P Lees and F Shojaee AliAbadi The Royal Veterinary College, UK

1. 8th ISAP SymposiumDevelopments in Pharmacokinetics and Pharmacodynamics (PK/PD):optimising efficacy and prevention of resistanceNijmegen, The Netherlands, July 4th-6th, 2001 Rational dosing: animals versus humans P Lees and F Shojaee AliAbadi The Royal Veterinary College, UK

2. Rational Dosing of Antimicrobial Drugs in Animals • General considerations • Legal guidelines for PK-PD • Aspects of pharmacokinetics in animals • PK-PD integration of danofloxacin in ruminants (tissue cage model) • PK-PD integration of danofloxacin in calf pneumonia • Rational dosing: future perspectives

3. Pharmacology of Antimicrobial Therapy Dose Serum Conc. Site of action Conc.

4. Application of PK/PD integration to optimisation of antibacterial therapy Efficacy Recovery rate Resistance Residues Toxicity Cost

5. Antimicrobial Drug Treatment Which drug ? How much ? How often ? How long ?

6. 4 3 2 1 0 0 4 8 12 16 20 24 Plasma Concentration-Time Relationship 2 x MIC 90 Concentration (ug/ml) 1 x MIC 90 Time (h)

7. Criteria for Setting Dose Schedules • Cmax > 2 x MIC90 for all bacterial species against which activity to be claimed • Plasma concentration > 1 x MIC90 for all bacterial species against which activity to be claimed for half inter-dose interval • Dosing schedules meeting these criteria will be effective in many patients but are unlikely to be optimal for any antimicrobial drug group

8. Aspects of Pharmacokinetics in Animals • inter-species differences (half-life, clearance) • intra-species differences (breed) • age • depot formulations • residues in food producing species • distribution to udder (blood:milk barrier) • ruminants • chicken • fish • honey bee

9. Elimination Half-life of Antimicrobial Agents : Species Differences HM = Hepatic metabolism, HE = hepatic excretion, RE= renal excretion Prescott, Baggot and Walker, 2000

10. Oral Dosing of Antimicrobial Drugs in Ruminants Oral dosing usually restricted to pre-ruminant calves (aged <4-6 weeks)

11. Parenteral Dosing of Antimicrobial Drugs in Ruminants and Pigs Use of depot formulations giving sustained release from intramuscular injection sites • aqueous suspensions e.g. Procaine benzylpenicillin, clavulanate potentiated amoxycillin • oily suspensions e.g. Procaine benzylpenicillin • high strength solutions in organic solvents, drug precipitating at injection site e.g. oxytetracycline

12. Use of Depot/Sustained Release Formulations CONSEQUENCES FOR PHARMACOKINETICS, EFFICACY, TOXICITY AND DOSING: • Commonly involve flip-flop pharmacokinetics • Rising phase half-life represents elimination • Declining phase half-life represents absorption • Avoidance of peaks and troughs of concentration • Maintenance of effective concentrations for 1-4 days • Useful for time-dependent drugs (maintenance of T>MIC) • Problem of injection site residue in muscle

14. Residues of Antimicrobial Drugs in Food Producing Species • Muscle, fat, liver, kidney, eggs, milk • In EU maximum residue limits (MRLs) set by CVMP • MRLs set on basis of residue concentration and • No Observable Effect Level (NOEL) in animal toxicity studies • No microbiological effect level (NMEL) • Acceptable daily intake (ADI) determined using safety factor (SF) of 100 to 1000 (NOEL) or 10 (NMEL)

16. Drug Pharmacokinetics in Mastitis Therapy in Cattle PASSAGE OF BLOOD : MILK BARRIER Blood pH = 7.35 – 7.40 Milk pH = 6.50 – 6.80   1 + 10 (pHm – pKa) Rm/p = --------------------------- Weak acid 1 + 10 (pHp - pKa)

17. Milk : Plasma Concentration Ratios in Cattle * Improved penetration in mastitis ** Improved/reduced penetration in mastitis Prescott, Baggot and Walker, 2000

18. Drug Pharmacokinetics in Mastitis Therapy in Cattle

19. Intramammary Dosing of Antimicrobial Drugs in Ruminants Use of intramammary infusion tubes for treatment of mastitis in cattle • lactation therapy • dry cow therapy

22. PHARMACOKINETIC (and Efficacy ?) Variability of Antimicrobial Drugs in Poultry • MEDICATION - Continuous dosing in water - Pulse dosing in water - In feed medication (pelletted food) • VARIABILITY - Inherent inter-animal variation in A, D, M, E - Inter-animal variation in intake

23. Metabolism Metabolites Absorption Blood Protein bound Excretion Distribution Tissue bound

24. PoultryUnique Anatomical Considerations

25. Poultry Unique Anatomical Considerations • Haematology / immunology • Respiratory / Pulmonary system • Musculoskeletal system • Reproductive system • Integument • Gastrointestinal • Excretory / urinary systems

26. Excretory / urinary systems • Bilateral tri-lobed elongated kidneys, “resting” in synsacrum / retroperitoneal fossae • No bladder (ureters traverse to cloaca) • Histologically “chaotic”, without specific medullary / cortical regions • Urine produced is rich in uric acid. Uric acid / urates are a “white cap” on darker GI excreta • Renal portal system supplies peritubular capillary network

28. Enrofloxacin Absorption: Oral Rapidly absorbed in monogastric species, preruminant calves and chicken. Absorption in adult ruminants is variable and has ranged from 10 to 50%.

29. Enrofloxacin Distribution: Rapidly and widely distributed into all measured body tissues and fluids in many species, including cats, cattle, chickens, dogs, horses, and rabbits.

30. Enrofloxacin Concentration in chicken tissues (mg/ml or g) 1 h post treatment (O.S. 10mg/kg) Brain 1.1 Kidney 1 Skin 1.1 Liver 4.6 Lung 2.4 Muscle 2 Heart 2.8 Spleen 2.5 Serum 1.4

31. Enrofloxacin Enrofloxacin is metabolised to ciprofloxacin in chickens.

32. Enrofloxacin Preparation of dosage form: • The stock solutions should be prepared fresh daily. • Protect stock solution or medicated water from: • Freezing • Direct sunlight. • Use water with low hardness. • Galvanized metal watering systems or containers should not be used to carry or store this product (possible chelation with metal ions) • Chlorinators should not be operated while administering this medication.

33. Enrofloxacin serum concentrations after continuous dosage at a dose rate of 50 ppm 1.2 g/ml) 1.0 m 0.8 0.6 Concentration ( 0.4 0.2 0 0 24 48 72 96 Time (h)

34. PK/PD integration for enrofloxacin in chickens following continuous OS administration at a dose rate of 50 ppm (10 mg/kg)

35. I Need Some Fresh Air

36. PHARMACOKINETIC (and Efficacy ?) Variability of Antimicrobial Drugs in Fish • MEDICATION e.g. FURUNCULOSIS Baths: Short-term baths Long-term baths Topical treatments Injection MEDICATED FOOD • VARIABILITY - Inherent inter-animal variation in A, D, M, E - Inter-animal variation in intake - Temperature dependency of pharmacokinetics - Temperature dependency of residues

38. Salmon Farming

39. Elimination Half-life of Antimicrobial Agents in Fish : Species and Temperature Differences

40. Antibacterial Therapy in Fish Major indications: Furunculosis

42. Bacterial Disease in Bees AMERICAN FOULBROOD • Spore forming bacterium: Paenibacillus larvae • Brood disease • High contagious • Treatment: burning hives and contaminated equipment EUROPEAN FOULBROOD • Non-spore forming bacterium: Melissococcus pluton • “Stress” disease, most prevalent in spring/early summer • Treatment: oxytetracycline, ampicillin, mirosamicin

44. European Foulbrood • Objective is to deliver drug to young larvae • Drug must have good bioavailability after oral intake in adult bee • Secreted from the jelly glands to jelly which is acidic (pH~4) • Lipophilic and/or basic drugs are likely to achieve high concentrations in jelly by ion-trapping • Drug should be stable in jelly

46. 3rd day the eggs hatch into worm-like larvae eggs are laid by the queen 7th day Fully grown larvae Cells sealed off by workers Royal Jelly (Queen) Royal Jelly + Pollen and Honey (Worker) Only Royal Jelly

47. Worker Pollen / Syrup Honey Crop Stomach absorption Jelly glands Body nutrients Royal Jelly Larva Ventricle Ventricle Nakajima C, Sakogawa T, Okayama A, et al. Disposition of mirosamicin in honeybee hives. J Vet Pharmacol Ther (England), Aug 1998, 21(4) p269-73

48. Disposition profile of Ampicillin (ABPC) in larvae after single dose of 30 mg/hives in syrup or paste. --- Syrup Paste Nakajima C, Okayama A, Sakogawa T, et al. Disposition of ampicillin in honeybees and hives. J Vet Med Sci (Japan), Sep 1997, 59(9) p765-7

49. Disposition profile of mirosamicin (MRM) in honey bees after continuous administration for a week at a dosage of 200 mg/hive/week in pollen-substitute paste (hive 1-6). Days after termination of dosing Nakajima C, Sakogawa T, Okayama A, et al. Disposition of mirosamicin in honeybee hives. J Vet Pharmacol Ther (England), Aug 1998, 21(4) p269-73

50. Disposition profile of mirosamicin (MRM) in honey bees after continuous administration for a week at a dosage of 200 mg/hive/week in pollen-substitute paste (hive 1-6). Days after termination of dosing Nakajima C, Sakogawa T, Okayama A, et al. Disposition of mirosamicin in honeybee hives. J Vet Pharmacol Ther (England), Aug 1998, 21(4) p269-73