J. Vet. Med. A 47, 501–505 (2000)© 2000 Blackwell Wissenschafts-Verlag, BerlinISSN 0931–184X

Department of Veterinary Pharmacology and Toxicology, CCS Haryana Agricultural University, Hisar, India

Pharmacokinetics and Urinary Excretion of Sulphadimidine inBuffalo Calves

S. K. JAIN1, J. S. PUNIA and B. D. GARG

Address of authors: Department of Veterinary Pharmacology and Toxicology, CCS Haryana AgriculturalUniversity, Hisar, 125 004, Haryana, India; 1Corresponding author

With 1 figure and 3 tables

(Received for publication October 18, 1999)

Summary

Pharmacokinetics and urinary excretion of sulphadimidine (SDI) were determined in buffalo calvesfollowing single oral administration (150mg/kg). The plasma levels of free sulphadimidine were aboveminimum effective therapeutic concentration (×40mg/ml) between 4 and 12 h and the N4-acetylatedform of the drug was in the range of 7.2–19.3%. Kinetic evaluation of plasma levels was performed usinga two-compartment open model. The absorption and elimination half-lives of SDI were 3.01 and 11.94 h,respectively. Based on this study, an optimal dosage regimen of sulphadimidine in buffalo calves would be100mg/kg, followed by 50mg/kg at 12 h intervals. Sulphadimidine was mainly excreted in the urine asfree amine. The percentage of N4-acetyl sulphadimidine in urine was comparatively higher than in plasma.

Introduction

The disposition kinetics and excretion of various sulphonamides have been described invarious species of animals (Silvestri et al., 1967; Baggot, 1977; Nielson and Rasmussen, 1977;Reddy et al., 1988; Jain et al., 1992; Jain and Hapke, 1995). In veterinary clinical practice,sulphadimidine is frequently used in the treatment of infections caused by Streptococci, Sta-phylococci, Salmonella, Escherichia coli and Pasturella (Bevill, 1982). Our studies have shownthat the optimal therapeutic regimen should be based on the kinetic data obtained in a particularanimal species and the environment in which the drug is to be clinically used ( Jain et al., 1992).Further, it is also essential to determine the extent of acetylation of sulphonamides, as acetylatedsulphonamides have no antibacterial activity and are more toxic than their parent compound(Williams, 1959). However, there is no systematic study of sulphadimidine reported on thisaspect in buffaloes. This investigation was therefore undertaken to determine the pharmaco-kinetics of sulphadimidine and its suitable dosage regimen and urinary excretion in buffalocalves in a semi-arid tropical environment (less rainfall, high temperature).

Materials and Methods

Six clinically healthy male buffalo calves, weighing 80–100 kg were used in the present study. Theanimals were acclimatized for 2 weeks in the departmental animal house and were maintained underidentical feeding conditions. Sulphadimidine was suspended in water (7.5 g/100ml) and administered orallyas drench at a dose rate of 150mg/kg body-weight. Blood samples were collected from the contralateraljugular vein into heparinized glass centrifuge tubes at various times from 0.5 to 48 h after oral administration.The samples were centrifuged within 10min of sampling at 1593 g for 15min at room temperature toobtain plasma. The day temperature of the animal house was between 37 and 40°C during the experimentalstage. Plastic bags were used for collection of urine. Urine samples were collected for assay during 0–3, 3–

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502 JAIN et al.

6, 6–12, 12–24 and 24–48 h after sulphadimidine administration. All samples were stored at –10°C andwere processed for analysis within 48 h of collection.

Sulphadimidine in plasma was measured spectrophotometrically according to the method of Brattonand Marshall (1939). The concentration of N4-acetylated sulphadimidine was determined by the samemethod after acid hydrolysis with 0.5N HCl for 1 h. The percentage of acetylation was calculated by thefollowing formula:

% of acetylation= [N4/(N4 + S)]× 100,

where N4 and S are the concentrations of acetylated and free sulphadimidine, respectively.

Analysis of data

The statistical calculations were carried out in accordance with standard methods and the results aregiven as mean2 SE The plasma sulphadimidine concentration–time data were fitted separately for eachanimal by a two-exponential equation using a computer program (Tallarida and Murray, 1987). Variouspharmacokinetic parameters were determined as described by Gibaldi and Perrier (1982) and using acomputer program (Tallarida and Murray, 1987). The dosage regimen for sulphadimidine was calculatedas described by Notari (1980).

Results

Concentrations of free and acetylated sulphadimidine in plasma at different time intervalsafter an oral dose of 150 mg/kg body weight are presented in Table 1. The maximal level offree sulphadimidine in plasma was reached at 12 h after administration and then declinedover the remaining time to 48 h. A concentration above the minimum effective therapeuticconcentration (×40 mg/ml), which is considered to be effective against most of the organismssusceptible to sulphadimidine, was observed between 4 and 12 h of administration. The drugwas found to be acetylated in the range of 7.2–19.3 %.

The data on the disposition kinetics and dosage regimen of sulphadimidine is presentedin Table 2. The biological half-life (t1/2b) of sulphadimidine after its oral administration was11.94 h, with an elimination rate constant (b) of 0.058 per h, whereas the absorption half-life(t1/2a) was 3.01 h, with an absorption rate constant (a) of 0.23 per h (Fig. 1). The calculatedmaximal concentration (Cmax) of sulphadimidine was 58.43 mg/ml attained in 8.01 h (tmax). Thetotal area under the plasma concentration curve (AUC) was 1645.05 mg × h/ml.

The calculated optimal dosage regimen of sulphadimidine in buffalo calves in the presentstudy would be a loading dose (D°) of 101.8 mg/kg (i.e. 100 mg/kg for use in practice) andmaintenance dose (D*) of 51 mg/kg (i.e. 50 mg/kg for use in practice) with a dosage intervalof 12 h to attain the desired minimum therapeutic level during the course of therapy.

Table 1. Plasma concentrations (mg/ml) of sulphadimidine (SDI) in buffalo calves following its singleoral administration (150 mg/kg)

Time (h) Free SDI N4-acet. SDI Acetylation (%)

0.5 9.92 0.65 2.3 2 0.35 18.81 12.9 2 0.78 2.5 2 0.30 16.22 29.0 2 1.59 2.3 2 0.22 7.23 36.5 2 2.82 7.4 2 1.25 16.84 40.5 2 1.39 8.7 2 1.64 17.66 47.0 2 3.13 6.4 2 0.99 11.99 51.8 2 2.12 6.7 2 1.02 11.4

12 53.4 2 2.04 7.7 2 0.36 12.624 33.4 2 1.50 8.0 2 0.71 19.348 6.8 2 0.64 1.4 2 0.38 17.1

Values are means 2 SE of six animals.

503Kinetics of Sulphadimidine in Buffalo Calves

Table 2. Kinetic parameter estimates for two-compartment open model of sulphadimidine in theplasma after a single oral administration (150 mg/kg) in buffalo calves

Kinetic parameters Unit Values

a h−1 0.23t1/2a h 3.01b h−1 0.058t1/2b h 11.94Cmax mg/ml 58.4tmax h 8.01AUC mg × h/ml 1645D° mg/kg 101.8D* mg/kg 51t h 12

a, t1/2a, slope and half-life during the absorption phase, respectively; b, t1/2b , slope and half-lifeduring the elimination phase, respective; Cmax, tmax, calculated maximum plasma concentration andtime when the drug concentration is highest, respectively; AUC, area under the curve; D°, loadingdose; D*, maintenance dose; t, dosage interval.

Fig. 1. Semi-logarithmic plot of sulphadimidine concentration (mg/ml) in buffalo plasma versus timeafter oral administration of a single dose of sulphadimidine (100 mg/kg). a and b are the hybrid rate

constants of drug disposition curve.

504 JAIN et al.

The urinary excretion of sulphadimidine as total, free and acetylated amine is presentedin Table 3. The peak level of free sulphadimidine was 897 mg/ml 6–12 h after drug adminis-tration. The data indicated that throughout the experiment, i.e. for 0–48 h, adequate therapeuticlevels of sulphadimidine (above 40 mg/ml) were observed in urine. The drug was acetylated inthe urine in the range of 40.7–62.5 %.

Discussion

Sulphonamides are bacteriostatic agents; the plasma concentration during the course oftherapy should therefore not fall below a certain effective plasma concentration. In the presentinvestigation a concentration above the minimum effective therapeutic concentration, i.e.×40 mg/ml, accepted for most sulphonamides for large domestic animals (Stowe and Sisodia,1963), was maintained in the period 4–12 h following oral administration of sulphadimidine inbuffalo calves. The levels of sulphadimidine observed in buffalo calves were higher thansulphadiazine (Jain et al., 1992). Sulphadimidine was slowly absorbed in buffalo calves (absorp-tion rate constant, a: 0.230 per h). The elimination half-life of sulphadimidine (11.94 h) asestablished in this study was very similar to sulphadiazine in buffalo calves (Jain et al., 1992).However, it was two-fold higher than that of sulphadiazine in cows after a single intravenousinfusion (Atef et al., 1979) and slightly less in comparison with sulphadimidine in poultry (Reddyet al., 1988). The area under the plasma concentration curve (AUC) of sulphadimidine was1645 mg × h/ml, which is much higher than that of sulphadiazine (953mg × h/ml) reportedby Jain et al. (1992).

Sulphonamides are acetylated at N4-position by the enzyme system N-acetyltransferaseand acetyl coenzyme A (Marshall et al., 1937). Sulphadimidine in plasma of buffalo calves wasacetylated in the range of 7.2–19.3 %, which is much lower compared to sulphadiazine (Jain etal., 1992) and sulphamethoxazole (Jain and Uppal, 1984). A comparatively low extent ofacetylation of sulphadimidine suggests its safe use in buffalo calves without much risk oftoxicity.

On the basis of the kinetic data obtained during this investigation, the optimal dosage ofsulphadimidine in buffalo calves is a loading dose of 100 mg/kg, followed by a maintenancedose of 50 mg/kg with a 12 h dosage interval, which is approximately comparable to the dosageof sulphonamides prescribed to treat the mild to severe bacterial infections in cattle (Bevill,1982). Thus, the results of the present investigation revealed marked species differences in thekinetic behaviour of sulphadimidine. This emphasizes the need to determine the optimaltherapeutic regimes on the basis of kinetic parameters in each species and environment, ascarried out in the present study.

The higher urinary levels of sulphadimidine in buffalo calves express its lower re-absorp-tion from renal tubules. These results are in agreement with those reported for other sul-phonamides by Singh and Ahmad (1977), Jain and Uppal (1983) and Jain et al. (1992). Re-absorption of a drug from tubules into blood occurs through passive diffusion, which isgoverned by lipid solubility and unionized fraction of the drug. The urine of herbivores is

Table 3. Urinary levels (mg/ml) of sulphadimidine (SDI) in buffalo calves following its single oraladministration (150 mg/kg)

Time (h) Free SDI N4-acet. SDI Acetylation (%)

0–3 78 2 13.4 56 2 7.2 41.73–6 182 2 31.8 304 2 46.1 62.56–12 897 2 76.8 614 2 57.2 40.7

12–24 724 2 68.7 584 2 71.6 44.824–48 128 2 16.6 165 2 27.8 56.2

Values are means 2 SE of six animals.

505Kinetics of Sulphadimidine in Buffalo Calves

alkaline in reaction. Therefore, sulphadimidine (pka 7.37) in this alkaline environment willremain in a nearly ionized state, which is unfavourable for its re-absorption.

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