Yosprala (Page 6 of 9)

12 CLINICAL PHARMACOLOGY

12.1 Mechanism of Action

Aspirin (acetylsalicylic acid) is an inhibitor of both prostaglandin synthesis and platelet aggregation. The differences in activity between aspirin and salicylic acid are thought to be due to the acetyl group on the aspirin molecule. This acetyl group is responsible for the inactivation of cyclo-oxygenase via acetylation.

Omeprazole belongs to a class of antisecretory compounds, the substituted benzimidazoles, that suppress gastric acid secretion by specific inhibition of the [H + /K + ]-ATPase enzyme system at the secretory surface of the gastric parietal cell. Because this enzyme system is regarded as the acid (proton) pump within the gastric mucosa, omeprazole has been characterized as a gastric acid-pump inhibitor, in that it blocks the final step of acid production. This effect is dose-related and leads to inhibition of both basal and stimulated acid secretion irrespective of the stimulus.

12.2 Pharmacodynamics

Anti-platelet Activity

Aspirin affects platelet aggregation by irreversibly inhibiting prostaglandin cyclo-oxygenase. This effect lasts for the life of the platelet and prevents the formation of the platelet aggregating factor thromboxane A2. Nonacetylated salicylates do not inhibit this enzyme and have no effect on platelet aggregation. At higher doses, aspirin reversibly inhibits the formation of prostaglandin I 2 (prostacyclin), which is an arterial vasodilator and inhibits platelet aggregation.

Antisecretory Activity

The effect of YOSPRALA 325 mg/40 mg tablets on intragastric pH was determined in a study of 26 healthy subjects dosed for 7 days. The mean percent time intragastric pH >4.0 was 51%.

Serum Gastrin Effects

In studies involving more than 200 patients, serum gastrin levels increased during the first 1 to 2 weeks of once-daily administration of therapeutic doses of omeprazole in parallel with inhibition of acid secretion. No further increase in serum gastrin occurred with continued treatment. In comparison with histamine H 2 -receptor antagonists, the median increases produced by 20 mg doses of omeprazole were higher (1.3 to 3.6 fold vs. 1.1 to 1.8 fold increase). Gastrin values returned to pretreatment levels, usually within 1 to 2 weeks after discontinuation of therapy.

Increased gastrin causes enterochromaffin-like cell hyperplasia and increased serum Chromogranin A (CgA) levels. The increased CgA levels may cause false positive results in diagnostic investigations for neuroendocrine tumors [see Warnings and Precautions (5.16), Drug Interactions (7)].

Enterochromaffin-like (ECL) Cell Effects

Human gastric biopsy specimens have been obtained from more than 3000 patients treated with omeprazole in long-term clinical trials. The incidence of ECL cell hyperplasia in these studies increased with time; however, no case of ECL cell carcinoids, dysplasia, or neoplasia has been found in these patients. However, these studies are of insufficient duration and size to rule out the possible influence of long-term administration of omeprazole on the development of any premalignant or malignant conditions.

Endocrine Effects

Omeprazole given in oral doses of 30 or 40 mg for 2 to 4 weeks had no effect on thyroid function, carbohydrate metabolism, circulating levels of parathyroid hormone, cortisol, estradiol, testosterone, prolactin, cholecystokinin or secretin.

Effects on Gastrointestinal Microbial Ecology

As do other agents that elevate intragastric pH, omeprazole administered for 14 days in healthy subjects produced a significant increase in the intragastric concentrations of viable bacteria. The pattern of the bacterial species was unchanged from that commonly found in saliva. All changes resolved within three days of stopping treatment.

Other Effects

Systemic effects of omeprazole in the CNS, cardiovascular and respiratory systems have not been found to date.

No effect on gastric emptying of the solid and liquid components of a test meal was demonstrated after a single dose of omeprazole 90 mg. In healthy subjects, a single intravenous dose of omeprazole (0.35 mg/kg) had no effect on intrinsic factor secretion. No systematic dose-dependent effect has been observed on basal or stimulated pepsin output in humans. However, when intragastric pH is maintained at 4.0 or above, basal pepsin output is low, and pepsin activity is decreased.

12.3 Pharmacokinetics

Absorption

Aspirin: Following absorption, aspirin (acetylsalicylic acid) is hydrolyzed to salicylic acid. The rate of absorption from the GI tract is dependent upon the presence or absence of food, gastric pH (the presence or absence of GI antacids or buffering agents), and other physiologic factors. Enteric coated aspirin products are erratically absorbed from the GI tract.

Following single dose administration of YOSPRALA, peak concentrations of acetylsalicylic acid were reached at 2.5 hours for YOSPRALA 81 mg/40 mg tablets and at 4 to 4.5 hours for YOSPRALA 325 mg/40 mg tablets. The C max and AUC of acetylsalicylic acid were 2.6 mcg/mL and 3 mcg.hr/mL following single dose administration of YOSPRALA 81 mg/40 mg tablets and were 2.5 mcg/mL and 2.9 mcg.hr/mL following single dose administration of YOSPRALA 325 mg/40 mg tablets. There is no significant accumulation of salicylic acid and acetylsalicylic acid following 7 days dosing of YOSPRALA 325 mg/40 mg tablets compared to the first day of dosing.

The inter-subject variability (CV%) of acetylsalicylic acid pharmacokinetic parameters ranged from 17% to 96%.

Omeprazole: Following administration of YOSPRALA, the peak plasma concentration of omeprazole is reached at 0.5 hours on both the first day of administration and at steady state. The C max and AUC of omeprazole ranged from 617 to 856 ng/mL and 880-1384 ng.hr/mL following single dose administration of YOSPRALA 325 mg/40 mg tablets. Dosing YOSPRALA 325 mg/40 mg for 7 days results in approximately 2.3-fold higher AUC and 2-fold higher C max of omeprazole at steady state compared to the first day of dosing.

The inter-subject variability of omeprazole pharmacokinetic parameters were high with % CVs ranging from 33% to 136%.

Food Effect:

Aspirin: Administration of YOSPRALA with high-fat (approximately 50%) and high-calorie (800-1000 calorie) meal in healthy subjects does not affect the extent of absorption of aspirin as measured by salicylic acid AUC and C max but significantly prolongs salicylic acid t max by about 10 hours. Administration of YOSPRALA 60 minutes before a high-fat, high-calorie meal has essentially no effect on salicylic acid AUCs, C max and t max .

Omeprazole: Administration of YOSPRALA with high-fat (approximately 50%) and high-calorie (800-1000 calories) meal in healthy subjects significantly reduces the extent of absorption of omeprazole resulting in 67% and 84% reductions of AUCs and C max respectively relative to fasting conditions. Administration of YOSPRALA 60 minutes before high-fat, high-calorie meal reduced both the omeprazole AUC and C max by approximately 15% relative to fasting conditions [see Dosage and Administration (2.2)].

Distribution

Aspirin: Salicylic acid is widely distributed to all tissues and fluids in the body including the central nervous system (CNS), breast milk, and fetal tissues. The highest concentrations are found in the plasma, liver, renal cortex, heart, and lungs. The protein binding of salicylate is concentration-dependent, i.e., nonlinear. At low concentrations (less than 100 mcg/mL), approximately 90% of plasma salicylate is bound to albumin while at higher concentrations (greater than 400 mcg/mL), only about 75% is bound.

Omeprazole: Protein binding is approximately 95%.

Elimination

Metabolism

Aspirin: Aspirin (acetylsalicylic acid) is rapidly hydrolyzed in the plasma to salicylic acid such that plasma levels of aspirin are essentially undetectable 1 to 2 hours after dosing with half-life of 0.35 hrs. Salicylic acid is primarily conjugated in the liver to form salicyluric acid, a phenolic glucuronide, an acyl glucuronide, and a number of minor metabolites. Salicylate metabolism is saturable and total body clearance decreases at higher serum concentrations due to the limited ability of the liver to form both salicyluric acid and phenolic glucuronide.

Omeprazole: Omeprazole is extensively metabolized by the cytochrome P450 (CYP) enzyme system. The major part of its metabolism is dependent on the polymorphically expressed CYP2C19, responsible for the formation of hydroxyomeprazole, the major metabolite in plasma. The remaining part is dependent on another specific isoform, CYP3A4, responsible for the formation of omeprazole sulphone.

Excretion

Aspirin: The elimination of salicylic acid follows zero order pharmacokinetics; (i.e., the rate of drug elimination is constant in relation to plasma concentration). Renal excretion of unchanged drug depends upon urine pH. As urinary pH rises above 6.5, the renal clearance of free salicylate increases from 5% to greater than 80%. Following therapeutic doses, approximately 10% is excreted in the urine as salicylic acid, 75% as salicyluric acid, and 10% phenolic and 5% acyl glucuronides of salicylic acid. Half-life of salicylic acid following YOSPRALA 325 mg/40 mg tablets is 2.4 hours.

Omeprazole: Following single dose oral administration of a buffered solution of omeprazole, little if any unchanged drug was excreted in urine. The majority of the dose (about 77%) was eliminated in urine as at least six metabolites. Two were identified as hydroxyomeprazole and the corresponding carboxylic acid. The remainder of the dose was recoverable in feces. This implies a significant biliary excretion of the metabolites of omeprazole. Three metabolites have been identified in plasma — the sulfide and sulfone derivatives of omeprazole, and hydroxyomeprazole. These metabolites have very little or no antisecretory activity. The half-life of the omeprazole component is 1 hour.

Specific Populations

Age: Geriatric Population

There is no specific data on the pharmacokinetics of YOSPRALA in patients over age 65.

Omeprazole: The elimination rate of omeprazole was somewhat decreased in the elderly, and bioavailability was increased. Omeprazole was 76% bioavailable when a single 40 mg oral dose of omeprazole (buffered solution) was administered to healthy elderly subjects, versus 58% in young subjects given the same dose. Nearly 70% of the dose was recovered in urine as metabolites of omeprazole and no unchanged drug was detected. The plasma clearance of omeprazole was 250 mL/min (about half that of young subjects) and its plasma half-life averaged one hour, about twice that of young healthy subjects.

Race

Pharmacokinetic differences of YOSPRALA due to race have not been studied.

Renal Impairment

The pharmacokinetics of YOSPRALA has not been determined in subjects with renal impairment.

Omeprazole: In patients with chronic renal impairment, whose creatinine clearance ranged between 10 and 62 mL/min/1.73 m 2 , the disposition of omeprazole was very similar to that in healthy subjects, although there was a slight increase in bioavailability. Because urinary excretion is a primary route of excretion of omeprazole metabolites, their elimination slowed in proportion to the decreased creatinine clearance.

Hepatic Impairment

The pharmacokinetics of YOSPRALA has not been determined in subjects with hepatic impairment.

Omeprazole: In patients with chronic hepatic disease, classified as Child-Pugh Class A (n=3), B (n=4) and C (n=1), the bioavailability of omeprazole increased by approximately 100% compared to healthy subjects, reflecting decreased first-pass effect, and the plasma half-life of the drug increased to nearly 3 hours compared with the half-life in healthy subjects of 0.5 to 1 hour. Plasma clearance averaged 70 mL/min, compared with a value of 500 to 600 mL/min in healthy subjects [see Use in Specific Populations (8.7)].

Drug Interaction Studies

Effect of YOSPRALA on Other Drugs

Omeprazole is a time-dependent inhibitor of CYP2C19 and can increase the systemic exposure of co-administered drugs that are CYP2C19 substrates. In addition, administration of omeprazole increases intragastric pH and can alter the systemic exposure of certain drugs that exhibit pH-dependent solubility.

Antiretrovirals: For some antiretroviral drugs, such as rilpivirine, atazanavir and nelfinavir, decreased serum concentrations have been reported when given together with omeprazole [see Drug Interactions (7)] .

Rilpivirine: Following multiple doses of rilpivirine (150 mg, daily) and omeprazole (20 mg, daily), AUC was decreased by 40%, C max by 40%, and C min by 33% for rilpivirine.

Nelfinavir: Following multiple doses of nelfinavir (1250 mg, twice daily) and omeprazole (40 mg daily), AUC was decreased by 36% and 92%, C max by 37% and 89% and C min by 39% and 75% respectively for nelfinavir and M8.

Atazanavir: Following multiple doses of atazanavir (400 mg, daily) and omeprazole (40 mg, daily, 2 hours before atazanavir), AUC was decreased by 94%, C max by 96%, and C min by 95%.

Saquinavir: Following multiple dosing of saquinavir/ritonavir (1000/100 mg) twice daily for 15 days with omeprazole 40 mg daily co-administered days 11 to 15.

AUC was increased by 82%, C max by 75%, and C min by 106%. The mechanism behind this interaction is not fully elucidated. Therefore, clinical and laboratory monitoring for saquinavir toxicity is recommended during concurrent use with omeprazole.

Clopidogrel: In a crossover clinical study, 72 healthy subjects were administered clopidogrel (300 mg loading dose followed by 75 mg per day) alone and with omeprazole (80 mg at the same time as clopidogrel) for 5 days. The exposure to the active metabolite of clopidogrel was decreased by 46% (Day 1) and 42% (Day 5) when clopidogrel and omeprazole were administered together.

Results from another crossover study in healthy subjects showed a similar pharmacokinetic interaction between clopidogrel (300 mg loading dose/75 mg daily maintenance dose) and omeprazole 80 mg daily when co-administered for 30 days. Exposure to the active metabolite of clopidogrel was reduced by 41% to 46% over this time period.

In another study, 72 healthy subjects were given the same doses of clopidogrel and 80 mg omeprazole but the drugs were administered 12 hours apart; the results were similar, indicating that administering clopidogrel and omeprazole at different times does not prevent their interaction [see Warnings and Precautions (5.4), Drug Interactions (7)].

Mycophenolate Mofetil: Administration of omeprazole 20 mg twice daily for 4 days and a single 1000 mg dose of MMF approximately one hour after the last dose of omeprazole to 12 healthy subjects in a cross-over study resulted in a 52% reduction in the C max and 23% reduction in the AUC of MPA [see Drug Interactions (7)] .

Cilostazol: Omeprazole acts as an inhibitor of CYP2C19. Omeprazole, given in doses of 40 mg daily for one week to 20 healthy subjects in cross-over study, increased C max and AUC of cilostazol by 18% and 26% respectively. The C max and AUC of one of the active metabolites, 3,4-dihydro-cilostazol, which has 4-7 times the activity of cilostazol, were increased by 29% and 69%, respectively. Co-administration of cilostazol with omeprazole is expected to increase concentrations of cilostazol and the above mentioned active metabolite [see Drug Interactions (7)].

Diazepam: Concomitant administration of omeprazole 20 mg once daily and diazepam 0.1 mg/kg given intravenously resulted in 27% decrease in clearance and 36% increase in diazepam half-life [see Drug Interactions (7)].

Digoxin: Concomitant administration of omeprazole 20 mg once daily and digoxin in healthy subjects increased the bioavailability of digoxin by 10% (30% in two subjects) [see Drug Interactions (7)].

Effect of Other Drugs on Yosprala

Voriconazole: Concomitant administration of omeprazole and voriconazole (a combined inhibitor of CYP2C19 and CYP3A4) resulted in more than doubling of the omeprazole exposure. When voriconazole (400 mg every 12 hours for one day, followed by 200 mg once daily for 6 days) was given with omeprazole (40 mg once daily for 7 days) to healthy subjects, the steady-state C max and AUC 0-24 of omeprazole significantly increased: an average of 2 times (90% CI: 1.8, 2.6) and 4 times (90% CI: 3.3, 4.4), respectively, as compared to when omeprazole was given without voriconazole [see Drug Interactions (7)] .

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