger Movement of A 'Captec' Device
Sulfone (ppb) Plunger (mm)
Detection l i m i t 10 ppb
Figure 5
Plasma Sulfone Levels vs. Plunger Movement vs. Days
Hutson et al.; Xenobiotics and Food-Producing Animals ACS Symposium Series; American Chemical Society: Washington, DC, 1992.
156
XENOBIOTICS AND FOOD-PRODUCING
ANIMALS
The ABZ tissue residue profile also shows marked contrasts between the single and sustained release dosage forms. Previous data (Wang, R.; Marker Residue Depletion Study in Liver from Cattle treated with Albendazole, SKB Applebrook Research Center Study Report, 1983) from single dose studies indicate that at 0-1 days withdrawal albendazole residues are 50% bound and 50% extractable with a marker concentration of 4500 ppb. After 4 days withdrawal, the residues are 95% bound and only 5% extractable with a marker concentration of 1200 ppb. At longer withdrawal times, the bound/extractable ratio is maintained at 95:5 while the marker depletes to less than 250 ppb at 20 days. The data generated in the present study using the 'Captec' devices indicate that nearly 100% of the albendazole residues are bound even at 0-Day withdrawal with a significantly lower marker residue of only 651 ppb. For tissue residue monitoring, the FDA uses the concept of the Rm value which is defined as the ratio of the concentration of the designated marker metabolite to that of the total residue, [Marker] [Total Residue] For a certain drug, the total residue is determined from a radioisotope study, and the marker concentration is determined by the approved regulatory method. Once the Rm value is known, a marker residue tolerance is established. This value is then used in field monitoring programs to ensure that no edible tissues containing drug residue above the safe concentration will reach the consumer. For albendazole, the Rm value for the 2-aminosulfone metabolite in 0.20 or 20% of the total residue. Since the safe concentration for albendazole residues in liver is 1.2 ppm (0.6 ppm in meat χ 2 (food factor)), the marker tolerance has been established at 240 ppb. The Rm concept, however, allows for only one value to be assigned for each drug and must be applied universally regardless of the method or route of drug administration (e.g. single dose or sustained release) as monitoring agencies receiving tissue sample for analysis have no information on drug treatment regimens for individual animals. The current Rm value and 28 day withdrawal time for albendazole were established using data submitted from single-dose studies. The substantial differences (from single dose ABZ) observed in the plasma and tissue residue profiles in this study, tend to indicate that the quantitative metabolic profile may be altered in the case of the sustained-release of albendazole. If the established Rm = 0.2 factor is applied to the marker metabolite concentration of 651 ppb observed at 0-day withdrawal in this study, a total residue of 3255 ppb (651x5) would be indicated. However, considering the facts that (a) the 2-aminosulfone is an end metabolite, (b) plasma levels were reduced 100 fold, and (c) tissue residues were nearly 100 % bound even at 0-Day withdrawal, it seems unlikely that the same relationship of marker/total residue (Rm) is applicable for the sustained release of ABZ. In fact, the data suggest that the majority of the residues are present as the 2-aminosulfone. If true, then the actual Rm value would be higher and possibly be significantly greater than 20%. When subsequently used in calculations of total residue, the overall effect would be to lower the total residue (multiply marker concentration by a lower number). The above discussion, of course, is only speculation at this point, since
Hutson et al.; Xenobiotics and Food-Producing Animals ACS Symposium Series; American Chemical Society: Washington, DC, 1992.
10. HO ET AL.
Albendazole in Cattle Administered via a "Captec" Device
radioisotope data would be required to firmly establish the Rm relationship for the sustained release dosage form. Generating this type of data is not straightforward, however, due to the large amount of radiolabeled drug required and the problems inherent in maintaining cattle in metabolism cages for up to 90 days or longer. A potential alteration of the Rm value for a sustained release dosage form of ABZ has regulatory consequences as well. Since the initial Rm = 0.2 was established for albendazole as a single dose, this value must be applied to all dosage forms and routes of administration. The regulatory method cannot distinguish between cattle given a single dose of ABZ or those dosed via 'Captec'. The data from the present study indicate that it is quite possible that cattle dosed with albendazole via the 'Captec' device would qualify for 0-Day withdrawal. Unfortunately, even if the radioisotope data were available at this time to definitively determine the Rm for sustained release ABZ, it could not be used to establish a new tolerance for the drug as long as both dosage forms remained commercial products. Acknowledgments. The authors would like to thank C. Gombatz for her advices and dicussions, and D. Hallman, F. Hallman, R. Kozan, J. Rizzo, S. Shuman, P. Stone, R. Supplée, Ε. Warrakeh and Dr. L. Weerasinghe for their technical support. Literature Cited 1. 2. 3. 4. 5. 6.
Glanzer, K.; Pfeiffer, H.; Wetzel, H. Acta Pharm. Technol. 1988, 34, pp108-114 Prichard, R.K.; Hennessy, D.R.; Steel, J.W; Vet. Parasitol. 1978, 4, pp 309-315 Kwan, L.C.; Gyurik, R.J.; Freeman, J. F.; Chimes, N.; Ritch, G. M.; Theodorides, V.J. J. of Control Release 1988,8,pp 31-38 Gyurik, R.J.; In Rumen Retention Devices; Tyle, P., Ed.; Drug Delivery Devices; Marcel Dekker: New York and Basel, Vol. 20; pp 549-561 Gyurik, R.J.; Chow, A.W.; Zaber, B; Brunner, E.L.; Miller, J. M.; Villani, A.J. Villani; Petka, L. Α.; Parish, R.C. Drug Metab. Dispos. 1981, 9, pp 503-508 Wishousky, T.; Wang, R. W. Quantification of Albendazole Marker Residue in Cattle Liver Tissue Using a Fluorescence HPLC Method On display in 3rd Additives Manuel, FOI Public Information Room, Room 12A-30, Food and Drug Adminstration, 5600 Fishers Lane, Rockville, MD 20857
Received March 13, 1992
Hutson et al.; Xenobiotics and Food-Producing Animals ACS Symposium Series; American Chemical Society: Washington, DC, 1992.
157
