How to calculate the endotoxin limit for a particular product?

Endotoxin Limit:

Endotoxin limits expressed in most pharmacopeial monographs are written as not to exceed a given endotoxin concentration. This suggest to that limit less than or equal to thew sated concentration. However, the USP <85>  Bacterial Endotoxins test chapter make clear that in order to meet the requirements of the test, the material under test must contain less than the endotoxin limit concentration.

According to the USP BET chapter, a sample containing a concentration equal to the limit fails the test (as does a concentration that exceeds the limit).

Parenteral Drugs

For parenterals other than radiopharmaceuticals and therapeutics administered on a per square meter of body surface basis the endotoxin  limit equation given in the USP is as follows:

Endotoxin limit = K/M

Where :

K=  Threshold Pyrogen Dose  or Threshold Unit Or Therapeutic Dose Limit

Parenteral route of administration K = 5  USP-EU/Kg  or  350 USP-EU/ 70 Kg

 70 kg =  Standard human adult weight.

Note : Parenterals are products that are not administered enterically. i.e. not vial intestime. They are generally given by injection or infusion.

Intrathecal route of administration K = 0.2  USP-EU/Kg  or  14 USP-EU/ 70 Kg

Note:  However there are no clearance mechanism in intraspinal spaces. So the (IT) intrathecal drugs. endotoxin limit much more stringent an limit of 0.2 USP-EU/kg.

intravenous route for radiopharmaceuticals: K = 2.5 USP-EU/Kg  or  175 USP-EU/ 70 Kg

M = Maximum human dose or maximum recommended bolus dose of drug per kg of body weight

Note: when the product is to be injected at frequent intervals or infused continuously, M becomes the maximum total dose administered in a single hour period.

Example -1

Calculate the endotoxin limit for a non -intrathecal drugs, injectable products.

1. One product maximum human dose (hole body) 1.0g.

Dose per Kg =1.0/70 = 0.0143g/kg/hr 

70 kg =  Standard human adult weight.

                                

Endo toxin limit =   5Eu/kg/hr / 14.3mg/kg/hr  =   = 0.35 EU/mg

                     

1 mg product endotoxin limit = 0.35 USP-EU/mg

100 mg Product endotoxin limit = 0.35 x 100 = 35 USP-EU/100mg

if bulk product dissolved to give 100 mg/mL = 0.35 x 100 = 35 USP-EU/mL

Example -2

Parenteral route of administration it means intramuscular (IM) or Intravenous(IV)

Maximum bolus dose of 2 mL / Person

Dose = 2mL/70Kg = 0.0286mL/kg

                              

Endotoxin limit =   5 USP-EU/kg  /  0.0286mL/kg   =  175 USP-EU/mL

                             

Example -3

Intrathecal (IT) route of administration

Maximum bolus dose of 2 mL / Person

Dose = 2mL/70Kg = 0.0286mL/kg

                               

Endotoxin limit =   0.2 USP-EU/kg  /  0.0286mL/kg   =  7 USP-EU/mL

                              

Example -4

Maximum bolus dose of 10 mg (product) / kg (body weight) and the product concentration is 5 mg/mL.

                             

Endotoxin limit =   5 USP-EU/kg  /  10 mg/ kg  =  0.5 USP- EU/mg
                            



Endotoxin limit =  0.5 EU/mg  X 5 mg/mL  = 2.5 USP-EU/mL

Anticancer Products administered on a per square meter of body surface, the formula is 

Endotoxin limit = K/M

Where,

K= 100 EU/m2

M is the  maximum dose /m2

Example : 

Drug maximum recommended dose is 30 mg/m2

Endotoxin limit =100 EU/m2 / 30 mg/m2  = 3.33 USP-EU/mg

Related : What is role of LAL, LRW and CSE in bacterial endotoxin testing?