Commercial products used to medicate drinking water must meet quality, safety and efficiency conditions throughout their life span, both in storage and in use, where stability is critical. Stability tests play a key role in the eventual development of a product. These tests are done with EMEA (European Medicines Agency) and CVMP (Committee for Medicinal Products for Veterinary Use) quality standards based on simulating the actual conditions at the farm.
A commercial product is formed by a combination of the active ingredients and excipients. The active ingredient is the compound with therapeutic properties and the excipient is what is added to transform the active ingredients into a combination suitable for administration. Its stability will depend first of all on the excipient - active ingredient compatibility: The excipients and some impurities may destabilize the medication. The degradation causes instability, and leads to loss of the medication’s potency, undesirable changes in performance (dissolution, bioavailability, etc..) and products that have broken down can cause toxicity. In a "solid" state chemical reactions are due to the low substance-excipient ratio, changes in the particles (shape, size, impurities and defects) and the effect of temperature (temp, pH, light and oxygen). When we are dealing with a "solution", the temp, pH, solvent-diluent ratio, light, oxygen and co-solutes (buffer salts, antioxidants, chelating agents, etc.) are responsible for the degradation.
|Examples of degradation|
|Penicillins||Ascorbic acid||Tetracycline||Folic acid||Ampicillin|
Crowley and Martini, Pharmaceutical technology. Oct 2001
The stability of different products is checked by applying various stability tests.
1. Proven stability of the commercial product:
The goal of "stability tests" is to evaluate the quality of the substances added to form the commercial product and recommended storage conditions and use. A product is considered stable if the active ingredient maintains its specified potency from the date of manufacture to final administration to the animal. The "stress test" helps determine the intrinsic stability of the molecule identifying products’ degradation through analytical procedures. We speak of "evidence of long-term stability" to monitor the physical, chemical and microbiological properties during the life of the product in the same package that is proposed to circulate in the market and "accelerated stability tests" designed to achieve an increased rate of chemical or physical degradation of a product in extreme or exaggerated circumstances and in their original packaging.
|Type of test||Storage Conditions||Minimum time|
|Long term stability||25ºC±2ºC/60%RH±5%||6-12 months|
|Accelerated stability||40ºC±2ºC/75%RH±5%||6 months|
Systems have been developed for laboratory degradation studies simulating different pharmaceutical field conditions.
2 Stability tests in storage and transportation:
The aim is to identify environmental conditions that give stability to the product from manufacture to administration to the animal, taking into account the expiration date based on: analysis, storage temperature recommended, exposure to environmental factors (temp extremes, light, humidity, etc.) and other special restrictions that should be reflected in the label.
3. Stability tests in sealed container of the product:
The goal is to keep the commercial product with a low % of impurities and with constant physicochemical and microbiological properties. The packaging must protect the product to prevent adverse reactions due to external factors.
4. Stability tests in use of the product:
The aim is to check how long the product remains stable after opening the package.
5. Stability tests in drinking water:
The different water qualities that can be found on farms make such tests really important. With water there can be physicochemical, microbiological and pH variations. You should check the stability and solubility of the product in all water conditions and temperatures, simulating real situations (see Chapter 1). Test samples of medicated water at different intervals of time checking the concentration of the active ingredient in hard water (pH 8-9) and soft (pH 5-7), and at different temperatures. The maximum solubility of the product when the concentration is several times higher than that used at the field level should be noted. Turbidity as reduced transparency due to the presence of suspended particles is measured and expressed in units NTU (Nephelometric Turbidity Units). The insoluble fraction can be measured by filtering the solution, drying and final weight of the residue. Also, it should be assured that the presence of chlorine in the water does not involve phenomena that will act adversely on the stability of the molecule.
Stability test sample of a commercial product in hard water and soft during 24 hours (left) and depending on the Temp (right):
Av. Tecnol. Porc. VI (3):110-113
6. Biofilm stability tests:
Biofilms are complex communities of microorganisms resistant to antibiotics, coated with an extracellular polymer that helps retain food and protect themselves from toxic agents. The presence of biofilm in water pipes, often due to poor application of sanitizing methods, may affect the stability of the medications. Stability testing can be performed by an antibiogram of these organisms along with a sample of the product to use and looking the result: if there is massive microbial growth, there is no inhibition, while if it has an effect its stability is compromised.
3 phases of biofilm formation: attachment, colonization and growth of complex structures of the biofilm.
Peg Dirckx. 1995. Center for Biofilm Engineering.
Biofilm bacteria can move in many ways: either collectively in waves, rolling on the surface, shedding in groups or individually dispersed in the stream.
Paul Stoodley / Peg Dirckx. 2003. Center for Biofilm Engineering.
7. Stability tests in maximum storage of medicated water:
Prolonged storage may affect the quality of medication (palatability and pollution). This period should correspond to the maximum time during which the concentrate is still effective and safe (expiration date). Factors associated with water-unstable products are poor bioavailability, inability to optimize the active components on the basis of efficacy and safety, lack of proportional response to dose, suboptimal doses and uncontrollable precipitation after dosing, among others. Interactions between products dissolved in water should also be considered. The graph shows how to modify the pH of water to mix florfenicol with other substances.
Average pH in solutions and in water pipes of various components in the presence of florfenicol.
AS: acetylsalicylic acid
MK: milk substitute