Reconstituting Azithromycin: Use Sterile or Distilled Water, Not Filtered Water
You should reconstitute azithromycin oral suspension with sterile or distilled water, not filtered water. While the FDA label does not explicitly prohibit filtered water, the standard of care and infection control guidelines strongly recommend against using tap water or filtered tap water for medication reconstitution, particularly for immunocompromised patients.
Why Filtered Water Is Not Recommended
The evidence from infection control guidelines consistently warns against tap water use in medical contexts:
Tap water contamination risk: Multiple guidelines 1, 2, 3 emphasize that tap water can harbor pathogens like Cryptosporidium and nontuberculous mycobacteria (NTM), even after filtration. Standard home water filters do not reliably remove all microorganisms.
Healthcare-associated infections: The ATS/IDSA statement 4 explicitly states that "surgical wounds, injection sites, and intravenous catheters should not be exposed to tap water or tap water-derived fluids" and that "clinical specimens contaminated with tap water or ice are not acceptable." This principle extends to medication preparation.
NTM contamination: Healthcare pseudo-outbreaks have been traced to tap water contamination of medications and medical equipment 4. Rapidly growing mycobacteria like M. abscessus are particularly problematic and can survive in water systems.
What Water Should You Use?
The safest approach for reconstituting azithromycin suspension:
- First choice: Use sterile water for reconstitution (available at pharmacies)
- Alternative: Use distilled water
- If neither available: Boil tap water for at least 1 minute and allow to cool completely before use 2, 3
Important Caveats
The FDA label 5 states that "azithromycin for oral suspension can be taken with or without food" but does not specify water quality requirements for reconstitution—this is a gap in labeling rather than permission to use any water source.
Filtered water is not equivalent to sterile water: Home filtration systems, including those with submicron filters, lack enforceable standards for pathogen removal 1, 2, 3.
Patient-specific risk: Immunocompromised patients (HIV-positive, transplant recipients, those on immunosuppressants) face higher risks from waterborne pathogens and should be especially cautious 1, 2, 3.
Practical Guidance
When preparing azithromycin suspension in a pharmacy or clinical setting, always use pharmaceutical-grade sterile water. For home reconstitution, instruct patients or caregivers to purchase sterile water from a pharmacy rather than using filtered tap water. This eliminates unnecessary infection risk from a simple, preventable source.