Alternatives to Sterile Water for Injection If You Can't Fill Your Prescription

When Sterile Water for Injection (SWFI) is unavailable—as has been the case off and on since 2021—healthcare providers and patients often need to consider alternatives. But substituting an injectable diluent is not as simple as swapping one liquid for another. The wrong substitute can cause medications to crystallize, deactivate the active ingredient, or create unsafe solutions for injection.

This guide reviews the main alternatives to Sterile Water for Injection, explains when each is appropriate, and clarifies what you should never do when SWFI is out of stock. Always consult your pharmacist or prescriber before making any substitution—this is for informational purposes only.

Why Can't You Just Use Any Water?

Sterile Water for Injection, USP is a tightly regulated pharmaceutical product. It must be free of particles, pyrogens (fever-causing contaminants), microorganisms, and added chemicals. Regular water—even distilled water or water for irrigation—does not meet these standards and is dangerous if injected. Sterile water for irrigation, for instance, is explicitly not FDA-labeled for injection use.

Alternative 1: Bacteriostatic Water for Injection (BWFI)

Bacteriostatic Water for Injection is sterile water containing 0.9% benzyl alcohol as a preservative. The preservative prevents bacterial growth after the vial is opened, allowing multiple withdrawals from a single 30 mL vial for up to 28 days. It is the most common alternative to SWFI and is generally more available, especially in the smaller retail market.

When it works: BWFI is acceptable for many medications when the prescribing information permits it. It is widely used for reconstituting hormones (growth hormone, testosterone), certain antibiotics, and other injectable drugs in multi-dose settings.

Critical warning: Bacteriostatic Water is CONTRAINDICATED for use in neonates, very small infants, and for medications given intrathecally (into the spinal fluid) or epidurally. Benzyl alcohol can be toxic to these populations. It should also never be used for medications that specifically require preservative-free SWFI.

Alternative 2: 0.9% Sodium Chloride Injection (Normal Saline / NS)

Normal saline (0.9% NaCl) is the most widely used IV fluid in medicine and is often the first alternative considered when SWFI is unavailable. Many antibiotics can be reconstituted with NS, and its isotonic composition makes it safe for IV administration.

When it works: Many common antibiotics including cefazolin (in 1 g vials), cefotaxime, and acyclovir have been shown to be safely reconstituted with NS in published studies. Your pharmacist or the ASHP guidance documents can confirm which drugs have documented NS compatibility.

Caution: Normal saline reconstitution for IV push administration can produce hyperosmotic solutions that may cause infusion-site reactions (phlebitis, pain, infiltration). High concentrations of some antibiotics reconstituted with NS can approach saturation points, risking crystallization. Do not use prefilled saline flush syringes to reconstitute IV push medications.

Alternative 3: Commercially Premixed Formulations

Many medications that come as powders requiring reconstitution are also available as commercially premixed liquid formulations in IV bags or dual-chamber flexible containers. These require no SWFI at all. If your medication has a premixed version, your pharmacist or prescriber may be able to switch your order to that formulation during the shortage.

Examples include premixed IV bags of vancomycin, piperacillin-tazobactam, meropenem, and many other hospital antibiotics. Ask your pharmacist about premixed alternatives for your specific drug.

Alternative 4: Dextrose 5% in Water (D5W)

D5W (5% dextrose in water) is sometimes used as an alternative diluent for medications that are compatible with it. However, not all medications are stable in dextrose solutions—some degrade faster or change activity. D5W must be confirmed as compatible before use.

What You Should NEVER Use as a Substitute

Sterile Water for Irrigation: Not FDA-labeled for injection and does not meet the particulate matter standards required for SWFI.

Tap water, distilled water, or mineral water: None of these meet pharmaceutical sterility requirements and can cause serious infections, fever, or other harm when injected.

Prefilled saline flush syringes: These are not intended for drug reconstitution and can produce dangerously concentrated solutions.

How to Decide Which Alternative Is Right for You

The right alternative depends entirely on the specific medication you are using, the route of administration (IV push, IV infusion, IM, subcutaneous), and patient-specific factors (age, renal function, allergies). Your pharmacist is the best resource for making this determination—they can check the prescribing information and stability literature for your specific drug.

If you are still looking for Sterile Water for Injection, read our guide on how to find SWFI in stock near you or use medfinder.com to locate pharmacies that have it available.