1. 1
Presenter: Ronald K Tessman, DVM, PhD, DACVIM, DACVPM

2. Special thanks to:
Laura Letendre, PhD and Rose Huang, PhD
For presentation development and technical assistance

3. Outline
• Principles of drug disposition
– ADME properties of drugs
– Routes of administration
• Pharmacokinetics (PK) of Gamithromycin
– Absorption
– Distribution
– Clearance
• Pharmacodynamics (PD) Gamithromycin in
lungs
– Comparison of Gamithromycin and Tulathromycin
PK parameters3

4. Drug disposition
4

5. Path of a drug in‐vivo:
parenteral administration
Absorption
Distribution
Metabolism
Excretion
SCIV
5
Tissues/Organs
Systemic Circulation
Free Drug Bound Drug
Liver
Drug & Metabolite
Drug &
Metabolite
Intestine
Drug &
Metabolite
Excretion in
Urine
Excretion in
Feces
Absorption
BiliaryExcretion
Distribution
Absorption

6. Parenteral routes
Epidermis
Dermis
Subcutaneous
Fat tissue
Muscle
6

7. Fast acting
Gamithromycin pharmacokinetics
Absorption and systemic exposure
7

8. Pharmacokinetics study
• Treatment groups
– 3 mg/kg IV dose; n =12
– 3, 6, or 9 mg/kg SC; n = 4/group
• Cattle characteristics
– 12 male castrate and 12 female angus cattle
– Less than 1 year old
– Weight = 182 to 260 kg
• Analysis
– Gamithromycin plasma concentration
– Pharmacokinetics
PR&D0099101:Evaluation of the pharmacokinetic profile of Gamithromycin in plasma from cattle treated
with a single intravenous dose (3mg/kg) or a single subcutaneous dose at 3, 6, or 9 mg/kg of Gamithromycin.
8

9. Complete absorption of
Gamithromycin
PR&D0099101
9
Fast, complete
absorption
Predictable
Pharmacokinetic
profile
Time (day)
GamithromycinConcentration (ng/mL)

10. 0
20
40
60
80
100
120
140
160
180
200
0 2 4 6 8 10 12
Time (hour)
Gamithromycin
PlasmaConcentration(ng/mL)
Prolonged absorption phase of
Gamithromycin
PR&D0099101
Absorption rate = Elimination rate
10
Fast absorption
•80% of max
within 15 mins
•Max within 1 Hr
High concentrations
maintained for 6 Hrs
plateau 30 min to 6
Hrs

11. Dose proportionality
• Dose adjustments are
made with the
assumption of dose
proportionality
PR&D0099101
Target dose
ZACTRAN has a
predictable response
11

12. Summary of pharmacokinetic results
• Absorption is fast
– 80% of max within 15 minutes
– Maximum within 1 hour
• Absorption is complete
– Bioavailability is 100%
• Predictable and proportional exposure with dose
from 3 to 9 mg/kg
12

13. Long lasting
Gamithromycin pharmacokinetics
Clearance and distribution
13

14. Definitions
14

15. Concentration gradient
driving distribution
Plasma Protein Tissue
Plasma Extracellular fluid
Membrane
15
Gamithromycin plasma protein binding = 26%

16. Volume of distribution:
a proportionality constant
Plasma Protein Tissue
Plasma Extracellular fluid
Membrane
Amount of drug in the body (t) = Vd * plasma concentration
16

17. Volume distribution
17

18. Physical chemical properties
Important to PK
• Log P: preference for
water or oil?
• Solubility in water
• pKa: how much drug is
ionized at each pH?
18
www.molecularstation.com

19. Gamithromycin
Physical chemical properties
• Lipophilic
– Log P = 4.69
• High H2O solubility
– 50 mg/mL
• Dibasic
– pKa = 9.78 and 8.88
19
O
O
Me
O
O
Me
HO OH
H
Me
N Me
H
H
H
Me
O O
R
S
S
R
R
R
S
R
S
R
Me
OH
OMe
Me
OH
Me
HO
N
H3C
CH3
Me
1
15 14
13
12
11
109
8
7
6
5
4
3
2

20. Ionization of Gamithromycin in plasma
Plasma pH 7.4; pKa = 9.78
20
pH = pKa ‐ 2 ~100% ionized
If pH = pKa 1:1 ratio
pH = pKa + 2 ~100% neutral
Ionized
Neutral

Neutral 1 Ionized 240

21. Ion trapping allows lung accumulation
Membrane Membrane
Neutral 1: Ionized 380Neutral 1: Ionized 240 Neutral 1: Ionized 95000
Plasma ‐ pH 7.4 Cytosol ‐ pH 7.2
Macrophage – Acidic
e.g. pH of 4.8
21
Non‐IonizedNon‐Ionized Non‐IonizedNon‐Ionized
For a pKa of 9.78

22. Pulmonary distribution study
• Treatment groups
– 6 mg/kg SC; n = 33
• Cattle characteristics
– 18 male and 15 female, crossbred beef calves
– Aged 7‐8 months
– Weight 100‐300 kg
• Gamithromycin analysis
• Plasma
• Lung tissue homogenate
• Other biofluids
PR&D0198501 : Evaluation of the Duration of the Concentration of Gamithromycin
in Plasma, PELF, Lung Tissue Homogenate, BAL Cells in Cattle using an LCMS Method throughout a Therapeutic Time Period
22

23. Gamithromycin tissue distribution
10 days after dosing
Systemic circulation
Tissues/Organs
PR&D0198501
23
Above
MIC
Ratio
487:1

24. Lung and plasma pharmacokinetics
PR&D0198501
24

25. Metabolism study
• Treatment groups
– 6 mg/kg SC; n = 14
• Cattle characteristics
– 7 steers and 7 heifers, healthy beef calves
– Aged 6‐7 months
– Weight 190‐240 kg
• Gamithromycin analysis
– Plasma
– Feces and urine
– Tissues and organs
• Liver, kidneys, lungs, muscle, abdominal fat and injection site
– Total radioactive residues of Gamithromycin
– Metabolite profiles
PR&D0078101 : Distribution and Excretion of Total Residues after the Subcutaneous Dosing in Cattle with Gamithromycin
and PR&D0078501: Metabolite Profiles in Selected Cattle Tissue Samples from PR&D0078101
25

26. Elimination of Gamithromycin
PR&D0078101, PR&D0078501
26
Drug
metabolism
is limited
Metabolites
proven
inactive and
safe

27. Summary of Gamithromycin
Metabolism/distribution studies
• Protein binding is low (26%)
• Extensive tissue distribution
– Lung >> plasma
– Intracellular ion trapping in the lung
• Quick systemic clearance of free drug
• Excreted primarily un‐metabolized in the bile
• Metabolites are not active
27

28. Effectively concentrates
in the lung
Gamithromycin pharmacodynamics
28

29. 29

30. Time dependence of Gamithromycin
activity
• Post‐antibiotic Effect (PAE) describes what
happens to the test organism after the
antibiotic is removed
• Common for macrolide class
• Gamithromycin PAE from 4.1 to 8.6 hours
• Consistent with other reported macrolides
30

31. Gamithromycin concentration
dependence studied
31
PR&D0169301: Activity of the Gamithromycin against Histophilus somni strains
associated with bovine respiratory disease: Determination of antibacterial kill kinetics.

32. Bronchoalveolar lavage study
• Treatment groups
– 6 mg/kg SC in the neck; n = 33
• Cattle characteristics
– Crossbred beef calves
– 7‐8 months old
– 100‐300 kg
• Analysis
– Gamithromycin concentrations in the
• Plasma
• Pulmonary Epithelial Lining Fluid (PELF)
• Lung tissue homogenate
• Bronchoalveolar lavage (BAL) cells
– Pharmacokinetics
32
PR&D0198501 : Evaluation of the Duration of the Concentration of Gamithromycin
in Plasma, PELF, Lung Tissue Homogenate, BAL Cells in Cattle using an LCMS Method throughout a Therapeutic Time Period

33. Uptake kinetics in clinically relevant
tissues and fluids
PR&D0198501: Disposition of Gamithromycin in plasma,
pulmonary epithelial lining fluid, bronchoalveolar cells, and lung tissue in cattle
PELF
(Pulmonary Epithelial Lining Fluid)
Alveolar macrophages
Capillary Wall
Interstitial Fluid
Alveolar
Epithelium
Bronchoalveolar biophase
33

34. Bronchoalveolar lavage
• Use
– Quantification of Gamithromycin in the BAL fluid
– BAL fluid
• Pulmonary epithelial lining fluid & cell content
(predominately alveolar macrophages)
• First line of defense against commensals and invading
pathogens
– Strong support for fast acting and long lasting
34

35. 1
10
100
1000
10000
100000
0 2 4 6 8 10 12 14 16
Time, days
GamithromycinConcentration
Lung (ng/g)
BAL cells (ng/mL)
PELF (ng/mL)
MIC of 1 ug/mL
Therapeutic lung concentrations
PR&D0198501
Peak lung concentration (12 hrs)
35
Fast
bacteria kill
Rapid
therapeutic
efficacy

36. Therapeutic lung concentrations
PR&D0198501
36
BAL and lung homogenate have high exposure
(AUC).
Concentrations are reached quickly – above MIC in
30 mins.
Long lasting: above MIC for 10‐15 days.

37. Time above MIC
PR&D0198501
37
Above MIC in
BAL cells for 15
days
Figure 1. Time over which concentrations of
gamithromycin in lung tissues exceed MIC90
0 5 10 15 20
M. haemolytica
P. multocida
H. somni
Time in days
BAL cells Whole lung PELF
1.0H. somni
1.0P. multocida
0.5M. haemolytica
MIC90 µg/mlEuropean
BRD isolates

38. • Conclusions and clinical relevance
– Fast absorption
– Preferential concentrates in PELF, BAL cells and lung tissue
– Concentrations in excess of the MIC90 for the common
bacterial pathogens:
• Mannheimia haemolytica
• Pasteurella multocida
• Histophilus somni
– Present in specific biophases within 30 minutes of
administration
– Persists for 7 days (PELF) to greater than 15 days (BAL cells
and lung tissue) following administration of a single dose
Summary
PR&D0198501
38

39. ZACTRAN
Comparison to Tulathromycin
39

40. Tulathromycin references
• Nowakowski, M.A., et al., "Pharmacokinetics and
Lung Tissue Concentrations of Tulathromycin a
New Triamilide Antibiotic Cattle"
Veterinary Therapeutics. 5. 1. 2004. Print.
• Evans, N. "Tulathromycin: An Overview of a New
Triamilide Antimicrobial for Livestock Respiratory
Disease"
Veterinary Therapeutics. 6. 2. 2005. Print.
40

41. Pharmacokinetic K comparison
ZACTRAN Data: PR&D0198501
Tulathromycin Data: Veterinary Therapeutics V5, N1, Spring 2004, p60.
41
Tulathromycin Lung
Gamithromycin Lung
Gamithromycin Plasma

42. Pharmacokinetic comparison
Absorption and distribution
42
Fast acting
Gamithromycin lung concentrations > MIC within 15 mins
Higher concentrations than Tulathromycin in lung

43. Pharmacokinetic comparison
Clearance
43
Fast uptake plasma to tissue
Persistent activity in tissue
Efficient terminal elimination

44. Pharmacokinetic comparison
Distribution
44
Gamithromycin:
higher lung concentrations

45. Conclusion
• All advantages associated with the macrolide
class
• Fast and complete absorption
• Fast and extensive lung distribution
• Lung concentrations > MIC
– From 15 minutes (Fast Acting)
– To 10‐15 days (Long Lasting)
• Effectively concentrates in the lung tissue faster
than Tulathromycin
45

46. Questions

47. 1
10
100
1000
0 1 2 3 4 5 6 7 8 9 10 11 12 13
GamithromycinPlasmaConcentration
(ng/mL)
Time (day)
Pharmacokinetics at the
Recommended dose of 6 mg/kg SC
PR&D0099101
47
Fast absorption