Diclofenac Potassium (Page 6 of 8)

8.5 Geriatric Use

Elderly patients, compared to younger patients, are at greater risk for NSAID-associated serious cardiovascular, gastrointestinal, and/or renal adverse reactions. If the anticipated benefit for the elderly patient outweighs these potential risks, start dosing at the low end of the dosing range, and monitor patients for adverse effects [ see Warnings and Precautions ( 5.1, 5.2, 5.3, 5.6, 5.13)].

Diclofenac is known to be substantially excreted by the kidney, and the risk of adverse reactions to this drug may be greater in patients with impaired renal function. Because elderly patients are more likely to have decreased renal function, care should be taken in dose selection, and it may be useful to monitor renal function.

10 OVERDOSAGE

Symptoms following acute NSAID overdosages have been typically limited to lethargy, drowsiness, nausea, vomiting, and epigastric pain, which have been generally reversible with supportive care. Gastrointestinal bleeding has occurred. Hypertension, acute renal failure, respiratory depression, and coma have occurred, but were rare [ see Warnings and Precautions ( 5.1, 5.2, 5.4, 5.6) ].

Manage patients with symptomatic and supportive care following an NSAID overdosage. There are no specific antidotes. Consider emesis and/or activated charcoal (60 to 100 grams in adults, 1 to 2 grams per kg of body weight in pediatric patients) and/or osmotic cathartic in symptomatic patients seen within four hours of ingestion or in patients with a large overdosage (5 to 10 times the recommended dosage). Forced diuresis, alkalinization of urine, hemodialysis, or hemoperfusion may not be useful due to high protein binding.

For additional information about overdosage treatment contact a poison control center (1-­800-222-1222).

11 DESCRIPTION

Diclofenac potassium capsules are a nonsteroidal anti-inflammatory drug, available as liquid-filled capsules of 25 mg for oral administration. Diclofenac potassium, USP is a white to slightly yellowish crystalline powder. It is sparingly soluble in water at 25°C. The chemical name is 2-[(2,6-dichlorophenyl) amino] benzeneacetic acid monopotassium salt. The molecular weight is 334.24. Its molecular formula is C 14 H 10 Cl 2 NKO 2 , and it has the following chemical structure.

Structure

The inactive ingredients in diclofenac potassium capsules include: lactic acid, polyethylene glycol, polysorbate 80, povidone, and water. The capsule shells contain bovine hydrolyzed collagen, gelatin, lecithin, medium chain triglycerides, sorbitans, sorbitol, and water. The capsules are printed with black ink composed of black iron oxide, polyvinyl acetate phthalate, polyethylene glycol and propylene glycol.

12 CLINICAL PHARMACOLOGY

12.1 Mechanism of Action

Diclofenac has analgesic, anti-inflammatory, and antipyretic properties.

The mechanism of action of diclofenac potassium, like that of other NSAIDs, is not completely understood but involves inhibition of cyclooxygenase (COX-1 and COX-2).

Diclofenac is a potent inhibitor of prostaglandin synthesis in vitro. Diclofenac concentrations reached during therapy have produced in vivo effects. Prostaglandins sensitize afferent nerves and potentiate the action of bradykinin in inducing pain in animal models. Prostaglandins are mediators of inflammation. Because diclofenac is an inhibitor of prostaglandin synthesis, its mode of action may be due to a decrease of prostaglandins in peripheral tissues.

12.3 Pharmacokinetics

The pharmacokinetics of diclofenac potassium was assessed in 24 healthy, normal adult volunteers who received 25 mg diclofenac potassium under fasting conditions. The mean pharmacokinetic parameters for diclofenac potassium are shown in Table 4.

Table 4 Mean Pharmacokinetics of Diclofenac Potassium in Adults
PK Parameter Number of Subjects Mean ± Standard Deviation
T max (hr) 24 0.47 ± 0.17
Terminal Half-life (hr) 24 1.07 ± 0.29
C max (ng/mL) 24 1087 ± 419
AUC ( 0-∞) (ng·h/mL) 24 597 ± 151

Absorption

Diclofenac is 100% absorbed after oral administration compared to IV administration as measured by urine recovery. However, due to first-pass metabolism, only about 50% of the absorbed dose is systemically available. After repeated oral administration, no accumulation of diclofenac in plasma occurred.

The extent of diclofenac absorption is not significantly affected when diclofenac potassium is taken with food. However, the rate of absorption is reduced by food, as indicated by a two-fold increase of T max and a 47% decrease in C max .

Distribution

The apparent volume of distribution (V/F) of diclofenac potassium is 1.3 L/kg.

Diclofenac is more than 99% bound to human serum proteins, primarily to albumin. Serum protein binding is constant over the concentration range (0.15 mcg/mL to 105 mcg/mL) achieved with recommended doses.

Diclofenac has been shown to cross the placental barrier in humans.

Diclofenac diffuses into and out of the synovial fluid. Diffusion into the joint occurs when plasma levels are higher than those in the synovial fluid, after which the process reverses and synovial fluid levels are higher than plasma levels. It is not known whether diffusion into the joint plays a role in the effectiveness of diclofenac.

Elimination

Metabolism

Five diclofenac metabolites have been identified in human plasma and urine. The metabolites include 4′-hydroxy-, 5-hydroxy-, 3′-hydroxy-, 4′,5-dihydroxy- and 3’­ hydroxy-4′-methoxy diclofenac. The major diclofenac metabolite, 4′-hydroxy-diclofenac, has very weak pharmacologic activity. The formation of 4′-hydroxy diclofenac is primarily mediated by CPY2C9. Both diclofenac and its oxidative metabolites undergo glucuronidation or sulfation followed by biliary excretion. Acylglucuronidation mediated by UGT2B7 and oxidation mediated by CPY2C8 may also play a role in diclofenac metabolism. CYP3A4 is responsible for the formation of minor metabolites, 5-hydroxy and 3′-hydroxy- diclofenac. In patients with renal dysfunction, peak concentrations of metabolites 4′-hydroxy-and 5-hydroxy-diclofenac were approximately 50% and 4% of the parent compound after single oral dosing compared to 27% and 1% in normal healthy subjects.

Excretion

Diclofenac is eliminated through metabolism and subsequent urinary and biliary excretion of the glucuronide and the sulfate conjugates of the metabolites. Little or no free unchanged diclofenac is excreted in the urine. Approximately 65% of the dose is excreted in the urine, and approximately 35% in the bile as conjugates of unchanged diclofenac plus metabolites. Because renal elimination is not a significant pathway of elimination for unchanged diclofenac, dosing adjustment in patients with mild to moderate renal dysfunction is not necessary. The terminal half-life of unchanged diclofenac is approximately 1 hour.

Specific Populations

Race: Pharmacokinetic differences due to race have not been studied.

Hepatic Impairment: Hepatic metabolism accounts for almost 100% of diclofenac elimination. Therefore, in patients with hepatic impairment, start with the lowest dose and if efficacy is not achieved, consider use of an alternate product [ see Warnings and Precautions ( 5.3) ].

Renal Impairment: Diclofenac pharmacokinetics has been investigated in subjects with renal insufficiency. In patients with renal impairment (inulin clearance 60 to 90, 30 to 60, and < 30 mL/min; N = 6 in each group), AUC values and elimination rate were comparable to those in healthy subjects [ see Warnings and Precautions ( 5.6) ].

Drug Interaction Studies

Aspirin: When NSAIDs were administered with aspirin, the protein binding of NSAIDs were reduced, although the clearance of free NSAID was not altered. The clinical significance of this interaction is not known. See Table 3 for clinically significant drug interactions of NSAIDs with aspirin [ see Drug Interactions ( 7) ] .

Pediatric use information is approved for Assertio Therapeutics Inc’s ZIPSOR (diclofenac potassium) Capsules. However, due to Assertio Therapeutics Inc’s marketing exclusivity rights, this drug product is not labeled with that information.

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