Veterinary Research Communications, 16 (1992) 355-364 Copyright C) Kluwer Academic Publishers by - Printed in the Netherlands
T H E I N F L U E N C E O F AGE O N T H E P H A R M A C O K I N E T I C S O F A D I T O P R I M IN P I G S A F T E R I N T R A V E N O U S AND O R A L ADMINISTRATION J.-L. RIOND, P. MI~ILLERAND M. WANNER Institute of Veterinary Physiology, Division of Animal Nutrition, University of Z~ich, Winterthurerstrasse 260, CH-8057 Ziirich, Switzerland
ABSTRACT Riond, J.-L., Miiller, P. and Wanner, M., 1992. The influence of age on the pharmacoldnetics of aditoprim in pigs after intravenous and oral administration. VeterinaryResearch Communications, 16 (5), 355-364 Some pharmacokinetic parameters of aditoprim were determined in 3- and 6-month-old pigs. After intravenous administration of 5 mg/kg body weight, the mean total body clearance of the older pigs was smaller than that of the younger pigs. This difference was not reflected in the elimination half-life. After oral administration of 5 mg/kg body weight, the mean absorption rate constant was smaller and the mean absorption half-life was longer in the older pigs. The age-related changes in the pharmacokinetics of aditoprim were not sufficiently pronounced to suggest the necessity of modifying the oral dosage regimen in pigs of this age range. The favourable pharmacokinetics of aditoprim in pigs (large apparent volume of distribution, long elimination half-life and high bioavailability) may permit introduction of this drug into swine practice, after safety and residue depletion studies.
Keywords: aditoprim, age, bioavailability, intestinal absorption, pharmacokinetics, pigs
INTRODUCTION Aditoprim (2,4-diamino-5-[4-(dimethylamino)-3,5-dimethoxybenzyl]pyrimidine) is a selective reversible inhibitor of bacterial dihydrofolate reductase (DHFR) with a potential for use in veterinary medicine (Then and Keller, 1988; Sutter et al., 1991). The in vitro bacteriostatic activity of aditoprim is, like that of its parent trimethoprim, excellent against both Gram-positive and Gram-negative bacteria, although Bordetella bronchiseptica demonstrated natural resistance to DHFR inhibitors (Mengelers et aL, 1990). The pharmacoldnetics of aditoprim has been determined in calves and pigs (Ludwig et al., 1985; Sutter et al., 1992), heifers (Jordan et aL, 1987), cows (Lohuis et aL, 1992), sheep (H/inni et aL, 1987), goats (Knoppert et al., 1988), horses (Von FeUenberg et aL, 1990) and dogs (Sutter et al., 1991). In all the species studied, the elimination half-life of aditoprim is longer and its volume of distribution is larger than that of trimethoprim. In neonatal and young animals, absorption, distribution, metabolism and elimination of drugs may differ markedly from those in adults (Heiman, 1980; Reinhard and Kusenbach, 1986; Ward and Green, 1988; Kietzman and L6scher, 1990). The effect of age on the disposition of some antimicrobials has been reported for a few species (Weisman et al., 1982; Brumbaugh et al., 1983; Burrows et al., 1983, 1987; Prescott et al., 1983; Reiche, 1983; Clarke et al., 1985). The purpose of this study was to investigate the effect of age on aditoprim pharmacokinetics in young pigs.
356 ANIMALS, MATERIALS AND METHODS Animals
Five 3-month-old and five 6-month-old crossbred castrated male pigs (groups A and B, respectively), originating from a ~ecific pathogen-free herd, were acclimatized for one week in individual boxes (2 m ") with straw bedding. The pigs were crossbred Swiss Large White (Edelschwein) and Improved Swiss Landrace (Veredeltes Landschwein). In the controlled environment of the stall, the temperature was maintained at 21"C and humidity at 60%. The piglets were fed 3.2 times their maintenance requirement of a commercial pelleted ration (20.8% crude protein, 13.4 MJ digestible energy/kg dry matter), of which 55% was given in the morning and 45% in the evening. Water was provided ad libitum. Before the beginning of the trial, the health status of the animals was evaluated by physical examination, packed cell volume, haemoglobin concentration, white blood cell count and blood chemistry and found to be normal.
Sample collection
To facilitate blood collection, an indwelling cannula was inserted into one vena helicis oralis or vena helicis aboralis under deep sedation with acepromazine (2 mg/kg body weight (bw)), ketamine (20 mg/kg bw) and atropine (0.06 mg/kg bw). After a recovery period of 24 h or more, a 10% aqueous solution of aditoprim (Ro 11-5697, Hoffmann-La Roche, Basel, Switzerland; 5 mg/kg bw) was rapidly administered via a butterfly catheter in one ear vein. One week later, the pigs were fasted for 12 h before ingestion of aditoprim (5 mg/kg bw) which was concentrated in a small amount of food (1000 ppm). The remaining portion of the ration was fed afterwards. Blood samples (4 ml each) were collected at 0, 0.08, 0.33, 0.67, 1, 2, 4, 6, 8, 12, 24 and 36 h after intravenous administration and at 0, 0.33, 0.67, 1, 2, 4, 6, 8, 12, 24 and 36 h after oral administration. Ammonium oxalate was used as anticoagulant. Plasma was separated within 30 min and frozen at -180C until assayed.
Aditoprim determination
Plasma aditoprim concentrations were determined by reversed-phase highperformance liquid chromatography, using a slightly modified version of a method whose performance with pig plasma was known (Ascalone et aL, 1986). The apparatus used included a Perkin-Elmer ISS-100 automatic sampler, a Merck L-6000 pump, a Merck L-6200 pump, a Merck Lichrocart 4-4 Lichrospher 100 RP-18 guard column, a Merck Lichrocart 25-4 Lichrosorp RP-8 HPLC cartridge, a Rheodyne EA 7000 valve, and a Perkin Elmer LC-95 UV/visible spectrophotometer detector. The internal standard was brodimoprim (Ro 10-5970, Hoffmann-La Roche, Basel, Switzerland). Liquid-liquid extraction of aditoprim and brodimoprim from buffered plasma (pH 9) was achieved with chloroform (Riedel-de-Ha~u AG, Seelze, Germany). The stainless-steel column (250 mm x 4 mm ID) filled with 7/zm Bondapak C-18 (Waters Assoc., Milford, MA, USA) was maintained at 36°C. The isocratic mobile phase
357 consisted of acetonitrile and a 0.5% aqueous ammonium carbonate solution (pH 8) in a 3:7 (v/v) ratio. The eluate was monitored at 285 urn. The data were collected and analysed by a 3000 Series Chromatography Data System (Perkin Elmer Nelson Systems Inc., Cupertino, CA, USA). Calibration curves of peak height versus concentration were constructed using weighted linear regression (weighting factor
1/y). Pharmacokinetic analyses A non-compartmental analysis was performed by use of the option modelindependent analysis plus moment analysis of the software Independ, version 1.1 (Independ User's Manual, 1987). By use of this routine, a regression line was fitted to the data of the terminal phase. Outliers were visually identified, deleted, and the linear regression analysis was repeated. The overall elimination rate constant (B) was the slope of the regression line. The program then calculated the area under the curve (AUC) and. area under the moment curve (AUMC) by the trapezoidal rule. AUC was extrapolated to the x-intercept (AUC(0_,**.) using the terminal elimination rate constant. The absorption rate constant (k(a)) was calculated by using the optional Wagner-Nelson Analysis in the Independ program. Pharmacokinetic parameters were subsequently derived from these values according to accepted formulae (Gibaldi and Perrier, 1982; Gouyette, 1983): Elimination half life
t~4t~
= 0.693/fl
Total body clearance
C1B
= dose/AUC(o_,** )
Area volume of distribution
l/area
= dose/AUC(o.,.)./~
Volume of distribution at steady state
VSS
= dose. AUMC/AUC(0_,**)2
Mean residence time
MRT
= AUMC/AUC(o_, ®)
Bioavailability
F
= AUC(°-'**)P/°" D°sei/v AUC(0-,®)i/v • Dosep/o
Absorption half-life
tv~(a)
= 0.693/k(a)
Statistical analysis The pharmacokinetic parameters in groups A and B were compared by the two-tailed Mann-Whitney U-test using the SAS procedure NPARlWAY (SAS/STAT User's Guide, 1989; Powers, 1990).
358
RESULTS The mean (-+SEM) plasma concentrations and pharmacokinetic parameters after intravenous and oral administration of aditoprim are listed in Tables I, II, III and IV.
TABLE I Mean (-+SEM) aditoprim concentration in plasma after a single intravenous administration of 5 mg/kg body weight to 3- and 6-month-old pigs. Age and mean (± SEM) body weight are indicated
Post-injection time (h)
Concentration (/zg/ml) Group A (n = 5) (3 months; 51.7 ± 1.6 kg)
0.08 033 0.67 1 2 4 6 8 12 24 36
2.13 0.68 0.56 0.41 0.37 0.27 0.22 0.18 0.12 0.07 0.05
± 0.32 ± 0.08 -+ 0.07 ± 0.07 _+ 0.05 _+ 0.05 _+ 0.02 ± 0.02 ± 0.02 ± 0.01 _+ 0.005
Group B (n = 5) (6 months; 97.2 _ 5.6 kg)
3.44 1.40 1.11 0.90 0.64 0.40 0.37 0.32 0.23 0.12 0.08
_+ 0.94 _+ 0.08 _+ 0.05 _+ 0.11 ± 0.10 -+ 0.08 ± 0.07 ± 0.06 + 0.04 ± 0.01 ± 0.007
After intravenous administration, the mean plasma aditoprim concentrations were higher in the older pigs (Table I). Consequently, the mean AUC(0_,**~ of group B was significantly larger than that of group A and the mean total body clearance of group B was significantly smaller than that of group A (Table III). The apparent volume of distribution calculated by the extrapolation method and the volume of distribution at steady state tended to be smaller in the pigs in group B. The difference in C1B between groups A and B was not reflected in t~t~, because both V and CIB were smaller in group B (t~_ = 0.693V/CIB). FoUowmg oral administration of adltoprim, the mean absorption rate constant for group B was significantly smaller than that for group A (Table IV). Consequently, the mean tw(a) for group B was larger than that for group A. .
~,
•
•
•
359 TABLE II Mean (_+SEM) aditoprim concentration in plasma after a single oral administration of 5 mg/kg body weight to 3- and 6-month-old pigs. Age and mean (_+SEM) body weight are indicated
Post-injection time (h)
Concentration (/zg/ml) Group A (n = 5) (3 months; 47.7 +_ 0.8 kg)
0.33 0.67
0.05 0.11 0.16 0.19 0.21 0.22 0.17 0.13 0.06 0.04
i
2 4 6 8 12 24 36
Group B (n = 5) (6 months; 98.4 _+ 6.3 kg)
-+ 0.01 _+ 0.02 _+ 0.03 _+ 0.04 +_ 0.04 _+ 0.04 _+ 0.03 _+ 0.02 + 0.01 __. 0.005
0.03 0.05 0.08 0.16 0.20 0.27 0.26 0.23 0.12 0.06
___0.01 +_ 0.01 __. 0.02 _+ 0.01 _+ 0.02 _+ 0.07 _+ 0.07 ± 0.04 _+ 0.03 _+ 0.008
10":
)
% v
c o
O"0
-t--t
0~0~
~o
a
- ~
t~ f,.. c
.1
0
c
0 (-3
.01 0
. . . .
lb
. . . .
2b
. . . .
3b
. . . .
4b
Time (h) Figure 1. Semilogarithmic plot of mean aditoprim serum concentrations vs time in 3-month-old (o) and 6-month-old (o) male castrated pigs after a single intravenous administration of 5 mg/kg body weight
1:
5" I= v tO .r--i
o
o/
o~
.t
f._
0 0
,01 0
. . . .
. . . .
2b
. . . .
3b
. . . .
4b
T±me (h) Figure 2. Semilogarithmic plot of mean aditoprim serum concentrations vs time in 3-month-old (o) and 6-month-old (o) male castrated pigs after a single oral administration of 5 mg/kg body weight DISCUSSION The C1B for aditoprim decreased with age. CI@ is the sum of all the individual organ clearances that contribute to drug elimination. Full functional maturity of the elimination organs is reached several weeks after birth, with wide differences across species (Baggot and Short, 1984; Kietzman and LSscher, 1990). The design of this study does not allow discrimination of which elimination processes for aditoprim are increased in the younger pigs. Data from other species suggest that biotransformation of aditoprim is minimal (Graser, Hoffman-La Roche, personal communication). Furthermore, the extent of binding to plasma proteins in neonatal and young animals differs from that in adults and may thus affect C1B (Baggot and Short, 1984; Koch-Weser and Sellers, 1976). However, it may be hypothesized that one of the routes of aditoprim elimination is passive diffusion into the intestinal lumen, where it binds to components of the intestinal contents such as dietary fibre. In younger animals, this process may be more pronounced than in older animals and in this way the larger CL of aditoprim would arise. In the pigs m this study, the k(a) of aditoprim decreased and its t .v~(a) . . . increased with age. Several factors influence the extent of drug absorption in young animals: (1) the lower secretion of HC1 and pepsin and the higher pH in the stomach; (2) the prolonged gastric emptying time; (3) the lower intestinal motility; (4) the immature intestinal blood flow; (5) a smaller first-pass effect; (6) better intestinal absorption of high-molecular-weight compounds; (7) the immature bilia U function; (8) a high concentration of fl-glucuronidase in the newborn intestine; (9) incomplete colonization of the intestine by the microbial flora; and (10) the shorter diffusion
361 distance related to the thinner intestinal wall (Hoffmann, 1971; Kietzman and L6scher, 1990). In a study involving 580 children, the absorption rate constant of several drugs and test substances (D(+)-xylose and L(+)-arabinose) was increased relative to adults (Heiman, 1980). However, the bioavailability calculated by the method of corresponding areas showed no age dependence in these children.
TABLE III Mean (+_SEM) aditoprim pharmacokinetic parameters after a single intravenous administration of 5 mg/kg body weight to 3- and 6-month-old pigs. Age and mean (__.SEM) body weights are indicated
Parameter a Unit
Group A (n = 5) (3 months; 51.7 _ 1.6 kg)
Group B (n =5) (6 months; 97.2 -+ 5.6 kg)
fl
(h -1)
0.074 +_ 0.015
0.058 _+ 0.006
tvzt~
(h)
9.08 _+ 2.08
11.91 _+ 1.16
AUC(~**)
(h./zg/ml)
5.92 _+ 0.81 b
11.51 +- 1.07b
AUMC
(h 2 ./zg/ml)
78.15 _+ 17.64c
146.41 _+ 16.92c
CIB
(ml min -1 kg -1)
15.56 _+ 2.82b
7.51 +- 0.73b
MRT
(h)
12.54 _+ 1.74
13.25 _+ 1.97
Varea
(L/kg)
12.65 +_ 1.23
8.00 _+ 1.54
Vss
(L/kg)
10.84 + 1.07
6.25 + 1.41
aft = overall elimination rate constant; t~t ~ = elimination half-life; A U C ,t,o-* , ..,) = area under the curve extrapolated to the x-intercept; A U M C = area under the moment curve; CI B = total body clearance; M R T = mean residence time; /"area = area apparent volume of distribution; Vs¢ = apparent volume of distribution at steady state bGroups A and B are significantly different ~¢ at the 0.01 level CGroups A and B are significantly different at the 0.05 level
Interestingly, both the C1B and the k(a) of aditoprim were larger in the younger pigs. Diffusion is a bidirectional process; whether absorption or elimination dominates depends on the concentration gradient. The equilibrium obeys the pH partition hypothesis. The factors listed above, the poor solubility of aditoprim in water, and the smaller surface area of the gut in younger animals may influence the diffusion process.
362 TABLE IV Mean (-.+SEM) aditoprim pharmacokinetic parameters after a single oral administration of 5 mg/kg body weight to 3- and 6-month-old pigs. Age and mean (_+SEM) body weights are indicated
Parameter a Unit
fl
(h -1)
t~#
(h)
AUC(0_,** )
Group A (n --5) (3 months; 47.7 + 0.8 kg)
0.060 _+ 0.003
Group B (n ---5) (6 months; 98.4 _+ 6.3 kg)
0.068 - 0.007
11.60 _ 0.63
10.28 +_ 1.06
(h./zg/ml)
4.10 _+ 0.73
6.12 ___1.09
AUMC
(h 2 ./zg/ml)
74.67 _+ 12.42
82.71 _+ 10.87
MRT
(h)
18.67 +_ 0.95
18.35 _+ 0.99
Cmax
(/zg/ml)
0.21 + 0.03
0.30 + 0.11
Tmax
(h)
4.53 -- 0.85
7.80 -+ 1.50
F
(%)
77.44 + 17.40
53.35 + 6.42
k(a)
(h -1)
0.85 _+ 0.06 b
0.35 -+ 0.11b
tV~(a)
(h)
0.83
2,82 _+ 0.82 b
-
0.05 b
a/~ = overall elimination rate constant; t~t ~ = elimination half-life; AUC(0_,~) = area under the curve; A U M C -- area under the moment curve; MRT = mean residence time; Cmax = maximum plasma concentration; Tmax = time to reach the maximum plasma concentration; F = bioavailability; k(a) = absorption rate constant; tWk(a) = absorption half-life bGroups A and B are significantly different at the 0.05 level
The estimates for the pharmacokinetic parameters of aditoprim in the piglets in this study confrrm a previous report (Ludwig et al., 1985). After intravenous administration, the mean t~^ of aditoprim in piglets is longer than that of trimethoprim (9.08 - 11.91 h vs 2.25 _+ 0.19 h) and its apparent volume of distribution is larger than that of trimethoprim (6.25 - 10.84 L/kg vs 1.4 ___0.05 L/kg; Nielsen and Rasmussen, 1975a,b; Friis et aL, 1984; L6scher, 1984). Aditoprim is well absorbed in pigs. No comparative data exist for the intestinal absorption of aditoprim and trimethoprim in pigs. However, in goats, the bioavailability of aditoprim was found to be many times superior to that of trimethoprim (71 _+. 8.9% vs 10.3 _ 3.2%; Knoppert
363 et aL, 1988). In dogs, the bioavailability of aditoprim is 90.3 --- 0.9% (Sutter et al.,
1991). In species of veterinary interest, the m e a n values for the t,~,2p . of aditoprim range from 6.7 to 12.5 h and the m e a n values for its Vss range from 4.6 to 13.11 L / k g , which suggest excellent tissue penetration (Jordan et aL, 1987; H~inni et al., 1987, K n o p p e r t et aL, 1988; Sutter et al., 1991; V o n Fellenberg et aL, 1990). In conclusion, the favourable pharmacokinetics of aditoprim in pigs m a y permit the introduction of this antimicrobial into swine practice, after safety and residue depletion studies. T h e pharmacokinetic parameters were affected by the age of the animals. However, these changes were not sufficiently p r o n o u n c e d to require modification of the oral dosage regimens for animals over this age range.
ACKNOWLEDGEMENTS This study was supported by H o f f m a n n - L a R o c h e & Co Ltd, Basel, Switzerland. T h e technical assistance of Ms Barbara Schneider is greatly appreciated.
REFERENCES Ascalone, V., Jordan, J.-C. and Ludwig, B.M., 1986. Determination of aditoprim, a new dihydrofolate reductase inhibitor, in the plasma of cows and pigs. Journal of Chromatography, 383, 111-118 Baggot, J.D. and Short, C.IL, 1984. Drug disposition in the neonatal animal, with particular reference to the foal. Equine Veterinary Journal, 16, 364-367 Brumbaugh, G.W., Martens, R.J., Knight, H.D. and Martin, M.T., 1983. Pharmacokinetics of ehloramphenicol in the neonatal horse. Journal of Veterinary Pharmacology and Therapeutics, 6, 219-227 Burrows, G.E., Barto, P.B., Martin, B. and Tripp, M.L., 1983. Comparative pharmacokinetics of antibiotics in newborn calves: chloramphenicol, lincomycin, and tylosin. American Journal of Veterinary Research, 44, 1053-1057 Burrows, G.E., Barto, P.B. and Martin, B., 1987. Comparative pharmacokinetics of gentamicin, neomycin and oxytetracycline in newborn calves.Journal of Veterinary Pharmacology and Therapeutics, 10, 54-63 Clarke, C.IL, Short, C.IL, Hsu, IL-C. and Baggot, J.D., 1985. Pharmacokinetics of gentamicin in the calf: developmental changes.American Journal of Veterinary Research, 46, 2461-2466 Friis, C., Gyrd-Hansen, N., Nielsen, P., Nordholm, L. and Rasmussen, F., 1984. Pharmacokinetics and metabolism of trimethoprim in neonatal and young pigs. Pediatric Pharmacology, 4, 231-238 Gibaldi, M. and Perrier, D., 1982.Pharmacola'netics, 2nd edn, (Marcel Dekker, New York) Gouyette, A., 1983. Pharmacokinetics: Statistical moments calculation.Arzneimittelforschung, 33, 173-176 H~inni, K., Jordan, J.-C., Ludwig, B. and Rehm, W.F., 1987. Pharmacokinetics of aditoprim, a new dihydrofolate reductase inhibitor, in sheep. Journal of Veterinary Pharmacology and Therapeutics, 10, 169-171 Heiman, G., 1980. Enteral absorption and bioavailability in children in relation to age. European Journal of Clinical Pharmacology, 18, 43-50 Hoffmann, H., 1971. Untersuchungen zur enteralen Absorption yon Pharmaka bei Ratten verschiedenen Alters. Acta Biologica et Medica Gerraanica, 26, 1229-1235 Independ User's Manual, 1987. Version 1.1, (Hoffmann-La Roche & Co Ltd, Basel) Jordan, J.-C., Klatt, P. and Ludwig, B., 1987. Pharmacokinetics of aditoprim, a new dihydrofolate reductase inhibitor, in heifers. Zentralblatt fi2r Feteriniirmedizin Reihe A (Journal of Veterinary Medicine A ), 34, 33-44 Kietzmann, M. and l.,6scher, W., 1990. Besonderheiten der Pharmakokinetik beim Jungtier. Berliner und Miinchener Tieriirzliche Wochenschrift, 103, 277-282 Knoppert, N.W., Mijmeijer, S.M., Van Duin, C.T.M., Korstanje, C., Van Gogh, H. and Van Miert, A.SJ.P.A.M., 1988. Some pharmacokinetic data of aditoprim and trimethoprim in healthy and tick-borne fever infected dwarf goats. Journal of Veterinary Pharmacology and Therapeutics, 11, 135-144
364 Koch-Weser, J. and Sellers, E.M., 1976. Binding of drugs to serum albumin (second of two parts). New England Journal of Medicine, 294, 526-531 Lohuls, J.A.C.M., Sutter, H.-M., Graser, T., Ludwig, B., van Miert, A.SJ.P.A.M., Rehm, W.F., Rhode, IL, Schneider, B., Wanner, M. and van Werven, T., 1992. The effect of endotoxin-induced mastitis on the pharmacokinetics of aditoprim in dairy cows. American Journal of VeterinaryResearch, 53, in press L6scher, W., 1984. Kritische Anmerkungen zu Trimethoprim/Sulfonamid-Kombinationen in der Veteriniirmedizin.Deutsche Tieriirzliche Wochenschrif~,91, 133-172 Ludwig, B., Jordan, J.C., Rehm, W.F. and Sehulze, J., 1985. Pharmacokinetics of aditoprim, a new dihydrofolate reductase inhibitor, in pig and calf. In: A.S.LP.A.M. van Miert, M.G. Bogaert and M. Debackere (eds), Comparative VeterinaryPharmacology, Toxicology and Therapy, (Proceedings of the 3rd Congress of the European Association for Veterinary Pharmacology and Toxicology, Ghent, Belgium), 114 Mengelers, MJ.B., Van Kiingeren, B. and Van Miert, A.SJ.P.A.M., 1990. In vitro susceptibility of some porcine respiratory tract pathogens to aditoprim, trimethoprim, sulfadimethoxine, sulfamethoxazole, and combinations of these agents. American Journal of VeterinaryResearch, 51, 1860-1864 Nielsen, P. and Rasmussen, F., 1975a. Half-life and renal excretion of trimethoprim in swine. Acta Pharmacologica et Toxicologica, 36, 123-136 Nielsen, P. and Rasmussen, F., 1975b. Trimethoprim and sulfadoxine in swine. Zentalblatt flir Veterird~rmedizinReihe A (Journal of VeterinaryMedicineA ), 22, 564-571 Powers, J., 1990. Statistical analysis of pharmacokinetic data. Journal of Veterinary Pharmacology and Therapeutics, 13, 113-120 Prescott, J.F., Hoover, D.J. and Dohoo, I.IL, 1983. Pharmacokinetics of erythromycin in foals and in adult horses. Journal of VeterinaryPharmacology and Therapeutics, 6, 67-74 Reiche, IL Drug disposition in the newborn, 1983. In: Y. Ruckebush, P. Toutain and G.D. Koritz (eds), VeterinaryPharmacology and Toxicology, (A VI, Westport), 49-56 Reinhard, D. and Kusenbach, G., 1986. Besonderheiten der Arzneimittel therapie im Kindesalter.
Monatsschrift Kinderheilkunde, 134, 772-778 SAS/STAT User'sGuide, 1989. Version 6, 4th edn, vol 1 and 2, (SAS Institute Inc., Cary, NC) Sutter, H.-M., Ludwig, B., Bremer, K.D., Jordan, J.-C., Rehm, W.F. and Wanner, M., 1991. Pharmacokinetics of aditoprim in dogs after intravenous and oral administration: a preliminary study. Journal of Small Animal Practice, 32, 517-520 Sutter, H.-M., Riond, J.-L. and Wanner, M., 1992. Comparative pharmacokinetics of aditoprim in milk-fed and conventionallyfed calves of different ages. Researchin VeterinaryScience, in press Then, ILL. and Keller, M., 1988. Properties of aditoprim, a new antibacterial dihydrofolate reduetase inhibitor. Zentralblattp3r Veterinf~medizinReihe B (Journal of VeterinaryMedicine B), 3S, 114-120 Von Fellenberg, IL-L., Jordan, J.-C., Ludwig, B. and Rehm, W.F., 1990. Plasma disposition and tolerance of aditoprim following a single intravenous administration of 5 mg/kg bodyweight in horses. Zentralblatt ~ r Veterini~nedizin Reihe A (Journal of VeterinaryMedicineA ), 37, 253-258 Weismann, D., Herrig, J. and McWeeny, O., 1982. Tissue distribution of gentamicin in lambs: Effect of postnatal age and acute hypoxemia. DevelopmentalPharmacology and Therapeutics, 5, 194-206 Ward, ILM. and Green, T.P., 1988. Developmental pharmacology and toxicology:, principles of study design and problems of methodology. Pharmacologyand Therapeutics, 36, 309-334 (Accepted: 25 August 1992)
T H E I N F L U E N C E O F AGE O N T H E P H A R M A C O K I N E T I C S O F A D I T O P R I M IN P I G S A F T E R I N T R A V E N O U S AND O R A L ADMINISTRATION J.-L. RIOND, P. MI~ILLERAND M. WANNER Institute of Veterinary Physiology, Division of Animal Nutrition, University of Z~ich, Winterthurerstrasse 260, CH-8057 Ziirich, Switzerland
ABSTRACT Riond, J.-L., Miiller, P. and Wanner, M., 1992. The influence of age on the pharmacoldnetics of aditoprim in pigs after intravenous and oral administration. VeterinaryResearch Communications, 16 (5), 355-364 Some pharmacokinetic parameters of aditoprim were determined in 3- and 6-month-old pigs. After intravenous administration of 5 mg/kg body weight, the mean total body clearance of the older pigs was smaller than that of the younger pigs. This difference was not reflected in the elimination half-life. After oral administration of 5 mg/kg body weight, the mean absorption rate constant was smaller and the mean absorption half-life was longer in the older pigs. The age-related changes in the pharmacokinetics of aditoprim were not sufficiently pronounced to suggest the necessity of modifying the oral dosage regimen in pigs of this age range. The favourable pharmacokinetics of aditoprim in pigs (large apparent volume of distribution, long elimination half-life and high bioavailability) may permit introduction of this drug into swine practice, after safety and residue depletion studies.
Keywords: aditoprim, age, bioavailability, intestinal absorption, pharmacokinetics, pigs
INTRODUCTION Aditoprim (2,4-diamino-5-[4-(dimethylamino)-3,5-dimethoxybenzyl]pyrimidine) is a selective reversible inhibitor of bacterial dihydrofolate reductase (DHFR) with a potential for use in veterinary medicine (Then and Keller, 1988; Sutter et al., 1991). The in vitro bacteriostatic activity of aditoprim is, like that of its parent trimethoprim, excellent against both Gram-positive and Gram-negative bacteria, although Bordetella bronchiseptica demonstrated natural resistance to DHFR inhibitors (Mengelers et aL, 1990). The pharmacoldnetics of aditoprim has been determined in calves and pigs (Ludwig et al., 1985; Sutter et al., 1992), heifers (Jordan et aL, 1987), cows (Lohuis et aL, 1992), sheep (H/inni et aL, 1987), goats (Knoppert et al., 1988), horses (Von FeUenberg et aL, 1990) and dogs (Sutter et al., 1991). In all the species studied, the elimination half-life of aditoprim is longer and its volume of distribution is larger than that of trimethoprim. In neonatal and young animals, absorption, distribution, metabolism and elimination of drugs may differ markedly from those in adults (Heiman, 1980; Reinhard and Kusenbach, 1986; Ward and Green, 1988; Kietzman and L6scher, 1990). The effect of age on the disposition of some antimicrobials has been reported for a few species (Weisman et al., 1982; Brumbaugh et al., 1983; Burrows et al., 1983, 1987; Prescott et al., 1983; Reiche, 1983; Clarke et al., 1985). The purpose of this study was to investigate the effect of age on aditoprim pharmacokinetics in young pigs.
356 ANIMALS, MATERIALS AND METHODS Animals
Five 3-month-old and five 6-month-old crossbred castrated male pigs (groups A and B, respectively), originating from a ~ecific pathogen-free herd, were acclimatized for one week in individual boxes (2 m ") with straw bedding. The pigs were crossbred Swiss Large White (Edelschwein) and Improved Swiss Landrace (Veredeltes Landschwein). In the controlled environment of the stall, the temperature was maintained at 21"C and humidity at 60%. The piglets were fed 3.2 times their maintenance requirement of a commercial pelleted ration (20.8% crude protein, 13.4 MJ digestible energy/kg dry matter), of which 55% was given in the morning and 45% in the evening. Water was provided ad libitum. Before the beginning of the trial, the health status of the animals was evaluated by physical examination, packed cell volume, haemoglobin concentration, white blood cell count and blood chemistry and found to be normal.
Sample collection
To facilitate blood collection, an indwelling cannula was inserted into one vena helicis oralis or vena helicis aboralis under deep sedation with acepromazine (2 mg/kg body weight (bw)), ketamine (20 mg/kg bw) and atropine (0.06 mg/kg bw). After a recovery period of 24 h or more, a 10% aqueous solution of aditoprim (Ro 11-5697, Hoffmann-La Roche, Basel, Switzerland; 5 mg/kg bw) was rapidly administered via a butterfly catheter in one ear vein. One week later, the pigs were fasted for 12 h before ingestion of aditoprim (5 mg/kg bw) which was concentrated in a small amount of food (1000 ppm). The remaining portion of the ration was fed afterwards. Blood samples (4 ml each) were collected at 0, 0.08, 0.33, 0.67, 1, 2, 4, 6, 8, 12, 24 and 36 h after intravenous administration and at 0, 0.33, 0.67, 1, 2, 4, 6, 8, 12, 24 and 36 h after oral administration. Ammonium oxalate was used as anticoagulant. Plasma was separated within 30 min and frozen at -180C until assayed.
Aditoprim determination
Plasma aditoprim concentrations were determined by reversed-phase highperformance liquid chromatography, using a slightly modified version of a method whose performance with pig plasma was known (Ascalone et aL, 1986). The apparatus used included a Perkin-Elmer ISS-100 automatic sampler, a Merck L-6000 pump, a Merck L-6200 pump, a Merck Lichrocart 4-4 Lichrospher 100 RP-18 guard column, a Merck Lichrocart 25-4 Lichrosorp RP-8 HPLC cartridge, a Rheodyne EA 7000 valve, and a Perkin Elmer LC-95 UV/visible spectrophotometer detector. The internal standard was brodimoprim (Ro 10-5970, Hoffmann-La Roche, Basel, Switzerland). Liquid-liquid extraction of aditoprim and brodimoprim from buffered plasma (pH 9) was achieved with chloroform (Riedel-de-Ha~u AG, Seelze, Germany). The stainless-steel column (250 mm x 4 mm ID) filled with 7/zm Bondapak C-18 (Waters Assoc., Milford, MA, USA) was maintained at 36°C. The isocratic mobile phase
357 consisted of acetonitrile and a 0.5% aqueous ammonium carbonate solution (pH 8) in a 3:7 (v/v) ratio. The eluate was monitored at 285 urn. The data were collected and analysed by a 3000 Series Chromatography Data System (Perkin Elmer Nelson Systems Inc., Cupertino, CA, USA). Calibration curves of peak height versus concentration were constructed using weighted linear regression (weighting factor
1/y). Pharmacokinetic analyses A non-compartmental analysis was performed by use of the option modelindependent analysis plus moment analysis of the software Independ, version 1.1 (Independ User's Manual, 1987). By use of this routine, a regression line was fitted to the data of the terminal phase. Outliers were visually identified, deleted, and the linear regression analysis was repeated. The overall elimination rate constant (B) was the slope of the regression line. The program then calculated the area under the curve (AUC) and. area under the moment curve (AUMC) by the trapezoidal rule. AUC was extrapolated to the x-intercept (AUC(0_,**.) using the terminal elimination rate constant. The absorption rate constant (k(a)) was calculated by using the optional Wagner-Nelson Analysis in the Independ program. Pharmacokinetic parameters were subsequently derived from these values according to accepted formulae (Gibaldi and Perrier, 1982; Gouyette, 1983): Elimination half life
t~4t~
= 0.693/fl
Total body clearance
C1B
= dose/AUC(o_,** )
Area volume of distribution
l/area
= dose/AUC(o.,.)./~
Volume of distribution at steady state
VSS
= dose. AUMC/AUC(0_,**)2
Mean residence time
MRT
= AUMC/AUC(o_, ®)
Bioavailability
F
= AUC(°-'**)P/°" D°sei/v AUC(0-,®)i/v • Dosep/o
Absorption half-life
tv~(a)
= 0.693/k(a)
Statistical analysis The pharmacokinetic parameters in groups A and B were compared by the two-tailed Mann-Whitney U-test using the SAS procedure NPARlWAY (SAS/STAT User's Guide, 1989; Powers, 1990).
358
RESULTS The mean (-+SEM) plasma concentrations and pharmacokinetic parameters after intravenous and oral administration of aditoprim are listed in Tables I, II, III and IV.
TABLE I Mean (-+SEM) aditoprim concentration in plasma after a single intravenous administration of 5 mg/kg body weight to 3- and 6-month-old pigs. Age and mean (± SEM) body weight are indicated
Post-injection time (h)
Concentration (/zg/ml) Group A (n = 5) (3 months; 51.7 ± 1.6 kg)
0.08 033 0.67 1 2 4 6 8 12 24 36
2.13 0.68 0.56 0.41 0.37 0.27 0.22 0.18 0.12 0.07 0.05
± 0.32 ± 0.08 -+ 0.07 ± 0.07 _+ 0.05 _+ 0.05 _+ 0.02 ± 0.02 ± 0.02 ± 0.01 _+ 0.005
Group B (n = 5) (6 months; 97.2 _ 5.6 kg)
3.44 1.40 1.11 0.90 0.64 0.40 0.37 0.32 0.23 0.12 0.08
_+ 0.94 _+ 0.08 _+ 0.05 _+ 0.11 ± 0.10 -+ 0.08 ± 0.07 ± 0.06 + 0.04 ± 0.01 ± 0.007
After intravenous administration, the mean plasma aditoprim concentrations were higher in the older pigs (Table I). Consequently, the mean AUC(0_,**~ of group B was significantly larger than that of group A and the mean total body clearance of group B was significantly smaller than that of group A (Table III). The apparent volume of distribution calculated by the extrapolation method and the volume of distribution at steady state tended to be smaller in the pigs in group B. The difference in C1B between groups A and B was not reflected in t~t~, because both V and CIB were smaller in group B (t~_ = 0.693V/CIB). FoUowmg oral administration of adltoprim, the mean absorption rate constant for group B was significantly smaller than that for group A (Table IV). Consequently, the mean tw(a) for group B was larger than that for group A. .
~,
•
•
•
359 TABLE II Mean (_+SEM) aditoprim concentration in plasma after a single oral administration of 5 mg/kg body weight to 3- and 6-month-old pigs. Age and mean (_+SEM) body weight are indicated
Post-injection time (h)
Concentration (/zg/ml) Group A (n = 5) (3 months; 47.7 +_ 0.8 kg)
0.33 0.67
0.05 0.11 0.16 0.19 0.21 0.22 0.17 0.13 0.06 0.04
i
2 4 6 8 12 24 36
Group B (n = 5) (6 months; 98.4 _+ 6.3 kg)
-+ 0.01 _+ 0.02 _+ 0.03 _+ 0.04 +_ 0.04 _+ 0.04 _+ 0.03 _+ 0.02 + 0.01 __. 0.005
0.03 0.05 0.08 0.16 0.20 0.27 0.26 0.23 0.12 0.06
___0.01 +_ 0.01 __. 0.02 _+ 0.01 _+ 0.02 _+ 0.07 _+ 0.07 ± 0.04 _+ 0.03 _+ 0.008
10":
)
% v
c o
O"0
-t--t
0~0~
~o
a
- ~
t~ f,.. c
.1
0
c
0 (-3
.01 0
. . . .
lb
. . . .
2b
. . . .
3b
. . . .
4b
Time (h) Figure 1. Semilogarithmic plot of mean aditoprim serum concentrations vs time in 3-month-old (o) and 6-month-old (o) male castrated pigs after a single intravenous administration of 5 mg/kg body weight
1:
5" I= v tO .r--i
o
o/
o~
.t
f._
0 0
,01 0
. . . .
. . . .
2b
. . . .
3b
. . . .
4b
T±me (h) Figure 2. Semilogarithmic plot of mean aditoprim serum concentrations vs time in 3-month-old (o) and 6-month-old (o) male castrated pigs after a single oral administration of 5 mg/kg body weight DISCUSSION The C1B for aditoprim decreased with age. CI@ is the sum of all the individual organ clearances that contribute to drug elimination. Full functional maturity of the elimination organs is reached several weeks after birth, with wide differences across species (Baggot and Short, 1984; Kietzman and LSscher, 1990). The design of this study does not allow discrimination of which elimination processes for aditoprim are increased in the younger pigs. Data from other species suggest that biotransformation of aditoprim is minimal (Graser, Hoffman-La Roche, personal communication). Furthermore, the extent of binding to plasma proteins in neonatal and young animals differs from that in adults and may thus affect C1B (Baggot and Short, 1984; Koch-Weser and Sellers, 1976). However, it may be hypothesized that one of the routes of aditoprim elimination is passive diffusion into the intestinal lumen, where it binds to components of the intestinal contents such as dietary fibre. In younger animals, this process may be more pronounced than in older animals and in this way the larger CL of aditoprim would arise. In the pigs m this study, the k(a) of aditoprim decreased and its t .v~(a) . . . increased with age. Several factors influence the extent of drug absorption in young animals: (1) the lower secretion of HC1 and pepsin and the higher pH in the stomach; (2) the prolonged gastric emptying time; (3) the lower intestinal motility; (4) the immature intestinal blood flow; (5) a smaller first-pass effect; (6) better intestinal absorption of high-molecular-weight compounds; (7) the immature bilia U function; (8) a high concentration of fl-glucuronidase in the newborn intestine; (9) incomplete colonization of the intestine by the microbial flora; and (10) the shorter diffusion
361 distance related to the thinner intestinal wall (Hoffmann, 1971; Kietzman and L6scher, 1990). In a study involving 580 children, the absorption rate constant of several drugs and test substances (D(+)-xylose and L(+)-arabinose) was increased relative to adults (Heiman, 1980). However, the bioavailability calculated by the method of corresponding areas showed no age dependence in these children.
TABLE III Mean (+_SEM) aditoprim pharmacokinetic parameters after a single intravenous administration of 5 mg/kg body weight to 3- and 6-month-old pigs. Age and mean (__.SEM) body weights are indicated
Parameter a Unit
Group A (n = 5) (3 months; 51.7 _ 1.6 kg)
Group B (n =5) (6 months; 97.2 -+ 5.6 kg)
fl
(h -1)
0.074 +_ 0.015
0.058 _+ 0.006
tvzt~
(h)
9.08 _+ 2.08
11.91 _+ 1.16
AUC(~**)
(h./zg/ml)
5.92 _+ 0.81 b
11.51 +- 1.07b
AUMC
(h 2 ./zg/ml)
78.15 _+ 17.64c
146.41 _+ 16.92c
CIB
(ml min -1 kg -1)
15.56 _+ 2.82b
7.51 +- 0.73b
MRT
(h)
12.54 _+ 1.74
13.25 _+ 1.97
Varea
(L/kg)
12.65 +_ 1.23
8.00 _+ 1.54
Vss
(L/kg)
10.84 + 1.07
6.25 + 1.41
aft = overall elimination rate constant; t~t ~ = elimination half-life; A U C ,t,o-* , ..,) = area under the curve extrapolated to the x-intercept; A U M C = area under the moment curve; CI B = total body clearance; M R T = mean residence time; /"area = area apparent volume of distribution; Vs¢ = apparent volume of distribution at steady state bGroups A and B are significantly different ~¢ at the 0.01 level CGroups A and B are significantly different at the 0.05 level
Interestingly, both the C1B and the k(a) of aditoprim were larger in the younger pigs. Diffusion is a bidirectional process; whether absorption or elimination dominates depends on the concentration gradient. The equilibrium obeys the pH partition hypothesis. The factors listed above, the poor solubility of aditoprim in water, and the smaller surface area of the gut in younger animals may influence the diffusion process.
362 TABLE IV Mean (-.+SEM) aditoprim pharmacokinetic parameters after a single oral administration of 5 mg/kg body weight to 3- and 6-month-old pigs. Age and mean (_+SEM) body weights are indicated
Parameter a Unit
fl
(h -1)
t~#
(h)
AUC(0_,** )
Group A (n --5) (3 months; 47.7 + 0.8 kg)
0.060 _+ 0.003
Group B (n ---5) (6 months; 98.4 _+ 6.3 kg)
0.068 - 0.007
11.60 _ 0.63
10.28 +_ 1.06
(h./zg/ml)
4.10 _+ 0.73
6.12 ___1.09
AUMC
(h 2 ./zg/ml)
74.67 _+ 12.42
82.71 _+ 10.87
MRT
(h)
18.67 +_ 0.95
18.35 _+ 0.99
Cmax
(/zg/ml)
0.21 + 0.03
0.30 + 0.11
Tmax
(h)
4.53 -- 0.85
7.80 -+ 1.50
F
(%)
77.44 + 17.40
53.35 + 6.42
k(a)
(h -1)
0.85 _+ 0.06 b
0.35 -+ 0.11b
tV~(a)
(h)
0.83
2,82 _+ 0.82 b
-
0.05 b
a/~ = overall elimination rate constant; t~t ~ = elimination half-life; AUC(0_,~) = area under the curve; A U M C -- area under the moment curve; MRT = mean residence time; Cmax = maximum plasma concentration; Tmax = time to reach the maximum plasma concentration; F = bioavailability; k(a) = absorption rate constant; tWk(a) = absorption half-life bGroups A and B are significantly different at the 0.05 level
The estimates for the pharmacokinetic parameters of aditoprim in the piglets in this study confrrm a previous report (Ludwig et al., 1985). After intravenous administration, the mean t~^ of aditoprim in piglets is longer than that of trimethoprim (9.08 - 11.91 h vs 2.25 _+ 0.19 h) and its apparent volume of distribution is larger than that of trimethoprim (6.25 - 10.84 L/kg vs 1.4 ___0.05 L/kg; Nielsen and Rasmussen, 1975a,b; Friis et aL, 1984; L6scher, 1984). Aditoprim is well absorbed in pigs. No comparative data exist for the intestinal absorption of aditoprim and trimethoprim in pigs. However, in goats, the bioavailability of aditoprim was found to be many times superior to that of trimethoprim (71 _+. 8.9% vs 10.3 _ 3.2%; Knoppert
363 et aL, 1988). In dogs, the bioavailability of aditoprim is 90.3 --- 0.9% (Sutter et al.,
1991). In species of veterinary interest, the m e a n values for the t,~,2p . of aditoprim range from 6.7 to 12.5 h and the m e a n values for its Vss range from 4.6 to 13.11 L / k g , which suggest excellent tissue penetration (Jordan et aL, 1987; H~inni et al., 1987, K n o p p e r t et aL, 1988; Sutter et al., 1991; V o n Fellenberg et aL, 1990). In conclusion, the favourable pharmacokinetics of aditoprim in pigs m a y permit the introduction of this antimicrobial into swine practice, after safety and residue depletion studies. T h e pharmacokinetic parameters were affected by the age of the animals. However, these changes were not sufficiently p r o n o u n c e d to require modification of the oral dosage regimens for animals over this age range.
ACKNOWLEDGEMENTS This study was supported by H o f f m a n n - L a R o c h e & Co Ltd, Basel, Switzerland. T h e technical assistance of Ms Barbara Schneider is greatly appreciated.
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