Assessing local reactions and serum enzyme changes from intramuscular injections. A preliminary evaluation

A pilot clinical trial of a recombinant ricin vaccine in normal humans

Ricin, a highly potent toxin produced by castor beans, is classified by the Centers for Disease Control and Prevention as a level B biothreat because it is easily produced, readily available, and highly stable. There have been >750 cases of documented ricin intoxication in humans. There is no approved vaccine for ricin. Ricin contains a lectin-binding B chain and a ribotoxic A chain (RTA). In addition to its ribotoxic site, we have identified a separate site on RTA that is responsible for inducing vascular leak syndrome (VLS) in humans. We have generated a recombinant RTA with two amino acid substitutions that disrupt its ribotoxic site (Y80A) and its VLS-inducing site (V76M). This mutant recombinant RTA (named RiVax) was expressed and produced in Escherichia coli and purified. When RiVax was injected i.m. into mice it protected them against a ricin challenge of 10 LD50s. Preclinical studies in both mice and rabbits demonstrated that RiVax was safe. Based on these results, we have now conducted a pilot clinical trial in humans under an investigational new drug application submitted to the Food and Drug Administration. In this study, three groups of five normal volunteers were injected three times at monthly intervals with 10, 33, or 100 mug of RiVax. The vaccine was safe and elicited ricin-neutralizing Abs in one of five individuals in the low-dose group, four of five in the intermediate-dose group, and five of five in the high-dose group. These results justify further development of the vaccine.

Creatine kinase

Creatine kinase is present in significant concentrations in skeletal muscle and cardiac muscle and to a lesser extent in gastrointestinal tract and brain tissue. The enzyme has been purified from a variety of tissues and an examination of its kinetic and physical properties reveal that the enzyme consists of two subunits and can exist as three isoenzymes containing essential cysteine residues. These properties are important in understanding its stability, the assay conditions, and the techniques used to identify the different isoenzymes. The relationship between the properties and the determination of the enzyme in biological fluids will be a main thrust of the review. Creatine kinase activity in serum rises rapidly in conditions such as acute myocardial infarction and trauma to skeletal muscle. However, the interpretation of such increases is dependent upon a sound knowledge of the factors which influence both the total and isoenzyme activities. The nature of these factors will be discussed in detail.

The loss of creatine phosphokinase (CK) from intramuscular injection sites in rabbits. A predictive tool for local toxicity

The CK activity was measured in muscle tissue taken from the injected area (dorsal longissimus muscle) and the contralateral side of the injection site 72 hours after intramuscular injection into rabbits of 1 ml of different dilutions of propylene glycol or glycerol formal in distilled water or 0.9% saline. The total loss of CK activity from the injection site was calculated as the difference between the CK concentration in the normal muscle tissue and that of the injection site from the same animal. From the results the arbitrary amount of muscle tissue depleted of CK activity was further calculated and compared with the severity of the gross pathological findings. A large necrotic area at the injection site was present in all samples with more than 1 g of muscle tissue depleted of CK activity. Minor and probably acceptable pathological changes were found in samples with less than 1 g of muscle tissue depleted of CK activity. The local damaging effect of drug preparations for intramuscular use can thus be evaluated from the calculated amount of muscle tissue depleted of CK activity.

Effects of I.M. Injections on Serum Creatine Phosphokinase (CPK) Values in Dogs

Intramuscular injections of compounds of low irritancy (bicillin, valium, saline) were found to cause significant elevations in serum CPK in dogs. This route of treatment must therefore be avoided in clinical conditions where CPK values have diagnostic or prognostic importance.

A comparative study of serum creatine phosphokinase (CPK) activity in rabbits, pigs and humans after intramuscular injection of local damaging drugs

Serum creatine phosphokinase (CPK) activity has been determined before and after intramuscular injection of lidocaine, diazepam or saline in humans and lidocaine, diazepam, digoxin and saline in pigs and rabbits. Two ml volum of each of the drugs was given to humans as well as to the experimental animals. No changes in CPK activity were found after saline in humans or rabbits but a minor increase was demonstrated in pigs. A marked increase of CPK activity was demonstrated after lidocaine or diazepam in humans and after lidocaine, diazepam or digoxin in pigs and rabbits. Post mortem examination of the injection sites in the animals revealed extensive muscle tissue necrosis after lidocaine, diazepam and digoxin. No damage of the tissue was found after saline. CPK activity was also determined in rabbits receiving 2 ml of dilutions of diazepam in saline. The injection sites were examined post mortem. The CPK activity was increased in animals receiving 1:2 and 1:8 dilutions while a 1:20 dilution did not give rise to changes in the enzyme activity. The necrotic area diminished when diazepam was diluted and no pathological changes were found at the injection sites after the 1:20 dilution. Measuring the CPK activity in rabbits after an intramuscular injection seems to be a sensitive method for the determination of local toxicity.