Engflag

Metronidazole Injection

Quick links to important sections

Metronidazole Injection

Metronidazole Injection_EN

Treatment option:

Medically reviewed

Marina Burgos

Last updated on 22/12/2025

This page provides general, reference-level information compiled from official medical sources. It is not a substitute for professional medical advice, diagnosis, or treatment. For decisions about your health, please consult a qualified healthcare professional.

Overview of Metronidazole Injection

What is Metronidazole Injection?

Metronidazole injection is a sterile, nonpyrogenic solution of metronidazole in a medium suitable for intravenous administration. It belongs to a class of medications known as nitroimidazole antimicrobials. This medication is designed to treat serious infections caused by specific susceptible bacteria and microorganisms, particularly anaerobic bacteria which thrive in environments with little to no oxygen.

Therapeutic Classification and Mechanism

As an anti-infective agent, metronidazole works by entering the cells of microorganisms and interfering with their DNA synthesis. By disrupting the genetic material of the pathogens, the medication prevents them from reproducing and functioning, eventually leading to the resolution of the infection. Because of its specific chemical structure, it is primarily effective against anaerobic bacteria and certain parasites, rather than aerobic bacteria or viral infections.

Clinical Applications

Metronidazole injection is typically utilized in hospital settings for systemic infections where oral administration is not feasible or where a rapid therapeutic effect is required. It is commonly used for:

  • Intra-abdominal Infections: Addressing complex infections within the abdominal cavity, such as peritonitis or abscesses.
  • Gynecologic Infections: Treating serious infections of the female reproductive system.
  • Septicemia: Managing bloodstream infections caused by susceptible anaerobic organisms.
  • Bone and Joint Infections: Assisting in the treatment of deep-tissue infections affecting the skeletal system.
  • Central Nervous System Infections: Treating specific infections like brain abscesses when caused by targeted pathogens.

Physical Characteristics

The intravenous form of this medication is usually provided as a clear, colorless to pale yellow solution. It is often supplied in single-dose containers, such as plastic bags or glass vials, formulated at a specific concentration and pH to ensure stability and compatibility for parenteral use.

What side effects are possible with Metronidazole Injection?

Possible Side Effects and Safety Information

The safety profile of Metronidazole Injection is based strictly on documentation from government regulatory agencies, detailing officially reported adverse effects and specific cautionary statements.

Official Adverse Reactions by Frequency and System

Adverse reactions are classified by how often they occur, as documented in regulatory sources such as the Summary of Product Characteristics (SmPC).

Classification Examples of Documented Reactions
Common Nausea, vomiting, diarrhea, abdominal discomfort, headache, metallic taste, and inflammation at the injection site (thrombo-phlebitis).
Rare / Very Rare Encephalopathy, optic neuropathy, anaphylaxis, severe skin reactions (SJS/TEN), and blood disorders like agranulocytosis.
Frequency Not Known Seizures, peripheral neuropathy, aseptic meningitis, and hearing impairment/loss.

Major System-Organ Classes officially involved include Nervous System Disorders, Gastrointestinal Disorders, Skin and Subcutaneous Tissue Disorders, and Blood and Lymphatic System Disorders.

Serious Adverse Reactions and Safety Constraints

Certain reactions are documented as clinically significant and serious, often requiring immediate evaluation. The serious adverse effects highlighted in regulatory warnings include Seizures (convulsive), Encephalopathy, and potentially irreversible Peripheral Neuropathy and Optic Neuropathy.

  • Duration-Related Risk: Regulatory labeling notes that the risk of Peripheral Neuropathy is explicitly associated with prolonged use or the administration of high doses.

  • Safety Restriction: The medication is contraindicated in individuals with a known prior hypersensitivity reaction to Metronidazole or other nitroimidazole derivatives. Furthermore, treatment must be discontinued immediately if signs of Central Nervous System (CNS) toxicity or neuropathy are observed.

  • Population Notes: Caution is officially advised for patients with hepatic impairment, as the drug's clearance is reduced, which can increase systemic exposure. Accumulation of metabolites may also occur with renal impairment.

Overdose and Emergency Response

Overdose and When to Seek Help

Metronidazole Injection overdose may be associated with symptoms such as nausea, vomiting, and lack of coordination, clinically referred to as ataxia. The official regulatory information documents that exposure to high doses (such as those involving single oral doses up to 15 grams or extended high-dose courses) can lead to severe neurotoxic effects. These severe outcomes include the occurrence of convulsive seizures and manifestations of peripheral neuropathy (nerve damage).

Emergency Action Required

Due to the potential for severe neurotoxicity and life-threatening symptoms, immediate medical attention must be sought if an overdose is suspected. This requirement for urgent professional care is mandated because there is no specific antidote known for metronidazole overdose, making clinical intervention essential.

Management for a confirmed overdose consists entirely of symptomatic and supportive therapy provided under professional supervision. Regulatory guidance recommends close monitoring of plasma metronidazole levels and general toxicity. Continuous observation is necessary to manage any severe or persistent neurological symptoms until the medication is safely cleared from the system.

Therapeutic Uses of Metronidazole Injection

What Metronidazole Injection Treats: Main Uses and Benefits

The medication is commonly used to manage severe established infections caused by susceptible anaerobic bacteria, which are organisms that are involved in conditions characterized by low-oxygen environments. The injection is used in the management of conditions such as septicemia (blood poisoning), deep intra-abdominal infections including peritonitis and liver abscess, and gynecologic infections. The primary therapeutic application is in conditions involving infection, which supports the easing of symptoms associated with acute episodes related to systemic imbalance, such as pronounced fever and severe inflammation, and assists with maintaining functional stability in critical situations.

The medication is also applied in a preventive clinical context for prophylaxis during specific high-risk surgical procedures, particularly elective colorectal surgery, where it helps reduce the risk of a severe postoperative infection. This supportive therapeutic action contributes to easing the overall symptom load by providing prophylactic support during high-risk scenarios.

“The use of the intravenous formulation is generally reserved for clinical settings that involve acute or unstable symptom patterns associated with serious deep-seated infections.”

Quick Fact: Use in Systemic Imbalance

The injection is commonly used when symptoms create noticeable physiological strain, helping to manage the symptom clusters of high fever and systemic inflammation that accompany conditions marked by heightened physiological stress.

Eligibility and Restrictions for Use

Official Eligibility for Metronidazole Injection

Metronidazole Injection eligibility is strictly defined by regulatory documents based on patient history, age, and existing medical conditions. The medicine is contraindicated and must not be used by patients with a history of hypersensitivity to metronidazole or any other nitroimidazole derivative. It is also prohibited for patients with Cockayne syndrome or for those who have consumed Disulfiram within the last two weeks.

Population Restrictions and Conditional Use

Population Group Regulatory Status
Age Groups Generally permitted for adults, adolescents, and the pediatric population; conditional use is required for neonates (gestational age < 40 weeks) and geriatric patients.
Organ Impairment Patients with severe hepatic impairment (Child-Pugh C) require a 50% dose reduction.
Pregnancy/Lactation Contraindicated in the first trimester of pregnancy according to some product labels. Use during lactation requires deciding between discontinuing nursing or discontinuing the drug.
Comorbidities Use with caution is advised for patients with active or chronic severe CNS disease or a history of blood dyscrasias.

Regulatory authorities classify use based on these specific exclusions and conditions to establish who may receive the medicine.

What should I know about interactions with other medicines?

Interactions with other medicines and products

Metronidazole Injection interacts with several medicines and substances, which can alter the effects of either drug or cause adverse reactions. Certain combinations are contraindicated and must be avoided.

Contraindicated Combinations and Substances

Substance/Drug Interaction Management
Alcohol and Propylene Glycol Risk of a disulfiram-like reaction (e.g., flushing, nausea, vomiting, abdominal cramps). Avoid all consumption during therapy and for at least three days (72 hours) after the final dose.
Disulfiram Risk of psychotic reactions or confusion. Do not administer metronidazole to patients who have taken disulfiram within the last two weeks.

Interactions Requiring Close Monitoring or Dose Adjustment

Interacting Drug Interaction Mechanism/Result Management
Warfarin (and other oral coumarin anticoagulants) Potentiates anticoagulant effect, increasing the risk of bleeding. Prothrombin time and INR must be closely monitored; anticoagulant dose may require reduction.
Lithium Can reduce lithium clearance, leading to elevated serum levels and potential toxicity or kidney damage. Serum lithium and creatinine levels must be closely monitored; lithium dose may need adjustment.
Phenytoin and Phenobarbital These enzyme inducers can accelerate metronidazole elimination, reducing its plasma levels. Metronidazole can also inhibit phenytoin clearance. Close monitoring of drug levels for both metronidazole and phenytoin is necessary.
Cimetidine This enzyme inhibitor can prolong metronidazole half-life, increasing its plasma concentration and potential for side effects. Monitoring for metronidazole side effects is recommended.
Busulfan Metronidazole increases busulfan plasma concentrations, raising the risk of severe busulfan toxicity. The combination is generally avoided or requires frequent monitoring of busulfan levels.

Metronidazole may also interfere with certain laboratory tests, potentially causing inaccurately low results for values like AST, ALT, and triglycerides.

Mechanism of Action

The mechanism of metronidazole is defined by its selective requirement for reductive activation within susceptible anaerobic microorganisms. As a prodrug, the metronidazole molecule enters the microbe and acts as an electron acceptor in the organism's unique anaerobic energy metabolism. Enzymes like ferredoxin facilitate the transfer of electrons to the drug's nitro group ( NO2), converting it into a highly toxic, unstable reactive nitroso radical. This conditional activation restricts the mechanism's cidal consequence to organisms that possess this specific, low-potential electron transport system and lack sufficient oxygen. The highly reactive radical directly targets the microbe’s DNA, causing irreparable strand breakage and loss of nucleic acid structure. The molecular damage permanently blocks the cell's ability to replicate and repair itself. The ultimate physiological consequence is the complete cessation of cellular function and death (cidal effect) of the microorganism.

Dosage and Administration Information

How to Use Metronidazole Injection

Metronidazole Injection is a sterile solution administered solely by the Intravenous (IV) Infusion route in a supervised setting, such as a hospital. This administration method ensures the medication is delivered directly into the systemic circulation at a controlled rate. The official instructions dictate that the infusion must be given slowly, typically over a period of 30 minutes to one hour, and should never be administered as a rapid IV bolus.

Official Dosing and Schedule

Treatment begins with a loading dose of 15 mg/kg by IV infusion. This is followed by maintenance doses of 7.5 mg/kg per dose. These maintenance doses are usually scheduled to be administered at regular six-hour or eight-hour intervals to maintain consistent levels of the compound. The total dose given in a single 24-hour period is officially limited and should generally not exceed 4.0 grams.

Procedural and Population Requirements

The standard duration of treatment is typically 7 to 10 days. A common usage pattern involves sequential therapy, where IV administration is discontinued, and the patient transitions to the oral form when their condition permits. Dosage adjustments are formally required for specific patient populations. For example, patients with severe hepatic impairment are instructed to receive a 50% dose reduction due to altered drug clearance. If a scheduled infusion is missed, the dose should be administered as soon as possible, and the solution must always be visually inspected for cloudiness or precipitate prior to use.

Recent Clinical Evidence

Research evidence / Overview of Studies for Metronidazole Injection

Evidence for use in Established Anaerobic Bacterial Infections

The evidence base includes studies of the use of Metronidazole Injection for infections caused by susceptible anaerobic bacteria, such as those in the abdomen or female reproductive system. The evidence base for this application includes foundational Non-Comparative Trials, Cohort Studies, and historical Randomized Controlled Trials (RCTs). These studies primarily focused on Adults with confirmed or suspected infections.

The studies monitored several outcomes related to physiological strain or stress, including measured changes in signs like fever and white blood cell counts. Researchers also examined the bacteriological outcomes, observing whether the specific infection-causing pathogens were observed to be reduced or absent shortly after the course of treatment was studied for a defined time interval. Findings describe patterns observed in the studies where the administration of the medication occurred during the monitored period for clinical response. It is important to note that these findings often relate to the drug's use in combination with other antimicrobial treatments.

Evidence for use in Surgical Infection Prophylaxis

Metronidazole Injection was studied for its use in surgical prophylaxis, which are research contexts involving fluctuating or unstable symptoms following specific high-risk operations, most notably elective colorectal surgery. The evidence base includes Meta-analyses of RCTs and Prospective Trials that compare various prophylactic regimens. The research focuses on the Adult surgical population.

The main focus of these studies was to monitor outcomes related to inflammatory or irritative states and outcomes describing episodic or acute changes, particularly the frequency of outcomes related to inflammatory or irritative states, such as Surgical Site Infection (SSI) in the weeks following the operation. Findings describe patterns observed in the studies where the use of the drug was associated with observed patterns in study outcomes when administered shortly before and during the procedure. This research describes patterns observed when the drug was used in combination with a second agent.

What is Still Uncertain About the Research

While a body of research describes the authorized uses of the injection, certain aspects of the evidence landscape remain uncertain. Evidence quality varies across studies, particularly due to the age of some of the foundational trials. Furthermore, data for certain groups remain insufficient, especially within various pediatric sub-groups, and long-term effects are not fully established, as the primary focus of the research is on the acute phase of infection and the short-term outcomes. Findings describe group patterns, not personal outcomes.

Key Studies & References

  1. WHO Model List of Essential Medicines (Essential status for anti-infective use)

Frequently Asked Questions (FAQ)

Common questions about Metronidazole Injection (FAQ)

Q: Can I take this medicine with alcohol?

Official regulatory information provides a specific warning against consuming alcohol while receiving this medicine. Combining the medicine with alcohol is warned against due to the potential for increased sedative effects or other serious adverse reactions. The official warning should be followed.

Q: How should I store this medication?

The official product information indicates the medication should be stored below 30°C (86°F). Additionally, the label advises keeping the medicine in its original packaging to protect it from moisture and light until it is ready for administration.

Q: Does it make you sleepy?

Yes, official regulatory documents list somnolence (drowsiness) as a reported undesirable effect or adverse reaction. Due to this potential effect, caution may be necessary when performing tasks that require mental alertness.

Q: Can children 2 years old use it?

According to the regulatory label, the safety and efficacy in pediatric patients under the age of 4 years have not been established. The labeled indication, or approved use, is specifically for patients 4 years of age and older.

Q: What should I do if I miss a dose?

The official instructions regarding missed doses state to take the missed dose as soon as it is remembered. However, if it is close to the time of the next scheduled dose, the regulatory instructions advise skipping the missed dose and returning to the regular schedule. The product label includes an explicit warning against taking two doses at the same time.

How should Metronidazole Injection be stored and disposed of?

How to Store and Dispose of Metronidazole Injection

Official regulatory documents define strict requirements for storing and disposing of this sterile intravenous solution.

Official Storage Conditions

Requirement Description
Temperature Store at a controlled room temperature, typically 20 C to 25 C (68 F to 77 F). Do not store above 25 C or 30 C (depending on the label).
Light Protection The container must be kept in its original packaging and protected from light until it is ready for immediate use.
Stability Rule The label prohibits the addition of supplementary medications (admixtures) to the IV solution, as this compromises product stability.

Disposal and Handling

Metronidazole Injection is supplied in a single-dose container. Any unused portion of the solution must be discarded immediately after the dose has been administered. The disposal of the product and all waste materials must be completed in accordance with local regulatory requirements for pharmaceutical waste.

Attention! Always consult to a doctor or pharmacist before using pills or medicines.

Equivalent of Metronidazole Injection found in:

A-Z Index: