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Chapter 20

Chapter 20

A Comparison of Antibiotic Concentrations in Plasma and Muscle

An Experimental Study

            Captain John D. Marshall, MSC, USAR
            First Lieutenant Joseph G. Strawitz, MC, USAR

Previous studies have demonstrated the bacterial flora of combat wounds,1, 2 the sensitivities of the anaerobic flora to antibiotics,3 and the plasma penicillin concentration in the combat casualties.4 The purpose of the present study has been to extend these observations in the laboratory to compare the concentrations of antibiotics in the plasma and muscle. The plasma level of any particular antibiotic has been known to be higher than the concentration in most organs which have been studied.4 Since the military surgeon is primarily interested in wound infection, this study was designed to compare the concentration in plasma with the concentration in skeletal muscles.

Materials and Methods

Rabbits, averaging 2 kilograms in weight, were selected as experimental animals. After having fasted for 24 hours, all four extremities were shaved. The appropriate antibiotic was then given intramuscularly or intravenously. The following large doses were used in order to facilitate analysis:

    Procaine penicillin: 30,000 units/kg. of body weight.
    Aureomycin HC1: 50 mg./kg.
    Terramycin HC1: 75 mg./kg. and 250 mg./kg.
    Chloramphenicol: 250 mg./kg.

Under ether anesthesia, and utilizing sterile surgical technic, blocks of skeletal muscle were taken from an extremity at hourly intervals for 4 or 5 hours. Simultaneously, heparinized blood samples were taken and the plasma was separated under sterile precautions. Care was taken not to excise muscle near the site of injection.

Maintaining sterile precautions, each block of excised muscle, weighing approximately 1 gram, was ground in the TenBrock tissue grinder. To each gram of tissue, 4 cc. of sterile saline was added, giving a dilution of 1:5. The suspension was transferred to a 15 cc.


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centrifuge tube and spun at 1,500 r. p. m. for 15 minutes. The plasma and the supernatant of the tissue suspension were aseptically transferred to sterile test tubes. The plasma was diluted with saline to final concentrations of 1:10 and 1:100. Petri dishes, 15 x 150 mm., containing a thin layer of blood agar, were streaked with an 18-hour broth culture of Shigella dysenteriae (ES110) for chloramphenicol and terramycin sensitivities and hemolytic Staphylococcus (Heatly strain) for the penicillin and aureomycin sensitivities. Nine stainless steel cylinders, measuring 10 mm. in height, with a 10 mm. inside diameter, were placed on the surface of the plate in three rows: 0.5 ml. amounts of undiluted 1:10 and 1:100 plasma respectively were placed in the upper row cups; 0.5 ml. amounts of saline containing 100, 10 and 1 micrograms respectively of the antibiotic standard were placed in the center row as controls. In the lower row, 0.5 ml. amounts of 1:5, 1:10 and 1:100 respectively of the diluted tissue extract were placed. The Petri dishes were then incubated at 37° C for 18 hours, after which time the zones of inhibition were measured and compared using the graph method.

Four animals were studied in each series.

Results

The average hourly antibiotic levels in blood and tissue of each determination on the four rabbits studied with each antibiotic are demonstrated in Figures 1 to 5.


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Penicillin

Following the intramuscular injection of penicillin, the tissue levels during the first and second hours after injection were approximately one-tenth the plasma level (Fig. 1).

FIGURE 1. This graph, representing the average of the four rabbits studied, demonstrates the low concentration of penicillin in the muscle. This probably reflects the rapid excretion of penicillin in the urine.


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Aureomycin

The intramuscular injection of aureomycin resulted in a tissue level which was approximately 70 per cent of the plasma level at 1 hour, 80 per cent of the plasma level at 2 hours, and then equaled or surpassed the plasma concentration (Fig. 2).

FIGURE 2. Since aureomycin is more slowly excreted, the plasma and tissue levels equilibrate at a high tissue concentration.


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Terramycin

Following the intramuscular injection of terramycin (250 mg./kg.), the muscle concentration rose to 90 per cent of the plasma concentration and remained at this relative level throughout the 4-hour period of study (Fig. 3).

FIGURE 3. This graph, representing the average values of four experiments, demonstrates that following its injection intramuscularly the concentration of terramycin in muscle approximates the plasma concentration throughout the 4-hour period.


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The intravenous injection of terramycin (75 mg./kg.) resulted in an immediate increase in the serum concentration so that at 1 hour the serum to muscle ratio was 2:1. Thereafter the serum concentration rapidly fell whereas the tissue concentration remained almost constant (Fig. 4).

FIGURE 4. Throughout a period of 4 hours the average concentration in muscle of these four animals was over 200 per cent higher than in the preceding four who received the antibiotic intramuscularly.


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Chloramphenicol

Chloramphenicol, intramuscularly, resulted in a muscle concentration of the antibiotic which ranged between 60 and 90 per cent of the plasma concentration for the first 3 hours and equaled the plasma concentration at the fourth hour (Fig. 5).

FIGURE 5. Demonstrating the close approximation of the muscle and plasma concentrations of chloramphenicol following its intramuscular injection.


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Discussion

The value of a high, sustained concentration of antibiotics in the muscles has not been conclusively demonstrated but would appear a desirable goal of therapy. Penicillin is rapidly excreted in the urine,6 and this is probably the explanation of its low concentration in the muscle. These assays were performed on healthy muscle which had not been previously traumatized by injury or infection. It is probable that the inflammatory response to injury would result in a higher concentration of antibiotics in injured muscle.5, 7 Nevertheless, the rapid excretion and low muscle concentration of penicillin again raises a question as to whether, in the treatment of combat casualties, primary reliance should be placed on penicillin for antibiotic coverage. This question becomes even more acute when the possibility of mass casualties from atomic warfare is considered. Under such conditions, débridement might have to be postponed indefinitely and the role of antibiotic therapy would assume greater importance.

References

1. Wetzler, T. F., Marshall, J. D., Newton, A., Lindberg, R. B., Strawitz, J. G., and Howard, J. M.: The Bacterial Flora of Battle Wounds at the Time of Primary Débridement. A Study of the Korean Battle Casualty. Submitted for Publication.

2. Strawitz, J. G., Wetzler, T. F., Marshall, J. D., Lindberg, R. B., Howard, J. M., and Artz, C. P.: The Bacterial Flora of Healing Wounds: A Study of the Korean Battle Casualty. Submitted for Publication.

3. Newton, A., Strawitz, J. G., Lindberg, R. B., Howard, J. M., and Artz, C. P.: Sensitivities of Ten Species of Clostridia to Penicillin, Aureomycin, Terramycin, and Chloramphenicol. Surgery 37: 392, 1955. (Chapter 16 in Volume III of this series.)

4. Strawitz, J. F., Li, K., Lindberg, R. B., Newton, A., Howard, J. M., and Artz, C. P.: The Plasma Concentration of Penicillin in Korean Battle Casualties. Submitted for Publication.

5. Ungar, J.: Penicillin in Tissue Exudates After Injection. Lancet 1:56, 1950.

6. Harries, E. H. R., and Mitman, M.: Clinical Practice in Infectious Diseases. E. and S. Livingstone, Ltd., Edinburgh, 1951.

7. Altemeier, W. A., Coith, R. L., and Culbertson, W. R.: Parenteral and Intestinal Absorption of Antibiotics in Traumatic Shock. Arch. Surg. 63: 403, 1951.

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