Benzylpenicillin kinetics in the ewe: influence of pregnancy and lactation

Research in Veterinary Science 1990, 49, 190-193

Benzylpenicillin kinetics in the ewe: influence of pregnancy and lactation M. OUKESSOU, S. BENLAMLIH, Department of Physiology and Therapeutics, Hassan II Agronomic and Veterinary Institute, Rabat, Morocco, P. L. TOUTAIN, INRA Station de Pharmacologie et Toxicologie, 180 Chemin de Tournefeuille, Toulouse, France

Benzylpenicillin kinetics were investigated in a breed Water loss via milk imposes a considerable strain of sheep adapted to life in barren areas. Important on water balance, exceeding that of pregnancy. Water pharmacokinetic differences, dependent on -repro- turnover increased by 50 per cent after parturition in ductive status (control, pregnancy, lactation),. were sheep (Lahlou-Kassi et al 1988) and the total body demonstrated. In control ewes, the steady stale water remained 23 per cent higher than in nonvolume of distribution was 0 -23 ±, 0 -IS Iit.-t kg'- 1 pregnant ewes (Hassan et aI1988). Glomerular filtraand the plasma clearance was 12-4 ± 3-19 .,1 kg- J tion rate decreases, however, to non-pregnant values min - J_ During pregnancy, these twolarameter~ were (Benlarnlih and de Pomyers 1989). not significantly modified. Durin lactanon, the o Extracellular water represents the main distribution plasma clearance and volume of distribution were compartment for numerous drugs, in particular the significantly higher than during the control period ; weak acids (Baggot 1977)., Consequently, physioand pregnancy' (27 -4 ± 3 -22 ml j.g -] min - 1 and logical variations in the volume of the various water 0·696 ± 0 -20 litre kg - 1, respectively (P < 0 -01) _ In compartments will tend to modify plasma concentracontrast the mean residence time' (25-0 1: 4-6 tions and, therefore, the action of such drugs. minutes) was similar to those of the control period Similarly, variations in plasma clearance related to (17-54 ± 6-25 minutes) and pregnancy ~3-18 ± physiological conditions can be expected for drugs 5-94 minutes). These modifications in benzyl- subject to renal elimination. penicillin kinetics were explained in terms of fluid The aim of this study was to investigate the effects balance adjustments and renal function adaptation of pregnancy and lactation on pharmacokinetic observed during pregnancy and lactation, and it is parameters of benzylpenicillin in a breed of sheep suggested that an appropriate dosage regimen for adapted to life in barren areas. Benzylpenicillin was benzylpenicillin should take into account the physio- chosen as the test drug because its volume of distribulogical status of the animal. tion consists of the extracellular fluid space only and because it is mainly eliminated via the kidneys (Huber A DRUG'S activity is generally correlated with its 1982, Weinstein 1985). plasma concentration and time of maintenance, Plasma concentration will depend on the drug's volume of distribution which is, in turn, controlled by water balance. The persistence of plasma concentra- Materials and methods tion will depend on elimination processes and particuAnimals larly on renal clearance. It has been shown, in different species, that Five adult sardi ewes (A, B, C, D and E) were pregnancy and lactation involve marked adjustments studied during pregnancy, lactation and after drying of fluid balance. In pregnant women, the total body off (control phase). They were housed loose in a stall, water increased by 6 to 8 litres, of which 4 to 6litres and were placed in a cage on the days of testing, They are extracellular (Nolten and Ehrlich 1980). Increases were fed hay and barley ad libitum and had free access of 24 per cent in total body water (Hassan et al 1988) to water. The ewes were mated in October; all ewes and of 20 per cent in total exchangeable sodium became pregnant, four (A, C, D and E) delivered (Wintour et al 1976) were reported in pregnant ewes, single lambs and one (B) had twins, The lambs were The glomerular filtration rate increased in pregnant left with their mothers. Drying off was carried out 75 sheep from 3· 0 to 3· 9 ml kg - I min - I (Benlamlih and to 90 days after lambing. The average weights of the de Pomyers 1989) or from 2· 3 to 2' 7 ml kg-I min " ' animals during pregnancy, lactation and drying off, (Kaufman and Bergman 1978). measured on the day of benzylpenicillin administra0

.I)

190

Benzylpenicillin kinetics in ewes

191

TABLE 1: Bodyweight of the ewes and timing of the penicillin administrations Time

A

Pregnancy Day Weight (kg)

-4 47

Ewe C

B

-8 51·6

E

D

-1 43·4

-7 51

Lactation Day \\'eight (kg)

+65 39·2

+61 39·2

+62 46'6

Control period (dry. empty) Day Weight (kg)

+116 38·6

+ 112 40·8

+ 113 46·2

-4

+68 32·8

43·2

47·24 ± 4·00

+65 34·0

38·36 ± 5·46

+ 116

+ 119 37

Mean ± so

34

39·32 ± 4· 58

Time (0) corresponds to the lambing date

tion, were: 47-24 ± 4-0,38-36 ± 5-5 and 39-32 ± 4-6 kg, respectively.

Experimental design The experiment started in February in Rabat (Morocco). Pharmacokinetic trials were made during the last month of pregnancy, during lactation (about two months after lambing) and one month after drying off. Individual anatomical characteristics and schedules are given in Table 1_

Drug administration and sampling Sodium benzylpenicillin (Penicillin G; RousselDiamant) was injected into a jugular vein for each of the three physiological stages at a dosage of 500,000 iu_ Blood was sampled by direct puncture from the other jugular vein two, four, eight, 15, 30, 45, 60, 90, 1,20, 180 and 240 minutes after injection. The blood samples were collected in dry tubes, and the serum recovered after centrifugation and stored at - 25°C until analysis.

A nalytical technique Benzylpenicillin activity was determined by microbiological assay, using an agar diffusion technique and Staphylococcus aureus ATCC 6538 P as testmicroorganism (Arret et a(1971). Antibiotic medium (Difco) was poured into assay plates (100 mm diameter) and. six 8 mm cylinders were placed on the agar surface (three containing the standardcurve and three containing the samples). For each dish, benzylpenicillin concentration was read against the standard curve. The detection limit was between 0·05 and 0-06 iu rnl- 1•

Pharmacokinetic analysis Non-compartmental analysis was carried out using an appropriate program.

Body clearance (CIB) was calculated from equation 1 CI B = Dose/Ave In 'equation 1, AVC is the area under the serum concentration vs time curve, calculated by the trapezoidal rule with extrapolation to infinity. C (lasn/), was used as an estimate of the infinite part of the curve where C (last) corresponds to the concentration of the last measured sample and X is the slope of the last phase estimated by linear regression on the terminal phase. The mean residence time (MRT), that is, the mean time for a molecule to remain in the body was calculated by the linear trapezoidal rule with extrapolation to infinity; the steady state volume of distribution (Vss) was calculated by use of equation 2

Vss = Cia. MRT With CIa and MRT as previously defined.

Statistical analysis The influence of physiological status on these kinetic parameters was determined by an analysis of variance (ANOVA). Within-class mean comparisons were made using the Newman Keuls (NK) test (Snedecor and Cochran 1967).

Results Mean serum benzylpenicillin concentration curves after intravenous injection of benzylpenicillin to five ewes during pregnancy, lactation and after drying off are shown in Fig 1. Body clearance in non-pregnant and non-lactating ewes (control period) was 12· 38 ± 3 - 19 ml kg - I min -I. This value was not significantly different during pregnancy (14-02 ± 2-25 ml kg-I min-I) but was doubled (27-45 ± 3-22 ml kg-I min-I) during lactation; the difference was highly significant (P < 0-01, NK test) (Table 2).

M_ Oukessou, S_ Benlamlih, P_ L_ Toutain

192 100

Discussion

10 ~

E

.2

0·1

o· 01 +-.........--..--r---1,.......,,.......,~--r-....--...-... ..............-,-"""W""""'''''T'''-.......o

20

40

60

80 100 Time (min)

120

140 160

180

FIG 1: Semi-logarithmic plot of plasma benzylpenicillin concentration vs time after intravenous administration of benzylpenicillin (500,000 iu in total) in five ewes during the control period ("), pregnancy (. ) and lactation (0)

The increase of clearance during lactation was parallel to that of the volumes of distribution. The steady state volume of distribution (Vss) rose from 0- 23 ± 0-15 litre kg ' ' in control ewes to 0-696 ± O-1991itre kg-I in lactating ewes. The difference was highly significant (P < 0 -001 t NK test). During pregnancy t Vss was 0 -352 ± 0 - 110 litre kg - I t which was not significantly different from that of the control period (P > 0 -05 t NK test). The mean residence time was similar for each of the three physiological states (17-54 :I:: 6-25 minutes for control ewes, 23 - 18 ± 5 -94 minutes during pregnancy' and 25 -00 :I:: 4 -57 minutes during lactation) (P > 0 -05 t ANDV A). Individual values are presented in Table 2.

Owing to its safety, penicillin is one of the antibiotics most widely used during pregnancy (Nau 1987). The various physiological adaptations observed during pregnancy are likely to affect drug kinetics. In the present experiment, the steady state volume of distribution rose by 51 per cent, but the increase was not statistically significant; nevertheless, it can be observed that this result closely resembles that reported for ampicillin in pregnant women (Philipson 1977) for which the volume of distribution. rose by 38 per cent and was consistent with the observation that ampicillin plasma concentration peaks were much lower in pregnant mares (8-75 J,tg ml " ') than in non-pregnant ones (21- 57 J,tg ml- 1) after an intramuscular ampicillin injection (Traver and Riviere 1982). During pregnancy t penicillin clearance was similar to the control value (non-pregnant and non-lactating ewes). It should be noted that the value (12- 38 ± 3 -19 ml kg - I min -I) is similar to that obtained for para.. aminohippuric (PAH) acid clearance (14-7 ± 0-2 ml kg - I min - I) during pregnancy in sheep (Kaufman and Bergman 1978). Penicillin, like PAH acid, is actively excreted by the renal tubules; in addition, the renal tubule plays a major role in total penicillin clearance (Brater 1980). Consequently, it may be suggested that penicillin, like PAH t is eliminated in ewes, by a first pass renal process and that clearance depends on renal plasma flow. It must be noted that in pregnant women ampicillin clearance is increased (Philipson 1977) in parallel with an increase of renal plasma flow (Lindheimer and Katz 1985). Lactation affected considerably the penicillin

TABLE 2: Kinetic parameters describing the disposition of benzylpenicillin In five ewes during the control period. pregnancy and lactation after an IntFavenousadmlnistratlon of benzylpenicillin (500,000 lu), Parameters weFe obtained from a noncompartmental analysis

A

B

Sheep C

0

E

Control Cis (ml kg- 1 min -1) Vas (litre kg - 1) MRT (min)

12·05 0·262 20'98

9·18 0·116 12·68

11·02 0·130 11·87

11·95 0·184 15·44

17·71 0·473 26·71

12·38 ± 3·19 0·23 0·15 17· 54 ± 6'25

Pregnancy Cis (ml kg- 1 min- 1 ) Vaa (litre kg -1) MRT (min)

13'35 0·286 21·43

10'93 0·220 18·61

15'31 0'514 33·57

13·60 0'369 20·48

16·93 0·369 21'83

14·02 ± 2·25 0·352 ± 0·110 23·18 5·94

Lactation Cis (ml kg- 1 min- 1 ) VIS (litre kg - 1) MRT (min)

25'58 0·613 24'18

22·86 0'426 18·65

28'79 0'787 27'33

29'00 0·692 23·89

31'02 0'961 30'98

27·45 ± 3·22 * * 0·696 ± 0·199** 25·00 ± 4·57

Cis Plasma clearance V8S Steady state volume of distribution MRT Mean residence time ** Significantly different from control and pregnancy values. P
Mean ± so

*

*

Benzylpenicillin kinetics in ewes kinetics, with a large increase in clearance (122 per cent), and Vss (199 per cent). It should be noted that during lactation in sheep, total body water rose by 23 per cent (Hassan et at 1988) and in rats, the rate of renal plasma flow rose by 30 per cent (Arthur and Green 1983). These changes support the results of the present experiment; the penicillin clearance increase suggests an increase in the renal plasma flow, while the increa, e in Vss suggests an expansion of the intracellular water compartment volume during lactation. In practice, when penicillin therapy is implemented one must take these changes into account, because the doses necessary to maintain a given minimal inhibitory concentration may vary considerably according to the physiological state. As far as dosage regimen is concerned, no simple recommendation can be given on the basis of the present experiment. Indeed, dosage regimen (that is, amounts and intervals) will depend on the method of administration, formulation and on the required minimum concentration. However, a higher penicillin dose must be expected during lactation than during other states to maintain the required concentration.

References ARRET, B., JOHNSON, D. P. & KIRSHBAUM, A. (1971) Journal of Pharmaceutical Sciences 60, 1689-1694 ARTHUR, S. 'K. & GREEN, R. (1983) Journal of Physiology 334, 379-393 BAGGOT, J. D. (1977) Principles of Drug Disposition in Domestic Animals: The Basis of Veterinary Clinical Pharmacology. Philadelphia, W. B. Saunders. pp 53-57

193

BENLAMLIH, S. & DE POMYERS, H. (1989) Reproduction, Nutrition. Development 29, 129-137 BRATER, D. C. (1980) Drugs 19,31-48 HASSAN, G. A., EL-NOUTY, F. D., SALEM, M. H., LATIF, M. G. & BADAWY, A. M. (1988) Proceedings Symposium lAEA, Vienna. pp 65-85 HUBER, W. G. (1982) Veterinary Pharmacology and Therapeutics. Eds N. H. Booth and L. E. McDonald. Ames, Iowa State University Press. pp 731-732 KAUFMAN, C. F. & BERGMAN, E. N. (1978) Cornell Veterinarian 68, 124-137 LAHLOU-KASS1, A., BENLAMLIH, S., BOUKLIQ, R., TIBARY, A. & BOUJENANE, I. (1988) Journal of Agricultural Science (Finland) 60, 566-575 LINDHEIMER, M. D. & KATZ, A. (1985) The Kidney: Physiology and Pathophysiology. Eds D. W. Selding and G. Giebisch. New York, Raven Press. pp 2017-2041 NAU, H. (1987) Developmental Pharmacology and Therapeutics 10,174-198 NOLTEN, W. E. & EHRLICH. E. N. (1980) Kidney International 18,162-172 PHILIPSON, A. (1977) Journal of Infectious Diseases 136, 370-376 SNEDECOR, G. W. & COCHRAN, W. G. (1967) Statistical Methods. 6th edn, Ames, Iowa State University Press. pp 273-338 TRA VER, D. S. & RIVIERE, J. E. (1982) American Journal of Veterinary Research 43, 402-404 WEINSTEIN, L. (1985) The Pharmacological Basis of Therapeutics. 7th edn. Eds L. S. Goodman and A. Gilman. New York, Macmillan. pp 1122-1223 WINTOUR, E. M., BLAIR-WEST, J. R., BROWN, E. H., COGHLAN, J. P., DENTON, D. A., NELSON, J., ODDIE, C. J., SCOGGINS, B. A., WHIPP, G. T. & WRIGHT, R. D. (1976) Clinical and Experimental Pharmacology and Physiology 3, 331-341

Received August 7. /989 Accepted February 6. /990