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TROBICIN Sterile Powder is rapidly absorbed after intramuscular injection. A single, two-gram injection produces peak serum concentrations averaging about 100 mcg/mL at one hour; a single, four-gram injection produces peak serum concentrations averaging 160 mcg/mL at two hours. Average serum concentrations of 15 mcg/mL for the two-gram dose and 31 mcg/mL for the four-gram dose were present eight hours after dosing.

Microbiology

Spectinomycin hydrochloride is an inhibitor of protein synthesis in the bacterial cell; the site of action is the 30S ribosomal subunit.

Definitive in vitro studies have shown no cross-resistance of N. gonorrhoeae between spectinomycin hydrochloride and penicillin. the antibiotic is not significantly bound to plasma protein.

The in vitro susceptibility of Neisseria gonorrhoeae to spectinomycin hydrochloride can be tested by dilution and diffusion techniques.

Dilution Techniques

Quantitative methods are used to determine antimicrobial minimum inhibitory concentrations (MICs). These MICs provide estimates of the susceptibility of bacteria to antimicrobial compounds. The MICs should be determined using a standardized procedure. Standardized procedures are based on dilution method^1,2 (broth, agar, or microdilution) or equivalent using standardized inoculum and concentrations of spectinomycin. The MIC values should be interpreted according to the criteria in Table 1.

Diffusion Techniques

Quantitative methods that require measurement of zone diameters also provide reproducible estimates of the susceptibility of bacteria to antimicrobial compounds. One such standardized procedure^2,3 requires the use of standardized inoculum concentrations. This procedure uses paper disks impregnated with 100 μg of spectinomycin to test the susceptibility of N. gonorrhoeae to spectinomycin. Interpretation involves correlation of the diameter obtained in the disk test with the MIC for spectinomycin. Reports from the laboratory providing results of the standard single-disk susceptibility test with a 100 μg spectinomycin disk should be interpreted according to the following criteria in Table 1.

Table 1 : Interpretive Criteria for Spectinomycin vs. Neisseria gonorrhoeae

Quality Control

Standardized susceptibility test procedures require the use of laboratory control microorganisms to monitor and ensure the accuracy and precision of the supplies and reagents used in the assay, and the techniques of the individuals performing the test. Standard spectinomycin powder should provide MIC values as given below. For the diffusion technique, the 100 μg spectinomycin disk should provide the following zone diameters with the quality control strains:

Table 2 : In Vitro Susceptibility Test Quality Control Ranges for Spectinomycin

REFERENCES

1. CLSI. Methods for Dilution Antimicrobial Susceptibility Tests for Bacteria That Grow Aerobically; Approved Standard- Eighth Edition. CLSI document M7-A8. Wayne, PA: Clinical and Laboratory Standards Institute; 2009.

2. CLSI. Performance Standards for Antimicrobial Susceptibility Testing; Nineteenth Informational Supplement. CLSI document M100-S20. Wayne, PA: Clinical and Laboratory Standards Institute; 2010.

3. CLSI. Performance Standards for Antimicrobial Disk Susceptibility Tests; Approved Standard – Tenth Edition. CLSI document M02-A10. Wayne, PA: Clinical and Laboratory Standards Institute; 2009.

Last reviewed on RxList: 12/12/2011
This monograph has been modified to include the generic and brand name in many instances.