Water medication can only be effective if the pharmaceutical product completely dissolves in water. Unfortunately, several factors may cause a product not to dissolve:
- The solubility of the active ingredient
For example, trimethoprim (widely used in combination with sulphonamides) is very difficult to dissolve. Ampicillin, amoxicillin and chlortetracycline have low solubility properties as well. On the other hand, doxycycline is far more soluble.
- The temperature of the water
In general, solubility in cold water is much lower. We recommend to use water at room temperature, if possible. Be careful with hot water; some active ingredients (e.g., amoxicillin) degrade rapidly at high temperatures. In addition, there is the risk of the product raining back down when the water cools off, causing clogged nipples.
- The pH of the solution
The solubility of certain active ingredients depends on the pH of the solution. Trimethoprim sulphonamide combinations and amoxicillin dissolve better at high pH, while tetracyclines dissolve best at either low or high pH.
- Other elements in the water
Some active ingredients can bind with ions in the water and form complexes:
- Tetracyclines can bind with calcium or magnesium if water hardness is >20 °DH.
- They can also bind with iron if the iron content in the water is > 5 mg/L. Doxycycline, however, is less likely to bind.
- Trimethoprim sulphonamide combinations do not bind with ions, but they can bind to organic substances in the water.
