CLINICAL PHARMACOLOGY
Mechanism of Action
Budesonide is an anti-inflammatory corticosteroid that exhibits potent glucocorticoid activity and weak mineralocorticoid activity. In standard in vitro and animal models, budesonide has approximately a 200-fold higher affinity for the glucocorticoid receptor and a 1000-fold higher topical anti-inflammatory potency than cortisol (rat croton oil ear edema assay). As a measure of systemic activity, budesonide is 40 times more potent than cortisol when administered subcutaneously and 25 times more potent when administered orally in the rat thymus involution assay. The clinical significance of this is unknown.
The activity of RHINOCORT AQUA Nasal Spray is due to the parent drug, budesonide. In glucocorticoid receptor affinity studies, the 22R form was two times as active as the 22S epimer. In vitro studies indicated that the two forms of budesonide do not interconvert.
The precise mechanism of corticosteroid actions on inflammation in seasonal and perennial allergic rhinitis is not well known. Inflammation is an important component in the pathogenesis of seasonal and perennial allergic rhinitis. Corticosteroids have a wide range of inhibitory activities against multiple cell types (e.g., mast cells, eosinophils, neutrophils, macrophages, and lymphocytes) and mediators (e.g., histamine, eicosanoids, leukotrienes, and cytokines) involved in allergic and non-allergic-mediated inflammation. These anti-inflammatory actions of corticosteroids may contribute to their efficacy in seasonal and perennial allergic rhinitis.
Pharmacodynamics
A 3-week clinical study in seasonal rhinitis, comparing RHINOCORT Nasal Inhaler, orally ingested budesonide, and placebo in 98 patients with allergic rhinitis due to birch pollen, demonstrated that the therapeutic effect of RHINOCORT Nasal Inhaler can be attributed to the topical effects of budesonide.
HPA Axis Effects:
The effects of RHINOCORT AQUA Nasal Spray on adrenal function have been evaluated in several clinical trials. In a four-week clinical trial, 61 adult patients who received 256 mcg daily of RHINOCORT AQUA Nasal Spray demonstrated no significant differences from patients receiving placebo in plasma cortisol levels measured before and 60 minutes after 0.25 mg intramuscular cosyntropin. There were no consistent differences in 24-hour urinary cortisol measurements in patients receiving up to 400 mcg daily. Similar results were seen in a study of 150 children and adolescents aged 6 to 17 with perennial rhinitis who were treated with 256 mcg daily for up to 12 months.
After treatment with the recommended maximal daily dose of RHINOCORT AQUA Nasal Spray (256 mcg) for seven days, there was a small, but statistically significant decrease in the area under the plasma cortisol-time curve over 24 hours (AUC0-24h) in healthy adult volunteers.
A dose-related suppression of 24-hour urinary cortisol excretion was observed after administration of RHINOCORT AQUA Nasal Spray doses ranging from 100-800 mcg daily for up to four days in 78 healthy adult volunteers. The clinical relevance of these results is unknown.
Pharmacokinetics
Absorption
After intranasal administration of a single dose of RHINOCORT AQUA Nasal Spray (128 mcg), the mean peak plasma concentration of approximately 0.3 nmol/L occurs about 0.5 hours post-dose. Compared to an intravenous dose, approximately 34% of the delivered intranasal dose reaches the systemic circulation, most of which is absorbed through the nasal mucosa. While budesonide is well absorbed from the GI tract, the oral bioavailability of budesonide is low (~10%) primarily due to extensive first pass metabolism in the liver.
Distribution
The volume of distribution of budesonide was approximately 2-3 L/kg. It was 85-90% bound to plasma proteins. The volume of distribution for the 22R epimer is almost twice that of the 22S epimer. Protein binding was constant over a concentration range (1-100 nmol/L) achieved with, and exceeding, recommended doses of RHINOCORT AQUA Nasal Spray. Budesonide showed little or no binding to corticosteroid binding globulin. Budesonide rapidly equilibrated with red blood cells in a concentration independent manner with a blood/plasma ratio of about 0.8.
Metabolism
In vitro studies with human liver homogenates have shown that budesonide is rapidly and extensively metabolized. Two major metabolites formed via cytochrome P450 (CYP) isoenzyme 3A4 (CYP3A4)-catalyzed biotransformation have been isolated and identified as 16α-hydroxyprednisolone and 6β-hydroxybudesonide. The corticosteroid activity of each of these two metabolites is less than 1% of that of the parent compound. No qualitative difference between the in vitro and in vivo metabolic patterns have been detected. Negligible metabolic inactivation was observed in human lung and serum preparations.
Excretion/Elimination
The 22R form of budesonide was preferentially cleared by the liver with systemic clearance of 1.4 L/min vs. 1.0 L/min for the 22S form. The terminal half-life, 2 to 3 hours, was the same for both epimers and was independent of dose. Budesonide was excreted in urine and feces in the form of metabolites. Approximately 2/3 of an intranasal radiolabeled dose was recovered in the urine and the remainder in the feces. No unchanged budesonide was detected in the urine.
Specific Populations
Geriatric
The pharmacokinetics of RHINOCORT AQUA Nasal Spray in geriatric patients have not been specifically studied.
Pediatric
Following administration of RHINOCORT AQUA Nasal Spray, the time to reach peak drug concentrations and plasma half-life were similar in children and in adults. Children had plasma concentrations approximately twice those observed in adults due primarily to differences in weight between children and adults.
Gender
No specific pharmacokinetic study has been conducted to evaluate the effect of gender on budesonide pharmacokinetics. However, following administration of 400 mcg of RHINOCORT AQUA Nasal Spray to 7 male and 8 female volunteers in a pharmacokinetic study, no major gender differences in the pharmacokinetic parameters were found.
Race
No specific study has been undertaken to evaluate the effect of race on budesonide pharmacokinetics.
Nursing Mothers
The disposition of budesonide when delivered by oral inhalation from a dry powder inhaler at doses of 200 or 400 mcg twice daily for at least 3 months was studied in eight lactating women with asthma from 1 to 6 months postpartum. Systemic exposure to budesonide in these women appears to be comparable to that in non-lactating women with asthma from other studies. Breast milk obtained over eight hours post-dose revealed that the maximum concentration of budesonide for the 400 and 800 mcg doses was 0.39 and 0.78 nmol/L, respectively, and occurred within 45 minutes after dosing. The estimated oral daily dose of budesonide from breast milk to the infant was approximately 0.007 and 0.014 mcg/kg/day for the two dose regimens used in this study, which represents approximately 0.3% to 1% of the dose inhaled by the mother. Budesonide levels in plasma samples obtained from five infants at about 90 minutes after breastfeeding (and about 140 minutes after drug administration to the mother) were below quantifiable levels (<0.02 nmol/L in four infants and <0.04 nmol/L in one infant) [see Use in Specific Populations, Nursing Mothers
].
Renal or Hepatic Impairment
The pharmacokinetics of budesonide have not been investigated in patients with renal impairment. Reduced liver function may affect the elimination of corticosteroids. The pharmacokinetics of budesonide were affected by compromised liver function as evidenced by a doubled systemic availability after oral ingestion. The relevance of this finding to intranasally administered budesonide has not been established.
Drug-Drug Interactions
Inhibitors of cytochrome P450 enzymes
Ketoconazole: Ketoconazole, a strong inhibitor of cytochrome P450 (CYP) isoenzyme 3A4 (CYP3A4), the main metabolic enzyme for corticosteroids, increased plasma levels of orally ingested budesonide [see Warnings and Precautions and Drug Interactions
].
Cimetidine: At recommended doses, cimetidine, a non-specific inhibitor of CYP enzymes, had a slight but clinically insignificant effect on the pharmacokinetics of oral budesonide.
NONCLINICAL TOXICOLOGY
Carcinogenesis, Mutagenesis, Impairment of Fertility
In a 104-week oral study in Sprague-Dawley rats, a statistically significant increase in the incidence of gliomas was observed in the male rats receiving an oral dose of budesonide 50 mcg/kg/day (approximately twice the maximum recommended daily intranasal dose in adults and children on a mcg/m2 basis). No tumorigenicity was seen in male rats at oral doses up to 25 mcg/kg (approximately equal to the maximum recommended daily intranasal dose in adults and children on a mcg/m2 basis, and in female rats at oral doses up to 50 mcg/kg approximately two times the maximum recommended daily intranasal dose in adults and children on a mcg/m2 basis). In two additional two-year studies in male Fischer and Sprague-Dawley rats, budesonide caused no gliomas at an oral dose of 50 mcg/kg (approximately twice the maximum recommended daily intranasal dose in adults and children on a mcg/m2 basis). However, in the male Sprague-Dawley rats, budesonide caused a statistically significant increase in the incidence of hepatocellular tumors at an oral dose of 50 mcg/kg (approximately twice the maximum recommended daily intranasal dose in adults and children on a mcg/m2 basis). The concurrent reference corticosteroids (prednisolone and triamcinolone acetonide) in these two studies showed similar findings.
There was no evidence of a carcinogenic effect when budesonide was administered orally for 91-weeks to mice at doses up to 200 mcg/kg/day (approximately 3 times the maximum recommended daily intranasal dose in adults and children on a mcg/m2 basis).
Budesonide was not mutagenic or clastogenic in six different test systems: Ames Salmonella/microsome plate test, mouse micronucleus test, mouse lymphoma test, chromosome aberration test in human lymphocytes, sex-linked recessive lethal test in Drosophila melanogaster, and DNA repair analysis in rat hepatocyte culture.
In rats, budesonide had no effect on fertility at subcutaneous doses up to 80 mcg/kg (approximately 3 times the maximum recommended daily intranasal dose in adults on mcg/m2 basis).
At a subcutaneous dose of 20 mcg/kg/day (less than the maximum recommended daily intranasal dose in adults on a mcg/m2 basis), decreases in maternal body weight gain, prenatal viability, and viability of the young at birth and during lactation were observed. No such effects were noted at 5 mcg/kg (less than the maximum recommended daily intranasal dose in adults on a mcg/m2 basis).
Animal Toxicology and/or Pharmacology
Budesonide was teratogenic and embryocidal in rabbits and rats. Budesonide produced fetal loss, decreased pup weights, and skeletal abnormalities at a subcutaneous dose of 25 mcg/kg in rabbits (approximately 2 times the maximum recommended daily intranasal dose in adults on a mcg/m2 basis) and at a subcutaneous dose of 500 mcg/kg in rats (approximately 16 times the maximum recommended daily intranasal dose in adults on a mcg/m2 basis). No teratogenic or embryocidal effects were observed in rats when budesonide was administered by inhalation doses up to 250 mcg/kg (approximately 8 times the maximum recommended daily intranasal dose in adults on a mcg/m2 basis).
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