Biological pyrogen

Biological (pyrogenicity, acute toxicity, haemolytic) and physico-chemical tests. 

One pyrogen test is a qualitative biological test based on the fever response of rabbits. If a pyrogenic substance is injected into the vein of a rabbit, a temperature elevation will occur within 3 hours. Many imitative medical agents will also cause a fever. 

The important attributes of liposomes as a drug carrier are (a) they are biologically inert and completely biodegradable (b) they pose no concerns of toxicity, antigenicity, or pyrogenicity, because phospholipids are natural components of all cell membranes (c) they can be prepared in various sizes, compositions, surface charges, and so forth, depending on the requirements of... 

Most of the LPS biological activity (pyrogenicity) is associated with its lipid A moiety. This usually consists of six or more fatty acids attached directly to sugars such as glucosamine. Again, as is the case in relation to the carbohydrate component, lipid A moieties of LPS isolated from different bacteria can vary somewhat. The structure of E coli s lipid A has been studied in the greatest detail its exact structure has been elucidated and it can be chemically synthesized. 

Its major disadvantage is its selectivity it only detects endotoxin-based pyrogens. In practice, however, endotoxin represents the pyrogen that is by far the most likely to be present in pharmaceutical products. The LAL method is used extensively within the industry. It is used not only to detect endotoxin in finished parenteral preparations, but also in WFI and in biological fluids, such as serum or cerebrospinal fluid. 

IL-l is also known as lymphocyte-activating factor (LAF), endogenous pyrogen and catabolin. It displays a wide variety of biological activities and has been appraised clinically in several trials. 

The preparation of parenteral dosage forms of approved and potential drugs for animals is the same as for humans. Turco and King (1974) provide a comprehensive review of the subject, which, though written with human therapeutics in mind, contains very little that is not applicable to animals. Sterility, lack of pyrogenicity, blood compatibility, and low to no irritation at the point of injection are biological requirements there are also a corresponding set of physicochemical requirements. 

The results from all biological assays performed showed that chemically synthesized E. coli lipid A (compound 506 or LA-15-PP) expresses, with similar doses, the same spectrum of endotoxic effects as bacterial (E. coli) free lipid A (5,234-237). Thus, lipid A constitutes the lethal, pyrogenic, leukopenic, and mediator-inducing, that is, the endotoxically essential region of LPS, its endotoxic properties being embedded in a molecule having the structure shown in Fig. 2. 

ECVAM has validated alternative test methods for acute oral toxicity, biologies, immunotoxicity, dermal corrosion and irritation, developmental toxicity, and pyrogenicity (ECVAM 2007). 

Succinylated or phthalylinated LPS displays significant reduction in toxicity (up to 100000-fold) while retaining its adjuvanticity. Acid treatment (0.1 M HCl) of LPS obtained from various Salmonella species resulted in the production of an LPS-derivative termed monophos-phoryl lipid A (MPL). This also displays adjuvanticity, with little associated pyrogenicity or toxicity. This alteration of biological activity can also be achieved by removal of some of the fatty acids found in the LPS lipid A region. As LPS is effective in activating both cellular and humoral immune responses, research in this area continues to be pursued. 

Validation studies conducted on dry-heat sterilizers can be divided into two basic components. One component envelops all the physical elements that must be qualified, such as temperature control, air particulate levels, and belt speeds. The other component is the biological constituent, which involves studies that prove that the process destroys both microbial and pyrogenic contaminants. 

Sensitive analytical procedures will be required to distinguish contaminants from lipid peaks within the preparation. By-products may be present from the synthetic processes used to produce the lipids or if copurified from the natural source. For example, common impurities in synthetic diacyl chain lipids are the monoacyl forms, which are generally more toxic to biological systems. Endotoxins and pyrogens either may be detectable in a lipid preparation " or difficult to detect due to the lipids shielding against the analytical reagents. ... 

Pharmaceutical products can be sterilized by steam sterilization, dry-heat sterilization, filtration sterilization, gas sterilization, and ionizing-radiation sterilization. The USP provides monographs and standards for biological indicators required to test the validity of the sterilization process. These products must also be tested for pyrogens—fever-producing substances that arise from microbial contamination most likely thought to be endotoxins or lipopolysaccharide in the bacterial outer cell membrane. 

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