Improved management of drugs, hormones and pesticides in Africa.

Drugs, hormones and pesticides are chemical compounds used for alleviation of various diseases in animals. There are many classes of drugs which have been used and in the case of natural steroid hormones these have been used to increase mass gain by stimulating protein anabolism. Pesticides have been used for many years in the control of ectoparasites which transmit important human and livestock diseases. The purpose of the present article is to review procedures for management of veterinary products to facilitate national and international trade. These compounds and/or their metabolites have the potential to cause undesirable health effects to either target animals or consumers. Most African countries do not have competent authorities to conduct risk analysis for veterinary drug and pesticide residues in edible tissues. Because of the possible undesirable health effects from residues of veterinary compounds, the FAO/WHO established expert groups to establish acceptable daily intake and maximum residue levels (MRLs) for each drug or pesticide. In the case of natural steroids like oestradiol, progesterone and testosterone implants, no withdrawal period is required since there is no risk to the consumer. Bulls can have levels of testosterone ranging from 535-10,950 pg/g, heifers 92-250 and treated steers 100 pg/g, respectively. Data to enable approval of drugs and pesticides is to a large extent similar and include toxicity studies, reproductive studies, stability studies, safety, efficacy, tissue residue depletion studies and environmental impact. Good practice in the use of acaricides as indicated on the label is inevitable so that residue levels of these compounds remain below the specified MRL. Enactment and enforcement of legislations by various countries for the control of registration, sale, distribution and usage of ethical products should be enforced including use of prescriptions by veterinarians. Good practice in the use of veterinary drugs is the recommended or authorized usage of drugs. It should be enforced to ensure safe animal products for human consumption and to facilitate regional or international trade. In conclusion, for efficient production of animal protein from food producing animals all veterinary products should be approved prior to use, residue monitoring programs should be implemented; veterinarians and producers must use these compounds prudently using recommended good practices.

Antimicrobial resistance in Salmonella serotypes isolated from slaughter animals in Kenya.

OBJECTIVES: To isolate Salmonella from food animals and characterise the antimicrobial resistance of the isolates. DESIGN: A random sampling of slaughter animals was carried out. SETTING: Department of Public Health, Pharmacology and Toxicology, University of Nairobi, Kenya and Institute for Animal Breeding, Neustadt-Mariensee, Germany. SUBJECTS: Two hundred and eighty five samples, including faecal samples and carcass, cloacal and pharyngeal swab samples were analysed. RESULTS: Sixteen (5.6%) of 285 samples were positive for Salmonella. The prevalence of Salmonella on pig carcasses (19%) was higher than in faeces (8.6%). Three Salmonella enterica sub-species enterica serovars, namely Saintpaul (S. Saintpaul), Braenderup (S. Braenderup), and Heidelberg (S. Heidelberg), were identified, with S. Saintpaul being the predominant serovar. Antimicrobial resistance was found in 35.7% of all the isolates. The S. Heidelberg isolates were susceptible to all the antimicrobial agents tested. Multidrug resistance was found in 7.1% of the resistant Salmonella isolates. Plasmids were only detected in S. Heidelberg. Ampicillin resistance was based on expression of a bla(TEM) gene, while chloramphenicol, streptomycin, and tetracycline resistances were encoded by the genes catAl, strA, and tet(A), respectively. CONCLUSION: Pigs may serve as reservoirs of antimicrobial resistant Salmonella and slaughterhouse cross-contamination of pork may be a food safety risk. We recommended that slaughterhouse hygiene be improved to minimise contamination of pig carcasses.

Streptomycin and chloramphenicol resistance genes in Escherichia coli isolates from cattle, pigs, and chicken in Kenya.

The aims of this study were to determine the genetic basis of streptomycin and chloramphenicol resistance in 30 Escherichia coli isolates from food animals in Kenya and the role of plasmids in the spread of the resistance. Seven of the 29 streptomycin-resistant isolates harbored both the strA and strB genes. Twenty-one of isolates had the strA, strB, and aadA1 genes. The strA gene was disrupted by a functional trimethoprim gene, dfrA14 in 10 of the 21 isolates harboring the three streptomycin resistance genes. Physical linkage of intact strA and sul2 genes was found in two different plasmids from four isolates. Linkage of cassette-borne aadA1 and dfrA1 genes in class 1 integrons was found in two of the isolates. Chloramphenicol resistance was due to the gene catA1 in all the chloramphenicol resistant isolates. The strB, strA, and catA1 genes were transferable by conjugation and this points to the significance of conjugative resistance plasmids in the spread and persistence of streptomycin and chloramphenicol resistance in food animals in Kenya.

Drug sensitivity of trypanosome populations from cattle in a peri-urban dairy production system in Uganda.

Cattle from 50 farms in Mukono County, Uganda, were monitored for trypanosomes every second month over an 18-month period (1995-1996) by mini-anion exchange chromatography and haematocrit centrifugation techniques. Eighteen trypanosome isolates collected from cattle during this period were characterised in cattle, goats and mice for their sensitivity to homidium, isometamidium and diminazene; 10 of the isolates were selected randomly, 8 were from animals that had the highest serum isometamidium concentrations at the time the isolates were collected. All the isolates contained only Trypanosoma brucei and/or T. vivax. In nai;ve Boran (Bos indicus) cattle the isolates exhibited low pathogenicity and were sensitive to diminazene aceturate at 3.5 mg/kg body weight (bw) and isometamidium chloride at 0.5 mg/kg bw. In goats, 5 of 8 isolates were highly pathogenic, producing clinical signs indicative of central nervous system involvement within 60 days of infection; all such isolates contained T. brucei. However, all 8 populations were sensitive in goats to diminazene aceturate at 3.5 mg/kg bw. In contrast, 4 populations were refractory to treatment with isometamidium chloride at 0.5 mg/kg bw in at least 1 out of 3 goats each. Furthermore, 5 populations were refractory to treatment with homidium chloride at 1.0 mg/kg bw in a minimum of 2 out of 3 goats each. In mice, the 50% curative dose values for 11 Mukono isolates that contained T. brucei ranged from 0.30 to 1.89 mg/kg bw for diminazene aceturate, from 0.02 to 0.17 mg/kg bw for isometamidium chloride and from 0.90 to 4.57 mg/kg bw for homidium chloride. Thus, by comparison to reference drug-sensitive populations, all the stabilates were highly sensitive to diminazene and isometamidium, while some expressed low levels of resistance to homidium.

The pharmacokinetics of a long-acting oxytetracycline formulation in healthy dogs and in dogs infected with Ehrlichia canis.

The pharmacokinetic properties of oxytetracycline were studied following a single injection of a long-acting formulation (20 mg/kg body weight) into the semimembranosus muscle of healthy dogs and of dogs that had been experimentally infected with Ehrlichia canis. The disposition curves of the long-acting oxytetracycline formulation before and after infection were best described by a bi-exponential decline after a first-order absorption. The mean maximum serum concentration (Cmax) following infection was significantly lower and the time taken to attain this concentration (tmax) was significantly shorter than that in the healthy dogs. The mean apparent elimination half-life (t(1/2) beta) was significantly increased following infection. The corresponding rate constant (beta) was significantly decreased. The absorption half-life (t(1/2) ab) was significantly decreased after infection. The volume of distribution at steady state (Vdss) increased significantly following infection. It was concluded that the pharmacokinetic behaviour of a long-acting oxytetracycline in dogs after intramuscular administration is characterized by a two-compartment model with a slow elimination phase. This could be due to flip-flop kinetics. The febrile reaction in experimental E. canis infection affected some pharmacokinetic parameters of oxytetracycline.

An assessment of antimicrobial consumption in food producing animals in Kenya.

Antimicrobial agents are useful for control of bacterial infections in food animals and man. Their prudent use in these animals is important to control any possible development and transfer of resistance between animals and man. The objective of this study was to generate quantitative information to evaluate antimicrobial usage patterns by animal species, route of administration, antimicrobial class and type of use from 1995 to 1999 in Kenya. Theses data are essential for risk analysis and planning and can be helpful in interpreting resistance surveillance data, and evaluating the effectiveness of prudent use efforts and antimicrobial resistance mitigation strategies. Data on quantities of active substance classes were collected from the official records of the Pharmacy and Poisons Board of the Ministry of Health and analysed in MS Excel 2000 program. The mean antimicrobial consumption for the 5-year period was 14 594 +/- 1457 kg per year. This was distributed in the various antimicrobial classes as follows: 7975 kg (54.65%) of tetracyclines, 3103.96 kg (21.27%) of sulfonamides and 954.5 kg (6.56%) of aminoglycosides, 905 kg (6.20%) of beta-lactams, 94 kg (0.64%) of quinolones, 35 kg (0.24%) of macrolides and 24 kg (0.16%) of others (tiamulin). Mean consumption per year among the various food animals was: 10 989 +/- 357 kg in large animals (cattle, sheep, pigs and goats), 2906 +/- 127 kg in poultry alone and 699 +/- 427 kg in both large animals and poultry. These quantities represented 56.56% (8255 kg) consumption per year for parenteral use, 41.79% (6098 kg) for oral use and 1.65% (241 kg) for topical use (intramammary and eye ointments) in cattle. With respect to intended use in food producing animals, the mean consumption per year was: 13 178 kg (90.30%) for therapeutic use (ST), 4 kg (0.03%) for prophylactic treatment (PT) and 1411 +/- 246 kg (9.67%) was used both for therapeutic and prophylactic purposes (GPT). The study confirmed that antimicrobials are not used for growth promotion in Kenya. There was no specific trend in the quantities of active antimicrobial classes. This study has revealed that the tetracyclines, sulfonamides and trimethoprim, nitrofurans aminoglycosides, beta-lactams and the quinolones are the most commonly used drugs in food-producing animals in Kenya. Tetracyclines contributed approximately 55% of the total consumption, and there was an increasing trend in the consumption of quinolones from 1998.

Tetracycline residue levels in cattle meat from Nairobi salughter house in Kenya.

Two hundred and fifty beef samples were collected from five slaughterhouses in and around the city of Nairobi. The beef animals were sourced from various parts of the country. Samples of 50-100 grams were collected randomly from the liver, kidney and muscle of different beef carcasses. The samples collected were processed using multiresidue analytical methods that included liquid-gas partitioning and set-pat C18 cartridges chromatographic clean up. Chlortetracycline and oxytetracycline detection was done using Knauer Model 128 HPLC with an electron capture detector. Out of the 250 samples that were analyses for tetracycline residues 114 (45.6%) had detectable tetracycline residues. Of the 114 samples with detectable tetracycline residues, 60 (24%) were liver samples, 35 (14%), were kidney samples and 19 (7.6%) were muscle samples. The mean (p>0.05) residue levels of tetracycline for the five slaughterhouses studied were as follows: Athi River 1,046 micro g/kg, Dandora 594 micro g/kg, Ngong 701 micro g/kg, Kiserian 524 micro g/kg and Dagoretti 640 micro g/kg. Of the 250 samples analysed 110 (44%) had oxytetracyclines while 4 (1.6%) had chlortetracyclines. The mean residue levels of the detected tetracyclines were higher than the recommended maximum levels in edible tissues. This study indicates the presence of tetracycline residues in the various edible tissues. Regulatory authorities should ensure proper withdrawal periods before slaughter. This study indicates the presence of tetracycline residues in the various edible tissues. Regulatory authorities should ensure proper withdrawal period before slaughter of the animals.

Comparative efficacy of pyrethrum marc with albendazole against sheep gastrointestinal nematodes.

The efficacies of pyrethrum marc and of albendazole against experimental sheep gastrointestinal nematode infection were compared. Sheep was infected orally with 10,000 larvae (Haemonchus spp. (60.1%), Oesophagostomum spp. (13.9%), Trichostrongylus spp. (13.2%), Cooperia spp. (8.3%), Nematodirus spp. (3.5%), Strongyloides spp. (0.8%) and Ostertagia spp. (0.2%). Faecal egg count reduction in albendazole-treated sheep was 100% by day 4 following treatment, compared to 37.03%, 31.3%, 38.9% and 51.8% on days 4, 6, 8 and 10 in pyrethrum mare-treated sheep. These reductions were statistically significant on days 8 and 10 post-treatment (p < 0.05). The potential for using pyrethrins for helminth treatment is discussed.

Aspects of the pharmacokinetics of doxycycline given to healthy and pneumonic East African dwarf goats by intramuscular injection.

The effect of experimentally induced Pasteurella haemolytica pneumonia on the pharmacokinetics of doxycycline (Doxycen Retard) administered intramuscularly was studied in seven East African dwarf goats. The study was conducted in two consecutive phases, separated by a washout period of four weeks. The experimental infection, induced by intratracheal administration of 5 ml of 10(7) to 10(9) cfu/ml of Pasteurella haemolytica, produced a temperature rise, depression and laboured breathing within 6-12 days after inoculation. The concentrations of doxycycline in the serum were determined by a quantitative microbiological assay using an agar-gel diffusion method employing Bacillus cereus var mycoides (ATCC 11778) as the test organism, with a level of detectability of approximately 0.05 micrograms/ml. The concentration-time curve of doxycycline in the serum after intramuscular injection of 20 mg/kg bodyweight of the long-acting formulation before and after experimental infection was adequately described by a one-compartment open model. The maximum serum concentrations (Cmax) of doxycycline were lower in pneumonic goats than in healthy goats (3.87 +/- 0.52 and 5.56 +/- 0.213 micrograms/ml, respectively), suggesting an increased distribution volume in the peripheral compartment. The mean +/- SEM absorption rate (ka) before infection (1.13 +/- 0.02 h-1) was smaller than the after infection (8.23 +/- 3.81 h-1), but the difference was not significant. The apparent elimination half-life (t 1/2 beta) (24.51 +/- 0.02 h) after infection was significantly increased (p < 0.05), while the corresponding rate constant (beta) was decreased (p < 0.01). The absorption half-life (t 1/2(alpha)) (0.137 +/- 0.03 h) was significantly decreased (p < 0.01) after infection. The distribution volume (Vd(beta)) was significantly increased after infection (p < 0.05). It is concluded that, although experimental infection had an effect on the disposition kinetics of doxycycline, this was not sufficiently pronounced to require alteration of the dosage during disease.

Efficacy of doxycycline in a goat model of Pasteurella pneumonia.

The clinical efficacy of doxycycline (Doxycen, Cenavisa, Spain), a long-acting preparation, was evaluated for treatment of Pasteurella haemolytica infection in 6 goats. One goat was not infected and served as a control. The disease was induced by intratracheal inoculation of 10(7) to 10(9) cfu of P. haemolytica. Confirmation of respiratory disease was based on evidence of appropriate clinical signs. Before and after initiation of doxycycline treatment on day 10, each goat was examined daily. Three clinical responses to doxycycline treatment were noted. Mean rectal temperatures decreased from 40.1 degrees C to normal, while mean respiratory rate decreased from the pre-treatment value of 32 to 27/min after 4 days. Other clinical signs associated with pneumonia resolved within 3-5 days post treatment. In addition the minimum inhibitory concentration of DOTC for the P. haemolytica isolate was found to be < 0.5 microgram/ml. The present study indicates that DOTC may be a useful antimicrobial agent in the treatment of caprine pasteurellosis.

A comparative bioavailability of four Carbamazepine tablet formulations available in the Kenyan market.

The relative bioavailabilities of three carbamazepine tablet formulations available in the Kenyan market (Temporal(R), Taver(R) and Carbamazepine Lincoln) compared with the innovator formulation (Tegretol(R)) were evaluated in seven healthy African volunteers (5 males, two females; aged 22-36 years), according to a randomised fourway crossover study design, following oral administration of single 200 mg doses with a three week washout period. In vitro dissolution profiles of the tablets were also evaluated. Relative bioavailabilities ((F)rel) of Temporal(R), Taver(R) and Carbamazepine Linocoln were 101.2%, 82.2% and 71.6% respectively, compared with Tegretol(R). Percent drug content dissolved in vitro after I hour were 91.3%, 75.9% and 39.3% for Temporal(R), Taver(R) and Carbamazepine Lincoln, respectively. It was concluded that Temporal(R) was bioequivalent to Tegretol(R) while Taver(R) and Carbamazepin Lincoln were bioinequivalent to Tegretol(R). Administration of Taver(R) or Carbamazepine Lincoln might lead to poor control of epileptic seizures.

Some pharmacokinetic parameters of doxycycline in east African goats after intramuscular administration of a long-acting formulation.

A compartmental and non-compartmental study was carried out on five adult goats following intramuscular administration of doxycycline at 20 mg/kg bodyweight. The concentration of the drug in serum was determined by a microbiological assay employing Bacillus cereus var mycoides (ATCC 11778) as the test organism. The mean serum concentration (Cmax) and the time of maximum concentration (Tmax) were 1.87 micrograms/ml and 0.85 h, respectively. Using compartmental analysis, the plasma concentration-time curve of doxycycline best fitted a three-compartment open model with first-order absorption. A three-phase disposition of doxycycline was found, the terminal elimination half-life being approximately 40 h. The statistical moment theory was mainly used for non-compartmental analysis. The value obtained for the mean residence time (MRT) was 16.4 h. The mean values for the volume of distribution at steady state (Vdss), determined by compartmental and non-compartmental analyses, were 8.73 and 13.19 L/kg, respectively. There were no statistically significant differences when the major pharmacokinetic parameters were compared. It was concluded that the pharmacokinetic behaviour of doxycycline in goats after intramuscular administration is characterized by a three-compartment model with a slow terminal elimination phase. Based on current knowledge, this could be due to enterohepatic recycling and/or flip-flop kinetics. The study indicated that a single intramuscular administration of 20 mg/kg of doxycycline may only provide therapeutic concentrations for up to 24 h owing to slow absorption at the injection site.

Oxytetracycline residue levels in chicken eggs after oral administration of medicated drinking water to laying chickens.

Twenty laying birds were divided into four groups (n = 5) and given drinking water containing 0, 400, 600, and 800 mg/l of oxytetracycline respectively for 7 days. Eggs were collected continuously for 17 days after drug administration and stored at +4 degrees C. The oxytetracycline residues in yolk and albumen were analysed using a microbiological method with Bacillus cereus var. mycoides ATCC 11778 as the test organism. The mean maximum concentration of oxytetracycline was observed 2 days earlier in the albumen than in the yolk. The mean values in yolk and albumen were 0.526 and 0.280 mg/kg respectively. The depletion period was shorter for albumen than for yolk and oxytetracycline was detected in the yolk and albumen up to days 13 and 10 respectively. Withdrawal periods depended on the concentration of the antibiotic administered. Oxytetracycline residues reached a peak faster in albumen than in yolk, although the residues persisted for longer periods in the yolk.

Effects of antiarrhythmic drugs (verapamil, propranolol and lignocaine) on the electrocardiogram and haematology in adrenaline-induced arrhythmias in dogs anaesthetized with halothane.

Twenty adult (1-3 year old) mongrel dogs of either sex were used to study the effects of antiarrhythmic drugs in adrenaline-induced arrhythmias. The dogs were divided randomly into four groups of five dogs each (n = 5), anaesthetized with halothane and pretreated intravenously (i.v.) with verapamil 0.1 mg kg-1, propranolol 0.06 mg kg-1, or lignocaine 4 mg kg-1 while the controls received sterile physiological saline. Adrenaline (4 micrograms kg-1) was administered i.v. 10 min after drug pretreatments. Lead II of the ECG was recorded and blood collected for haematology. Ventricular fibrillations preceded by ventricular tachycardia occurred in the control dogs and three died within one minute of adrenaline administration. The predominant arrhythmias were ventricular premature beats, ventricular tachycardia, and second degree heart block. A significant increase (P < 0.05) in T wave amplitude was observed in the control group from 0.16 +/- 0.05 mV to 0.43 +/- 0.09 mV while only minimal increases were noted in the drug pretreated groups and there were no deaths. Data obtained from this study suggest that verapamil when administered early compares well with propranolol in the control of adrenaline-induced ventricular arrhythmias in the dog. Lignocaine when administered early prior to the induction of the arrhythmias protected against death but not arrhythmias. Drug pretreatments did not have any clinically significant effects on electrocardiographic parameters.

Field application of an ELISA using redefined Leishmania antigens for the detection of visceral leishmaniasis.

Two soluble antigens from Leishmania donovani of 116 kDa and 70 kDa molecular mass, and a soluble mixture of crude antigens, were used in an enzyme-linked immunosorbent assay (ELISA) for the detection of visceral leishmaniasis (VL) in the field, and compared with the direct agglutination test (DAT). The tests were carried out on 8 VL patients, 34 normal individuals from an area endemic for the disease, and 68 former visceral leishmaniasis patients 1-5 years after treatment. The 70 kDa ELISA and the DAT had a sensitivity and specificity of 100% (95% confidence interval 63-100%), while the 116 kDa ELISA and the soluble crude antigen ELISA were 37.5% (9-76%) and 50% (16-84%) sensitive, respectively. When using ELISA (116 kDa or 70 kDa), 68-69% of sera tested 1-2 years, and 92-94% of sera tested 5 years, after treatment were negative. In contrast, when DAT or ELISA with crude antigen were used, the negativity rate was 31% 1-2 years, and 53% 5 years, after treatment. DAT was therefore not an accurate test for diagnosis in the field. The use of the 70 kDa antigen in ELISA was an accurate alternative to DAT in the detection of VL.

Activity of buparvaquone against Theileria cervi in white-tailed deer.

Buparvaquone, a naphthoquinone with known efficacy against Theileria parva parva in cattle, was tested for activity against Theileria cervi piroplasms in both an in vitro culture system and in vivo in experimentally infected white-tailed deer. The in vitro data showed a significant decrease in the incorporation of 3H-hypoxanthine by infected red blood cells treated with buparvaquone when compared to that seen with imidocarb and chloroquine treatment. In both intact and splenectomized deer treated with buparvaquone (2.5 mg kg-1) a gradual decrease in piroplasm parasitaemia was observed following treatment. However, in the splenectomized deer, parasitaemia levels returned to near pretreatment values after approximately 2 weeks.

Effects of some calcium modulators on monensin toxicity.

Monensin is extremely toxic to some domestic animals, like the equine species, if they ingest poultry or cattle rations containing the drug. From a treatment standpoint, no specific compounds are known to alleviate or interact with monensin. Effects of some cardiovascular drugs which antagonize calcium influx in cardioskeletal and smooth muscles were evaluated in mice receiving varying lethal doses (80, 100, 120 or 140 mg/kg ip). Calcium channel blockers (verapamil, diltiazem and lidocaine), a calmodulin antagonist (chlorpromazine), adrenergic receptor blockers (yohimbine, tolazoline and propranolol), and a cardiac glycoside (digoxin) were evaluated for their effects on monensin toxicity following their 30 min pretreatments in mice ip. All the calcium modulators evaluated apart from chlorpromazine, propranolol, and digoxin, potentiated monensin toxicity significantly (p less than 0.05) by decreasing the calculated LD50 of monensin (108 mg/kg); the latter 3 drugs had no effect on monensin toxicity. This study suggests that excess calcium ion influx may not be the only factor responsible for monensin toxicosis in mice.

Comparative studies of the effects of quinuronium sulfate and diminazene diaceturate in sheep.

Biochemical parameters in 20 sheep were investigated following administration of quinuronium sulfate or diminazene diaceturate. The usual signs of salivation, micturition, anorexia, depression, muscular tremors and ataxia were observed within 20 min in sheep receiving therapeutic and double doses of quinuronium sulfate. There was an increased dose dependent plasma LDH activity above baseline values following administration of quinuronium sulfate and a non-dose dependent increased trend in diminazene diaceturate treatment. Plasma CK activity had an increased trend (p less than 0.05) above baseline values following administration of the two babesicides. Plasma BUN levels increased significantly (p less than 0.05) following administration of the two drugs. This study indicated that quinuronium sulfate is more organotoxic and hypotensive than diminazene diaceturate at therapeutic and/or above therapeutic dosages.