Depyrogenation Endotoxin Removal

In humans, contact with LPS may occur not only during a bacterial infection but also via LPS-contaminated medicaments and solutions administrated intravenously (parenteralia). Since the biological effects of LPS may appear even at concentrations of 1 ng per 1 kg of body weight, drugs intended for parenteral use, have to be endotoxin-free , i.e., thoroughly depyrogenated. In fact parenteralia have to comply with LPS threshold limits (in EU , endotoxin unit) regulated by pharmacopoeias. For example, tetracycline hydrochloride may not contain more than 0.5 ELf/mg. Similar limits exist for insulin (0.8 EU/insulin unit), hyaluronidase (2.3 EU/ hyaluronidase unit), the sodium salt ofheparin for injection (0.003 EU/heparin unit).  

Depyrogenation thus quickly becomes a critical point in the formulation especially of high-molecular-mass pharmaceuticals such as proteins. Amongst the many methods for depyrogenation, membrane adsorbers appear to have a number of important advantages. Their application for endotoxin removal as well as aspects to consider during process development is therefore discussed below. 

The efficiency of a clean-up step by (membrane) adsorption depends, in addition to the chemistry of the membrane, strongly on the physicochemical properties of the substance to be adsorbed. The physical state of LPS in aqueous media depends among other things on the bacterial strain from which it was derived and composition of the suspending liquid. LPS 

Membranes Based on Nonfunctionalized Polymers for Endotoxin Removal 

In contrast to membrane filtration, in which adsorption is an undesirable phenomenon because of the possible loss of target substance, membrane adsorption is in fact based on this phenomenon and high sorption capacities improve in this case the efficiency of the operation from the economical point of view. However, virtually all membrane materials (surfaces), even the ones designed primarily with membrane filtration in mind, exhibit a more or less pronounced but nonspecific adsorption tendency, due to the general possibility of establishing hydrophobic, dipole-dipole and electrostatic interactions as well as hydrogen bonds with the various dissolved molecules. It was also observed by many investigators that mechanical filter may retain particles/molecules that are smaller than the filter s pores, presumably as a result of an impaction of the particles on the filter surface. However, whatever the cause, if the forces 

---

A process that removes or destroys endotoxin in a solution or on a material is termed depyrogenation. Endotoxin is difficult to eliminate because it is ubiquitous... 

Hou, K.C. Zaniewski, R. Depyrogenation by endotoxin removal with positively charged depth filter cartridge. J. Parenter. Sci. Technol. 1990, 44, 204-209. 

Hou KC, Zaniewski R. Depyrogenation by endotoxin removal with positively charged depth filter... 

Data should be available that demonstrates a knowledge of the (or endotoxin) loading on components prior to treatment in a depyrogenation process. When a depyrogenation process is used, the data shall demonstrate that the process will remove a greater quantity of endotoxin than may have been originally present in the component or product... 

---