From the Guidelines
Expired metronidazole is not known to become toxic, but its effectiveness may decrease over time, and using it is not recommended due to potential treatment failure and contribution to antibiotic resistance. While most medications don't become harmful after their expiration date, they can lose potency and may not work as intended. Metronidazole, an antibiotic used to treat various bacterial and parasitic infections, should ideally be used before its expiration date to ensure optimal therapeutic effect. The chemical stability of metronidazole generally remains intact for some time after expiration, but the manufacturer can no longer guarantee its full potency or effectiveness. Unlike tetracycline antibiotics, which have been documented to develop toxic degradation products when expired, metronidazole has not shown evidence of developing harmful compounds after expiration.
According to the provided guidelines, metronidazole is still acceptable for the treatment of nonsevere Clostridioides difficile infection (CDI) in children and as a second-line agent for adults with nonsevere CDI 1. However, the effectiveness of metronidazole may decrease over time, and using expired medication for treating infections is not recommended. The 2020 guidelines for the treatment of CDI in Taiwan recommend metronidazole 500 mg tid PO for 10 days for the first episode of CDI, but do not address the issue of expired medication 1.
In real-life clinical practice, it is essential to prioritize the patient's safety and ensure the effectiveness of the treatment. Therefore, it is recommended to dispose of expired metronidazole and obtain a new prescription if treatment is needed, rather than risking treatment failure and potential contribution to antibiotic resistance. Key points to consider include:
- Metronidazole's effectiveness may decrease over time
- Using expired medication is not recommended due to potential treatment failure and contribution to antibiotic resistance
- Metronidazole is still acceptable for the treatment of nonsevere CDI in children and as a second-line agent for adults with nonsevere CDI
- It is essential to prioritize the patient's safety and ensure the effectiveness of the treatment.
From the Research
Metronidazole Toxicity
- Metronidazole is considered to be a cost-effective drug with minor adverse effects 2.
- However, its use has been associated with toxicity, including neurotoxicity, optic neuropathy, peripheral neuropathy, and encephalopathy in rare cases 3.
- The drug is strictly speaking a prodrug and needs to be reduced at its nitro group in order to become toxic, which only takes place under very low concentrations of oxygen 4.
- There is no direct evidence to suggest that metronidazole becomes toxic when expired, but its effectiveness and potential toxicity may be affected by its expiration date.
Expiration Date and Toxicity
- The provided studies do not specifically address the issue of metronidazole toxicity when expired.
- However, it is known that metronidazole's therapeutic use has increased worldwide, and its side effects are not well established 3.
- Further studies are needed to discover the secure use of metronidazole and describe new usages for this drug, including its potential toxicity when expired.
Metronidazole's Mode of Action
- Metronidazole has a pleiotropic mode of action and reacts with a large number of molecules 4.
- Its reduction only takes place under very low concentrations of oxygen, explaining why metronidazole is exclusively toxic to microaerophilic and anaerobic microorganisms 4.
- The drug's mode of action and potential toxicity are complex and require further research to fully understand its effects.