The testing of  Antibiotic potency assays is crucial in the field of microbiology for evaluating the efficiency of antibiotics against particular microorganisms. These tests play a vital role in guaranteeing the effectiveness and quality of antibiotics intended for medical purposes. Typically, the potency of an antibiotic is evaluated by examining its capacity to either inhibit the growth of bacteria or remove them.

The FDA mandates that antibiotic drug products must meet the potency stated on their labels to be distributed in the United States. The USP General Chapter <81> titled “Antibiotic Potency Assays” offers approved techniques for evaluating the potency of various antibiotic active ingredients by their effectiveness against particular microorganisms. We at Chromak Research have a highly skilled and experienced team who specialize in conducting antibiotic potency testing.

Methods of Antibiotic Potency Assays

Antibiotic potency assays are essential for ensuring the effectiveness of antibiotics in treating bacterial infections. These assays help determine the concentration or activity of an antibiotic in a given sample. Several methods are employed for antibiotic potency assays, and the choice of method depends on the specific characteristics of the antibiotic and the desired outcome. USP General Chapter <81> entitled “Antibiotic Potency Assays” provides two types of methods for determining antibiotic potency: Cylinder-Plate Assay and Turbidimetric Assay.

  1. Cylinder-Plate Assay: To test antibiotics, their active ingredients are extracted using solvents and phosphate buffers following USP <81> guidelines. The extracted sample is diluted to reach the median dose using a Standard curve. The sample and Reference Standard are pipetted into Peni cylinders in a petri dish with antibiotic growth medium and a susceptible microorganism. After incubation, the ‘zones of clearing’ or ‘zones of inhibition’ are measured in millimeters to determine the concentration of antibiotic present. The results are compared with known amounts of antibiotic in the Reference Standard. The test must be repeated three times on different days for accuracy.
  1. Turbidimetric Assay: It measures the decrease in turbidity (cloudiness) of a bacterial suspension in the presence of antibiotics. The test determines if the antibiotic can eliminate a specific microorganism, leading to a decrease in cloudiness of the solution. Turbidity reduction is directly proportional to antibiotic amount. The Turbidimetric Assay inhibits microorganism growth in a solution of the antibiotic. Different concentrations of the antibiotic are used. Turbidity is measured using spectrophotometry and results are calculated based on USP guidelines. USP determines whether to use Cylinder-Plate or Turbidimetric Assay for each antibiotic.

In short, the diffusion technique or cylinder plate method relies on the diffusion of the antibiotic within the solid culture medium. Both the test sample and the reference standard are positioned on the solid medium surface that has been inoculated with a suspension of microorganisms; the growth of the microorganism within the culture medium will be visibly inhibited following the incubation period. On the other hand, the turbidimetric method, is centered on impeding the growth of a susceptible microorganism in a liquid culture that has been exposed to varying concentrations of the antibiotic. The level of inhibition is determined by the varying turbidity levels of the suspension, which are directly proportional to the different levels of microbial growth.

While the two Antibiotic Potency Testing methods outlined in USP <81> have been validated, it is still necessary to verify them when utilized for the first time by a laboratory on a particular sample type (formulation). Method Verification involves assessing method precision, accuracy, linearity, and specificity to guarantee precise results are achieved by the laboratory under real operating conditions. Method Verification is conducted once for each sample type (formulation) unless there are modifications to the USP method or sample formulation.

Our team at Chromak Research possesses the necessary expertise and knowledge to test these assays according to USP <81> and also can validate the methods to give accurate and reliable results to our clients. We have the necessary equipment and facilities to carry out these tests efficiently and effectively.

We adhere to strict quality control measures throughout the testing process to ensure that our results are precise and reproducible. Our team is trained to handle samples with care and precision, minimizing the risk of contamination or errors.

Overall, Chromak Research is a trusted partner for antibiotic potency testing and consultation services. Our team’s expertise, dedication to quality, and commitment to client satisfaction make us the ideal choice for all your antibiotic testing needs.