General Pharmacokinetic Characteristics
The pharmacokinetic profiles of diclofenac and misoprostol administered as the fixed combination (diclofenac sodium and misoprostol delayed-release tablets 50 mg/200 mcg or 75 mg/200 mcg) are similar to the profiles when the two drugs are administered as separate tablets (see Table 2). No pharmacokinetic interaction between the two drugs has been observed following multiple dosing. The diclofenac total exposure [area under the curve (AUC)] is dose-proportional within the range of 25 mg to 150 mg. Approximately dose-proportional increase in misoprostol exposure was also observed within the range of 200 mcg to 400 mcg. Neither diclofenac nor misoprostol accumulated in plasma following repeated doses of diclofenac sodium and misoprostol delayed-release tablets given every 12 hours under fasted conditions.
Table 2: Pharmacokinetic Parameters of Diclofenac and Misoprostol Acid Following Single Oral Doses ofDiclofenac Sodium and Misoprostol Delayed-Release Tabletsor Separate Products in Healthy Subjects
MISOPROSTOL ACID Mean (SD)
|
Treatment (n=36)
| C
max(pg/mL)
| T
max(hr)
| AUC
(0 to 4h) (pg
●hr/mL)
|
Diclofenac sodium and misoprostol delayed-release tablets 50 mg/200 mcg
Misoprostol
| 441 (137)
478 (201)
| 0.30 (0.13)
0.30 (0.10)
| 266 (95)
295 (143)
|
Diclofenac sodium and misoprostol delayed-release tablets 75 mg/200 mcg
Misoprostol
| 304 (110)
290 (130)
| 0.26 (0.09)
0.35 (0.12)
| 117 (49)
176 (58)
|
DICLOFENAC Mean (SD)
|
Treatment (n=36)
| C
max(ng/mL)
| T
max(hr)
| AUC
(0 to 12h) (ng●hr/mL)
|
Diclofenac sodium and misoprostol delayed-release tablets 50 mg/200 mcg
Diclofenac Sodium
| 1207 (364)
1298 (441)
| 2.4 (1.0)
2.4 (1.0)
| 1380 (272)
1357 (290)
|
Diclofenac sodium and misoprostol delayed-release tablets 75 mg/200 mcg
Diclofenac Sodium
| 2025 (2005)
2367 (1318)
| 2.0 (1.4)
1.9 (0.7)
| 2773 (1347)
2609 (1185)
|
SD: Standard deviation of the mean; AUC: Area under the curve; C
max: Peak concentration; T
max: Time to peak concentration
Absorption
Diclofenac: Diclofenac is completely absorbed from the GI tract after oral administration under fasted condition, and peak plasma levels are achieved in 2 hours (range 1 to 4 hours), and the area under the plasma concentration curve (AUC) is dose-proportional within the range of 25 mg to 150 mg. Peak plasma levels are less than dose-proportional and are approximately 1.5 and 2 mcg/mL for 50 mg and 75 mg doses, respectively. The diclofenac in diclofenac sodium and misoprostol delayed-release tablets is in a pharmaceutical formulation that resists dissolution in the low pH of gastric fluid but allows a rapid release of drug in the higher pH environment of the duodenum. Only 50% of the absorbed dose is systemically available due to first pass metabolism (i.e., oral bioavailability is 50%).
Misoprostol: Misoprostol is rapidly absorbed following oral administration of diclofenac sodium and misoprostol delayed-release tablets, and misoprostol acid (active metabolite) reaches a maximum plasma concentration in approximately 20 minutes. Maximum plasma concentrations of misoprostol acid are diminished when the dose is taken with food, and total availability of misoprostol acid is reduced by use of concomitant antacid. Clinical trials were conducted with concomitant antacid; this effect does not appear to be clinically important.
Food decreases the multiple-dose bioavailability profile of diclofenac sodium and misoprostol delayed-release tablets 50 mg/200 mcg and diclofenac sodium and misoprostol delayed-release tablets 75 mg/200 mcg.
Distribution
Diclofenac: The volume of distribution of diclofenac is approximately 0.55 L/kg. More than 99% of diclofenac is bound to plasma albumin.
Misoprostol: The plasma protein binding of misoprostol acid is less than 90% and is concentration-independent in the therapeutic range.
After a single oral dose of misoprostol to nursing mothers, misoprostol acid was excreted in breast milk. The maximum concentration of misoprostol acid in expressed breast milk was achieved within 1 hour after dosing and was 7.6 pg/mL (CV 37%) and 20.9 pg/mL (CV 77%) after single 200 mcg and 600 mcg misoprostol administration, respectively. The misoprostol acid concentrations in breast milk declined to <1 pg/mL at 5 hours post-dose. These data may not reflect drug level in mature milk and in a daily dosing regimen for osteoarthritis or rheumatoid arthritis.
Elimination
Metabolism
Diclofenac: Metabolism is predominantly mediated via CYP2C9 in the liver. Five metabolites (4'hydroxy-, 5-hydroxy-, 3'-hydroxy-, 4',5-dihydroxy- and 3'-hydroxy-4'-methoxy diclofenac) have been identified. The major metabolite (4'-hydroxy-diclofenac) has very weak pharmacologic activity.
Both diclofenac and its oxidative metabolites undergo glucuronidation or sulfation followed by biliary excretion. Acylglucuronidation mediated by UGT2B7 and oxidation mediated by CYP2C8 may also play a role in diclofenac metabolism. CYP3A4 is responsible for the formation of minor metabolites, 5-hydroxy and 3'-hydroxy-diclofenac.
Misoprostol: Undergoes rapid and extensive metabolism to its biologically active metabolite, misoprostol acid.
Excretion
Diclofenac: Diclofenac is eliminated through metabolism and subsequent urinary and biliary excretion of the glucuronide and the sulfate conjugates of the metabolites. Approximately 65% of the dose is excreted in the urine and 35% in the bile. The elimination half-life of diclofenac is approximately 2 hours. The clearance of diclofenac is approximately 350 mL/min (equivalent to 21 L/h).
Conjugates of unchanged diclofenac account for 5% to 10% of the dose excreted in the urine and for less than 5% excreted in the bile. Little or no unchanged unconjugated drug is excreted. Conjugates of the principal metabolite account for 20% to 30% of the dose excreted in the urine and for 10% to 20% of the dose excreted in the bile.
Conjugates of three other metabolites together account for 10% to 20% of the dose excreted in the urine and for small amounts excreted in the bile. The elimination half-life values for these metabolites are shorter than those for the parent drug. Urinary excretion of an additional metabolite (half-life = 80 hours) accounts for only 1.4% of the oral dose. The degree of accumulation of diclofenac metabolites is unknown. Some of the metabolites may have activity.
Misoprostol: After oral administration of radio-labeled misoprostol, approximately 70% of detected radioactivity appears in the urine. The elimination half-life is approximately 30 minutes.
Specific Populations
Geriatric Patients
No differences in the pharmacokinetics of diclofenac were observed in geriatric subjects (66 to 81 years; N=10) compared to younger adult subjects (26 to 46 years; N=10) following administration of diclofenac 50 mg twice daily for 4 weeks.
Though the mean AUC value of misoprostol acid for elderly subjects was 41% higher in geriatric healthy subjects (mean age, 69.5±4.6 years, N=24) compared to younger adult healthy subjects (mean age, 25.4±4.2 years, N=24) following single dose of misoprostol 400 μg, the increase in exposure is not clinically meaningful.
In a multiple-dose crossover study of diclofenac sodium and misoprostol delayed-release tablets administered twice daily to 24 subjects aged 65 years of age and older, misoprostol did not affect the pharmacokinetics of diclofenac
[see Use in Specific Populations (
8.5)]
.
Racial or Ethnic Groups
Pharmacokinetic differences due to race have not been identified.
Patients with Renal Impairment
In patients with renal impairment (N=5, creatinine clearance 3 to 42 mL/min) following intravenous administration of 50 mg diclofenac, AUC values and elimination rates were comparable to those in healthy subjects.
Pharmacokinetic studies with misoprostol in patients with severe renal impairment requiring hemodialysis (n=8, mean creatinine clearance 6.2±3.3 mL/min/1.73m
2) who received a single dose of 400 mcg misoprostol during a interdialytic period showed an approximate doubling of elimination half-life, C
max, and AUC of misoprostol acid compared to healthy subjects
[see Use in Specific Populations (
8.6)]
.
Patients with Hepatic Impairment
In patients with biopsy-confirmed cirrhosis or chronic active hepatitis (variably elevated transaminases and mildly elevated bilirubin, N=10), diclofenac concentrations and urinary elimination values following administration of 100 mg oral solution were comparable to those in healthy subjects.
In a study of subjects with mild to moderate hepatic impairment, mean misoprostol acid AUC and C
maxshowed approximately twice high as the mean values obtained in healthy subjects. Three subjects who had the lowest antipyrine and lowest indocyanine green clearance values had the highest misoprostol acid AUC and C
maxvalues.
Drug Interaction Studies
Diclofenac
Aspirin:When diclofenac sodium and misoprostol delayed-release tablets was administered with aspirin, the protein binding of diclofenac was reduced, although the clearance of the free diclofenac was not altered. The clinical significance of this interaction is not known. See Table 1 for clinically significant drug interactions of NSAIDs with aspirin
[see Drug Interactions (
7)]
.
Voriconazole: When a single dose diclofenac (50 mg) was co-administered with the last dose of voriconazole (400 mg every 12 hours on Day 1, followed by 200 mg every 12 hours on Day 2), the mean C
maxand AUC of diclofenac were increased by 114% and 78%, respectively, when compared to diclofenac alone
[see Drug Interactions (
7)]
.
In vitro, diclofenac interferes minimally with the protein binding of prednisolone (10% decrease in binding). Benzylpenicillin, ampicillin, oxacillin, chlortetracycline, doxycycline, cephalothin, erythromycin, and sulfamethoxazole have no influence,
in vitro, on the protein binding of diclofenac in human serum.
Other drugs: In small groups of patients (7 to 10 patients/interaction study), the concomitant administration of azathioprine, gold, chloroquine, D-penicillamine, prednisolone, doxycycline or digitoxin did not significantly affect C
maxand AUC of diclofenac.
Misoprostol
Diazepam: Misoprostol given for 1 week had no effect on the steady-state pharmacokinetics of diazepam when the two drugs were administered 2 hours apart.
Other drugs: Pharmacokinetic studies also showed a lack of drug interaction with antipyrine or propranolol given with misoprostol.