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Factors Influencing Disinfection, Antiseptics and Their Evaluation

Chemical Structure of Disinfectant, Interfering Substance in Environment, Surface Tension, Temperature, pH of the surrounding, Formulation

Factors Influencing Disinfection and Antiseptics

  • Disinfection is the process of removing or destroying germs and lowering their population to a safe level.
  • Disinfection often destroys the vegetative form of germs while leaving the endospores alone.
  • Inanimate objects (inanimate objects) are disinfected with disinfectants.
  • "Antiseptics" are substances that are used to disinfect living things.
The rate and breadth of the disinfectant's antibacterial action are determined by a variety of parameters, including

Chemical Structure of Disinfectant

  • Disinfectants have a chemical action that is influenced by their chemical structure.
  • The addition of an alkyl chain to the para position of phenol boosts its activity; however, adding more than 6 carbon atoms to the chain reduces its solubility and disinfecting effect.
  • When halogenated, phenol's antibacterial properties are enhanced, while when nitrated, the effect is attenuated.

Interfering Substance in Environment

  • Organic elements such as pus, blood, and other bodily fluids present at the disinfectant's site of action considerably limit the disinfectant's efficacy.
  • The presence of fats and oils at the phenol's site of action considerably inhibits its effectiveness.

Surface Tension

  • Surface tension is the propensity of liquid surfaces to contract into the smallest feasible surface area.
  • The disinfectant's adsorption on the microbial cell is increased by lowering the surface tension in an aqueous solution, as are the solution's wetting characteristics and solubility.
  • Because soap has the virtue of lowering surface tension, combining phenol with soap results in greater disinfection effect.

Types and Number of Microbes Present

  • Disinfectants are most effective against microorganisms in their vegetative phase rather than their spore form.
  • Even so, formaldehyde, an aldehyde that is sporicidal, is considered effective in the removal of bacteria spores.
  • Acid fast bacilli are essentially impervious to disinfection aqueous solutions due to the presence of fats in their cell membrane, but can be destroyed by phenols, aldehydes, and halogen compounds.


  • There is a specific temperature beyond which disinfectant activity declines, depending on the material.
  • The influence of temperature on antibacterial activity is indicated using the "Temperature coefficient," denoted by "𝞡" where 10°C is denoted by Q10.
  • In order to determine the Q10, use the following formula.

Potentiation and antagonism of disinfectants

The efficacy of some disinfectants depends on their interactions with others, while the efficacy of others is diminished.

pH of the surrounding

  • Most bacteria thrive best at a pH of 6-8.
  • Acidic disinfectants have the greatest action at an acidic pH because they remain ionized.
  • Basic dyes, such as acridine and quaternary ammonium compounds, have the greatest activity at basic pH because they stay ionized at that pH.
  • Tego compounds, for example, are amphoteric surfactants with high action at a wide range of pH.

Formulation of disinfectant

  • A good formulation improves the disinfectant's effectiveness.
  • Because iodine is nearly insoluble in water, it is dissolved using alcohol and potassium iodide solution.
  • The addition of a surfactant to iodine solution reduces its odour, staining issue, and boosts the preparation's stability.
  • Chlorhexidine and Quaternary ammonium compounds perform better in 70% alcohol solution than in aqueous solution.

Concentration of disinfectant

  • The pace at which the bacteria are killed varies directly with disinfectant concentration.
  • A linear relationship exists instead of a proportional relationship between death and disinfectant concentration.
  • The disinfectant has an optimal concentration at which it is most effective; below and beyond this concentration, the efficiency declines.
  • The Dilution Coefficient is a crucial disinfection property that defines how much dilution is required for optimal effectiveness.
  • The dilution coefficient is computed using the formula below.

n = Disinfectant Dilution Coefficient
t1 = Time of Death at Concentration C1.
t2 = Time of Death at Concentration C2.


Disinfectants used in hospitals and labs must be evaluated on a regular basis to ensure their potency and efficacy. It is essential to evaluate the efficacy of certain disinfectants since they gradually lose their effectiveness with increased exposure to organic matter. While some methods aid in the selection of the appropriate disinfectant dilution for use, others examine the efficacy of disinfectants that are already in use. Some approaches evaluate the disinfectant's performance to that of phenol, whilst others simply declare whether or not the disinfectant is effective. Disinfectants can be assessed in various ways, each with benefits and drawbacks. All of these tests may be classified as disinfection testing: carrier tests, suspension tests, capacity tests, practical tests, field tests, or in-use tests.

"Making more records that prove a disinfection method consistently eliminates or inactivates known or potential pathogens from inanimate objects" is described as "validating the disinfection process.".

Carrier tests

The tests conducted here are the earliest tests. According to Robert Koch, the carrier test was conducted. By immersing them in a liquid culture of the test organism, the carrier is contaminated in these experiments, such as silk or catgut threads. A set period of time is then allowed for the carrier to dry and be exposed to the disinfectant. It is cultivated in a nutrient broth after exposure; no growth shows that the disinfectant tested is active, whereas growth indicates that the disinfectant is failing. Two limitations arise from carrier testing: 1) it is difficult to standardize the number of bacteria dried on a carrier and 2) it is not easy to predict the survival of bacteria on a dried carrier.

Suspension tests

As a result of this test, a sample of the bacterial culture is suspended in the disinfectant solution, and its viability is assessed by subculture after exposure to the disinfectant. Suspension tests are favoured over carrier testing because the bacteria are exposed to the disinfectant equally. There are three types of suspension testing: qualitative suspension tests, phenol coefficient tests (Rideal and Walker, 1903), and quantitative suspension tests. The process was initially qualitative. In a loopful of bacterial suspension, the disinfectant was mixed with a loopful of the suspension, and surviving organisms were gathered from this loopful of bacteria. Quantitative approaches count and compare the number of surviving organisms to the original inoculum size to determine whether an outcome was a growth or not.

Capacity tests

When a filthy instrument is placed in a disinfectant-containing container, a certain amount of dirt and germs is added to the solution. The disinfectant's capacity is defined as its ability to retain action in the midst of an increasing load. During capacity tests, successive additions of bacterial solution are added to the disinfectant until its killing ability is depleted. Capacity tests mimic real-world scenarios such as housekeeping and instrument cleaning. Most people are familiar with the Kelsey-Sykes test (Kelsey and Sykes, 1969).

The Kelsey-Sykes test is a triple challenge test used to identify disinfectant doses that will be effective in clean and unclean settings. During the test, the disinfectant is challenged by three repeated additions of a bacterial solution. More than 30 minutes are needed to complete the test. The approach can be used in either "clean" or "dirty" settings. The disinfectant is diluted in hard water for clean circumstances and yeast suspension for unclean conditions. At 0-, 10-, and 20-minute intervals, the test organism is introduced alone or with yeast. It takes approximately 8 minutes for the disinfectant to become in contact with the test organism. A clean and dirty environment can be analyzed using the approach. The disinfectant is diluted in hard water for clean circumstances and yeast suspension for unclean conditions. At 0-, 10-, and 20-minute intervals, the test organism is introduced alone or with yeast. The contact duration between the disinfectant and the test organism is 8 minutes.
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Ankur Choudhary is India's first professional pharmaceutical blogger, author and founder of Pharmaceutical Guidelines, a widely-read pharmaceutical blog since 2008. Sign-up for the free email updates for your daily dose of pharmaceutical tips.
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