Pharmaceutical Water Testing

Testing Options

The USP establishes specifications for each of the various types of water that are used by the pharmaceutical industry here in the USA. The most common type is Purified Water, which may be used as an ingredient in non-sterile/non-parenteral drug products, as an agent for cleaning processing equipment, and in the testing of drug products and their related materials.   Specifications for the various types of Pharmaceutical Water will vary, depending on the application.  Thus the testing requirements for Water for Injection or Water for Hemodialysis will be different than the requirements for Purified Water.  The USP Monograph for each type of Pharmaceutical Water includes testing requirements that are specifically designed for the type of drug product or application in which the water will be used.

• Total Organic Carbon: Although there are some tests which are only performed on a specific type of Pharmaceutical Water, there are others tests of a more general nature which apply to most, if not all water types.  The first of these ‘common’ water tests is Total Organic Carbon (or “TOC”). This test is required for nearly all types of Pharmaceutical Water here in the USA and in jurisdictions around the world.  Pharmaceutical Water must be relatively free (< 500 parts per billion here in the USA) of organic carbon-containing compounds, which indicate the presence of chemical and/or microbiological impurities in the water.  Examples of chemical contaminants that are detected by TOC testing would include but not be limited to acetone, methyl ethyl ketone and gasoline.  Since all microbiological organisms are composed primarily of carbon molecules, they would also be detected by TOC testing, examples of which include pseudomonas aeruginosa and E. coli.
   
  

• Water Conductivity: Another common test that is performed on Pharmaceutical Water is Water Conductivity.  Electrical conductivity in water is defined by USP as “a measure of the ion-facilitated electron flow through it”.  Hence, the presence of ions in water will allow an electrical current to flow through it, whereas the total absence of such ions would not support the flow of electrical current.  The Water Conductivity test is used for detecting the presence of extraneous ions in water which facilitate a flow of electrical current through the water. Examples of extraneous ions include but are not limited to metallic cations (Fe⁺³ or Mg⁺²) and specific anions such as Phosphate (PO₄^-3), Chloride (Cl^–) and Ammonium (NH₄⁺). Since extremely low levels of ions will facilitate an electrical current, USP provides a specification for an acceptable level, expressed as microsiemens which are minute units of electrical current. 
   
  
• Oxidizable Substances and Particulate Matter in Injections: Other Pharmaceutical Water tests include Oxidizable Substances and Particulate Matter in Injections.  Oxidizable Substances tests for the presence of molecules which readily combine with oxygen.  Potassium Permanganate, a strong and brightly colored oxidizing agent is used to indicate the presence of oxidizable substances in water.  Examples of contaminants that are detected by this test would include but not be limited to microbiological organisms, biological compounds, and compounds containing metals.  Regarding Particulate Matter in Injections, as its title would suggest, this test is used for determining the presence of particulates which may be present in Pharmaceutical Water.  Particulates are of great concern if the water is being used for an ophthalmic or injectable product.
   
• Microbiological Testing: Although Microbiological Testing is not included in the USP Monograph for every type of Pharmaceutical Water, FDA views the individual Monographs as providing only the “minimum” quality requirements, and fully expects all types of Pharmaceutical Water that are produced from a purification system at the site where they are used (“bulk” waters) to be regularly monitored for microbiological contamination.  USP General Chapter <1231> entitled “Water for Pharmaceutical Purposes” indicates testing methods that are adapted from USP <61> entitled “Tests for Microbial Enumeration” and USP <62> “Test for Specific Organisms” are suitable for monitoring the quality of Pharmaceutical Water.
   
• Biofilms: One of the greatest concerns regarding purified water systems is the formation of Biofilms.  USP General Chapter <1231> Section 8.2 defines a biofilm as a “three-dimensional structured community of immobile microbial cells embedded in a matrix of extracellular polymeric substances (EPS).”  Biofilms form when bacteria attach to surfaces in moist environments and produce a slimy, glue like substance, the EPS matrix, whilst proliferating at that location.  Once established, other microorganisms may attach themselves to the EPS matrix, thus establishing a microbial ‘community’.  The three-dimensional structure of biofilms accounts for their resistance to most chemical sanitizing agents, which have difficulty penetrating through the EPS.  The most effective method of biofilm removal from a water system is heat sanitization.
   
• Design of a Water Purification System: It is important to understand that water, and any purification system that is used to produce Pharmaceutical Water provides an excellent environment for microbial growth.  Thus, the Design of a Water Purification System is a crucial matter.  A poorly designed system can result in the contamination of the water that it produces.  When deciding upon the design of a water purification system there are many options to choose from. The most common methods of Pharmaceutical Water production include Deionization, Reverse Osmosis, Filtration and Distillation.  There are also “hot” systems that are designed to maintain the water at a microbiological “kill” temperature (minimum 80^oC).  Design choices should be based upon the specific needs of the manufacturing site that the water purification system must support.  Quality of water, rate of production, storage and distribution needs, ease of maintenance and cost all come into play when designing a water system.
   
• Validation and Qualification: Regardless of what design choices are made, ultimately each system must undergo Validation and Qualification of the Water Purification, Storage and Distribution portions of which it is comprised.  Validation and qualification activities establish the reliability of the entire system by demonstrating control of the process over an appropriate period of monitoring and observation.  USP <1231> Section 4.2 states “Validation is a program of documenting, to a high level of assurance, that a specific process is capable of consistently delivering product conforming to an established set of quality attributes.” 
   
• Sampling and Testing: The monitoring of a purified water system requires Sampling and Testing of the Pharmaceutical Water from various locations within the system, including the water generation system, storage tank(s) and the distribution network (points-of-use).  Although many systems are equipped with “in-line” monitoring devices such as TOC Analyzers and Conductivity Meters, there is always the need to physically sample the system for conducting “off-line” testing.  Whenever water systems are physically sampled, precautions must be taken so as to prevent introducing contaminants into the sampled water.  Sample valves should be sanitized and allowed to dry prior to sampling.  Suitable flush volumes should be established prior to collecting the sample.  The sampler should be trained in sampling water systems and should wear sterile gloves and any other apparel/devices as deemed necessary.  Sterile containers should be used for sample collection.  Samples for TOC testing should be collected in specially prepared vials.  Once samples are collected, they should be tested as quickly as possible.  If testing cannot be initiated within a few hours, the samples should be refrigerated until testing can begin.  Even refrigerated water samples have a short lifespan of only a few days at most.