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Penicillin G benzathine and penicillin G procaine have a low solubility and, thus, the drugs are slowly released from intramuscular injection sites. The drugs are hydrolyzed to penicillin G. This combination of hydrolysis and slow absorption results in blood serum levels much lower but more prolonged than other parenteral penicillins.
Intramuscular administration of 600,000 units of Bicillin C-R in adults usually produces peak blood levels of 1.0 to 1.3 units per mL within 3 hours; this level falls to an average concentration of 0.32 units per mL at 12 hours, 0.19 units per mL at 24 hours, and 0.03 units per mL at seven days.
Intramuscular administration of 1,200,000 units of Bicillin C-R in adults usually produces peak blood levels of 2.1 to 2.6 units per mL within 3 hours; this level falls to an average concentration of 0.75 units per mL at 12 hours, 0.28 units per mL at 24 hours, and 0.04 units per mL at seven days.
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 resulting in death of the bacterium.
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.
Beta-hemolytic streptococci (groups A, B, C, G, H, L and M)
Streptococcus pneumoniae (penicillin-susceptible isolates only)
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.
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 test method (broth or agar).10,11 The MIC should be interpreted according to the following criteria.
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 and penicillin G procaine 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)||Intermedi ate (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
βhemolytic streptococcus and have not been reported in 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
bThe lack of data precludes defining any other interpretive criteria than 'susceptible'.
Streptococcus pneumoniae (non-meningitis)
Interpretive Criteria for Penicillina
|≤ 2||Susceptible (S)|
|a Disc susceptibility testing of isolates of pneumococci is performed using 1 mcg oxacillin discs. Isolates with oxacillin zone sizes of ≥ 20 mm are susceptible to penicillin. For isolates with oxacillin zones of < 19 mm do not report penicillin as resistant without performing a penicillin MIC test.|
A report of Susceptible indicates that the antimicrobial is likely to inhibit growth of the pathogen if the antimicrobial compound reaches the concentrations at the infection site necessary to inhibit growth of the pathogen. A report of Intermediate indicates that the results should be considered equivocal, and, if the microorganism is not fully susceptible to alternative, clinically feasible drugs, the test should be repeated. This category implies possible clinical applicability in body sites where the drug product is physiologically concentrated or in situations where a high dosage of the drug can be used. This category also provides a buffer zone that prevents small uncontrolled technical factors from causing major discrepancies in interpretation. A report of Resistant indicates that the antimicrobial is not likely to inhibit growth of the pathogen if the antimicrobial compound reaches the concentrations usually achievable at the infection site; other therapy should be selected.
Standardized susceptibility test procedures 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)||Disk Diffusion (zone diameter in mm)|
|Streptococcus pneumoniae (ATCC®) 49619||0.25 - 1||24 -30|
10. Clinical and Laboratory Standards Institute. Methods for Dilution Antimicrobial Susceptibility Tests for Bacteria that Grow Aerobically; Approved Standard -9th ed. CLSI document M07-A9. CLSI, Wayne, PA, 2012.
11. Clinical and Laboratory Standards Institute, Performance Standards for Antimicrobial Susceptibility Testing; Twenty-Second Informational Supplement. CLSI document M100S22 CLSI, Wayne, PA, 2012.
12. CLSI. Performance Standards for Antimicrobial Disk Susceptibility Tests, Approved Standard – 11th ed. CLSI document M02-A11, 2012
Last reviewed on RxList: 10/29/2015
This monograph has been modified to include the generic and brand name in many instances.
Additional Bicillin CR Information
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