Effects of piroxicam on tissue distribution of sulfadimidine in West African Dwarf male and female goats

Abstract

Cases of Stevens–Johnson syndrome have been increasingly reported in Nigeria by individuals who consumed meat products of animals especially goats injected sulfonamides. Hence, tissue distribution and residues of intramuscular sulfadimidine were studied in West African Dwarf (WAD) goats. Twenty goats divided into two groups of 10 each (five males; five females) weighing 10.4 ± 1.63 kg were administered intramuscular sulfadimidine (100 mg/kg body weight), and the second group was coadministered 5 mg/kg of piroxicam via right and left thigh muscle, respectively. Samples of the liver, kidney, spleen, heart, lung, intestine, brain, and skeletal muscle were collected into sterile cellophane bags. Two untreated goats were killed and used for preparation of tissue standards. The tissue samples were stored frozen for analysis. High concentration of sulfadimidine residues was found in all the tissues of goats administered sulfadimidine as well as tissues of goats coadministered sulfadimidine/piroxicam for up to 30 days postdrug administration. Generally, residues of sulfadimidine were observed to be significantly higher than the acceptable limit (0.1 ppm). Hence, consumption of meats from WAD goats administered sulfadimidine may pose very high risk of Stevens–Johnson syndrome in sensitive humans. As such consumption of such meats should be avoided.

Keywords

Piroxicam sulfadimidine tissue kinetics West African Dwarf goats Stevens–Johnson syndrome

Introduction

Piroxicam is used in ruminants to reduce pain, fever, and inflammation and in the treatment of different clinical conditions such as rheumatoid disorders and mastitis.^1

–4 It binds to plasma proteins, has a half-life of 50 h, and is excreted in urine and faeces.⁵ The therapeutic effects are evident early in the treatment, and the response increases over several weeks.⁶

Sulfadimidine has proven to be clinically useful since its introduction in both human and veterinary medicine as therapeutic agent for a wide range of microbial diseases, including Chlamydiosis, toxoplasmosis and coccidiosis.^7

–10 Several investigations in other species of ruminants such as cow, buffaloes, sheep, calves, and goat have shown that the dosage regimen of a drug should be determined clinically in the animal species.^11,12 Sulfadimidine is 79% bound to plasma proteins with a half-life of 3.88–15.4 h and has a particularly large percentage (60–90%) excretion as acetylated derivatives.¹³

Quality and safety of food from animal products are of widely growing concern among public and health agencies around the world because of accumulation of drug residues.¹⁴ A residue means any compound present in edible tissues that result from the use of a drug.¹⁵ European Union reported that 51–52% noncompliant results of residues in animals were antibacterial drugs.¹⁶ The maximum residue limit and minimum residue limit (MRL) of sulfonamides is 0.1 µg/g.¹⁴ Hence, the “withdrawal period” which is defined as the time taken for the level of residues in the tissues to be depleted below the MRLs after the last dose must be determined.¹⁷

Residue levels are correlated with the rates of tissue clearance, which in turn are related to the drug’s physicochemical properties and routes of metabolism and excretion.¹⁸ Drug residues can accumulate in any tissue but are found commonly in liver, being an organ of metabolism and then kidney which is the main organ of excretion.¹⁹

Small ruminates, particularly goats, play an important role in the economic life of small holder farmers converting low-cost inputs to high-valued products: meat, milk, and skin.²⁰ The money realized from sale of goats is used for the purchase of crop and inputs such as fertilizer and to meet compelling family financial obligations.^21,22 Owing to the common use of West African Dwarf (WAD) goats, the effect of piroxicam on the tissue kinetics of sulfadimidine was studied.

Piroxicam has a plasma protein binding capacity of 91% compared to sulfadimidine (79%). Simultaneous administration of the two drugs could lead to toxicity, prolonged stay of the drug in the body, and also interferes with the therapeutic efficacy of the drug with the lesser affinity. The use of sulfadimidine in food-producing animals has potential to generate residues in edible tissues, and piroxicam might increase the residence time. This could lead to Stevens–Johnson syndrome in humans.

There is a paucity of information on the effects of piroxicam on the tissue kinetics and distribution of sulfadimidine in WAD goats. This study intends to provide a rationale for adjustment in dosage regimen of intramuscular sulfadimidine when coadministered with piroxicam. The study is designed to demonstrate the basis for withdrawal period of intramuscular sulfadimidine when coadministered with piroxicam. The study will determine the intramuscular use of piroxicam and sulfadimidine in WAD goats and may also establish possible drug–drug interaction between sulfadimidine and piroxicam.

Materials and methods

Drugs and dosage

Sulfadimidine sodium (33.3 mg/ml) produced by Kepro, Holland, was used for the study at a single dose of 100 mg/kg body weight. Piroxicam (0.5%) produced by Hanbet, Shandong, China, was used for the study at a single dose of 5 mg/kg body weight.

Human equivalent dose (HED) formula was used to determine therapeutic dose of (5 mg/kg) piroxicam in WAD goats.^23,24

$HED = \frac{animal dose \times animal K_{m}}{H k_{m}}$ whereas $K_{m} = \frac{Body surface area}{Body weight}$

But human BSA = H ^0.528 × W ^0.528 × K.

Goat BSA = BW^0.67 × 10⁻³.

Experimental animals

This study was conducted in the Department of Veterinary Physiology, Pharmacology and Biochemistry laboratory, College of Veterinary Medicine, University of Agriculture Makurdi. A sample size of five goats was used.

Twenty goats of both sexes aged 1 year weighing 10.4 ± 1.63 kg were used for this study. They were randomly selected and assigned into two groups of 10 each. The goats were fed corn offal and fresh grass, clean water was provided ad libitum. The animals were housed at the Veterinary Teaching Hospital of the University of Agriculture, Makurdi, during the period of study. All the animals were handled according to international standard for biomedical research involving animals as approved by Ethical Committee of the Department of Veterinary Physiology, Pharmacology and Biochemistry, University of Agriculture, Makurdi, Nigeria.²⁵

Administration and sampling of sulfadimidine

Five male and five female goats were administered intramuscular sulfadimidine (100 mg/kg body weight), and the second group of five male and five female goats was intramuscularly coadministered 100 mg/kg of sulfadimidine and 5 mg/kg of piroxicam, respectively, via right and left thigh muscle, respectively.

One goat from each group was killed on days 6, 12, 18, 24, and 30 post administration of sulfadimidine.

Samples of the liver, kidney, spleen, heart, lung, intestine, brain, abdominal fat, and skeletal muscle were collected into sterile cellophane bags and sample bottles. Two untreated goats were killed and used for preparation of tissue standards. The tissue samples were stored frozen until analyzed.

Assay of tissue sulfadimidine

For the analysis of sulfadimidine in tissues, 0.2 g of each tissue sample was crushed into fine particles and mixed with 3.80 ml of distilled water and treated with 1 ml of 20% trichloroacetic acid. After thorough mixing, the samples were allowed to stand for 10 min. They were centrifuged at 3000 rpm for 10 min. To 2 ml of clear supernatant, 0.1 ml of 0.1% sodium nitrate was added and mixed. The mixtures were allowed to stand for 3 min followed by addition of 0.2 ml 0.5% ammonium sulfamate and mixed. The samples were allowed to stand for 2 min before adding 0.2 ml 0.5% N-(1-naphthyl) ethylenediamine dihydrochloride. The samples were mixed, and the optical density of the resulting color determined at 540 nm wavelength using a spectrophotometer (spectrum lab 23A, 340–1000 nm).^26,27 The limit of detection of the assay was 0.05 µg/ml. The linear calibration curve of sulfadimidine in the tissues, within the range of 1–5 µg/ml, was obtained by plotting percentage absorbance against drug concentration. The correlation coefficient (R ²) was between 0.90 and 0.93 for all the tissues sampled.

Calculation of sulfadimidine concentration in tissue

The concentration of sulfadimidine in tissue was calculated using the following formula

Concentration of the drug (D) = \frac{concentration of standard \times optical density of drug}{optical density of standard}

Calculation of pharmacokinetic parameters of sulfadimidine in tissues

Tissue elimination half-life (T _1/2β) and elimination rate constant (β) were calculated using established equations.²⁸

Statistical analysis

Tissue concentrations, half-life, and elimination rate constant of goats administered sulfadimidine alone and sulfadimidine coadministered with piroxicam were presented as mean ± standard error of mean and analyzed by two-way analysis of variance using GraphPad Prism 5.03 for windows followed by Bonferroni posttest for individual comparisons. The significance level was set at p < 0.05.

Results

The distribution of sulfadimidine in the tissues of WAD goats administered sulfadimidine alone was not significantly different (p > 0.05) from the tissues of goats administered sulfadimidine/piroxicam (Tables 1 to 9).

Table 1.

Concentration of sulfadimidine residues (ppm) in liver of West African Dwarf goats administered sulfadimidine alone and sulfadimidine/piroxicam.^a

Time (days)	Sulfadimidine alone (ppm)	Sulfadimidine/piroxicam (ppm)
0	0.00 ± 0.00	0.00 ± 0.00
6	8.50 ± 1.00	9.75 ± 0.34
12	7.76 ± 0.97	7.71 ± 0.63
18	6.89 ± 0.97	6.60 ± 0.39
24	6.79 ± 0.97	5.77 ± 0.14
30	5.29 ± 0.29	5.33 ± 0.29

^aData were presented as mean ± standard error of mean and analyzed by two-way analysis of variance using GraphPad Prism 5.03 for windows followed by Bonferroni posttest. p > 0.05 within and between the groups.

Table 2.

Concentration of sulfadimidine residues (ppm) in kidney of West African Dwarf goats administered sulfadimidine alone and sulfadimidine/piroxicam.^a

Time (days)	Sulfadimidine alone (ppm)	Sulfadimidine/piroxicam (ppm)
0	0.00 + 0.00	0.00 + 0.00
6	6.43 ± 0.37	7.25 ± 0.25
12	5.85 ± 0.43	6.52 ± 0.22
18	5.20 ± 0.19	5.32 ± 0.43
24	4.45 ± 0.08	5.06 ± 0.34
30	3.84 ± 0.17	4.79 ± 0.60

^aData were presented as mean ± standard error of mean and analyzed by two way analysis of variance using GraphPad Prism 5.03 for windows followed by Bonferroni posttest. p > 0.05 within and between the groups.

Table 3.

Concentration of sulfadimidine residues (ppm) in spleen of West African Dwarf goats administered sulfadimidine alone and sulfadimidine/piroxicam.^a

Time (days)	Sulfadimidine alone (ppm)	Sulfadimidine/piroxicam (ppm)
0	0.00 + 0.00	0.00 + 0.00
6	7.18 ± 0.68	7.94 ± 0.07
12	6.21 ± 0.28	7.93 ± 0.06
18	5.87 ± 0.05	6.50 ± 0.93
24	5.87 ± 0.05	5.14 ± 1.27
30	5.35 ± 0.26	4.54 ± 0.66

Table 4.

Concentration of sulfadimidine residues (ppm) in heart of West African Dwarf goats administered sulfadimidine alone and sulfadimidine/piroxicam.^a

Time (days)	Sulfadimidine alone (ppm)	Sulfadimidine/piroxicam (ppm)
0	0.00 ± 0.00	0.00 ± 0.00
6	6.52 ± 0.47	6.68 ± 0.68
12	4.63 ± 1.07	4.39 ± 0.82
18	6.00 ± 1.49	6.41 ± 1.19
24	5.69 ± 1.18	5.57 ± 1.07
30	5.01 ± 0.98	4.39 ± 1.31

Table 5.

Concentration of sulfadimidine residues (ppm) in lungs of West African Dwarf goats administered sulfadimidine alone and sulfadimidine/piroxicam.^a

Time (days)	Sulfadimidine alone (ppm)	Sulfadimidine/piroxicam (ppm)
0	0.00 ± 0.00	0.00 ± 0.00
6	6.28 ± 1.72	6.23 ± 1.82
12	5.93 ± 1.36	6.27 ± 2.22
18	6.55 ± 0.75	7.40 ± 1.39
24	5.32 ± 0.00	5.93 ± 0.14
30	4.32 ± 0.97	5.55 ± 0.22

Table 6.

Concentration of sulfadimidine residues (ppm) in intestine of West African Dwarf goats administered sulfadimidine alone and sulfadimidine/piroxicam.^a

Time (days)	Sulfadimidine alone (ppm)	Sulfadimidine/piroxicam (ppm)
0	0.00 ± 0.00	0.00 ± 0.00
6	7.72 ± 0.13	8.32 ± 0.21
12	7.72 ± 0.13	8.16 ± 0.51
18	6.68 ± 0.19	9.91 ± 1.80
24	7.28 ± 1.26	7.04 ± 0.00
30	5.68 ± 0.31	6.67 ± 0.32

Table 7.

Concentration of sulfadimidine residues (ppm) in brain tissues of West African Dwarf goats administered sulfadimidine alone and sulfadimidine/piroxicam.^a

Time (days)	Sulfadimidine alone (ppm)	Sulfadimidine/piroxicam (ppm)
0	0.00 ± 0.00	0.00 ± 0.00
6	2.67 ± 0.34	2.16 ± 0.34
12	2.66 ± 0.33	2.65 ± 0.34
18	2.67 ± 0.34	2.06 ± 0.41
24	1.98 ± 0.49	1.05 ± 0.16
30	1.24 ± 0.12	1.40 ± 0.08

Table 8.

Concentration of sulfadimidine residues (ppm) in skeletal muscle tissues of West African Dwarf goats administered sulfadimidine alone and sulfadimidine/piroxicam.^a

Time (days)	Sulfadimidine alone (ppm)	Sulfadimidine/piroxicam (ppm)
0	0.00 ± 0.00	0.00 ± 0.00
6	3.50 ± 0.49	2.75 ± 0.90
12	3.07 ± 0.76	2.01 ± 0.48
18	3.07 ± 0.57	2.04 ± 0.64
24	2.30 ± 0.57	1.64 ± 0.10
30	2.01 ± 0.28	1.38 ± 0.03

Table 9.

Concentration of sulfadimidine residues (ppm) in fatty tissues of West African Dwarf goats administered sulfadimidine alone and sulfadimidine/piroxicam.^a

Time (days)	Sulfadimidine alone (ppm)	Sulfadimidine/piroxicam (ppm)
0	0.00 ±0.00	0.00 ± 0.00
6	5.27 ± 0.21	5.80 ± 0.75
12	5.52 ± 0.49	4.86 ± 0.18
18	6.10 ± 1.07	4.84 ± 1.09
24	4.84 ± 0.46	4.84 ± 1.72
30	4.84 ± 0.46	4.53 ± 1.41

The elimination half-life and elimination rate constant of sulfadimidine were not significantly different (p > 0.05) between the tissues of WAD goats administered sulfadimidine alone and sulfadimidine/piroxicam (Tables 10 and 11).

Table 10.

Elimination half-life (h) of intramuscular sulfadimidine in the various tissues of West African Dwarf goats administered sulfadimidine alone and sulfadimidine/piroxicam.^a

Tissues	Sulfadimidine alone (h)	Sulfadimidine/piroxicam (h)
Liver	885.7 ± 60.92	829.2 ± 59.40
Kidney	787.9 ± 17.95	1820 ± 107.0
Spleen	130.4 ± 29.64	631.7 ± 68.49
Heart	883.6 ± 28.22	553.5 ± 25.30
Lung	1006 ± 254.1	1700 ± 868.4
Intestine	836.8 ± 40.45	1134 ± 198.6
Brain	630.1 ± 77.26	924.1 ± 12.35
Muscle	679.7 ± 49.88	470.3 ± 62.90
Fat	764.4 ± 71.67	652.8 ± 35.24

Table 11.

Elimination rate constants (h⁻¹) of intramuscular sulfadimidine in the various tissues of West African Dwarf goats administered sulfadimidine alone and sulfadimidine/piroxicam.^a

Tissues	Sulfadimidine alone (h⁻¹)	Sulfadimidine/piroxicam (h⁻¹)
Liver	0.00078 ± 0.000045	0.00084 ± 0.000060
Kidney	0.00084 ± 0.000020	0.00058 ± 0.00034
Spleen	0.00065 ± 0.00017	0.00109 ± 0.000105
Heart	0.00078 ± 0.000025	0.00158 ± 0.00070
Lung	0.00073 ± 0.00018	0.00055 ± 0.00028
Intestine	0.00083 ± 0.000040	0.00063 ± 0.00011
Brain	0.00114 ± 0.00016	0.00075 ± 0.000010
Muscle	0.00597 ± 0.0050	0.0015 ± 0.00020
Fat	0.00091 ± 0.000085	0.00149 ± 0.00080

Discussion

The presence of sulfadimidine residues on the sixth day postadministration in liver, kidney, skeletal muscle, spleen, lung, and heart of WAD goats shows that sulfadimidine can be absorbed when injected intramuscularly and distributed and resides in tissues in significant quantity in this species of animal. The absorption rate of sulfadimidine is affected by its solubility.²⁹ The increased level of sulfadimidine residues on days 3–30 in all the tissues of goats sampled showed that the administration of sulfadimidine at 100 mg/kg body weight alone or in combination with piroxicam (5 mg/kg) cannot be eliminated from WAD goats within 30 days. It has been reported that sulfadimidine is not easily excreted in some species of animals.³⁰ The highest level of residue was observed in the liver of goats administered sulfadimidine/piroxicam on day 6 (9.75 ± 0.34 ppm) and intestine on day 18 (9.91 ± 1.80 ppm), indicating that piroxicam can cause high accumulation of sulfadimidine residues in the liver and intestine of WAD goats and that sulfadimidine reside much more in the liver (the main organ of drug metabolism) and intestine than in the rest organs. This may be due to desamino-sulfonamide that has also been identified as residues of the parent drug³¹ and may prefer liver to other organ, since liver is the main organ of drug metabolism. The desamino-metabolite is thought to be formed by bacteria in the gut following oral administration of the drug. Although sulfadimidine was administered via muscle, it occurred in high quantity in the intestine, signifying that even after intramuscular administration, it undergoes enterohepatic circulation, so that it can be metabolized by enteric bacteria. Desamino-sulfonamide is less polar, it is cleared more slowly, and this possibly explains why it is present at high concentration in the tissues thereby increasing withdrawal time.³² Very high concentration of sulfadimidine in the affected tissue mostly liver and kidney may pose high risk of toxicity to the organs. Sulfadimidine is nephrotoxic.³³ The presence of residues (>0.1 ppm) of sulfadimidine in all the affected tissues of the sulfadimidine and sulfadimidine/piroxicam injected WAD goats on day 30 may pose a risk of Stevens–Johnson syndrome to consumers. The concentration of sulfadimidine residues in tissues reported in this work is unlikely to be nephrotoxic to consumers. Our findings disagree with the report that sulfadimidine is an intermediate acting sulfonamide that last for 12–24 h in the body.³⁴ Sulfadimidine residues (0.1–0.4 ppm) in the kidney, liver, and spleen of turkeys after 3 days of withdrawal and as long as 14 days and³⁵ in hen, 0.01–0.47 ppm of sulfadimidine residue have been reported.³⁶ Therefore, variation of withdrawal time of sulfadimidine has been reported as 3 days for broilers,³⁷ 5–6 days for skeletal muscle and 7 days for liver of fattening chickens,³⁸ and 4 days for tissues in hen.³⁹

Very high tissue levels of sulfadimidne recorded in the present study (>0.2 ppm) poses high risk to consumers. In Australia, the minimum residue limit (MRL) of sulfonamide in turkey is 0.2 ppm.⁴⁰ In the Europe, the MRL of sulfonamide in most edible tissues is 0.1 ppm.¹⁴ But the tissue residue of sulfadimidine in liver, kidney, skeletal muscle, heart, and brain of rabbit were undetectable after 12 days of administration in rabbit.¹⁴ In pig, the tissue residue of sulfadimidine was depleted to <0.1 ppm in 4 days and 8–10 days in liver and kidney, respectively.⁴¹ In sheep, sulfadimidine residue was detected at the level <0.14 ppm after 3.5 days.⁴² In the present study, the half-life of sulfadimidine residues in the affected organs is 470.35–1700.79 h. This is at variance with the report indicating that the tissue half-life was between 5.63 and 16.31 h.⁴³ This may be due to the difference in the route of administration. However, the most obvious reason for unacceptable residues might be due to the failure to keep the withdrawal period including using overdose and long-acting drugs.⁴⁴ Lack of difference in the half-life and elimination rate constant between residue of sulfadimidine in sulfadimidine and sulfadimidine/piroxicam injected WAD goats shows that piroxicam does not affect half-life and elimination rate constant of tissue residue of sulfadimidine in the goats. But our present finding is at variance with the report indicating that rabbit has higher elimination rate constant (0.010–0.23 h)⁴³ in comparison with turkeys 0.002–0.001 h⁴⁵ and WAD goats (0.00058–0.00149 h) signifying difference in the route of administration, mode of metabolism, drug interaction, and elimination. Higher elimination half-life of sulfadimidine in WAD goats may also pose risk of environmental contamination, most especially, when droppings from goats administered sulfadimidine are used as organic manure. Sulfadimidine concentration of ground water was 0.6 ng/L.⁴⁶ Sulfadimidine in manure and soil may affect soil microbial and enzyme activities.⁴⁷ For example, it was found to have significant effects on soil respiration with an effective concentration (EC₁₀) of 13 mg/kg in the first 2 days of an experimental test.⁴⁸ Sulfonamides affect both the functioning (i.e., enzymatic activities) and the structural diversity of a soil microbial community at relatively low antibiotic concentration, 1–900 µg/g,⁴⁹ signifying that sulfonamides are a persistent organic pollutant due to its resistance to biological decomposition and it is regularly detected in surface waters even up to 1 µg/dm³ levels because of their widespread human and veterinary application.⁵⁰

Conclusion

Since piroxicam competes with sulfadimidine for same binding site (albumin), piroxicam must have delayed the elimination of sulfadimidine from the kidney, spleen, lung, intestine, and brain of WAD goats. Tissue residues exceeded recommended maximum residue limit (>1 ppm). Hence, piroxicam could aggravate Stevens–Johnson syndrome in sensitive individuals who consume the meat of WAD goats administered sulfadimidine and piroxicam concurrently.

Footnotes

Declaration of Conflicting Interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) received no financial support for the research, authorship, and/or publication of this article.

References

Deleforge

Thomas

Divot

. A field evaluation of the efficacy of tolfenamic acid and oxytetracycline in the treatment of bovine respiratory disease. J Vet Pharmacol Ther 1994; 17(1): 43–47.

Godson

Campos

Attah-poku

. Serum heptoglobin as an indicator of the acute phase responser in bovine respiratory disease. Vet Immunol Immunopathol 1996; 51(3–4): 277–292.

Huskisson

Ghozlan

Kurthen

. A long term study to evaluate the safety and efficacy of meloxicam therapy in patients with rheumatoid arthritis. Br J Rheumathol 1996; 35(1): 29–34.

Daniel

Regina

Timothy

. Cyclooxygenase isozymes: the biology of prostaglandin synthesis and inhibition. Pharmacol Rev 2004; 56(3): 387–437.

Brayfield

. Matindale: the complete drug reference. 34th ed. London: Pharmaceutical Press, 2004, p. 2756.

Ballington

Laughlin

. Pharmacology for technicians: understanding drugs and their uses. 5th ed. New Delhi: Scientific International Printing Limited, 2012.

Brander

Pugh

Bywater

. Veterinary applied pharmacology and therapeutics, 4th ed. London: Bailliere Tindal, 1982, p. 582.

Bevil

. Sulphonamides. In: Booth

Mcdonald

(eds) Jones veterinary pharmacology and therapeutics. 6th ed. Ames: Iowa State University Press, 1991, p. 1227.

Grahame-smith

Aronson

. Oxford textbooks of clinical medicine and drug therapy, 2nd ed. Oxford: Oxford University Press, 1992, p. 656.

10.

Bevil

. Sulphonamide. In: Booth

Mcdonald

(eds) Jones veterinary pharmacology and therapeutics. New Delhi: Kalyani Publications, 1982, p. 1134.

11.

Nawaz

. Pharmacokinetics and dosage of sulphadimidine in dogs. Zbl Vet Med 1980; 26(1): 75–80.

12.

Nawaz

Khan

. Pharmacokinetics of and urinary excretion of sulphadimidine in sheep and goats. J Vet Pharmacol Ther 1979; 2(2): 129–132.

13.

Saganuwan

Elsa

Mahammad

. Disposition kinetics of sulphadimidine in Nigerian mongrel dogs. J Sci Ind Res 2003; 1(2): 35–38.

14.

Council Regulation. Community procedure for the establishment of maximum residue limits of veterinary medicinal products in food stuffs of animal origin. OJEC 1990; 224: 1–8.

15.

FDA. Definition of residues, code of federal regulations. USA: Food and Drug Administration, 2015.

16.

Council Directives. On measures to monitor certain substances and residues thereof in live animals and animal products and repealing directives and decisions. OJEC 1996; 224: 1–23.

17.

Khan

. The Merck veterinary manual, 10th ed. Whitehouse station: Merck & Co., 2010, p. 2945.

18.

Saganuwan

. Physiochemical and structure-activity properties of piroxicam—a mini review. Comp Clin Pathol 2016; 25(5): 941–945.

19.

Doyle

. Veterinary drug residues in processed meats, potential health risk. Food Research institute briefings, http://www.wisc.Edu/fri/briefs/FRIBrief_VetDrgRes.pdf, 2006 (accessed 25 August 2016).

20.

Williamson

Payne

WJA

. An introduction to animal husbandary in the tropics. London: Longman, 1978, p. 483.

21.

Ikwuegbu

Tarawali

Igwe

. The role of West African dwarf goat in the economy of the small holder arable farmers in the subhumid zone of Nigeria. In: Proceedings of the second biennial conference of African small ruminant research network AICC, Arusha, Tanzania, 7–11 December 1992.

22.

Ademosun

. Trends in small ruminant production for the last two decades and its future in West and Central Africa. In: Adeniji

(ed) Improvement of small ruminant. Nairobi: OAU, 1988, pp. 18–22.

23.

Saganuwan

. Principles of pharmacological calculations. Zaria: Ahmadu Bello University Press, 2012, p. 544.

24.

Saganuwan

Orinya

. Toxico-neurological effects of piroxicam in monogastric animals. J Exp Neurosci 2016; 10: 121–128.

25.

CIOMS, ICLAS. http://www.cioms.ch/index.php/12-newsflash/326-cioms-and-iclas-release-thenew-international-guiding-principles-for-biomedical-research-involving-animals, 2012 (accessed 12 December 2015).

26.

Bratton

Marshall

. A new coupling component of sulphonamide determination. J Biochem 1939; 128: 537–550.

27.

Salinas

Mansilla

Nevado

JJB

. Derivative spectrophotometric determination of sulphonamides by Bratton-Marshall reaction. Analyt Chem Acta 1990; 233: 289–294.

28.

Baggot

. The physiological basis of veterinary clinical pharmacology. Oxford: Blackwell Science, 2001.

29.

Shoaf

Schwark

Guard

. The effect of age and diet on sulfadizine/trimethoprim disposition following oral and subcutaneous administration to calves. J Vet Pharmacol Ther 1987; 10: 331–345.

30.

Brander

Pugh

Bywater

. Veterinary applied pharmacology and therapeutics. 5th ed. London: Baillière Tindall, 1991, p. 582.

31.

Wooley

Jr Siegel

. Development of pharmacokinetic models for sulphanamides in food animals: metabolic depletion profile of sulfadiazine in the calf. Am J Res 1982; 43(5): 768–774.

32.

Kietzmann

. Metabolism of sulphonamides. Arch Gelflugelkd 1981; 45: 233–239.

33.

Kemper

. Veterinary antibiotics in the aquatic and terrestrial environment. Ecol Indic 2008; 8(1): 1–13.

34.

Sandhu

Rampal

. Essentials of veterinary pharmacology and therapeutics. 1st ed. New Delhi: Kalyani Publishers, 2006, p. 1529.

35.

Heath

Kline

Bamess

. Elimination of sulphamethazine from edible tissues, blood, urine and feces of turkey poults. American J Vete Res 1975; 36(7): 913–197.

36.

Righter

Worthington

Mercer

. Tissue-residue depletion of Sulfamethazine in calves and chickens. Am J Vet Res 1971; 32(7): 1003–1006.

37.

Lüders

Lai

Hinz

. Blood and tissue content of sulfamethazine and sulfaquinoxaline in broilers following medication with drinking water. A combination to mass medication in poultry. Zentralbl Veterinärmed 1974; 21(1): 110–118.

38.

Vlahović

Rajić

Cmiljanić

. Dynamics of excretion of sulphonamides from the tissue of fattening chicks. Acta Vet Brunen 1996; 46(4): 221–226.

39.

Nouws

JFM

Geertsma

Grondel

. Plasma disposition and renal clearance of sulphadimidine and its metabolites in laying hens. Res Vet Sci 1988; 44(2): 202–207.

40.

National Registration Authority (NRA). Review of Sulphonamides, National Regulatory Authority for Agricultural and Veterinary Chemicals in Australia , 2000, p. 42.

41.

Duffee

Berill

Thurmon

. Pharmacokinetics of sulphadimidine in male, female and castrated male swine. J Vet Pharmacol Ther 1984; 7(3): 203–211.

42.

Bevill

Sharma

Meachum

. Disposition of sulphonamides in food-producing animals: concentrations of sulfamethazine and its metabolites in plasma, urine, and tissues of lambs following intravenous administration. Am J Vete Res 1977; 38(7): 973–977.

43.

Etuk

Umarudeen

Onyeyili

. Effect of short term starvation on the plasma kinetics of sulphadimidine in rabbits. Int J Pharmacol 2006; 2: 331–334.

44.

Shearer

. Veterinary drugs including antibiotics. In: Moffat

Whittle

(eds) Enviromental contaminants in food. 1st ed. London: Sheffield Academic Press Ltd., 1999.

45.

Agbo

Saganuwan

Onyeyili

. Tissue distribution of sulphadimidine sodium in non-starved and starved grower turkeys Meleagris gallopavo. Int J Pharm Toxicol 2016; 4(2): 154–158.

46.

Watanabe

Bergamaschi

Laftin

. Use and environmental occurrence of antibiotics in free stall dairy farms with manure forage fields. Environ Sci Technol 2000; 44(17): 6591–6600.

47.

Carriciolo

Toop

Grenni

. Pharmaceuticals in the environment: biodegradation and effects on natural microbial communities. A review. J Pharm Biomed Anal 2015; 106: 25–36.

48.

Liu

Ting

Tao

. Effects of six selected antibiotics on plant growth and soil microbial and enzymatic activities. Environ pollut 2009; 157(5): 1636–1642.

49.

Gutierrez

Watanabe

Harter

. Effect of sulphonamide antibiotics on microbial diversity and activity in a Californian mollic haploxeralf. J Soil Sediment 2010; 10(3): 537–544.

50.

Garcia-Galan

Diaz-cruz

Barcelo

. Identification and determination of metabolites and degradation products of sulphonamide antibiotics. Trends Anal Chem 2008; 27(11): 1008–1022.