BUDESONIDE (ENTERIC COATED) (Page 5 of 8)

12.3 Pharmacokinetics

Absorption

Following administration of budesonide capsules (enteric coated), the time to peak concentration varied in individual patients between 30 and 600 minutes. Mean oral bioavailability of budesonide ranged from 9% to 21% both in patients and in healthy subjects, demonstrating a high first-pass elimination of the drug.

Budesonide pharmacokinetics were dose-proportional following repeated administration in the dose range of 3 to 15 mg. No accumulation of budesonide was observed following repeated dosing.

Following oral administration of 9 mg of budesonide capsules (enteric coated) for five days in healthy subjects, the mean peak plasma concentration and the steady state area under the plasma concentration time curve for budesonide were 5.3 ± 1.8 nmol/L and 37.0 ± 14.6 nmol∙hr/L, respectively.

Following administration of 9 mg of budesonide capsules (enteric coated) once daily in patients with active Crohn’s disease, the mean peak plasma concentration and AUC were 4.0 ± 2.1 nmol/L and 35.0 ± 19.8 nmol∙hr/L, respectively.

Concomitant administration of a high-fat meal delayed the time to the peak concentration of budesonide from budesonide capsules (enteric coated) by 2.3 hours but did not significantly affect the AUC in healthy subjects.

Distribution

The mean volume of distribution (V ss ) of budesonide varied between 2.2 and 3.9 L/kg in healthy subjects and in patients. Plasma protein binding is estimated to be 85% to 90% in the concentration range 1 to 230 nmol/L, independent of gender. The erythrocyte/plasma partition ratio at clinically relevant concentrations was about 0.8.

Elimination

Budesonide had a plasma clearance, 0.9 to 1.8 L/min in healthy adults. Mean plasma clearance after intravenous administration of budesonide in patients with Crohn’s disease was 1.0 L/min. These plasma clearance values approached the estimated liver blood flow, and, accordingly, suggest that budesonide is a high hepatic clearance drug. The plasma elimination half-life, after administration of intravenous doses ranged between 2 and 3.6 hours, and did not differ between healthy adults and patients with Crohn’s disease.

Metabolism

Following absorption, budesonide is subject to high first pass metabolism (80% to 90%). In vitro experiments in human liver microsomes demonstrate that budesonide is rapidly and extensively biotransformed, mainly by CYP3A4, to its 2 major metabolites, 6β-hydroxy budesonide and 16α-hydroxy prednisolone. The corticosteroid activity of these metabolites was negligible (less than 1/100) in relation to that of the parent compound. In vivo investigations with intravenous doses in healthy subjects were in agreement with the in vitro findings.

Excretion

Budesonide was excreted in urine and feces in the form of metabolites. After oral as well as intravenous administration of micronized [ 3 H]-budesonide, approximately 60% of the recovered radioactivity was found in urine. The major metabolites, including 6β-hydroxy budesonide and 16α-hydroxy prednisolone, are mainly renally excreted, intact or in conjugated forms. No unchanged budesonide is detected in urine.

Specific Populations

Age: Pediatric Population (8 years and older)

The pharmacokinetics of budesonide were investigated in pediatric patients aged 9 to 14 years (n=8) after oral administration of budesonide capsules (enteric coated) and intravenous administration of budesonide. Following administration of 9 mg budesonide capsules (enteric coated) once daily for 7 days, the median time to peak plasma concentration of budesonide was 5 hours and the mean peak plasma concentration was 6.0 ± 3.5 nmol/L. The mean AUC was 41.3 ± 12.2 nmol∙h/L and 17% higher than that in adult patients with Crohn’s disease in the same study. The mean absolute oral availability was 9.2% (3 to 17%; n=4) in pediatric patients.

After single dose administration of intravenous budesonide (n=4), the mean volume of distribution (V ss ) was 2.2 ± 0.4 L/kg and mean clearance was 0.81 ± 0.2 L/min. The mean elimination half-life was 1.9 hours in pediatric patients. The body-weight normalized clearance in pediatric patients was 20.5 mL/min/kg in comparison to 15.9 mL/min/kg in adult patients after intravenous administration [see Warnings and Precautions (5.1), Use in Specific Population (8.4)] .

Hepatic Impairment

In patients with mild (Child-Pugh Class A, n=4) or moderate (Child-Pugh Class B, n=4) hepatic impairment, budesonide 4 mg was administered orally as a single dose. The patients with moderate hepatic impairment had a 3.5-fold higher AUC compared to the healthy subjects with normal hepatic function while the patients with mild hepatic impairment had an approximately 1.4-fold higher AUC. The C max values demonstrated similar increases [see Dosage and Administration (2.4), Warnings and Precautions (5.1)] . The increased systemic exposure in patients with mild hepatic impairment was not considered to be clinically relevant. Patients with severe liver impairment (Child-Pugh Class C) were not studied.

Drug Interaction Studies

Budesonide is metabolized via CYP3A4. Potent inhibitors of CYP3A4 can increase the plasma concentrations of budesonide several-fold. Conversely, induction of CYP3A4 potentially could result in the lowering of budesonide plasma concentrations.

Effects of Other Drugs on Budesonide

Ketoconazole

In an open, non-randomized, cross-over study, 6 healthy subjects were given budesonide 10 mg as a single dose, either alone or concomitantly with the last ketoconazole dose of 3 days treatment with ketoconazole 100 mg twice daily. Coadministration of ketoconazole resulted in an eight-fold increase in AUC of budesonide, compared to budesonide alone [see Drug Interactions (7.1)] .

Grapefruit Juice

In an open, randomized, cross-over study, 8 healthy subjects were given budesonide capsules (enteric coated) 3 mg, either alone, or concomitantly with 600 mL concentrated grapefruit juice (which inhibits CYP3A4 activity predominantly in the intestinal mucosa), on the last of 4 daily administrations. Concomitant administration of grapefruit juice resulted in a 2-fold increase of the bioavailability of budesonide compared to budesonide alone [see Drug Interactions (7.1)] .

Oral Contraceptives (CYP3A4 Substrates)

In a parallel study, the pharmacokinetics of budesonide were not significantly different between healthy female subjects who received oral contraceptives containing desogestrel 0.15 mg and ethinyl estradiol 30 μg and healthy female subjects who did not receive oral contraceptives. Budesonide 4.5 mg once daily (one-half the recommended dose) for one week did not affect the plasma concentrations of ethinyl estradiol, a CYP3A4 substrate. The effect of budesonide 9 mg once daily on the plasma concentrations of ethinyl estradiol was not studied.

Omeprazole

In a study in 11 healthy subjects, performed in a double-blind, randomized, placebo controlled manner, the effect of 5 to 6 days treatment with omeprazole 20 mg once daily on the pharmacokinetics of budesonide administered as budesonide capsules (enteric coated) 9 mg as a single dose was investigated. Omeprazole 20 mg once daily did not affect the absorption or pharmacokinetics of budesonide.

Cimetidine

In an open, non-randomized, cross-over study, the potential effect of cimetidine on the pharmacokinetics of budesonide was studied. Six healthy subjects received cimetidine 1 gram daily (200 mg with meals and 400 mg at night) for 2 separate 3-day periods. Budesonide 4 mg was administered either alone or on the last day of one of the cimetidine treatment periods. Co-administration of cimetidine resulted in a 52% and 31% increase in the budesonide peak plasma concentration and the AUC of budesonide, respectively.

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