Læknablaðið : fylgirit - 01.05.1978, Page 58

Anna-Liisa Makela
Department of Paediatrics, Turku University
Hospital, Turku, Finland.
THE METABOLISM OF
NAPROXEN IN CHILDREN
Since October 1974, naproxen is used in the
treatment of juvenile rheumatoid arthritis at our
clinic.
Naproxen is a highly albuminbound drug, with
a relatively long metabolic half-life, which in
various experiments in man has been found to
range from 11 to 20 hours, with a mean of 13
hours. This metabolic persistence of naproxen
makes it possible to administer it less frequently
than is conventional for most nonsteroidal anti-
inflammatory agents. In children, the plasma
halflife of naproxen equals to that in adults,
being of 12 to 14 hours. A twice daily dosage
regime appears to be suitable for therapeutic
use of Naproxen in children, too.
The excretion of naproxen in man takes place
almost entirely via urine, with less than 5 per
cent appearing in faeces. The inactive metabolite
of naproxen in the urine is 6-demethyl-naproxen,
which in man accounts for approximately 307o of
the administered dose.
Characterization of the distribution and the
metabolism of naproxen is carried out with
radiolabeled naproxen by Runkel and coworkers.
(Table 1) Demethylated naproxen and its conju-
gates account for approximately 307o of the
administered dose. (1,2).
Table 1.
DISTRIBUTION OF NAPROXEN METABO LJTES
IN HUMAN URINE
Naproxen 1C%
Glucuronide of naproxen 4C%
Other conjugates of naproxen 207o
DEMETHYLATED NAPROXEN5%
Glucuronide of demethylated
naproxen 12%
Other conjugates of
demethylated naproxen 11%
(THOMPSON & COLLINS: J.Pharm.Sci. 62:937
1973)
In our study, naproxen was administered to
21 children with juveniie rheumatoid arthritis,
the dosage being 10 mg/kg/day. During the
TOTAL
7C%
TOTAL
287o
first 14 days the patients were given naproxen
in tablet form twice daily. After that, the
treatment was discontinued and the elimination
rate of the drug was followed up during the next
six days.
The age and sex of the patients ar shown in
Table 2.
Age
(years)
5-8
9-11
12-16
Girls Boys
8
4 1
6 2
TOTAL 18 3
Table 2. Age and sex of the patients.
The metabolism of naproxen was followed up
by estimating the plasma levels of the drug,
pg/ml Naproxen plasma levels gg/ml
Fig. 1 Naproxen plasma levels (ug/ml) after the
intake of the very first tablet. Dose
approximately 5 mg per kg body weight
per dose.
(Mean * S.D.) 8 patients.
56