F0 value – What it means, how to calculate it and how to use it in moist-heat sterilization

Introduction

The purpose of this Fedegari Technical Note, firstly distributed in 1988 and perseveringly revised, is to clarify the nature of F0 and its related parameters (D, z, PNSU/SAL), and to explain their use and limits for the setting, adjustment, control and validation of moist-heat sterilization processes.

The F0 algorithm was first introduced in 1968 in the international practice of food industry, and proposed by FDA in 1976 for the pharmaceutical sterilization of Large Volume Parenterals: it is now officially included in most Pharmacopoeias. Yet, F0 is still regarded with some suspicion from a conceptual point of view, and frequently misinterpreted. It is always necessary to remember that F0 has been invented in the industrial field of heat sterilization processes of water-containing products.

CONTENTS

1. ESSENTIALS OF MOIST HEAT STERILIZATION KINETICS 5
1.1. D-VALUE OR DECIMAL DECAY TIME 7
1.2. STERILITY AS “PROBABLE EFFECT” OF EXPOSURE TIME 7
1.3. Z-VALUE OR TEMPERATURE COEFFICIENT 9
1.4. F0 OR EQUIVALENT EXPOSURE TIME AT 121°C 11
1.5. LETHAL RATES 14
1.6. EXAMPLE OF POST-CALCULATION OF F0 17
1.7. SYMBOLS AND DEFINITIONS USED IN STERILIZATION TECHNOLOGY 18
2. DEFINITION OF “STERILE” AND “STERILIZATION” 19
3. REAL TIME CALCULATION OF F0 WITH
A COMPUTERIZED AUTOCLAVE 20
3.1. “TRADITIONAL” CONTROL BASED ON EXPOSURE TIME 20
3.2. F0-BASED CONTROL 22
3.3. STERILIZATION TIME-BASED CONTROL WITH
CALCULATION/PRINTOUT OF F0 VALUES 26
4. SUMMARY OF PRECEDING CONCEPTS
IN LAYMAN’S TERMS 27
5. BIBLIOGRAPHY 33
5.1 LITERATURE CITED 33
5.2 SIGNIFICANT REFERENCES 33

2. DEFINITION OF “STERILE”AND “STERILIZATION”

Sterile
Free from viable microorganisms

Sterilization
Any physical or chemical process which destroys all life forms, with special regard to
microorganisms (including bacteria and sporogenous forms), and inactivates viruses.

Therefore the terms “sterile” and “sterilization”, in a strictly biological sense, describe
the absence and, respectively, the destruction of all viable microorganisms. In other
words, they are absolute terms: an object or system is either “sterile” or “non-sterile”.
The destruction of a microbial population subjected to a sterilization process follows a
logarithmic progression: only a treatment of infinite duration can provide the absolute
certainty that the entire microbial population has been destroyed, and that the system is
sterile.

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