Estimation of tulathromycin depletion in plasma and milk after subcutaneous injection in lactating goats using a nonlinear mixed-effects pharmacokinetic modeling approach

Table 1 Noncompartmental pharmacokinetic parameters for tulathromycin in plasma and the marker residue CP-60,300 in milk of lactating goats following two subcutaneous injections of 2.5 mg/kg tulathromycin at 7-day interval

Pharmacokinetic parameters (units)	Plasma (injection 2 only)		Milk (injection 1)		Milk (injection 2)
Pharmacokinetic parameters (units)	mean	SD	mean	SD	mean	SD	p value^#
C_{max (obs)} (ng/mL)	155.211	39.501	1806.280	660.824	1457.238	282.876	0.191
T_{max (obs)} (h)	16.828	8.880	15.016	5.240	17.930	9.017	0.574
λz (1/h)	0.013	0.002	0.017	0.006	0.005	0.001	<0.001
T_1/2λz (h)	56.421	8.265	51.752	35.768	158.002	40.291	<0.001
AUC_last (h*ng/mL)	8050.601	1532.931	61805.331	6351.608	68156.845	12472.633	0.220
AUC_inf (h*ng/mL)	9120.588	1599.754	65147.987	7889.685	68978.306	12598.494	0.478

C_{max (obs)}: observed maximum plasma or milk concentration; T_{max (obs)}: time to observed maximum plasma or milk concentration after each injection; λz: elimination rate constant; T_1/2λz: elimination half-life; AUC_last: area under the plasma or milk concentration vs. time curve to the last sampled value; AUC_inf: area under the plasma or milk concentration vs. time curve extrapolated to infinity
^# p values of Student’s t test of the difference in the milk pharmacokinetic parameters between the first injection and the second injection

ISSN: 1746-6148