Generic name: aztreonam (inhalation)
Drug class: Miscellaneous antibiotics

Medically reviewed by  A Ras MD.

What is Cayston?

Cayston is a prescription medicine that is used in some people with cystic fibrosis to make breathing better.


A dose of CAYSTON consists of a 2 mL amber glass vial containing lyophilized aztreonam (75 mg) and lysine (46.7 mg), and a low-density polyethylene ampule containing 1 mL sterile diluent (0.17% sodium chloride). The reconstituted solution is for inhalation. The formulation contains no preservatives or arginine.

The active ingredient in CAYSTON is aztreonam, a monobactam antibacterial. The monobactams are structurally different from beta-lactam antibiotics (e.g., penicillins, cephalosporins, carbapenems) due to a monocyclic nucleus. This nucleus contains several side chains; sulfonic acid in the 1-position activates the nucleus, an aminothiazolyl oxime side chain in the 3-position confers specificity for aerobic Gram-negative bacteria including Pseudomonas spp., and a methyl group in the 4-position enhances beta-lactamase stability.

Aztreonam is designated chemically as (Z)-2-[[[(2-amino-4-thiazolyl)[[(2S,3S)-2-methyl-4-oxo-1-sulfo-3-azetidinyl]carbamoyl]methylene]amino]oxy]-2-methylpropionic acid. The structural formula is presented below:

Chemical Structure

CAYSTON is a white to off-white powder. CAYSTON is sterile, hygroscopic, and light sensitive. Once reconstituted with the supplied diluent, the pH range is 4.5 to 6.0.

Before taking Cayston, tell your doctor:

  • If you are allergic to Cayston; any part of this medicine; or any other drugs, foods, or substances. Tell your doctor about the allergy and what signs you had.

This medicine may interact with other drugs or health problems.

Tell your doctor and pharmacist about all of your drugs (prescription or OTC, natural products, vitamins) and health problems. You must check to make sure that it is safe for you to take Cayston with all of your drugs and health problems. Do not start, stop, or change the dose of any drug without checking with your doctor.

What are some things I need to know or do while I take Cayston?

  • Tell all of your health care providers that you take Cayston. This includes your doctors, nurses, pharmacists, and dentists.
  • Unsafe allergic effects may rarely happen.
  • Do not use longer than you have been told. A second infection may happen.
  • Tell your doctor if you are pregnant, plan on getting pregnant, or are breast-feeding. You will need to talk about the benefits and risks to you and the baby.

How is Cayston best taken?

Use Cayston as ordered by your doctor. Read all information given to you. Follow all instructions closely.

  • Follow how to take Cayston as you have been told by your doctor. Do not use more than you were told to use.
  • Keep taking Cayston as you have been told by your doctor or other health care provider, even if you feel well.
  • For breathing in only.
  • You will use by breathing in from the mouth with a special machine (nebulizer). Your doctor will teach you the right way to use.
  • Only use the type of nebulizer that you have been told to use. If you are not sure what type of nebulizer to use, talk with the doctor.
  • This medicine needs to be mixed before use. Follow how to mix as you were told by the doctor.
  • Do not mix Cayston until you are ready to use it.
  • Use right away after mixing.
  • Do not mix other drugs in nebulizer.
  • Use an inhaler that helps open your airways before using Cayston. Talk with your doctor.
  • Use Cayston after other breathed in drugs.
  • Do not use if the solution is cloudy or has particles.

What do I do if I miss a dose?

  • Take a missed dose as soon as you think about it.
  • If the next dose is less than 4 hours away, skip the missed dose and go back to your normal time.
  • Do not take 2 doses at the same time or extra doses.

What are the side effects of Cayston that I need to call my doctor about immediately?

WARNING/CAUTION: Even though it may be rare, some people may have very bad and sometimes deadly side effects when taking a drug. Tell your doctor or get medical help right away if you have any of the following signs or symptoms that may be related to a very bad side effect:

  • Signs of an allergic reaction, like rash; hives; itching; red, swollen, blistered, or peeling skin with or without fever; wheezing; tightness in the chest or throat; trouble breathing, swallowing, or talking; unusual hoarseness; or swelling of the mouth, face, lips, tongue, or throat.
  • Chest pain.
  • Cough that does not go away.
  • Fever.
  • Lung function has gotten worse in some people after taking Cayston for 28 days. Have your lung function checked while taking Cayston. Call your doctor right away if breathing problems are new or worse after starting Cayston.

What are some other side effects of Cayston?

All drugs may cause side effects. However, many people have no side effects or only have minor side effects. Call your doctor or get medical help if any of these side effects or any other side effects bother you or do not go away:

  • Throwing up.
  • Cough.
  • Stuffy nose.
  • Throat pain.
  • Stomach pain.

These are not all of the side effects that may occur. If you have questions about side effects, call your doctor. Call your doctor for medical advice about side effects.

You may report side effects to the FDA at 1-800-332-1088. You may also report side effects at

If overdose is suspected:

If you think there has been an overdose, call your poison control center or get medical care right away. Be ready to tell or show what was taken, how much, and when it happened.

How do I store and/or throw out Cayston?

  • Store in a refrigerator. Do not freeze.
  • You may store unopened containers at room temperature. If you store at room temperature, throw away any part not used after 28 days.
  • Protect from light.
  • Keep all drugs in a safe place. Keep all drugs out of the reach of children and pets.
  • Throw away unused or expired drugs. Do not flush down a toilet or pour down a drain unless you are told to do so. Check with your pharmacist if you have questions about the best way to throw out drugs. There may be drug take-back programs in your area.



Principal Display Panel – Cayston 28 Day Carton – Representative Label

Principal Display Panel - Cayston 28 Day Carton - Representative Label