Risk Summary
Available data on CAYSTON use in pregnant women is insufficient to inform a drug-associated risk of major birth defects, miscarriage, or adverse maternal or fetal outcomes; however, systemic absorption of aztreonam following inhaled administration is expected to be minimal [see Clinical Pharmacology (12.3)]. There are risks to the mother associated with cystic fibrosis in pregnancy (see Clinical Considerations). In animal reproduction studies with aztreonam for injection administered parenterally to pregnant rats and rabbits during organogenesis, there was no evidence of developmental toxicity. A peri/postnatal study in rats revealed no drug-induced changes in maternal, fetal, or neonatal parameters.
The estimated background risk of major birth defects and miscarriage for the indicated population are unknown. All pregnancies have a background risk of birth defect, loss, or other adverse outcomes. In the U.S. general population, the estimated background risk of major birth defects and miscarriage in clinically recognized pregnancies is 2% to 4% and 15% to 20%, respectively.
Clinical Considerations
Disease-Associated Maternal and/or Embryo/Fetal Risk
Cystic fibrosis may increase the risk for preterm delivery.
Data
Animal Data
No reproductive toxicity studies have been conducted with CAYSTON. However, studies were conducted with aztreonam for injection. No evidence of developmental toxicity has been shown in studies with pregnant rats and rabbits that received parenteral doses of aztreonam during organogenesis of up to 1800 and 1200 mg/kg/day, respectively. In rats receiving aztreonam for injection during late gestation and lactation at up to 1800 mg/kg/day, no drug induced changes in maternal, fetal or neonatal parameters were observed. These animal reproduction and developmental toxicity studies used parenteral routes of administration that would provide systemic exposures significantly greater than the average peak plasma levels measured in humans following CAYSTON therapy.
Risk Summary
Following intravenous administration of aztreonam for injection, aztreonam is excreted in human milk at concentrations that are less than one percent of those determined in simultaneously obtained maternal serum. Peak plasma concentrations of aztreonam following administration of CAYSTON (75 mg) are approximately 1% of peak concentrations observed following IV aztreonam (500 mg). Systemic absorption of aztreonam following inhaled administration is expected to be minimal [see Clinical Pharmacology (12.3)]. There are no data on the effects of aztreonam on the breastfed infant or the effects on milk production. The developmental and health benefits of breastfeeding should be considered along with the mother's clinical need for CAYSTON and any potential adverse effects on the breastfed infant from CAYSTON or from the underlying maternal condition.
Sputum Concentrations
Sputum aztreonam concentrations exhibited considerable variability between patients receiving CAYSTON (75 mg) in clinical trials. The mean sputum concentration 10 minutes following the first dose of CAYSTON (n = 195 patients with CF) was 726 mcg/g. Mean sputum concentrations of aztreonam in patients receiving CAYSTON 3 times a day for 28 days were 984 mcg/g, 793 mcg/g, and 715 mcg/g 10 minutes after dose administration on Days 0, 14, and 28, respectively, indicating no accumulation of aztreonam in sputum.
Plasma Concentrations
Plasma aztreonam concentrations exhibited considerable variability between patients receiving CAYSTON (75 mg) in the clinical trials. The mean plasma concentration one hour following the first dose of CAYSTON (at approximately the peak plasma concentration) was 0.59 mcg/mL. Mean peak plasma concentrations in patients receiving CAYSTON 3 times a day for 28 days were 0.55 mcg/mL, 0.67 mcg/mL, and 0.65 mcg/mL on Days 0, 14, and 28, respectively, indicating no systemic accumulation of aztreonam. In contrast, the serum concentration of aztreonam following administration of aztreonam for injection (500 mg) is approximately 54 mcg/mL.
Absorption
Evaluation of plasma and urine aztreonam concentrations following administration of CAYSTON indicates low systemic absorption of aztreonam. Approximately 10% of the total CAYSTON dose is excreted in the urine as unchanged drug, as compared to 60–65% following intravenous administration of aztreonam for injection.
Distribution
The protein binding of aztreonam in plasma is approximately 77% within the clinical dose range of concentrations achieved following CAYSTON administration.
Metabolism
Following intramuscular administration of aztreonam for injection 500 mg every 8 hours for 7 days, approximately 6% of the dose was excreted as a microbiologically inactive open β-lactam ring hydrolysis product in an 8-hour urine collection on the last day of multiple dosing.
Excretion
The elimination half-life of aztreonam from plasma is approximately 2.1 hours following administration of CAYSTON to adult patients with CF, similar to what has been reported for aztreonam for injection. Approximately 10% of the total CAYSTON dose is excreted in the urine as unchanged drug. Systemically absorbed aztreonam is eliminated about equally by active tubular secretion and glomerular filtration. Following administration of a single intravenous dose of radiolabeled aztreonam for injection, about 12% of the dose was recovered in the feces.
Mechanism of Action
Aztreonam exhibits activity in vitro against Gram-negative aerobic pathogens including P. aeruginosa. Aztreonam binds to penicillin-binding proteins of susceptible bacteria, which leads to inhibition of bacterial cell wall synthesis and death of the cell. Aztreonam activity is not decreased in the presence of CF lung secretions.
Susceptibility Testing
A single sputum sample from a patient with CF may contain multiple morphotypes of P. aeruginosa and each morphotype may have a different level of in vitro susceptibility to aztreonam. There are no in vitro susceptibility test interpretive criteria for isolates of P. aeruginosa obtained from the sputum of CF patients.1
Development of Resistance
No changes in the susceptibility of P. aeruginosa to aztreonam were observed following a 28-day course of CAYSTON in the placebo-controlled trials.
Cross-Resistance
No cross-resistance to other classes of antibiotics, including aminoglycosides, quinolones, and beta-lactams, was observed following a 28-day course of CAYSTON in the Phase 3 placebo-controlled trials or in an open-label follow-on trial of up to nine 28-day courses of 75 mg CAYSTON 3 times a day.
Other
No trends in the treatment-emergent isolation of other bacterial respiratory pathogens (Burkholderia cepacia, Stenotrophomonas maltophilia, Achromobacter xylosoxidans, and Staphylococcus aureus) were observed in clinical trials. There was a slight increase in the isolation of Candida spp. following up to nine 28-day courses of CAYSTON therapy.
Allergic Reactions
Advise patients to tell their healthcare provider immediately if they believe they are experiencing new or worsening symptoms or believe they are having an allergic reaction to CAYSTON [see Warnings and Precautions (5.1)].
Development of Drug-Resistant Bacteria
Counsel patients that antibacterial drugs including CAYSTON should only be used to treat bacterial infections. They do not treat viral infection (e.g., the common cold). When CAYSTON is prescribed to treat a bacterial infection, inform patients that although it is common to feel better early in the course of therapy, the medication should be taken exactly as directed. Skipping doses or not completing the full course of therapy may (1) decrease the effectiveness of the immediate treatment and (2) increase the likelihood that bacteria will develop resistance and will not be treatable by CAYSTON or other antibacterial drugs in the future [see Warnings and Precautions (5.4)].
Reconstitution and Administration
Advise patients that:
- CAYSTON is for inhalation use only and should only be administered using the Altera Nebulizer System.
- CAYSTON should only be reconstituted with the provided diluent. Instruct patients not to mix other drugs with CAYSTON in the Altera Nebulizer System.
Advise patients to:
- use a bronchodilator prior to administration of CAYSTON.
- complete the full 28-day course of CAYSTON even if they are feeling better.
Advise patients taking several inhaled medications to use the medications in the following order: bronchodilator, mucolytics, and lastly, CAYSTON.
Missed Dose
Inform the patient that if they miss a dose, they should take all 3 daily doses as long as the doses are at least 4 hours apart.
CAYSTON is a trademark of Gilead Sciences, Inc. All other trademarks referenced herein are the property of their respective owners.
© 2019 Gilead Sciences, Inc. All rights reserved.
50-814-GS-004
Manufactured by: Gilead Sciences, Inc., Foster City, CA 94404
CAYSTON is a trademark of Gilead Sciences, Inc. All other trademarks referenced herein are the property of their respective owners.
© 2019 Gilead Sciences, Inc. All rights reserved.
50-814-GS-004
Revised: November 2019