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Imipenem/Cilastatin (Monograph)

Brand name: Primaxin
Drug class: Carbapenems
Chemical name: [5R-[5α,6α(R*)]]-6-(1-Hydroxyethyl)-3-[[2-(iminomethyl)amino]ethyl]thio]-7-oxo-1-azabicyclo[3.2.0]hept-2-ene-2carboxylic acid monohydrate mixt. with [R-[R*,S*-(Z)]]-7-[(2-Amino-2-carboxyethyl)thio]-2-[[(2,2-dimethylcyclopropyl) carbonyl]amino]-2-heptenoic acid monosodium salt
Molecular formula: C12H17N3O4S•H2
CAS number: 92309-29-0

Medically reviewed by on Dec 14, 2021. Written by ASHP.


Antibacterial; fixed combination of imipenem (a carbapenem β-lactam antibiotic) and cilastatin (a renal dehydropeptidase inhibitor that prevents renal metabolism of imipenem).

Uses for Imipenem/Cilastatin

Bone and Joint Infections

Treatment of serious bone and joint infections caused by susceptible Staphylococcus aureus (penicillinase-producing strains), S. epidermidis, Enterococcus faecalis, Enterobacter, or Pseudomonas aeruginosa.


Has been used for treatment of endocarditis caused by susceptible S. aureus (penicillinase-producing strains). Not included in AHA guidelines for treatment of staphylococcal endocarditis in adults or pediatric patients.

Gynecologic Infections

Treatment of gynecologic infections (including mixed aerobic-anaerobic infections) caused by susceptible S. aureus (penicillinase-producing strains), S. epidermidis, S. agalactiae (group B streptococci), E. faecalis, Enterobacter, E. coli, Gardnerella vaginalis, Klebsiella, Proteus, Bacteroides (including B. fragilis), Bifidobacterium, Peptococcus, Peptostreptococcus, or Propionibacterium.

Intra-abdominal Infections

Treatment of intra-abdominal infections (including mixed aerobic-anaerobic infections) caused by susceptible S. aureus (penicillinase-producing strains), S. epidermidis, E. faecalis, Citrobacter, Enterobacter, E. coli, Klebsiella, Morganella morganii, Proteus, Ps. aeruginosa, Bacteroides (including B. fragilis), Bifidobacterium, Clostridium, Eubacterium, Fusobacterium, Peptococcus, Peptostreptococcus, or Propionibacterium. .

Respiratory Tract Infections

Treatment of lower respiratory tract infections caused by susceptible S. aureus (penicillinase-producing strains), Haemophilus influenzae, H. parainfluenzae, Acinetobacter, Enterobacter, E. coli, Klebsiella, or Serratia marcescens.

ATS and IDSA state that imipenem and cilastatin (imipenem/cilastatin) is one of several options that can be included in empiric treatment regimens to provide coverage against Ps. aeruginosa in hospitalized patients with community-acquired pneumoniae (CAP) who are at risk for Ps. aeruginosa infections (e.g., those with prior Ps. aeruginosa infections, hospitalization and treatment with parenteral anti-infectives in the last 90 days).

Has been recommended as one of several options for initial empiric treatment in certain patients with hospital-acquired pneumonia and ventilator-associated pneumonia.


Treatment of septicemia caused by susceptible S. aureus (penicillinase-producing strains), E. faecalis, Enterobacter, E. coli, Klebsiella, Serratia, Ps. aeruginosa, or Bacteroides (including B. fragilis).

Skin and Skin Structure Infections

Treatment of serious skin and skin structure infections caused by susceptible S. aureus (penicillinase-producing strains), S. epidermidis, E. faecalis, Acinetobacter, Citrobacter, Enterobacter, E. coli, Klebsiella, M. morganii, P. vulgaris, P. rettgeri, Serratia or Ps. aeruginosa.

Treatment of serious skin and skin structure infections caused by susceptible Bacteroides (including B. fragilis), Fusobacterium, Peptococcus, or Peptostreptococcus.

Urinary Tract Infections (UTIs)

Treatment of complicated and uncomplicated UTIs caused by susceptible S. aureus (penicillinase-producing strains), E. faecalis, Enterobacter, E. coli, Klebsiella, M. morganii, P. vulgaris, Providencia rettgeri, or Ps. aeruginosa.

Burkholderia Infections

Has been used for treatment of localized or septicemic melioidosis [off-label], a potentially life-threatening disease caused by Burkholderia pseudomallei. Ceftazidime or meropenem usually drugs of choice for treatment of melioidosis. B. pseudomallei is difficult to eradicate (relapse of melioidosis is common).

Treatment of glanders [off-label] caused by B. mallei. Optimum regimens not identified; imipenem/cilastatin is recommended as one option for treatment of nodular skin and mucous membrane lesions caused by B. mallei based on results of in vitro susceptibility testing.

Mycobacterial Infections

Recommended by ATS, CDC, IDSA, WHO, and others as a possible option for inclusion in multiple-drug regimens used for treatment of multidrug-resistant (MDR) tuberculosis [off-label] (i.e., caused by Mycobacterium tuberculosis resistant to isoniazid and rifampin). If a carbapenem (e.g., imipenem/cilastatin) used in such regimens, these experts state that the fixed combination of amoxicillin and clavulanate (amoxicillin/clavulanate) should be administered with the carbapenem. Patients with MDR tuberculosis are at high risk for treatment failure and acquisition of further drug resistance; such patients should be referred to or consultation should be obtained from a specialized treatment center as identified by local or state health departments or the CDC.

Recommended by ATS, IDSA, and others as one of several preferred options for inclusion in multiple-drug regimens used for treatment of pulmonary infections caused by M. abscessus [off-label].

Nocardia Infections

Treatment of infections caused by Nocardia [off-label], including pulmonary nocardiosis caused by N. asteroides and primary cutaneous nocardiosis. Co-trimoxazole or a sulfonamide alone usually recommended for Nocardia infections; alternatives include a fluoroquinolone or a carbapenem. Multiple-drug regimens may be required.

Rhodococcus Infections

Has been used for treatment of infections caused by Rhodococcus equi; used in conjunction with other anti-infectives (e.g., vancomycin). Optimum regimens not identified; multiple-drug regimens usually recommended and prolonged treatment may be required.

Empiric Therapy in Febrile Neutropenic Patients

Has been used for empiric anti-infective therapy of presumed bacterial infections in febrile neutropenic patients. Used alone or in conjunction with other anti-infectives.

Imipenem/Cilastatin Dosage and Administration


Administer by IV infusion.

IV Infusion

Available as powder containing a mixture of imipenem and cilastatin (imipenem/cilastatin) that must be reconstituted and diluted prior to IV infusion.

For solution and drug compatibility information, see Compatibility under Stability.

Do not admix with other antibacterials.

Reconstitution and Dilution

Reconstitute single-dose vials containing 250 mg of imipenem and 250 mg of cilastatin or single-dose vials containing 500 mg of imipenem and 500 mg of cilastatin by adding approximately 10 mL of compatible IV solution to provide a suspension and shake well. Suspension should appear colorless to yellow; variations in color do not affect potency.

Dilute the suspension by transferring into 100 mL of a compatible IV solution. To ensure complete transfer of vial contents, add an additional 10 mL from the IV solution container to the vial and transfer back into the IV solution container. Agitate diluted solution until clear.

Rate of Administration

Rate of IV infusion depends on dose of imipenem (given as imipenem/cilastatin). If nausea occurs during administration, may decrease rate of IV infusion.

Imipenem doses ≤500 mg: Administer by IV infusion over 20–30 minutes.

Imipenem doses >500 mg: Administer by IV infusion over 40–60 minutes.


Available as preparations containing imipenem monohydrate and cilastatin sodium; dosage usually expressed in terms of the imipenem content (as anhydrous imipenem).

Pediatric Patients

Dosage of imipenem (given as imipenem/cilastatin) recommended in pediatric patients is based on age.

General Dosage for Neonates

Neonates <1 week of age weighing ≥1.5 kg: 25 mg/kg every 12 hours.

Neonates 1–4 weeks of age weighing ≥1.5 kg: 25 mg/kg every 8 hours.

General Dosage for Infants and Children

Infants 1–3 months of age weighing ≥1.5 kg: 25 mg every 6 hours.

Children ≥3 months of age: 15–25 mg/kg every 6 hours.


Dosage of imipenem (given as imipenem/cilastatin) recommended in adults is based on imipenem susceptibility of the suspected or confirmed causative organism(s) and the patient's renal function.

Infections Suspected or Proven to be Caused by Susceptible Bacteria

Adults with Clcr ≥90 mL/minute: 500 mg every 6 hours or 1 g every 8 hours.

Infections Suspected or Proven to be Caused by Bacteria with Intermediate Susceptibility

Adults with Clcr ≥90 mL/minute: 1 g every 6 hours.

Empiric Therapy in Febrile Neutropenic Patients†

500 mg every 6 hours (1 g daily) has been recommended.

Prescribing Limits

Pediatric Patients


4 g daily.



4 g daily.

Special Populations

Renal Impairment

Infections in Adults with Clcr <90 mL/minute

Dosage of imipenem (given as imipenem/cilastatin) must be reduced in adults with Clcr <90 mL/minute. (See Table 1.)

Calculate Clcr based on the Cockcroft-Gault method.

Patients with Clcr 15 to <30 mL/minute may be at increased risk of seizures.

Table 1. Dosage of Imipenem for Adults with Clcr <90 mL/minute15

Imipenem Susceptibility

Clcr 60 to <90 mL/minute

Clcr 30 to <60 mL/minute

Clcr 15 to <30 mL/minute

Infections suspected or proven to be caused by susceptible bacteria

400 mg every 6 hours OR 500 mg every 6 hours

300 mg every 6 hours OR 500 mg every 8 hours

200 mg every 6 hours OR 500 mg every 12 hours

Infections suspected or proven to be caused by bacteria with intermediate susceptibility

750 mg every 8 hours

500 mg every 6 hours

500 mg every 12 hours

Do not use in those with Clcr <15 mL/minute unless hemodialysis is initiated within 48 hours.

Patients receiving hemodialysis: Use only if benefits outweigh potential risk for seizures. (See CNS Effects and Seizure Potential under Cautions.) If used in patients with Clcr <15 mL/minute undergoing hemodialysis, use dosage recommended for patients with Clcr 15 to <30 mL/minute (see Table 1). Both imipenem and cilastatin are removed by hemodialysis; administer after hemodialysis and at intervals timed from the end of that hemodialysis session. Carefully monitor dialysis patients during imipenem/cilastatin treatment, especially those with underlying CNS disease.

Patients receiving peritoneal dialysis: Manufacturer states information insufficient to recommend use in such patients.

Infections in Pediatric Patients with Renal Impairment

Not recommended in pediatric patients weighing <30 kg with impaired renal function.

Geriatric Patients

No dosage adjustments except those related to renal impairment. (See Renal Impairment under Dosage and Administration.)

Cautions for Imipenem/Cilastatin


  • Hypersensitivity to any ingredient in the formulation.


Sensitivity Reactions

Hypersensitivity Reactions

Serious and occasionally fatal hypersensitivity reactions (e.g., anaphylaxis) reported with β-lactams. More likely to occur in individuals with a history of sensitivity to multiple allergens.

If hypersensitivity occurs, immediately discontinue imipenem/cilastatin; serious anaphylactic reactions require immediate emergency treatment as clinically indicated.


Partial cross-allergenicity among β-lactam antibiotics, including penicillins, cephalosporins, and other β-lactams.

Prior to initiation of imipenem/cilastatin, make careful inquiry concerning previous hypersensitivity reactions to imipenem, cephalosporins, penicillins, other β-lactams, or other allergens.

CNS Effects and Seizure Potential

Seizures and other CNS effects (e.g., confusional states, myoclonic activity) have occurred, especially when recommended dosage exceeded. Reported most frequently in those with CNS disorders (e.g., brain lesions, history of seizures) and/or renal impairment, but also reported in patients with no recognized or documented underlying CNS disorder or renal impairment.

Continue anticonvulsant therapy in those with known seizure disorders. If focal tremors, myoclonus, or seizures occur, evaluate the patient neurologically, initiate anticonvulsant therapy if necessary, and determine whether imipenem dosage should be decreased or the drug discontinued. Do not exceed recommended dosage, especially in those with known factors that predispose to seizures.

Patients with Clcr <30 mL/minute are at increased risk of seizures during imipenem/cilastatin treatment; do not use in those with Clcr <15 mL/minute unless hemodialysis is initiated within 48 hours. For patients undergoing hemodialysis, use only if benefits outweigh potential risk of seizures.

Potential for seizures may be increased if imipenem/cilastatin is used in patients receiving valproic acid or divalproex; concomitant use generally not recommended. (See Specific Drugs and Laboratory Tests under Interactions.)

Superinfection/Clostridioides difficile-associated Colitis

Possible emergence and overgrowth of nonsusceptible organism. Careful observation of the patient is essential. Institute appropriate therapy if superinfection occurs.

Treatment with anti-infectives alters normal colon flora and may permit overgrowth of Clostridioides difficile (formerly Clostridium difficile). C. difficile infection (CDI) and C. difficile-associated diarrhea and colitis (CDAD; also known as antibiotic-associated diarrhea and colitis or pseudomembranous colitis) reported with nearly all anti-infectives, including imipenem/cilastatin, and may range in severity from mild diarrhea to fatal colitis. C. difficile produces toxins A and B which contribute to development of CDAD; hypertoxin-producing strains of C. difficile are associated with increased morbidity and mortality since they may be refractory to anti-infectives and colectomy may be required.

Consider CDAD if diarrhea develops during or after therapy and manage accordingly. Obtain careful medical history since CDAD may occur as late as 2 months or longer after anti-infective therapy is discontinued.

If CDAD is suspected or confirmed, discontinue anti-infectives not directed against C. difficile whenever possible. Initiate appropriate anti-infective therapy directed against C. difficile (e.g., fidaxomicin, vancomycin, metronidazole), supportive therapy (e.g., fluid and electrolyte management, protein supplementation), and surgical evaluation as clinically indicated.

Ps. aeruginosa Infections

Because resistant strains of Ps. aeruginosa have emerged during imipenem /cilastatin therapy, most clinicians recommend that an aminoglycoside be used concomitantly whenever the drug is used in the treatment of serious infections known or suspected to be caused by Ps. aeruginosa.

Meningitis and Other CNS Infections

Safety and efficacy for treatment of meningitis not established; not indicated in patients with meningitis. High incidence of seizures reported in children 3 months to 12 years of age who received the drug for empiric treatment of bacterial meningitis.

Selection and Use of Anti-infectives

To reduce development of drug-resistant bacteria and maintain effectiveness of imipenem/cilastatin and other antibacterials, use only for treatment of infections proven or strongly suspected to be caused by susceptible bacteria. Prescribing imipenem/cilastatin in the absence of proven or strongly suspected bacterial infection unlikely to provide benefit to the patient and increases risk of development of drug-resistant bacteria.

When selecting or modifying anti-infective therapy, use results of culture and in vitro susceptibility testing. In the absence of such data, consider local epidemiology and susceptibility patterns when selecting anti-infectives for empiric therapy.

Information on test methods and quality control standards for in vitro susceptibility testing of antibacterial agents and specific interpretive criteria for such testing recognized by FDA is available at [Web]. For most antibacterials, including imipenem/cilastatin, FDA recognizes the standards published by the Clinical and Laboratory Standards Institute (CLSI).

Laboratory Monitoring

Periodically assess organ system functions, including renal, hepatic, and hematopoietic, during prolonged therapy.

Sodium Content

Preparations of imipenem/cilastatin contain approximately 1.6 mEq (37.5 mg) of sodium per 500 mg of imipenem.

Specific Populations


Data available from small numbers of postmarketing cases of imipenem/cilastatin use during pregnancy are insufficient to identify any drug-associated risks for major birth defects, miscarriage, or adverse maternal or fetal outcomes.

Developmental toxicity studies in animals (mice, rats, rabbits, monkeys) using imipenem and cilastatin (alone or in combination) administered at doses 0.4–2.9 times the recommended human dose (based on body surface area) showed no evidence of drug-induced fetal malformations. Embryofetal development studies using imipenem/cilastatin in cynomolgus monkeys at doses similar to the recommended human dose (based on body surface area) showed an increase in embryonic loss.


Imipenem is distributed into milk. Data insufficient regarding presence of imipenem and cilastatin in human milk; data not available on possible effects on the breast-fed child or effects on milk production.

Consider benefits of breast-feeding along with importance of imipenem/cilastatin to the woman; also consider potential adverse effects on breast-fed child from the drug or underlying maternal condition.

Pediatric Use

Use of imipenem/cilastatin in pediatric patients is supported by evidence from adequate and well-controlled trials of the drug in adults and clinical studies in pediatric patients.

Imipenem/cilastatin not recommended in pediatric patients weighing <30 kg with renal impairment; data not available for such patients.

Because of risk of seizures, imipenem/cilastatin not recommended in pediatric patients with CNS infections.

Diluents containing benzyl alcohol should not be used to reconstitute imipenem/cilastatin for administration to neonates; injections preserved with benzyl alcohol have been associated with toxicity in neonates. While toxicity has not been demonstrated in pediatric patients >3 months of age, small pediatric patients in this age range may also be at risk for benzyl alcohol toxicity.

Geriatric Use

No overall differences in safety and efficacy relative to younger adults, but increased sensitivity cannot be ruled out.

Substantially eliminated by kidneys; risk of toxicity may be greater in patients with impaired renal function. Because geriatric patients are more likely to have decreased renal function, select dosage with caution; it may be useful to assess renal function periodically.

Dosage adjustments not required based on age; adjust dosage based on renal function. (See Renal Impairment under Dosage and Administration.)

Renal Impairment

Half-lives of both imipenem and cilastatin prolonged in patients with impaired renal function.

Patients with renal impairment are at increased risk for adverse CNS effects (e.g., seizures), especially if usual dosage exceeded. Patients with Clcr <15 mL/minute should not receive imipenem/cilastatin unless hemodialysis is instituted within 48 hours. Do not use in patients undergoing hemodialysis unless benefits outweigh possible risk of drug-induced seizures. Monitor closely for adverse CNS effects (e.g., confusion, myoclonic activity, seizures), especially in those with CNS disease.

Dosage must be adjusted in adults with Clcr <90 mL/minute. (See Renal Impairment under Dosage and Administration.)

Common Adverse Effects

Adults: Most common adverse effects (>0.2%) include local reactions at the IV infusion site (phlebitis, pain, erythema, vein induration), GI effects (nausea, diarrhea, vomiting), rash, pruritus, urticaria, fever, hypotension, seizures, dizziness, somnolence.

Pediatric patients ≥3 months of age: Most common adverse effects (>1%) include diarrhea, gastroenteritis, vomiting, IV site irritation, phlebitis, rash, urine discoloration.

Neonates and infants <3 months of age: Most common adverse effects (>1%) include convulsions, diarrhea, oliguria/anuria, oral candidiasis, rash, tachycardia.

Interactions for Imipenem/Cilastatin

Specific Drugs and Laboratory Tests

Drug or Test




In vitro evidence of additive or synergistic antibacterial effects against E. faecalis, S. aureus, and Listeria monocytogenes

β-Lactam anti-infectives

In vitro evidence of antagonism with other β-lactam anti-infectives against Enterobacteriaceae and Ps. aeruginosa

Clinical importance unclear; probably should not be used in conjunction with other β-lactam anti-infectives


In vitro evidence of antagonism with chloramphenicol against K. pneumoniae

If used concomitantly, consider administering chloramphenicol a few hours after imipenem


In vitro evidence of synergistic antibacterial effect against Nocardia asteroides

Clinical importance unclear


Generalized seizures reported with concomitant use

Do not use concomitantly unless potential benefits outweigh possible risks


Increased plasma concentrations and half-life of imipenem

Concomitant use not recommended

Tests for glucose

Possible false-positive reactions in urine glucose tests using Clinitest, Benedict’s solution, or Fehling’s solution

Use glucose tests based on enzymatic glucose oxidase reactions (e.g., Clinistix, Tes-Tape)

Valproic acid, divalproex

Concomitant use with carbapenems, including imipenem/cilastatin, has resulted in decreased valproic acid concentrations, which may fall below therapeutic range and increase risk of breakthrough seizures

Concomitant use generally not recommended; if seizures are well-controlled on valproic acid or divalproex, consider antibacterials other than carbapenems; if concomitant use necessary, consider supplemental anti-convulsant therapy

Imipenem/Cilastatin Pharmacokinetics


Neither imipenem nor cilastatin appreciably absorbed from GI tract; must be given parenterally.

Plasma Concentrations

Following a 500-mg or 1-g dose of imipenem (given as imipenem/cilastatin by IV infusion over 20 minutes), peak plasma concentrations of imipenem antimicrobial activity range from 21–58 or 41–83 mcg/mL, respectively, and decline to ≤1 mcg/mL at 4–6 hours after the dose. Peak plasma concentrations of cilastatin are 31–49 mcg/mL after the 500-mg dose and 56–88 mcg/mL after the 1-g dose.

No accumulation of imipenem or cilastatin occurs following multiple doses in patients with normal renal function.



Following IV administration, imipenem distributed into saliva, sputum, aqueous humor, bone, bile, reproductive organs, myometrium, endometrium, heart valve, intestine, and pleural, interstitial, blister, and wound fluids.

Only low imipenem concentrations distribute into CSF following IV administration.

Both imipenem and cilastatin cross the placenta and are distributed into cord blood and amniotic fluid. Imipenem is distributed into milk.

Plasma Protein Binding

Imipenem: 13–21%.

Cilastatin: Approximately 40%.



If imipenem is administered alone, the drug is partially hydrolyzed in kidneys by dehydropeptidase I (DHP I) to a microbiologically inactive metabolite. Concurrent administration of cilastatin (a renal dehydropeptidase inhibitor) prevents metabolism of imipenem by DHP I.

Imipenem also is metabolized to some extent by a nonrenal mechanism unrelated to DHP I to an inactive metabolite identical to that formed by renal DHP I; this nonspecific hydrolysis is unaffected by concurrent administration of cilastatin.

Cilastatin is partially metabolized in the kidneys to N-acetylcilastatin, which also is an effective inhibitor of DHP I.

Elimination Route

Imipenem, cilastatin, and their metabolites eliminated principally in urine.

Both imipenem and cilastatin are removed by hemodialysis;


IV imipenem in adults with normal renal function: Distribution half-life averages 0.23–0.31 hours and elimination half-life averages 0.85–1.35 hours.

IV cilastatin in adults with normal renal function: Elimination half-life of 0.83–1.1 hours.

IV imipenem/cilastatin in infants and children: Elimination half-life of imipenem averages 1–1.3 hours in children and 1.5–2.6 hours in neonates. Elimination half-life of cilastatin is 3.1–8.8 hours in neonates.

Special Populations

Serum half-lives of both imipenem and cilastatin are prolonged in patients with impaired renal function; half-life of cilastatin is prolonged to a greater extent than that of imipenem.

In healthy geriatric adults, mean plasma half-lives of imipenem and cilastatin are similar to half-lives expected in individuals with slight renal impairment.




Powder for Injection, for IV use

Single-dose vials of powder: <25°C.

Following reconstitution with compatible IV solution, suspension maintains satisfactory potency for 4 hours at room temperature or for 24 hours when refrigerated (5°C). Do not freeze reconstituted suspensions or final diluted solutions of the drug.


For information on systemic interactions resulting from concomitant use, see Interactions.


Solution Compatibility


Dextrose 5%

Dextrose 5% in sodium chloride 0.225, 0.45, or 0.9%

Sodium chloride 0.9%


Dextrose 5% in Ringer’s injection, lactated

Ringer’s injection, lactated

Sodium lactate 1/6 M

Drug Compatibility
Y-Site CompatibilityHID


Acyclovir sodium




Caspofungin acetate

Ceftazidime-avibactam sodium

Ceftolozane sulfate-tazobactam sodium

Cisatracurium besylate

Colistimethate sodium

Defibrotide sodium

Diltiazem HCl


Eravacycline dihydrochloride


Fludarabine phosphate

Foscarnet sodium

Granisetron HCl

Idarubicin HCl

Insulin, regular


Melphalan HCl



Methotrexate sodium

Ondansetron HCl

Plazomicin sulfate


Remifentanil HCl


Tedizolid phosphate





Vinorelbine tartrate



Allopurinol sodium

Amiodarone HCl


Etoposide phosphate


Gallium nitrate

Gemcitabine HCl


Meperidine HCl

Midazolam HCl

Milrinone lactate


Sodium bicarbonate



Telavancin HCl

Actions and Spectrum

  • Fixed combination of imipenem monohydrate and the sodium salt of cilastatin. Imipenem is carbapenem antibiotic structurally and pharmacologically related to meropenem and ertapenem. Cilastatin is a specific and reversible inhibitor of dehydropeptidase I (DHP I).

  • Concomitant use of cilastatin prevents in vivo metabolism of imipenem by DHP I and results in urinary concentrations of active imipenem that are higher than could be obtained following use of the antibiotic alone.

  • Usually bactericidal in action.

  • Like other β-lactam antibiotics, antibacterial activity results from inhibition of bacterial cell wall synthesis.

  • Spectrum of activity includes many gram-positive and -negative aerobic bacteria and some gram-positive and -negative anaerobic bacteria. Stable in the presence of a variety of β-lactamases (including penicillinases, cephalosporinases, and extended-spectrum β-lactamases).

  • Gram-positive aerobes: Active in vitro and in clinical infections against Enterococcus faecalis, Staphylococcus aureus (including penicillinase-producing strains), S. epidermidis, Streptococcus agalactiae (group B streptococci), S. pneumoniae, and S. pyogenes (group A β-hemolytic streptococci). Also active in vitro against S, saprophyticus, groups C and G streptococci, viridans streptococci, Bacillus, Listeria monocytogenes, and Nocardia. Methicillin-resistant staphylococci are resistant.

  • Gram-negative aerobes: Active in vitro and in clinical infections against Acinetobacter, Citrobacter, Enterobacter, Escherichia coli, Gardnerella vaginalis, Haemophilus influenzae, H. parainfluenzae, Klebsiella, Morganella morganii, Proteus vulgaris, Providencia rettgeri, Pseudomonas aeruginosa, and Serratia (including S. marcescens). Also active in vitro against Aeromonas hydrophila, Alcaligenes, Capnocytophaga, H. ducreyi, Neisseria gonorrhoeae, Pasteurella, and P. stuartii.

  • Anaerobes: Active in vitro and in clinical infections against Bacteroides (including B. fragilis), Bifidobacterium, Clostridium, Eubacterium, Fusobacterium, Peptococcus, Peptostreptococcus, and Propionibacterium. Also active in vitro against Prevotella bivia, P. disiens, P. melaninogenica, and Veillonella.

Advice to Patients

  • Advise patients that antibacterials, including imipenem/cilastatin, should only be used to treat bacterial infections and not used to treat viral infections (e.g., the common cold).

  • Importance of completing full course of therapy, even if feeling better after a few days. Advise patients that skipping doses or not completing the full course of therapy may decrease effectiveness and increase the likelihood that bacteria will develop resistance and will not be treatable with imipenem/cilastatin or other antibacterials in the future.

  • Inform patients that allergic reactions, including serious allergic reactions, could occur and that serious reactions require immediate treatment. Importance of informing clinician of any previous hypersensitivity reactions to imipenem, other carbapenems, β-lactams, or other allergens.

  • Inform patients that seizures have been reported with imipenem/cilastatin and closely related antibacterials; importance of informing clinician of any CNS disorders such as stroke or history of seizures.

  • Importance of informing clinicians if taking valproic acid or sodium valproate. Valproic acid concentrations in the blood may drop below the therapeutic range when used with imipenem/cilastatin. If treatment with the drug is necessary and continued, alternative or supplemental anti-convulsant medication to prevent and/or treat seizures may be needed.

  • Advise patients that diarrhea is a common problem caused by antibacterials, including imipenem/cilastatin, and usually resolves when the antibacterial is discontinued. Frequent watery or bloody diarrhea may occur and may be a sign of a more serious intestinal infection. Importance of contacting a clinician if severe watery and bloody diarrhea occurs.

  • Importance of informing clinicians of existing or contemplated concomitant therapy, including prescription and OTC drugs, and any concomitant illnesses.

  • Importance of women informing clinicians if they are or plan to become pregnant or plan to breast-feed.

  • Importance of informing patient of other important precautionary information. (See Cautions.)


Excipients in commercially available drug preparations may have clinically important effects in some individuals; consult specific product labeling for details.

Please refer to the ASHP Drug Shortages Resource Center for information on shortages of one or more of these preparations.

* available from one or more manufacturer, distributor, and/or repackager by generic (nonproprietary) name

Imipenem and Cilastatin Sodium


Dosage Forms


Brand Names



For injection, for IV infusion

250 mg (of anhydrous imipenem) and 250 mg (of cilastatin)*

Imipenem and Cilastatin for Injection, for IV Infusion

500 mg (of anhydrous imipenem) and 500 mg (of cilastatin)*

Imipenem and Cilastatin for Injection, for IV Infusion

Primaxin I.V.


AHFS DI Essentials™. © Copyright 2023, Selected Revisions December 14, 2021. American Society of Health-System Pharmacists, Inc., 4500 East-West Highway, Suite 900, Bethesda, Maryland 20814.

† Off-label: Use is not currently included in the labeling approved by the US Food and Drug Administration.

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