I don't know if Azactam / aztreonam is still available.

Azactam Injectable Antibiotic
Azactam - by Doc Johnson
Azactam
I am really "liking" Azactam for the bacteral infections I am seeing this year. I have used it i the same syringe with Amikacin and would have to say that it's the silver bullet to use in the absence of a proper culture with sensitivity testing.
Aztreonam: Is available from SQUIBB labs in an injectible form.
Once reconstituted, the drug has a short useful life. After 7-14 days, th potencey of the drug begins to deteriorate. (The same is true for Chloramphenicol unless it is frozen) I do not know whether Azactam can safely be frozen.
Azactam is a 'monobactam' type antibiotic in a class by itself. At usual doses it is Bactericidal, which means it kills, and doesn't stun bacteria. It has a published spectrum against gram negative and aerobic pathogens. Most notably, it is effective against Pseudomonas. No research information exists about its efficacy against Aeromonas, the more common cause of Ulcer Disease but we are finding it very effective.
There are several strengths available, so 'mil-per-inch' doses are impossible.

If you obtain Azactam 500mg vials:
Put 5 cc (same as 5 ml) of Sterile Saline (0.9% saline) in the vial with the 500 mg of Azactam. This will give you a strength of 100 mg per milliliter.

The dosing chart for the use of Azactam is in the book, "Koi Health & Disease"

Posted: Thurs, Jul 30, 1998 at 15:48:11 (EDT)

Original: NA
Posted by: Dr. Wong
Recipient: All
Subject: Aztreonam can be frozen!
Message:
Aztreonam powder for injection should be stored at room temperature and should not be exposed to temperatures warmer than 40DGC. The powder for injection also should be protected from moisture. If exposed to strong light, the powder may yellow slightly.
Following reconstitution with sterile water for injection or 0.9% sodium chloride injection, IM injections of aztreonam are stable for 48 hours at 15-30DGC or for 7 days when refrigerated at 2-8DGC. IM injections of the drug reconstituted with bacteriostatic water for injection (with benzyl alcohol or parabens) or bacteriostatic sodium chloride injection (with benzyl alcohol or parabens) should be used immediately after reconstitution.
Aztreonam solutions can be frozen immediately after preparation and are stable for up to 3 months at -20DGC.

Above is a link for API's dechlor / Stress Coat, Pond Strength

Frozen solutions may be thawed either at 15-30DGC or by overnight refrigeration. Frozen solutions that have been thawed and stored at room temperature should be used within 24 hours, and those that have been thawed and refrigerated at 2-8DGC should be used within 72 hours after removal from the freezer. Once thawed, aztreonam solutions should not be refrozen. The manufacturer states that the stability of the commercially avilable frozen aztreonam injection may vary. These injections are stable for at least 90 days from the date of shipment when stored at -20DGC. The frozen injection should be thawed at room temperature (25DGC) or under refrigeration (2-8DGC) and, once thawed, should not be refrozen. Thawed solutions of the commercially available frozen injection are stable for 48 hours at room temperature (25DGC) or 14 days when refrigerated at 5DGC. Aztreonam frozen injections should be removed from their original carton according to the manufacturer's directions and may be thawed individually; when thawing is complete, the container should be inverted to assure a well-mixed solution. The manufacturer states that aztreonam frozen injections are single-dose units and unused contents of any container should be discarded.
The commercially available frozen injection of the drug is provided in a plastic container fabricated from specially formulated polyvinyl chloride (PL 146 plastic). Solutions in contact with the plastic can leach out some of its chemical components in very small amounts (e.g., bis(2-ethylhexyl)phthalate [BEHP, DEHP]in up to 5 ppm) within the expiration period of the injection; however, safety of the plastic has been confirmed in tests in animals according to USP biological tests for plastic containers as well as by tissue culture toxicity studies.
"Azactam is not hard to find. Your veterinarian won't have it in stock but he can write a prescription for it if so motivated." Doc Johnson