Can I still use ornidazole if I am allergic to metronidazole?

Can I still use ornidazole if I am allergic to metronidazole?

One day, a patient who had just undergone an abortion was encountered at the outpatient clinic window. The prescriptions given were: Motherwort Dispersible Tablets, Kangfuling Capsules and Ornidazole Dispersible Tablets. When picking up the medicine, the patient murmured to himself: Can I take Ornidazole Tablets if I am allergic to metronidazole? The pharmacist at the window reacted quickly and immediately stopped dispensing the medicine. He asked the patient about her allergy history. The patient said that she had been allergic to metronidazole and had rashes in many parts of her body, which were extremely itchy and showed signs of ulceration. After learning the details, the pharmacist refused to dispense the prescription and contacted the clinical physician, who replaced it with another antibacterial drug. So why can't ornidazole be used if you are allergic to metronidazole? What are the adverse reactions of metronidazole and ornidazole? What should you pay attention to in daily use?

Metronidazole and ornidazole seem to be just one letter apart, but they are actually very different

Metronidazole and ornidazole, just by hearing their names, you can tell that they have a deep relationship. Clinically, both metronidazole and ornidazole belong to the nitroimidazole class of drugs. Nitroimidazole drugs have the advantages of a broad spectrum of anti-anaerobic bacteria, strong bactericidal effect, low price, and significant efficacy. They are used in combination with other antibacterial drugs for mixed anaerobic and aerobic infections in various clinical systems. [1] The antibacterial mechanism of the two is the same, which is mainly to play an antibacterial role by interfering with the metabolic process of pathogens in an anaerobic environment. Metronidazole is the first generation of nitroimidazoles, and ornidazole is the third generation of nitroimidazoles.

Ornidazole is optimized based on metronidazole. Ornidazole has a faster onset and stronger effect than metronidazole, and its half-life is longer than that of metronidazole. After the half-life is extended, the number of dosing times per day can be reduced. Reducing the number of dosing times increases patient compliance, and after increased compliance, the efficacy can be better improved and recurrence can be reduced. At the same time, some bacteria may develop resistance to metronidazole in clinical practice, and ornidazole is effective in clinical application against metronidazole-resistant bacteria.

Ornidazole has a stronger therapeutic effect than metronidazole. In clinical practice, if there is an anaerobic infection, metronidazole is the first choice. Ornidazole is selected when metronidazole is not effective, or when there is a serious anaerobic infection. It is used to treat Helicobacter pylori-related digestive tract diseases, but the first choice recommended by relevant guidelines is metronidazole. Although some clinical research results show that ornidazole and metronidazole have similar efficacy, most guidelines and consensus have not yet formally recommended ornidazole as a routine drug for the treatment of Helicobacter pylori-related digestive tract diseases.

In addition, the side effects of ornidazole are less than those of metronidazole, and the severity of the side effects is relatively mild. Most patients can resolve them on their own without the need for drug intervention and treatment. Metronidazole causes relatively more side effects in clinical practice. About 15%-30% of patients using metronidazole may experience gastrointestinal reactions, such as nausea, vomiting, or dizziness.

Ornidazole has no inhibitory effect on aldehyde dehydrogenase, so drinking alcohol during the use of ornidazole generally does not cause a disulfiram-like reaction, but it is best to avoid it as much as possible. Metronidazole has an inhibitory effect on aldehyde dehydrogenase, so alcohol should be strictly avoided while using metronidazole. Therefore, ornidazole is also superior to metronidazole in terms of drug safety.

Metronidazole and ornidazole are common medicines in life, and their adverse reactions should also be known.

Metronidazole: Adverse reactions occur in 15% to 30% of cases, with gastrointestinal reactions being the most common, including nausea, vomiting, loss of appetite, and abdominal cramps, which generally do not affect treatment; neurological symptoms include headache, dizziness, occasional paresthesia, limb numbness, ataxia, multiple neuritis, etc., and high doses can cause convulsions. A small number of cases develop urticaria, flushing, itching, cystitis, dysuria, metallic taste in the mouth, and leukopenia, all of which are reversible and recover on their own after stopping the drug. [2]

Ornidazole: Mild side effects may include drowsiness, headache, gastrointestinal discomfort (including nausea and vomiting). Some patients may experience central nervous system disorders such as headache, tremor, rigidity, seizures, ataxia, fatigue, dizziness, temporary loss of consciousness or peripheral neuropathy. Taste disorders, abnormal liver function and skin reactions. [3]

From the adverse reactions of metronidazole and ornidazole, it can be seen that both can cause skin reactions such as itching and flushing. The contraindications in the instructions for use of metronidazole and ornidazole also clearly state that patients who are allergic to this product or nitroimidazole drugs are prohibited from using it. Therefore, the patient had taken metronidazole and had severe itching and rash, so the use of ornidazole, a similar drug, should be prohibited. The pharmacist responded quickly, contacted the clinical physician in time to explain the situation, and handled it properly, which is worth learning from.

Do not take metronidazole while drinking alcohol, and do not take ornidazole while driving.

Metronidazole and ethanol can cause a disulfiram-like reaction. Disulfiram-like reaction is also called disulfiram-like reaction or drunkenness reaction. It refers to the fact that disulfiram inhibits acetaldehyde dehydrogenase and hinders the normal metabolism of ethanol, so that drinking a small amount of ethanol can also cause acetaldehyde poisoning. Disulfiram, also known as disulfiram, will cause weakness, dizziness, drowsiness, hallucinations, whole body flushing, headache, nausea, vomiting, low blood pressure, and even shock after drinking. If you drink alcoholic beverages or products containing propylene glycol during or after metronidazole treatment, you may experience abdominal cramps, nausea, vomiting, headache, and flushing. Ornidazole does not inhibit acetaldehyde dehydrogenase and is incompatible with alcohol, but unpredictable interactions may occur when used together, so you should still avoid drinking alcoholic beverages during ornidazole treatment.

During treatment with ornidazole, exacerbation of peripheral nervous system disorders may occur. If symptoms of peripheral neuropathy, ataxia, dizziness, or unconsciousness occur, ornidazole treatment should be discontinued. Driving a vehicle or operating machinery during treatment is not recommended. Or engaging in other activities that require high concentration and rapid reaction.

References:

Guiding principles for clinical application of antimicrobial drugs (2015 edition) 3. Chen Qian et al. Research progress on the metabolism of nitroimidazole drugs in the human body [J]. Chinese Journal of Pharmaceutical Sciences, 2015, 50 (14): 1169-11724.

Metronidazole instructions

Ornidazole instructions

Author: Department of Pharmacy, Sports New City Campus, Dalian Women and Children's Medical Center (Group)

Deputy Chief Pharmacist Yu Hong

Reviewer: Department of Pharmacy, Dalian Women and Children's Medical Center (Group), Sports New City Campus

Deputy Chief Pharmacist Wu Gaolei