Sterilization temperature/time cycles

Low temperature steam and formaldehyde Reactive chemical Indicator paper impregnated with a formaldehyde-, steam- and temperature-sensitive reactive chemical which changes colour during the sterilization process Gas concentration, temperature, time (selected cycles)... 

The sterilization process time is determined from the design F value and the product heat transfer data. The sterilization cycle design must be based on the heating characteristics of the load and of containers located in the slowest heating zone of the load. The variation in the rate of heating of the slowest heating zone must be known, so this variation must be determined under fully loaded conditions. The effect of load-to-load variation on the time-temperature profile must also be determined. Then, the statistically worst-case conditions should be used in the final sterilization process design. 

Five variables are critical to the EtO process. They are EtO concentration, relative humidity, temperature, time, and pressure/vacuum. Temperature is the easiest variable to measure and monitor, therefore temperature is used as the indicator of the worst-case location within the loaded EtO sterilizer. Once the worst-case location is identified the validation studies are conducted with the goal of inactivating a known concentration of indicator micro-organisms in the worst-case location using a specific loading pattern with a specific EtO cycle with all variables defined and controlled. 

Pasteurization Sterilization pH control Temperature control Cycle timing... 

The critical parameters of ethylene oxide sterilization are temperature, time, gas concentration, and relative humidity. The critical role of humidity has been demonstrated by a number of studies (11,18,19). Temperature, time, and gas concentration requirements are dependent not only on the bioburden, but also on the type of hardware and gas mixture used. If cycle development is not possible, as in the case of hospital sterilization the manufacturer s recommendations should be followed. 

Each heat sterilization cycle should be recorded on a temperature-time chart or by other suitable automatic means. The time-temperature record should form part of the batch record. Chemical or biological indicators may be used in addition to but should not take the place of physical controls. 

Each heat sterilization cycle should be recorded on a temperature-time chart or by other suitable automatic means. 

Product Heat Treatment. Equivalent heat treatment for destmction of microorganisms or inactivation of enzymes can be represented by plotting the logarithm of time versus temperature. These relationships were originally developed for sterilization of food at 121.1°C, therefore the time to destroy the microorganism is the V value at 121.1°C (250°F). The slope of the curve is and the temperature span is one log cycle. The heat treatment at 131°C for one minute is equivalent to 121.1°C for 10 minutes (Fig. 10). 

Dry-heat sterilization is generally conducted at 160—170°C for >2 h. Specific exposures are dictated by the bioburden concentration and the temperature tolerance of the products under sterilization. At considerably higher temperatures, the required exposure times are much shorter. The effectiveness of any cycle type must be tested. For dry-heat sterilization, forced-air-type ovens are usually specified for better temperature distribution. Temperature-recording devices are recommended. 

Great care is needed in the design of autoclaves and sterilization cycles because of the requirement for the presence of moisture. The autoclave must be loaded to allow complete steam penetration to occur in all parts of the load before timing of the sterilization cycle commences. The time required for complete penetration, the so-called heat-up time, varies with different autoclave constmction and different types of loads and packaging materials. The time may not exceed specific limits in order to guarantee reproducibility and, for porous loads, saturated steam. The volume of each container has a considerable effect on the heatup time whenever fluids are sterilized. Thermocouples led into the chamber through a special connector are often employed to determine heatup times and peak temperatures. The pressure is refleved at the end of each sterilization cycle. Either vented containers must be used or... 

The resistance of an organism to a sterilizing agent can be described by means of the D-value. For heat and radiation treatments, respectively, this is defined as the time taken at a fixed temperature or the radiation dose required to achieve a 90% reduction in viable cells (i.e. a 1 log cycle reduction in survivors Fig. 20.2k). The calculation of the D-value assumes a linear type A survivor curve (Fig. 20.1), and must be corrected to allow for any deviation from linearity with type B or C curves. Some typical D-values for resistant bacterial spores are given in Table 23.2 (Chapter 23). 

In the case of ethylene oxide sterilization, rather more detail is included on the information expected in an MAA description of the sterilizer and associated facilities, the gas concentration used, bioburden monitoring and limits prior to exposure to gas, gas exposure time, temperature and humidity prior to exposure and during the exposure cycle, and the conditions under which ethylene oxide desorption is undertaken. 

The collected oocytes need to be individually isolated from the connective ovarian tissue and the layer of follicular cells that surround each oocyte (Goldin, 1992). For a detailed description, see Yao et al. (2000). Briefly, the excised ovarian lobe is washed in MBM and dissected using sterile forceps into smaller sections containing approximately 5-10 oocytes each. The sectioned clumps of oocytes are treated with MBM supplemented with 2 mg/mL type I collagenase (Worthington, Lakewood, NJ) for 2 h at room temperature with constant shaking to separate the oocytes from the follicular cell layer. The oocytes are subsequently washed five times with a BSA solution (bovine serum albumin, 1 mg/mL in MBM), followed immediately by five wash cycles in MBM. 

Heat penetration studies are also employed to determine points within a load configuration that achieve higher temperatures and consequently greater Fq values. The temperature data obtained may be significant when heatable products are involved in the sterilization process and the potential for product degradation exists. The cool points established for a specified load and configuration will eventually be utilized to control the exposure time in subsequent routine production runs. The temperature sensors that control sterilization-cycle-exposure time at process temperature may be positioned within the load at the previously detected cool point. Consequently the entire load is exposed to sufficient heat lethality and achieves the desired Fq value. 

Where tunnel peak dwell temperature and time are to be used for routine production cycle control, or as back-up control, correlation of sterilizer peak dwell time and temperature with the hottest and coldest profile container must be shown for each run, where applicable. 

The dye ingress challenge test is performed at the end of expiry to show container-closure integrity over the production shelf life. Dye ingress testing is performed on vials having rubber stoppers exposed to the maximum exposure time and temperature during sterilization cycle. 

The sterilization cycle exposure time, exposure temperature, minimum lethality, and spore log reduction with acceptance criteria and results are provided in Table 2. 

Eollowing is the summary of test results achieved on three individual sterilization cycles of the freeze-drying unit. The results of the three runs met the acceptance criteria of exposure time, exposure temperature. 

If the degree of sterilization (Wf/Wo) and the temperature duringthe holding cycle are given, the holding time can be calculated. 

---