Pharmacokinetics and renal excretion of diphenhydramine and its metabolites, diphenylmethoxyacetic acid and diphenhydramine-N-oxide, in developing lambs.
The developmental disposition of diphenhydramine (DPHM) and its metabolites, diphenylmethoxyacetic acid (DPMA) and DPHM-N-oxide (DPHMNO), was investigated in postnatal lambs. Lambs received a DPHM intravenous (iv) bolus 15 days (Group A; n = 5) or 2 months (Group B; n = 6) after birth. Total body clearance of DPHM in postnatal lambs (Group A = 138.7 +/- 80.5 mL/min/kg; Group B = 165.7 +/- 51.3 mL/min/kg) was similar to the nonplacental clearance values (i.e., the component of fetal total body clearance that is not due to elimination via the placenta) estimated for fetal lamb (116.3 +/- 49. 6 mL/min/kg), and significantly greater than estimates in adult sheep (38.5 +/- 12.3 mL/min/kg). In addition, Group A DPHM renal clearance (CL(r), >1.80 +/- 1.24 mL/min/kg) was similar to that of the fetus (2.06 +/- 0.24 mL/min/kg), and significantly greater than that for Group B (0.26 +/- 0.17 mL/min/kg) and the adult (0.012 +/- 0.005 mL/min/kg). In contrast, similar to the fetal situation, postnatal DPMA CL(r) (Group A = 0.02 +/- 0.02 mL/min/kg; Group B = 0.05 +/- 0.01 mL/min/kg) was significantly less than adult values (0. 53 +/- 0.19 mL/min/kg). Because DPMA is not sequentially metabolized in sheep, the lower CL(r) in postnatal lambs results in longer apparent elimination half-lives of this metabolite (Group A = 90.4 +/- 32.2 h; Group B = 13.13 +/- 11.0 h) compared with that in the adult (2.9 +/- 1.6 h). No age-related difference in DPHMNO CL(R) was observed. Alterations in the CL(r) of DPHM and DPMA are likely related to differences in the rate of development of mechanisms (i.e. , tubular secretion and reabsorption and glomerular filtration rate) involved in the urinary drug excretion of organic acids and bases.
Wong
H
H
Division of Pharmaceutics and Biopharmaceutics, Faculty of Pharmaceutical Sciences, The University of British Columbia, 950 West 28(th) Avenue, Vancouver, British Columbia, Canada V5Z 4H4.
Kumar
S
S
Riggs
K W
KW
Rurak
D W
DW
D000085:Acetates / Q000097:blood / Q000493:pharmacokinetics*; D000367:Age Factors; D000818:Animals; D000831:Animals, Newborn; D001559:Benzhydryl Compounds / Q000097:blood / Q000493:pharmacokinetics*; D004155:Diphenhydramine / Q000097:blood / Q000493:pharmacokinetics*; D005333:Fetus / Q000378:metabolism*; D006634:Histamine H1 Antagonists / Q000097:blood / Q000493:pharmacokinetics*; D012756:Sheep
D000085:Acetates; D001559:Benzhydryl Compounds; D006634:Histamine H1 Antagonists; C092923:diphenylmethoxyacetic acid; D004155:Diphenhydramine