Statistical procedure for evaluating the sensitivity of Limulus amoebocyte lysate by using a reference lysate.

A study was designed to estimate variability of the Limulus amoebocyte lysate test by comparing a reference lysate against itself. Three technicians performed parallel tests, i.e., titrated side by side, the contents of two vials of reference lysate on 4 different days using 24 vials of the United States reference lysate and 12 vials of the United States reference endotoxin. Each parallel test was replicated three times. From the sensitivity endpoints, ratios were calculated for each parallel test. These ratios were converted to the logarithm for estimating variability among technicians and among vials of endotoxin. By using the overall variability of log ratios, a statistical procedure was developed to evaluate the sensitivity of each lot of licensed lysate submitted to the Bureau of Biologics for release.

Optimization of parameters in protein nitrogen unit precipitation procedure for allergenic extracts.

This work establishes the optimum conditions for the protein nitrogen unit (PNU) phosphotungstic acid (PTA) precipitation procedure for allergenic extracts. The volume of extract analyzed, the dilution of the extract prior to precipitation, the percent PTA in the precipitating solution, the washing of the precipitate, and the volume of concentrated HCl initially added to the extract were optimized, as they were found to be the factors which affected the amount of PTA precipitate obtained. Varying the digestion time, the digestion temperature, and the percent HCl in the 15% PTA precipitating solution did not cause detectable differences in the PNU values of the extracts studied.

Limulus amebocyte lysate testing of nomral serum albumin (human) in the United States since 1975.

In order to determine the reactivity of Limulus Amebocyte Lysate to albumin products, over 1500 lots of 25% Normal Serum (Human) produced by 12 U.S. licensed manufacturers were tested over the past 4 years. Representative samples of 5% Normal Serum Albumin (Human) and Purified Protein Fraction (human) were also tested with Limulus Amebocyte Lysate. Problems associated with apparent false negative reactions are discussed. Model test protocols are presented that might be useful in determining the degree of false positivity of albumin products. These models could be adopted by blood fractionators to gather validation data to support substitution of the Limulus Amebocyte Lysate test for the rabbit pyrogen test.

Use of the antibody assay in immunized mice for the determination of rabies vaccine potency.

At present, the NIH potency test is the most widely used method for determining the potency of rabies virus vaccines. The drawbacks of this test are well known and include significant test variability as well as the use of an unnatural challenge route. The antibody assay in immunized mice involves the assay of sera from mice immunized with serial dilutions of rabies vaccine. The amount of antibody in the sera is expressed in International Units per ml (IU/ml). Sera from identical dilutions of different vaccines are compared for potency with serum from the same dilution of U.S. Reference Rabies Vaccine. A "unit ratio" is calculated by dividing the serum potency value for the test vaccine by that for the reference vaccine at each dilution tested. This unit ratio may then be compared to the antigenic value generated by the NIH test performed on the same vaccines. In this study, results are reported for both duck embryo and human diploid cell culture vaccines using the Serum Neutralization Test in mice as well as the Rapid Fluorescent Focus Inhibition Test to assay the antisera. Correlations are presented between the unit ratio and antigenic value for all vaccines tested. Also, practical applications and limitations of the test are discussed.

Pyrogen reactions associated with the infusion of normal serum albumin (human).

In November, 1974, eight patients in three hospitals had pyrogen reactions associated with the infusion of 25% Normal Serum Albumin from the same lot. The reactions were recognized because the same physician or nurse observed several patients having recurrent reactions or because a single patient receiving several vials had consecutive reactions. The remaining albumin in three vials associated with reactions had apparent endotoxin concentrations of 4, 16, and 32 ng/ml and that 22 vials from recalled supplies had a median concentration of 4 ng/ml (range: 2 to 64) as determined by the Limulus amebocyte lysate test, but the lot again passed the rabbit pyrogen test. In a prospective study to determine the efficacy of the Limulus test in quality control, patients had their temperatures taken hourly during albumin infusions and the remaining fluid was tested by the Limulus assay. The albumin in 443 of the 662 vials infused (65%) gave a positive test and 311 of these vials (45%) had apparent endotoxin concentrations of 4 to 64 ng/ml, but no patient had a reaction. Because of the limitations of both the rabbit pyrogen and Limulus test, the detection of some pyrogenic lots continues to depend on hospital surveillance and reporting os suspect reactions.

Evaluation and control of vaccines for the National Influenza Immunization Program.

The National Influenza Immunization Program of 1976 offered an ideal opportunity to test the capability of the system in the United States for production and distribution of maximal amounts of inactivated influenza virus vaccine of carefully regulated quality. The four licensed manufacturers were able to produce and distribute greater than 10 million doses of vaccine per week over a 14-week period. Assays showed that the quality of these vaccines was comparable to or exceeded that of vaccines produced in recent years under less stressful circumstances. Because of the extensive clinical trials conducted as part of the program, it was possible to make an unprecedented evaluation of the significance of various laboratory tests of vaccines in relation to their pertinence in prediction of immunogenicity and reactivity for humans. This experience demonstrated the superiority of immunodiffusion methods as compared with the standard chick cell-agglutination method for assay of vaccine potency. Qualitative differences in immunogenicity between whole-virus and disrupted-virus vaccines were recognized that are not measured by in vitro potency tests. The results also indicated that influenza viral components are responsible for most febrile reactions to the vaccine.

Statistical determination of endotoxin content in influenza virus vaccine by the limulus amoebocyte lysate test.

To determine laboratory-to-laboratory variability of the limulus amoebocyte lysate (LAL) test for evaluating endotoxin content in influenza virus vaccine, a collaborative study was designed. Participants were six influenza virus vaccine manufacturers and the Bureau of Biologics (BoB). Lysate lot 116, Reference Influenza Virus Vaccine for Endotoxin Assay E-1, and four test vaccines having different ratios of LAL activity relative to reference E-1 were supplied by the BoB. Each laboratory used its normal test procedure. All vaccines were coded. One pair (reference and test) of vaccines per day was tested for 4 days a week over a 4-week period. All data were analyzed at the BoB. The degree of variability experienced by testing laboratories was estimated by the study. This estimate did not conflict with experience gained from previous routine testing in any of the participating laboratories. A statistical approach to the evaluation of LAL data from testing influenza virus vaccine for endotoxin content was developed based upon the overall variation obtained from the collaborative study.

Review of United States requirements for residual moisture in drugs.

Officially recognized procedures for residual moisture determinations on biological products are described. These include gravimetric at ambient temperature and thermogravimetric analysis at specified temperatures for specific products. The bases for selecting the optimum residual moisture for a new product are discussed and values established for currently licensed products are listed. Comparisons are made between the procedures and requirements for biological products and the water determinations specificed in U.S. Pharmacopeia XIX.

Parathyroid necrosis and hypocalcemic tetany induced in rabbits by L-asparaginase.

Fifty percent of New Zealand white rabbits became profoundly weak, had generalized seizures and died between 22 and 47 hours after an intravenous injection of 1000 IU/kg of L-asparaginase. The biochemical correlate of this syndrome is severe hypocalcemia associated with marked, single cell, oxyphilic necrosis in the parathyroid glands. Although survivors remained clinically well, they also developed hypocalcemia and parathyroid necrosis but to a lesser degree. Rabbits given an equivolumetric amount of saline did not develop alterations in any of these parameters. L-Asparaginase, therefore, exerts a direct toxic effect on the parathyroid glands of rabbits. The implications of this finding for man are briefly discussed.