Geocillin, a semisynthetic penicillin, is the sodium salt of the indanyl ester of Geopen® (carbenicillin disodium). The chemical name is:

1-(5-Indanyl)-N-(2-carboxy-3,3-dimethyl-7-oxo-4-thia-1-aza-bicyclo[3.2.0]hept-6-yl)-2-phenylmalonamate monosodium salt.

The structural formula is:


The empirical formula is: C 26 H 25 N 2 NaO 6 S and mol. wt. is 516.55.

Geocillin tablets are yellow, capsule-shaped and film-coated, made of a white crystalline solid. Carbenicillin is freely soluble in water. Each Geocillin tablet contains 382 mg of carbenicillin, 118 mg of indanyl sodium ester. Each Geocillin tablet contains 23 mg of sodium.

Inert ingredients are: glycine; magnesium stearate and sodium lauryl sulfate. May also include the following: hydroxypropyl cellulose; hydroxypropyl methylcellulose; opaspray (which may include Blue 2 Lake, Yellow 6 Lake, Yellow 10 Lake, and other inert ingredients); opadry light yellow (which may contain D&C Yellow 10 Lake, FD&C Yellow 6 Lake and other inert ingredients); opadry clear (which may contain other inert ingredients).

Free carbenicillin is the predominant pharmacologically active fraction of Geocillin. Carbenicillin exerts its antibacterial activity by interference with final cell wall synthesis of susceptible bacteria.

Geocillin 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 is rapidly converted to carbenicillin by hydrolysis of the ester linkage. Following ingestion of a single 500 mg tablet of Geocillin, 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
        0-3   3-6 6-24  
1 tablet q.6 hr
        1130   352 292  
2 tablets q.6 hr
        1428   789 809  
Mean serum concentrations of carbenicillin in this study for these dosages are:
Mean Serum Concentration mcg/ml
Hours After Initial Dose
1 / 2  1  2  4  6  24  25  26  28
1 tablet q.6 hr
5.1 6.5 3.2 1.9 0.0 0.4  8.8  5.4 0.4
2 tablets q.6 hr
6.1 9.6 7.9 2.6 0.4 0.8 13.2 12.8 3.8


The antibacterial activity of Geocillin is due to its rapid conversion to carbenicillin by hydrolysis after absorption. Though Geocillin 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 has demonstrated clinical efficacy in urinary infections due to susceptible strains of:

   Escherichia coli

  Proteus mirabilis

  Proteus vulgaris

  Morganella morganii (formerly Proteus morganii )

  Pseudomonas species

  Providencia rettgeri (formerly Proteus rettgeri )

  Enterobacter species

  Enterococci (S. faecalis)

In addition, in vitro data, not substantiated by clinical studies, indicate the following pathogens to be usually susceptible to Geocillin:

  Staphylococcus species (nonpenicillinase producing)

  Streptococcus species


Most Klebsiella species are usually resistant to the action of Geocillin. Some strains of Pseudomonas species have developed resistance to carbenicillin.

Susceptibility Testing

Geopen (carbenicillin disodium) Susceptibility Powder or 100 ug Geopen Susceptibility Discs may be used to determine microbial susceptibility to Geocillin 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)
Intermed. Resist.
>/=23 18-22 </=17
Pseudomonas sp.
>/=17 14-16 </=13
MIC (µ/ml)
Suscept. Moderately
</=16 32 >/=64
Pseudomonas sp.
>/=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.

Geocillin (carbenicillin indanyl sodium) is indicated in the treatment of acute and chronic infections of the upper and lower urinary tract and in asymptomatic bacteriuria due to susceptible strains of the following organisms:

  Escherichia coli

  Proteus mirabilis

  Morganella morganii

    (formerly Proteus morganii )

  Providencia rettgeri

    (formerly Proteus rettgeri )

  Proteus vulgaris




Geocillin is also indicated in the treatment of prostatitis due to susceptible strains of the following organisms:

Escherichia coli

  Enterococcus (S. faecalis)

Proteus mirabilis

Enterobacter sp.


NOTE: Susceptibility testing should be performed prior to and during the course of therapy to detect the possible emergence of resistant organisms which may develop.


Geocillin is ordinarily contraindicated in patients who have a known penicillin allergy.

Serious and occasionally fatal hypersensitivity (anaphylactic) reactions have been reported in patients on oral penicillin therapy. Although anaphylaxis is more frequent following parenteral therapy, it has occurred in patients on oral penicillins. These reactions are more apt to occur in individuals with a history of penicillin hypersensitivity and/or a history of sensitivity to multiple allergens.

There have been reports of individuals with a history of penicillin hypersensitivity who have experienced severe hypersensitivity reactions when treated with a cephalosporin, and vice versa. Before initiating therapy with a penicillin, careful inquiry should be made concerning previous hypersensitivity reactions to penicillins, cephalosporins, or other allergens. If an allergic reaction occurs, the drug should be discontinued and the appropriate therapy instituted.



General:   As with any penicillin preparation, an allergic response, including anaphylaxis, may occur particularly in a hypersensitive individual.

Long term use of Geocillin may result in the overgrowth of nonsusceptible organisms. If superinfection occurs during therapy, appropriate measures should be taken.

Since carbenicillin is primarily excreted by the kidney, patients with severe renal impairment (creatinine clearance of less than 10 ml/min) will not achieve therapeutic urine levels of carbenicillin.

In patients with creatinine clearance of 10-20 ml/min it may be necessary to adjust dosage to prevent accumulation of drug.

Laboratory Tests:   As with other penicillins, periodic assessment of organ system function including renal, hepatic, and hematopoietic systems is recommended during prolonged therapy.

Drug Interactions:   Geocillin (carbenicillin indanyl sodium) blood levels may be increased and prolonged by concurrent administration of probenecid.

Carcinogenesis, Mutagenesis, Impairment of Fertility: There are no long-term animal or human studies to evaluate carcinogenic potential. Rats fed 250-1000 mg/kg/day for 18 months developed mild liver pathology (e.g., bile duct hyperplasia) at all dose levels, but there was no evidence of drug-related neoplasia. Geocillin administered at daily doses ranging to 1000 mg/kg had no apparent effect on the fertility or reproductive performance of rats.

Pregnancy Category B:   Reproduction studies have been performed at dose levels of 1000 or 500 mg/kg in rats, 200 mg/kg in mice, and at 500 mg/kg in monkeys with no harm to fetus due to Geocillin. There are, however, no adequate and well controlled studies in pregnant women. Because animal reproduction studies are not always predictive of human response, this drug should be used during pregnancy only if clearly needed.

Labor and Delivery: It is not known whether the use of Geocillin in humans during labor or delivery has immediate or delayed adverse effects on the fetus, prolongs the duration of labor, or increases the likelihood that forceps delivery or other obstetrical intervention or resuscitation of the newborn will be necessary.

Nursing Mothers:   Carbenicillin class antibiotics are excreted in milk although the amounts excreted are unknown; therefore, caution should be exercised if administered to a nursing woman.

Pediatric Use:   Since only limited clinical data is available to date in children, the safety of Geocillin administration in this age group has not yet been established.


The following adverse reactions have been reported as possibly related to Geocillin administration in controlled studies which include 344 patients receiving Geocillin.

Gastrointestinal:   The most frequent adverse reactions associated with Geocillin therapy are related to the gastrointestinal tract. Nausea, bad taste, diarrhea, vomiting, flatulence, and glossitis were reported. Abdominal cramps, dry mouth, furry tongue, rectal bleeding, anorexia, and unspecified epigastric distress were rarely reported.

Dermatologic:   Hypersensitivity reactions such as skin rash, urticaria, and less frequently pruritus.

Hematologic:   As with other penicillins, anemia, thrombocytopenia, leukopenia, neutropenia, and eosinophilia have infrequently been observed. The clinical significance of these abnormalities is not known.

Miscellaneous:   Other reactions rarely reported were hyperthermia, headache, itchy eyes, vaginitis, and loose stools.

Abnormalities of Hepatic Function Tests:   Mild SGOT elevations have been observed following Geocillin administration.


Geocillin is generally nontoxic. Geocillin when taken in excessive amounts may produce mild gastrointestinal irritation. The drug is rapidly excreted in the urine and symptoms are transitory. The usual symptoms of anaphylaxis may occur in hypersensitive individuals.

Carbenicillin blood levels achievable with Geocillin are very low, and toxic reactions as a function of overdosage should not occur systematically. The oral LD 50 in mice is 3,600 mg/ kg, in rats 2,000 mg/kg, and in dogs is in excess of 500 mg/kg. The lethal human dose is not known.

Although never reported, the possibility of accumulation of indanyl should be considered when large amounts of Geocillin are ingested. Free indole, which is a phenol derivative, may be potentially toxic. In general 8-15 grams of phenol, and presumably a similar amount of indole, are required orally before toxicity (peripheral vascular collapse) may occur. The metabolic by-products of indole are nontoxic. In patients with hepatic failure it may be possible for unmetabolized indole to accumulate.

The metabolic by-products of Geocillin, indanyl sulfate and glucuronide, as well as free carbenicillin, are dialyzable.


Geocillin is available as a coated tablet to be administered orally.

Usual Adult Dose

Escherichia coli, Proteus 1-2 tablets
  species, and Enterobacter 4 times daily
Pseudomonas and Enterococcus 2 tablets
4 times daily

Escherichia coli, Proteus 2 tablets
  mirabilis, Enterobacter and 4 times daily


Geocillin is available as film-coated tablets in bottles of 100's (NDC 0049-1430-66), and unit-dose packages of 100 (10 × 10's) (NDC 0049-1430-41). Each tablet contains carbenicillin indanyl sodium equivalent to 382 mg of carbenicillin.

Revised Sept. 1991       69-1970-00-2