Systemic Exposure & Microbiology

CAYSTON has low systemic exposure

SPUTUM CONCENTRATIONS

  • Mean sputum concentrations of aztreonam 10 minutes after dose administration in patients receiving CAYSTON (75 mg) 3 times a day for 28 days are shown below*:
Day 0
984 mcg/g
Day 14
793 mcg/g
Day 28
715 mcg/g

*There was considerable variability observed between patients.

PLASMA CONCENTRATIONS

  • Mean peak plasma concentrations were reached 1 hour postdose in patients receiving CAYSTON (75 mg) 3 times a day. Values shown below:
Day 0
0.55 mcg/mL
Day 14
0.67 mcg/mL
Day 28
0.65 mcg/mL

There was considerable variability observed between patients.

  • In contrast, serum concentration following a one-time, 30-minute IV administration of aztreonam for injection (500 mg) was approximately 54 mcg/mL
  • There was no systemic accumulation of CAYSTON

ABSORPTION

  • Evaluation of plasma and urine aztreonam concentrations in patients following administration of CAYSTON indicated low systemic absorption of aztreonam
  • About 10% of the total CAYSTON dose was excreted in the urine as unchanged drug, as compared to 60%-65% following IV administration of aztreonam for injection

Microbiology

CAYSTON did not negatively affect the lung microbiology profile

Resistance to CAYSTON was not increased

No changes in susceptibility of Pseudomonas aeruginosa (Pa) to aztreonam were observed following 28-day course of CAYSTON in the phase 3 placebo-controlled trials.

In the followon study of up to 18 months, crossresistance did not increase

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.

No trends in the treatmentemergent isolation of other bacterial respiratory pathogens were observed in clinical trials

Burkholderia cepacia, Stenotrophomonas maltophilia, Achromobacter xylosoxidans, and Staphylococcus aureus were not 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.

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