Pharmacodynamics
Etodolac extended-release tablets are a nonsteroidal anti-inflammatory drug
(NSAID) that exhibit anti-inflammatory, analgesic, and antipyretic activities
in animal models. The mechanism of action of etodolac extended-release tablets,
like that of other NSAIDs, is not completely understood, but may be related
to prostaglandin synthetase inhibition.
Pharmacokinetics
Absorption
Etodolac extended-release tablets and etodolac tablets both contain etodolac,
but differ in their release characteristics. The systemic availability of etodolac
from etodolac extended-release tablets is generally greater than 80%. Etodolac
does not undergo significant first-pass metabolism following oral administration.
After oral administration of etodolac extended-release tablets in doses up to
800 mg once daily, peak concentrations occur approximately 6 hours after dosing
and are dose proportional for both total and free etodolac.
Table 1 shows the comparison of etodolac pharmacokinetic parameters after the
administration of etodolac tablets and etodolac extended-release tablets.
Table 2 shows the etodolac pharmacokinetic parameters in various populations.
The data from patients with renal and hepatic impairment were obtained following
administration of (immediaterelease) etodolac tablets.
Table 1.
| Pharmacokinetic Parameters |
Mean (CV) % † |
| etodolac tablets |
etodolac extended-release tablets |
| Extent of Oral Absorption (Bioavailability) [F] |
≥ 80% |
≥ 80% |
| Time to Peak Concentration (Tmax), h |
1.4 (61%) |
6.7 (47%) |
| Oral Clearance (CL/F), mL/h/kg |
49.1 (33%) |
46.8 (37%) |
| Apparent Volume of Distribution (Vd/F), mL/kg |
393 (29%) |
566 (26%) |
| Terminal Half-life (t½), h |
6.4 (22%) |
8.4 (30%) |
| † % Coefficient of variation |
Table 2. Mean (CV%) † Pharmacokinetic Parameters of
Etodolac in Normal Healthy Adults and Various Special Populations
| PK Parameters |
etodolac extended-release tablets |
etodolac tablets |
Normal
Healthy Adults
(18-44)*
(n=116) |
Healthy
Males
(18-43)
(n=102) |
Healthy
Females
(25-44)
(n=14) |
Elderly
( > 65 yr)
(66-88)
(n=24) |
Hemodialysis†
(24-65 )
(n=9) |
Renal Impairment‡
(46-73)
(n=10) |
Hepatic Impairment‡
(34-60)
(n=9) |
| Dialysis On |
Dialysis Off |
| Tmax,h |
6.7 (47%) † |
6.8 (45%) |
4.5 (56%) |
6.2 (51%) |
1.7 (88%) |
0.9 (67%) |
2.1 (46%) |
1.1 (15%) |
| Oral Clearance, mL/h/kg (CL/F) |
46.8 (37%) |
46.8 (37%) |
47.2 (38%) |
51.6 (40%) |
NA |
NA |
58.3 (19%) |
42.0 (43%) |
| Apparent Volume of Distribution mL/kg (Vd/F) |
566 (26%) |
580 (26%) |
459 (28%) |
552 (34%) |
NA |
NA |
NA |
NA |
| Terminal Half-life, h |
8.4 (30%) |
8.4 (29%) |
7.6 (45%) |
7.8 (26%) |
5.1 (22%) |
7.5 (34%) |
NA |
5.7 (24%) |
† % Coefficient of variation
* Age range (years)
‡ Pharmacokinetic parameters obtained following administration
of etodolac tablets
NA = not available |
Food/Antacid Effects
Food has no significant effect on the extent of etodolac extended-release tablets
absorption, however, food significantly increased Cmax (54%) following a 600
mg dose.
The extent of absorption of etodolac is not affected when etodolac is administered
with an antacid. Co-administration, with an antacid, decreases the peak concentration
reached by about 15 to 20% with no measurable effect on time-to-peak.
Distribution
The mean apparent volume of distribution (Vd/F) of etodolac following administration
of etodolac extended-release tablets is 566 mL/kg. Etodolac is more than 99%
bound to plasma proteins, primarily to albumin, and is independent of etodolac
concentration over the dose range studied. It is not known whether etodolac
is excreted in human milk. However, based on its physical-chemical properties,
excretion into breast milk is expected.
Metabolism
Etodolac metabolites do not contribute significantly to the pharmacological
activity of etodolac extended-release tablets.
Following administration of immediate-release etodolac, several metabolites
have been identified in human plasma and urine. Other metabolites remain to
be identified. The metabolites include 6-, 7-, and 8- hydroxylated etodolac
and etodolac glucuronide. After a single dose of 14C-etodolac, hydroxylated
metabolites accounted for less than 10% of total drug in serum. On chronic dosing,
hydroxylated-etodolac metabolites do not accumulate in the plasma of patients
with normal renal function. The extent of accumulation of hydroxylated-etodolac
metabolites in patients with renal dysfunction has not been studied. The role,
if any, of a specific cytochrome P450 system in the metabolism of etodolac is
unknown. The hydroxylated-etodolac metabolites undergo further glucuronidation
followed by renal excretion and partial elimination in the feces.
Excretion
The mean oral clearance of etodolac following oral etodolac extended-release
tablets dosing is 47 (±17) mL/h/kg. The terminal half-life (t½) of
etodolac after etodolac extended-release tablets administration is 8.4 hours
compared to 6.4 hours for etodolac tablets. Approximately 1% of an etodolac
tablet dose is excreted unchanged in the urine, with 72% of the dose excreted
into the urine as parent drug plus metabolites:
| --etodolac, unchanged |
1% |
| --etodolac glucuronide |
13% |
| --hydroxylated metabolites (6-, 7-, and 8-OH) |
5% |
| --hydroxylated metabolite glucuronides |
20% |
| --unidentified metabolites |
33% |
Fecal excretion accounted for 16% of the dose.
Special Populations
Geriatric
In clinical studies, age was not shown to have any effect on half-life or protein
binding, and demonstrated no change in expected drug accumulation. No dosage
adjustment is generally necessary in the elderly on the basis of pharmacokinetics.
The elderly may need dosage adjustment, however, as they may be more sensitive
to antiprostaglandin effects than younger patients (see PRECAUTIONS,
Geriatric Use).
Pediatric
The pharmacokinetics of etodolac extended-release tablets were assessed in
an open-label, 12-week clinical trial which included plasma sampling for population
pharmacokinetics. Seventy-two (72) patients, 6 to 16 years of age, with juvenile
rheumatoid arthritis, received etodolac extended-release tablets in doses of
13.3 to 21.3 mg/kg given as 400 to 1000 mg once daily. The results from a population
pharmacokinetic analysis based on the 59 subjects who completed the trial are
as follows:
Table 3. Pharmacokinetic Parameter Estimates for Etodolac
Extended-release Tablets in Patients with Juvenile Rheumatoid Arthritis
| Parameter |
JRAa
(Age: 6-16)b
n=59 |
| Oral Clearance (CL/F), mL/h/kg |
47.8 (38%) |
| Apparent Volume of Distribution (Vd/F), mL/kg |
78.9 (61%) |
| Half-life (t½), h |
12.1 (75%) |
a: Mean (CV) of parameter estimates predicted
from population pharmacokinetics
b: Age range (years) |
While similar, the pharmacokinetic parameters for children with juvenile rheumatoid
arthritis did not directly correlate with adult pharmacokinetic data in rheumatoid
arthritis. In the population pharmacokinetic analysis, body weights below 50
kg were found to correlate with CL/F (see DOSAGE AND ADMINISTRATION).
Race
Pharmacokinetic differences due to race have not been identified. Clinical
studies included patients of many races, all of whom responded in a similar
fashion.
Hepatic Insufficiency
The pharmacokinetics of etodolac following administration of etodolac extended-release
tablets have not been investigated in subjects with hepatic insufficiency. Following
administration of etodolac tablets, the plasma protein binding and disposition
of total and free etodolac were unchanged in the presence of compensated hepatic
cirrhosis. Although no dosage adjustment is generally required in patients with
chronic hepatic diseases, etodolac clearance is dependent on liver function
and could be reduced in patients with severe hepatic failure.
Renal Insufficiency
The pharmacokinetics of etodolac following administration of etodolac extended-release
tablets have not been investigated in subjects with renal insufficiency. Etodolac
renal clearance following administration of etodolac tablets was unchanged in
the presence of mild-to-moderate renal failure (creatinine clearance, 37 to
88 mL/min). Although renal elimination is a significant pathway of excretion
for etodolac metabolites, no dosing adjustment in patients with mild to moderate
renal dysfunction is generally necessary. Etodolac plasma protein binding decreases
in patients with severe renal deficiency. Etodolac should be used with caution
in such patients because, as with other NSAIDs, it may further decrease renal
function in some patients. Etodolac is not significantly removed from the blood
in patients undergoing hemodialysis.
Clinical Studies
Arthritis
The use of etodolac extended-release tablets in managing the signs and symptoms
of osteoarthritis of the knee and rheumatoid arthritis was assessed in double-blind,
randomized, parallel, controlled clinical trials in 1552 patients. In these
trials, etodolac extended-release tablets, given once daily, provided efficacy
comparable to immediate-release etodolac.
The safety, efficacy, and pharmacokinetics of etodolac extended-release tablets
were assessed in an open-label, 12-week clinical trial. Seventy-two (72) patients,
6 to 16 years of age, with juvenile rheumatoid arthritis, received etodolac
extended-release tablets in doses of 400 to 1000 mg (13.3 – 21.3 mg/kg body
weight) once daily. At these doses, etodolac extended-release tablets controlled
the signs and symptoms of juvenile rheumatoid arthritis. Based on the results
of this study, the safety profile of etodolac extended-release tablets (at doses
not exceeding 20 mg/kg) appeared to be similar to that observed in the adult
arthritic patients in clinical trials. (See PRECAUTIONS,
Pediatric Use).
Last updated on RxList: 12/9/2008