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Bicillin L-A Inj / Tubex

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Bicillin L-A Injectable in Tubex



Penicillin G benzathine has an extremely low solubility and, thus, the drug is slowly released from intramuscular injection sites. The drug is hydrolyzed to penicillin G. This combination of hydrolysis and slow absorption results in blood serum levels much lower but much more prolonged than other parenteral penicillins.

Intramuscular administration of 300,000 units of penicillin G benzathine in adults results in blood levels of 0.03 to 0.05 units per mL, which are maintained for 4 to 5 days. Similar blood levels may persist for 10 days following administration of 600,000 units and for 14 days following administration of 1,200,000 units. Blood concentrations of 0.003 units per mL may still be detectable 4 weeks following administration of 1,200,000 units.

Approximately 60% of penicillin G is bound to serum protein. The drug is distributed throughout the body tissues in widely varying amounts. Highest levels are found in the kidneys with lesser amounts in the liver, skin, and intestines. Penicillin G penetrates into all other tissues and the spinal fluid to a lesser degree. With normal kidney function, the drug is excreted rapidly by tubular excretion. In neonates and young infants and in individuals with impaired kidney function, excretion is considerably delayed.


Mechanism of Action

Penicillin G exerts a bactericidal action against penicillin-susceptible microorganisms during the stage of active multiplication. It acts through the inhibition of biosynthesis of cell-wall peptidoglycan, rendering the cell wall osmotically unstable.

Mechanism of Resistance

Penicillin is not active against penicillinase-producing bacteria or against organisms resistant to beta-lactams because of alterations in the penicillin-binding proteins. Resistance to penicillin G has not been reported in Streptococcus pyogenes.

Penicillin has been shown to be active against most isolates of the following bacteria, both in vitro and in clinical infections as described in the INDICATIONS AND USAGE section.

Gram-positive bacteria

Beta-hemolytic streptococci (groups A, B, C, G, H, L and M)

Other microorganisms

Treponema pallidum
Treponema carateum

Susceptibility Test Methods

When available, the clinical microbiology laboratory should provide the results of in vitro susceptibility test results for antimicrobial drug products used in resident hospitals to the physician as periodic reports that describe the susceptibility profile of nosocomial and community-acquired pathogens. These reports should aid the physician in selecting an antibacterial drug product for treatment.

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.10,11 The MIC values should be interpreted according to the following criteria:

Diffusion techniques

Quantitative methods that require the measurement of zone diameters can also provide reproducible estimates of the susceptibility of bacteria to antimicrobial compounds. The zone size provides an estimate of the susceptibility of bacteria to antimicrobial compounds. The zone size should be determined using a standardized test method.11,12 This procedure uses paper discs impregnated with 10 units penicillin to test the susceptibility of microorganisms to penicillin G benzathine injectable solution. The disc diffusion interpretive criteria are provided in the table below.

Streptococcus pyogenes (Group A)

Susceptibility Test Interpretive Criteria for Penicillin

Pathogen MIC (mcg/mL) Disk Diffusion (zone diameter in mm)
Susceptible (S) Intermediate (I) Resistant (R) Susceptible (S) Intermediate (I) Resistant (R)
Streptococcus pyogenesa,b ≤ 0.12 - - ≥ 24 - -
aSusceptibility testing of penicillins for treatment of β-hemolytic streptococcal infections need not be performed routinely, because non-susceptible isolates are extremely rare in any β-hemolytic streptococcus and have not been reported from Streptococcus pyogenes. Any β -hemolytic streptococcal isolate found to be non-susceptible to penicillin should be re-identified, retested, and, if confirmed, submitted to a public health authority. 10,11
The lack of data precludes defining any other interpretive criteria than 'susceptible'.

Quality Control

Standardized susceptibility test procedure require the use of laboratory controls 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.10,11,12 Standard penicillin powder should provide the range of MIC values noted in the following table . For the diffusion technique using the 10 unit penicillin disc, the criteria in the following table should be achieved. Acceptable Quality Control Ranges for Penicillin

QC Strain MIC (mcg/ml) Disc Diffusion (zone diameter in mm)
Streptococcus pneumoniae ATCC 49619 0.25-1 24 -30
ATCC = American Type Culture Collection


10. Clinical and Laboratory Standards Institute (CLSI). Methods for Dilution Antimicrobial Susceptibility Tests for Bacteria that Grow Aerobically; Approved Standard -9TH ed. CLSI document M07-A9. CLSI, 950 West Valley Rd., Suite 2500, Wayne, PA 19087, 2012

11. CLSI. Performance Standards for Antimicrobial Susceptibility Testing; 22ND Informational Supplement. CLSI document M100-S22, 2012.

12. CLSI. Performance Standards for Antimicrobial Disk Susceptibility Tests, Approved Standard – 11th ed. CLSI document M02-A11, 2012

Last reviewed on RxList: 10/22/2012
This monograph has been modified to include the generic and brand name in many instances.


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