METROZOL SUSPENSION

Indications

• Food preservative
• Treatment of urea cycle disorders
• Metabolic disorders involving benzoyl-CoA

Dosage

Children: Refer to the BNF for Children for specific dosing guidelines based on condition.

Adults: Refer to the BNF for specific dosing guidelines based on condition.

Mechanism of action

Benzoate acts mainly by inhibiting the growth of bacteria and fungi through its ability to lower the pH, creating an environment that is less favorable for microbial growth. It is also involved in metabolic pathways where it helps in the conjugation of toxic substances, facilitating their excretion from the body.

Pharmacodynamics

Benzoate is known for its antimicrobial properties, which are particularly effective against a wide range of fungi and bacteria. Its efficacy as a preservative is due to its ability to penetrate microbial cell membranes and disrupt their metabolic processes. Additionally, it has been observed to modulate various metabolic pathways, particularly those associated with aromatic compound degradation.

Pharmacokinetics

After ingestion, benzoate is rapidly absorbed in the gastrointestinal tract. It is metabolized primarily in the liver, where it undergoes conjugation with glycine to form hippurate, which is then excreted in the urine. The half-life of benzoate varies depending on individual metabolic rates but is generally short due to its efficient conversion and excretion.

Pregnancy

There is limited data on the use of benzoate in pregnancy. Consultation with healthcare professionals is advised before use.

Breast-feeding

Limited data is available on the excretion of benzoate in breast milk. Caution is recommended when administering to nursing mothers.

Storage

Store in a cool, dry place away from direct sunlight. Keep out of reach of children.

Indications

• Amebiasis
• Trichomoniasis
• Giardiasis
• Anaerobic bacterial infections
• Bacterial vaginosis
• Clostridium difficile infection

Dosage

Children: For children aged 1 month to 11 years, 7.5 mg/kg every 8 hours for 7 days (maximum dose 400 mg). For children aged 12-17 years, 400 mg every 8 hours for 7 days.

Adults: 1 g three times a day for 3 days, then 1 g twice daily for a total treatment duration of 7 days. In cases of Clostridium difficile infection, treatment may extend to 10 days.

Mechanism of action

The exact mechanism of action of metronidazole is not fully established. However, it is believed that anaerobic bacteria and protozoa reduce metronidazole to reactive intermediates that bind to DNA and inhibit nucleic acid synthesis, leading to cell death. Metronidazole is selectively activated in anaerobic conditions, making it effective against obligate anaerobes.

Pharmacodynamics

Metronidazole exhibits both antibacterial and antiprotozoal activities, effectively treating infections caused by anaerobic bacteria. It demonstrates significant antibacterial activity against most obligate anaerobes but is less effective against facultative anaerobes and obligate aerobes. The drug's cytotoxic effects result from DNA strand damage in susceptible microorganisms, which can lead to cell death. Caution is advised due to the potential for peripheral neuropathy and convulsions, especially at higher doses.

Pharmacokinetics

Metronidazole is well absorbed following oral administration and is distributed widely throughout the body, including the central nervous system. It undergoes hepatic metabolism, primarily through oxidation and conjugation, and is excreted mainly in urine. The pharmacokinetic profile may vary in patients with hepatic impairment, and dosage adjustments may be necessary.

Adverse effects

• Peripheral neuropathy
• Convulsions
• Nausea
• Vomiting
• Diarrhea
• Headache
• Dizziness
• Abdominal cramps
• Metallic taste
• Skin rash

Interactions

• Metronidazole + Coumarins: Increases anticoagulant effect
• Metronidazole + Lithium: Increases concentration
• Metronidazole + Busulfan: Increases risk of toxicity (unknown)
• Metronidazole + Capecitabine: Increases risk of capecitabine toxicity (unknown)
• Metronidazole + Fluorouracil: Increases risk of toxicity (unknown)
• Metronidazole + Alkylating agents: Increases risk of toxicity (unknown)

Precautions

• Caution in patients with history of neurological disorders
• Monitor for signs of peripheral neuropathy
• Use with caution in patients with hepatic impairment
• Avoid excessive alcohol consumption during treatment

Pregnancy

No information available; manufacturer advises avoidance unless essential.

Breast-feeding

Amount in milk probably too small to be harmful.

Storage

Store in a cool, dry place, away from light. Keep out of reach of children.

Formulations

• Metronidazole 0.75% gel
• Metronidazole 0.75% cream
• Metronidazole powder and solvent for nebuliser solution
• Metronidazole injection
• Metronidazole oral tablets (various strengths)

Mechanism of action

The exact mechanism of action of metronidazole has not been fully established, however, it is possible that an intermediate in the reduction of metronidazole which is only made by anaerobic bacteria and protozoa, binds deoxyribonucleic acid and electron-transport proteins of organisms, blocking nucleic acid synthesis. After administration, metronidazole enters cells by passive diffusion. Following this, ferredoxin or flavodoxin reduce its nitro group to nitro radicals. The redox potential of the electron transport portions of anaerobic or microaerophilic microorganisms renders metronidazole selective to these organisms, which cause nitro group reduction, leading to the production of toxic metabolites. These include N-(2-hydroxyethyl) oxamic acid and acetamide, which may damage DNA of replicating organisms. Microbicidal; active against most obligate anaerobic bacteria and protozoa by undergoing intracellular chemical reduction via mechanisms unique to anaerobic metabolism. Reduced metronidazole, which is cytotoxic but short-lived, interacts with DNA to cause loss of helical structure, strand breakage, and resultant inhibition of nucleic acid synthesis and cell death. Metronidazole is bactericidal, amebicidal, and trichomonacidal in action. The exact mechanism of action of the drug has not been fully elucidated. Metronidazole is un-ionized at physiologic pH and is readily taken up by anaerobic organisms or cells. In susceptible organisms or cells, metronidazole is reduced by low-redox-potential electron transport proteins (e.g., nitroreductases such as ferredoxin) to unidentified polar product(s) which lack the nitro group. The reduction product(s) appears to be responsible for the cytotoxic and antimicrobial effects of the drug which include disruption of DNA and inhibition of nucleic acid synthesis. Metronidazole is equally effective against dividing and nondividing cells. In in vivo studies in rats given metronidazole in dosages of 2-4 mg/100 g of body weight, the drug reportedly inhibited the development of formalin-induced edema in the rat paw. In vitro in neutrophils, metronidazole has a dose-dependent inhibitory effect on generation of hydrogen peroxide and hydroxyl radicals, oxidants that may cause tissue injury at the site of inflammation. This antioxidant effect appears to be caused by a direct effect on neutrophil function and may contribute to the drug's anti-inflammatory effect in vivo. Results of in vitro studies using leukocytes obtained from patients with Crohn's disease indicate that exposing the cells to metronidazole concentrations of 10 or 50 mcg/mL improved both spontaneous and induced leukocyte migration in cells that previously exhibited reduced migration; the drug had no effect on leukocytes obtained from healthy adults or patients with Crohn's disease when the cells exhibited normal migration prior to exposure to the drug. This effect on leukocyte migration also was observed in vivo in adults with Crohn's disease who received a single 400-mg dose of metronidazole. It has been suggested that metronidazole may increase leukocyte migration by a direct effect on the leukocytes, possibly by causing the release of surface-bound immune complexes from the cell surface.

Pharmacodynamics

Metronidazole treats amebiasis, trichomoniasis, and giardiasis, exerting both antibacterial and antiprotozoal activities. Metronidazole is an effective treatment for some anaerobic bacterial infections. Metronidazole has shown antibacterial activity against the majority of obligate anaerobes, however, during in vitro studies, it does not demonstrate significant action against facultative anaerobes or obligate aerobes. The nitro group reduction of metronidazole by anaerobic organisms is likely responsible for the drug's antimicrobial cytotoxic effects, causing DNA strand damage to microbes. A note on convulsions and neuropathy and carcinogenesis It is important to be aware of the risk of peripheral neuropathy and convulsions associated with metronidazole, especially at higher doses. If convulsions or numbness of an extremity occur, discontinue the drug immediately. Metronidazole has been found to be carcinogenic in mice and rats. The relevance to this effect in humans is unknown. It is advisable to only administer metronidazole when clinically necessary and only for its approved indications.