Cilastatin,Imipenem

Imipenem plus cilastatin is an injectable antibacterial combination containing imipenem, a broad-spectrum carbapenem antibiotic, and cilastatin, a renal dehydropeptidase-I inhibitor. Imipenem acts by binding to bacterial penicillin-binding proteins and interfering with bacterial cell-wall synthesis, resulting in inhibition of bacterial growth and cell death. Cilastatin does not provide antibacterial activity itself; instead, it inhibits renal metabolism of imipenem by dehydropeptidase-I, helping maintain effective concentrations of imipenem and increasing its antibacterial activity. The combination is administered intravenously and is used for a range of serious infections caused by susceptible bacteria, including complicated intra-abdominal infections, severe pneumonia, complicated urinary tract infections, complicated skin and soft-tissue infections, certain gynecological infections, septicemia, bone and joint infections, and endocarditis. Imipenem has activity against a broad range of Gram-positive, Gram-negative, and anaerobic organisms, although antimicrobial susceptibility testing and local resistance patterns remain important in treatment selection. Because imipenem is substantially eliminated through the kidneys, renal function has a major influence on dosing and safety. The combination has been clinically established for several decades and remains an important hospital antibacterial option when appropriate for the suspected or confirmed pathogen.

Imipenem was developed as a carbapenem derivative of thienamycin, while cilastatin was developed to inhibit renal dehydropeptidase-I, the enzyme responsible for rapid breakdown of imipenem in the kidney. The fixed combination was developed to extend imipenem exposure and permit effective systemic antibacterial treatment. Imipenem and cilastatin received initial U.S. FDA approval in 1985 as PRIMAXIN for intravenous use. In Europe, the combination was authorised as Tienam and associated names, with European authorisation dating to 1985. The European Medicines Agency subsequently conducted an Article 30 referral to harmonise prescribing information across European countries, with the European Commission decision issued on March 10, 2011. The harmonised European indications included complicated intra-abdominal infections, severe pneumonia including hospital- and ventilator-associated pneumonia, intra- and post-partum infections, complicated urinary tract infections, complicated skin and soft-tissue infections, suspected bacterial infection in febrile neutropenic patients, and bacteraemia associated with or suspected to be associated with these infections. The clinical development and subsequent regulatory experience of imipenem-cilastatin established its role as a broad-spectrum carbapenem for serious bacterial infections.

Imipenem plus cilastatin is indicated for the treatment of serious infections caused by susceptible bacteria. Depending on the applicable regulatory labeling, indications include lower respiratory tract infections, complicated and uncomplicated urinary tract infections, complicated intra-abdominal infections, gynecological infections, bacterial septicemia, bone and joint infections, skin and skin-structure infections, and endocarditis. European harmonised information additionally specifies severe pneumonia, including hospital- and ventilator-associated pneumonia, complicated intra-abdominal infections, complicated urinary tract infections, intra- and post-partum infections, complicated skin and soft-tissue infections, and treatment of fever in neutropenic patients when bacterial infection is suspected. The medicine is generally used as monotherapy for susceptible bacterial infections rather than as a routine combination with another antibacterial agent, although additional antimicrobial therapy may be required when the suspected infection involves organisms outside its spectrum or when clinical circumstances warrant broader initial coverage. Treatment should be guided by culture results, antimicrobial susceptibility testing, infection severity, infection site, and local antimicrobial stewardship recommendations.

Imipenem plus cilastatin is administered by intravenous infusion, with dosing determined by the infection, susceptibility of the suspected or confirmed pathogen, patient age, and renal function. For adults with normal renal function, commonly recommended regimens include 500 mg every six hours or 1,000 mg every eight hours for susceptible infections, while a higher-frequency regimen may be used for organisms with intermediate susceptibility when appropriate. The total daily dose should generally not exceed 4 g in adults. A 500 mg dose is infused over approximately 20 to 30 minutes, while a 1,000 mg dose is generally infused over approximately 40 to 60 minutes. Dose reduction is required in patients with reduced creatinine clearance, and specific dosing considerations apply to patients receiving hemodialysis. The medicine should not ordinarily be administered to patients with very severe renal impairment unless appropriate hemodialysis arrangements are in place. Treatment duration depends on the type and severity of infection, microbiological findings, and clinical response, and should follow the applicable prescribing information and antimicrobial stewardship principles.

Common side effects of imipenem plus cilastatin include inflammation or irritation at the intravenous administration site, phlebitis, nausea, diarrhea, vomiting, rash, itching, fever, dizziness, and low blood pressure. Changes in liver enzymes and other laboratory abnormalities may also occur during treatment. Some patients may experience headache, drowsiness, urticaria, or other gastrointestinal or skin-related symptoms. The frequency and severity of adverse effects can vary according to the patient's age, underlying illness, renal function, infection severity, treatment duration, and other medicines being used. Most adverse effects are monitored clinically and managed according to their severity, but new or worsening neurological symptoms or significant allergic reactions require prompt medical assessment.

Important risks associated with imipenem plus cilastatin include serious hypersensitivity reactions, anaphylaxis, seizures, encephalopathy, confusion, myoclonus, and other central nervous system effects. The risk of seizures is particularly relevant in patients with central nervous system disorders, renal impairment, or excessive drug exposure. Antibiotic-associated diarrhea caused by Clostridioides difficile can occur and may range from mild diarrhea to severe colitis. Imipenem can also interact clinically with valproic acid or divalproex sodium by reducing valproic acid concentrations and increasing the risk of breakthrough seizures; concomitant use is generally not recommended. Treatment should be discontinued promptly in the event of a serious hypersensitivity reaction, while dose reassessment or discontinuation should be considered if significant neurological toxicity develops. As with other broad-spectrum antibiotics, prolonged or inappropriate use may promote resistant organisms or secondary infections.

Renal function should be assessed before treatment and monitored during therapy because imipenem is primarily eliminated through the kidneys and accumulation can increase the risk of central nervous system toxicity. Particular caution is appropriate in elderly patients, individuals with renal impairment, and patients with a history of seizures or other neurological disorders. A history of serious hypersensitivity to imipenem, other carbapenems, penicillins, cephalosporins, or other beta-lactam antibiotics should be reviewed before administration. Valproic acid and divalproex sodium are clinically important interactions because imipenem-cilastatin can substantially lower valproic acid concentrations and potentially reduce seizure control. Concomitant ganciclovir has also been associated with an increased risk of generalized seizures and should generally be avoided unless the potential benefits outweigh the risks. Probenecid can alter imipenem exposure and should be considered when reviewing concomitant medicines. Appropriate microbiological testing should be performed whenever feasible, and unnecessary prolonged antibacterial treatment should be avoided to reduce antimicrobial resistance.

Prescribers and pharmacists should verify the indication, suspected or confirmed pathogen, renal function, patient weight where relevant, allergy history, seizure history, and interacting medicines before initiating imipenem plus cilastatin. Culture and antimicrobial susceptibility results should be reviewed when available so therapy can be narrowed or modified when appropriate. Renal-dose adjustment is particularly important because excessive imipenem exposure can increase neurological toxicity. Patients receiving valproic acid or divalproex sodium require special attention because the combination can reduce anticonvulsant concentrations and compromise seizure control. During treatment, monitor for hypersensitivity, diarrhea, infusion-site reactions, neurological symptoms, and clinically relevant laboratory abnormalities. New confusion, myoclonus, tremor, altered consciousness, or seizures should prompt immediate clinical evaluation and reassessment of dosing and renal function. Pharmacists should also verify intravenous preparation, infusion duration, compatibility requirements, and the maximum appropriate daily dose. Antibacterial treatment should be reviewed when microbiological results become available and continued only for the clinically appropriate duration.