The Akers–Agalloco Method - Pharmaceutical Technology

Latest Issue

Latest Issue
PharmTech Europe

The Akers–Agalloco Method

Pharmaceutical Technology
Volume 29, Issue 11

Number of microbes deposited on product = C S Pd Pa T

in which C is the concentration of microbes in the source (people), S is the quantity of air or material dispersed from a source over time (usually cfu/m3/s), Pd is the proportion of organisms effectively transferred, Pa is the proportion of organisms that arrive into the product area, and T is the time during which microbes could be transferred.

Whyte also has proposed a slightly simpler deposition model for risk evaluation in which the risk from microbial contamination is defined as:

Risk = A B C D

in which A is the microbial contamination on or arising from a source (e.g., glove or air), B is the ease of dispersion or transfer, C is the proximity of the source to the critical area (one can assume the contamination decreases as the inverse of the square of the distance), and D is the effectiveness of the control method (e.g., isolator, restricted-access barrier systems [RABS], automation, sealed container, intervention frequency).

Whyte chose five levels of risk for each of the terms in the equation: 0 indicates no risk, 0.5 indicates very low risk, 1 indicates low risk, 1.5 indicates medium risk, and 2 indicates high risk. In the case of factor D (effectiveness of control), he suggests 0 for "full barrier control." This means that, should a truly full barrier exist, the overall risk effectively would be zero. Products such as sealed vials that mimic the capabilities of a closed isolator system logically would fall into the "full barrier control" category (9, 10).

The authors' main criticism of this risk model is that it may underestimate process risk because it implies that an exclusionary process such as aseptic processing could produce a level of contamination control effectively equivalent to terminal sterilization. Certainly aseptic processing, in its present state, cannot be considered equivalent to terminal sterilization. Although it may be possible in the future for extremely advanced aseptic processing to achieve levels of actual product safety equivalent to those attained using terminal sterilization processes, there are no aseptic systems currently in operation that can attain process capability comparable with that of a terminal sterilization process. Furthermore, the destructive control afforded by terminal processes enables scientists and engineers to assess risk far more reliably than is possible in aseptic processing.

The deposition models for contamination risk analysis have their advantages and disadvantages. They take into account the following technical conditions that have been included in informal risk assessment for years:

  • the size of container opening;
  • the exposure time for the container;
  • the estimated microbial content of the surrounding air.

The authors believe that a major disadvantage of these models is their inherent assumption that the deposition of microorganisms from the air represents the only vector for contamination. Having observed numerous aseptic processes over the years, the authors find that approach inadequate. In many aseptic processes, operators must approach sterile materials with tools and protective measures. Focusing on personnel seems more appropriate. Although deposition may be the mechanism of dispersion, one must not be so focused on the containers that one ignores the potential presence of microorganisms in other stages of the aseptic process. The authors have developed an approach that is much broader and is not limited to the effect on the container alone.

In addition, the authors believe that assumptions regarding the microbial content of air are potentially misleading. It is tempting to consider that the worst-case content of airborne microbial contamination is that given in the common international recommendations (i.e., <1 cfu/m3).


blog comments powered by Disqus
LCGC E-mail Newsletters

Subscribe: Click to learn more about the newsletter
| Weekly
| Monthly
| Weekly

What role should the US government play in the current Ebola outbreak?
Finance development of drugs to treat/prevent disease.
Oversee medical treatment of patients in the US.
Provide treatment for patients globally.
All of the above.
No government involvement in patient treatment or drug development.
Finance development of drugs to treat/prevent disease.
Oversee medical treatment of patients in the US.
Provide treatment for patients globally.
All of the above.
No government involvement in patient treatment or drug development.
Jim Miller Outsourcing Outlook Jim MillerCMO Industry Thins Out
Cynthia Challener, PhD Ingredients Insider Cynthia ChallenerFluorination Remains Key Challenge in API Synthesis
Marilyn E. Morris Guest EditorialMarilyn E. MorrisBolstering Graduate Education and Research Programs
Jill Wechsler Regulatory Watch Jill Wechsler Biopharma Manufacturers Respond to Ebola Crisis
Sean Milmo European Regulatory WatchSean MilmoHarmonizing Marketing Approval of Generic Drugs in Europe
FDA Reorganization to Promote Drug Quality
FDA Readies Quality Metrics Measures
New FDA Team to Spur Modern Drug Manufacturing
From Generics to Supergenerics
CMOs and the Track-and-Trace Race: Are You Engaged Yet?
Source: Pharmaceutical Technology,
Click here