CLINICAL PHARMACOLOGY
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 method1,2
(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 procedure2,3 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
sonorrhoeae
MIC
(mcg/mL) |
Disk diffusion (zone diameter mm) |
S |
I* |
R |
S |
I* |
R |
≤32 |
64 |
≥128 |
≥18 |
15-17 |
≤14 |
*The clinical effectiveness of spectinomycin for treating organisms that
produce intermediate results is unknown.
|
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 jag spectinomycin disk should provide the following zone diameters with the quality control strains:
Table 2: In Vitro Susceptibility Test Quality Control
Ranges for Spectinomycin
Organism |
MIC range
mcg/mL |
Disk Diffusion range (mm) |
N. gonorrhoeae
ATCC® 49226 |
8-32 |
23-29 |
ATCC = American Type Culture Collection
|
REFERENCE
1. Clinical and Laboratory Standards Institute. Methods for Dilution Antimicrobial
Susceptibility Tests for Bacteria that Grow Aerobically; Approved Standard -
8th ed. CLSI document M07-A8. (ISBN 1-56238-689-1). CLSI, 940 West Valley
Road, Suite 1400, Wayne, PA, 19087-1898 USA. 2009.
2. Clinical and Laboratory Standards Institute. Performance Standards for
Antimicrobial Susceptibility Testing; 21st Informational Supplement. CLSI
document M100-S21. (ISBN 1-56238-742-1). CLSI, 940 West Valley Road, Suite 1400,
Wayne, PA, 19087-1898 USA. 2011
3. Clinical and Laboratory Standards Institute. Performance Standards for
Antimicrobial Disk Susceptibility Tests; Approved Standard - 10fh ed. CLSI
document M02-A10. (ISBN 1-56238-688-3). CLSI, 940 West Valley Road, Suite 1400,
Wayne, PA, 19087-1898 USA. 2009.