Free carbenicillin is the predominant pharmacologically active fraction of Geocillin (carbenicillin indanyl sodium) . Carbenicillin exerts its antibacterial activity by interference with final cell wall synthesis of susceptible bacteria.
Geocillin (carbenicillin indanyl sodium) is acid stable, and rapidly absorbed from the small intestine following oral administration. It provides relatively low plasma concentrations of antibiotic
and is primarily excreted in the urine. After absorption, Geocillin (carbenicillin indanyl sodium) is rapidly
converted to carbenicillin by hydrolysis of the ester linkage. Following ingestion of a single 500 mg tablet of Geocillin (carbenicillin indanyl sodium) , a peak carbenicillin plasma concentration of approximately 6.5 mcg/ml is reached in 1 hour. About 30% of this dose is excreted in the urine unchanged within 12 hours, with another 6% excreted over the next 12 hours.
In a multiple dose study utilizing volunteers with normal renal function, the
following mean urine and serum levels of carbenicillin were achieved:
||Mean Urine Concentration of Carbenicillin
mcg/ml Hours After Initial Dose
||1 tablet q.6 hr
||2 tablets q.6 hr
|Mean serum concentrations of carbenicillin in this study for these dosages are:
||Mean Serum Concentration mcg/ml Hours After Initial Dose
||1 tablet q.6 hr
||2 tablets q.6 hr
The antibacterial activity of Geocillin (carbenicillin indanyl sodium) is due to its rapid conversion to carbenicillin
by hydrolysis after absorption. Though Geocillin (carbenicillin indanyl sodium) provides substantial in
vitro activity against a variety of both gram-positive and gram-negative
microorganisms, the most important aspect of its profile is in its antipseudomonal
and antiproteal activity. Because of the high urine levels obtained following
administration, Geocillin (carbenicillin indanyl sodium) has demonstrated clinical efficacy in urinary infections
due to susceptible strains of:
Morganella morganii (formerly Proteus morganii)
Providencia rettgeri (formerly Proteus rettgeri)
Enterococci (S. faecalis)
In addition, in vitro data, not substantiated by clinical studies, indicate the following pathogens to be usually susceptible to Geocillin (carbenicillin indanyl sodium) :
Staphylococcus species (nonpenicillinase producing)
Most Klebsiella species are usually resistant to the action of Geocillin (carbenicillin indanyl sodium) . Some strains of Pseudomonas species have developed resistance to carbenicillin.
Geopen (carbenicillin disodium) Susceptibility Powder or 100 g Geopen Susceptibility
Discs may be used to determine microbial susceptibility to Geocillin (carbenicillin indanyl sodium) using one
of the following standard methods recommended by the National Committee for Clinical Laboratory Standards:
M2-A3, “Performance Standards for Antimicrobial Disk Susceptibility Tests"
M7-A, “Methods for Dilution Antimicrobial Susceptibility Tests for Bacteria that Grow Aerobically"
M11-A, “Reference Agar Dilution Procedure for Antimicrobial Susceptibility Testing of Anaerobic Bacteria"
M17-P, “Alternative Methods for Antimicrobial Susceptibility Testing of Anaerobic Bacteria"
Tests should be interpreted by the following criteria:
||Disk Diffusion Zone diameter (mm)
|| ≥ 23
|| ≤ 17
|| ≥ 17
|| ≤ 13
||Dilution MIC ( g/ml) Moderately
|| ≤ 16
|| ≥ 64
|| ≤ 128
|| ≥ 156
Interpretations of susceptible, intermediate, and resistant correlate zone
size diameters with MIC values. A laboratory report of “susceptible"
indicates that the suspected causative microorganism most likely will respond to therapy with carbenicillin. A laboratory report of “resistant" indicates that the infecting microorganism most likely will not respond to therapy.
A laboratory report of “moderately susceptible" indicates that the microorganism is most likely susceptible if a high dosage of carbenicillin is used, or if the infection is such that high levels of carbenicillin may be attained as in urine. A report of “intermediate" using the disk diffusion method may be considered an equivocal result, and dilution tests may be indicated.