Метронидазол

Описание

Metronidazole is a nitroimidazole antibiotic first isolated in the 1950s. Many nitroimidazoles were being studied at the time, as the class was found to have trichomonacidal properties. Metronidazole was of particular interest due to its high activity against Trichomonas vaginalis and Entamoeba histolytica both in vitro and in vivo as well as clinical activity against many anaerobic pathogens including Gram-positive and Gramnegative bacteria and Giardia lamblia. Metronidazole is often used clinically for intra-abdominal infections and is the firstline treatment for Clostridium difficile–associated diarrhea.

Химические свойства

Metronidazole is an odorless, white, yellow, or cream-colored crystalline solid. Darkens on exposure to light. Bitter, salty taste (do not test). Soluble in hot water, slightly soluble in ethanol, slightly soluble in water or chloroform, very slightly soluble in ether.

Использование

Metronidazole is the drug of choice for amebiases, vaginal trichomonasis and trichlomonadic urethritis in men, lambliosis, amebic dysentery, and anaerobic infections caused by microorganisms that are sensitive to the drug. Synonyms of this drug are flagyl, protostat, trichopol, and vagimid.

Показания

Metronidazole (Flagyl, Metrogel) exerts activity against most anaerobic bacteria and several protozoa.The drug freely penetrates protozoal and bacterial cells but not mammalian cells. Metronidazole can function as an electron sink, and because it does so, its 5-nitro group is reduced. The enzyme, pyruvate-ferredoxin oxidoreductase, found only in anaerobic organisms, reduces metronidazole and thereby activates the drug. Reduced metronidazole disrupts replication and transcription and inhibits DNA repair.

Определение

ChEBI: Metronidazole is a member of the class of imidazoles substituted at C-1, -2 and -5 with 2-hydroxyethyl, nitro and methyl groups respectively. It has activity against anaerobic bacteria and protozoa, and has a radiosensitising effect on hypoxic tumour cells. It may be given by mouth in tablets, or as the benzoate in an oral suspension. The hydrochloride salt can be used in intravenous infusions. Metronidazole is a prodrug and is selective for anaerobic bacteria due to their ability to intracellularly reduce the nitro group of metronidazole to give nitroso-containing intermediates. These can covalently bind to DNA, disrupting its helical structure, inducing DNA strand breaks and inhibiting bacterial nucleic acid synthesis, ultimately resulting in bacterial cell death. It has a role as an antitrichomonal drug, a prodrug, an antibacterial drug, an antimicrobial agent, an antiparasitic agent, a xenobiotic, an environmental contaminant, a radiosensitizing agent and an antiamoebic agent. It is a member of imidazoles, a C-nitro compound and a primary alcohol. It is a conjugate base of a metronidazole(1+).

Приобретенная устойчивость

Although resistance in Bacteroides spp. and T. vaginalis is well documented, it is uncommon. Resistance occurs more frequently in H. pylori and failure of treatment with triple drug regimens may be associated with resistance to the metronidazole component.

Общее описание

White to pale-yellow crystalline powder with a slight odor. Bitter and saline taste. pH (saturated aqueous solution) about 6.5.

Реакции воздуха и воды

Insoluble in water.

Профиль реактивности

Metronidazole darkens on exposure to light. Metronidazole is incompatible with strong oxidizing agents. .

Пожароопасность

Flash point data for Metronidazole are not available; however, Metronidazole is probably combustible.

Фармацевтические приложения

A 5-nitroimidazole available for oral administration or as a suppository; also formulated as the hydrochloride for intravenous use, and as the benzoate in an oral suspension and a dental gel. Aqueous solubility: 10 g/L at 20°C. Soluble in dilute acids. It is photolabile and preparations should be protected from light. Metronidazole hydrochloride has a low pH (0.5–2.0) when reconstituted, and reacts with aluminum in equipment, including needles, to produce a reddish-brown discoloration. It is incompatible with several agents and other drugs should not be added to intravenous solutions.

Контактные аллергены

Metronidazole is a nitro-6-imidazole compound with antiprotozoal and antibacterial properties. Topical exposure may induce allergic contact dermatitis. Sensitization is mainly observed with the treatment of rosacea and rarely occurs from handling of table.

Механизм действия

Despite the availability of metronidazole since the late 1950s, the mechanism of action of the drug is still unknown. It generally is agreed that metronidazole is a pro-drug and that anaerobic organisms reduce the nitro group in metronidazole to a hydroxylamine, as shown in Figure 39.2, during which a reactive derivative or reactive species are produced that cause destructive effects on cell components (i.e., DNA, proteins, and membranes). Specifically, DoCampo has reported that nitroaryl compounds (nitroimidazoles, metronidazole; nitrofurans, nifurtomox) are reduced to nitro radical anions, which in turn react with oxygen to regenerate the nitroaryl and the superoxide radical anion. Further reduction of superoxide radical anion leads to hydrogen peroxide and homolytic cleavage of the latter leads to hydroxyl radical formation. Superoxide radical anion, hydrogen peroxide, and hydroxyl radicals are referred to as reactive oxygen species (ROS) and are the reactive substances that are implicated in damage to critical cellular components of the parasite.

Фармаколо?гия

Absorption from the intestinal tract is usually good. Food delays but does not reduce absorption.The drug is distributed in body fluids and has a half-life of about 8 hours. High levels are found in plasma and cerebrospinal fluid (CSF). Less than 20% binds to plasma proteins. Metronidazole is metabolized by oxidation and glucuronide formation in the liver and is primarily excreted by the kidneys, although small amounts can be found in saliva and breast milk. Dose reduction is generally unnecessary in renal failure.

Клиническое использование

Metronidazole is the most effective agent available for the treatment of individuals with all forms of amebiasis, with perhaps the exception of the person who is asymptomatic but continues to excrete cysts. That situation calls for an effective intraluminal amebicide, such as diloxanide furoate, paromomycin sulfate, or diiodohydroxyquin. Metronidazole is active against intestinal and extraintestinal cysts and trophozoites.
Although quinacrine hydrochloride has been used for the treatment of giardiasis, many physicians prefer metronidazole. Furazolidone is an alternate choice.
Metronidazole is the drug of choice in Europe for anaerobic bacterial infections; concern about possible carcinogenicity has led to some caution in its use in the United States.Recently it has been found to be effective in treating D. medinensis (Guinea worm) infections and Helicobacter pylori.

Побочные эффекты

The most frequently observed adverse reactions to metronidazole include nausea, vomiting, cramps, diarrhea, and a metallic taste.The urine is often dark or redbrown. Less frequently, unsteadiness, vertigo, ataxia, paresthesias, peripheral neuropathy, encephalopathy, and neutropenia have been reported. Since metronidazole is a weak inhibitor of alcohol dehydrogenase, alcohol ingestion should be avoided during treatment. A psychotic reaction also may be produced. Metronidazole interferes with the metabolism of warfarin and may potentiate its anticoagulant activity. Phenobarbital and corticosteroids lower metronidazole plasma levels by increasing its metabolism, whereas cimetidine raises levels by impairing metronidazole metabolism.The drug is not recommended for use during pregnancy.

Профиль безопасности

Confirmed carcinogen with experimental carcinogenic, neoplastigenic, tumorigenic, and teratogenic data. Moderately toxic by ingestion, intraperitoneal, and subcutaneous routes. Human systemic effects by ingestion: paresthesia, nerve or sheath structural changes, eye changes, tremors, fever, jaundice and other liver changes, hearingacuity changes, somnolence, and ataxia. Experimental reproductive effects. Human mutation data reported. When heated to decomposition it emits toxic fumes of NOx.

Возможный контакт

Metronidazole is an orally administered drug for the treatment of infections due to entamoeba histolytica; trichomonas vaginalis; giardia lamblia, and has also been used for treating Vincent’s infection. It can be used as a trichomonacide in veterinary medicine. One firm has petitioned EPA to use metronidazole as a disinfectant for cooling tower water.

Канцерогенность

Metronidazole is reasonably anticipated to be a human carcinogenbased on sufficient evidence of carcinogenicity from studies in experimental animals.

Экологическая судьба

Due to metronidazole’s use as a pesticide, it may have been directly released into the environment. It lacks an adequate chromophore for absorbing light and undergoing photolytic degradation. In addition, in vitro assays demonstrated the compound’s robust stability in the atmosphere or aqueous environments. Metronidazole exhibited a soil half-life between 10 and 27 days.

Метаболизм

Metronidazole is available in a variety of dosage forms, including IV, oral, rectal, and vaginal suppositories. The bioavailability of metronidazole is nearly 100% when administered orally but is significantly less when administered via the rectal route (67–82%) or the vaginal route (19–56%). The drug is not bound to plasma protein. Distribution of the drug is fairly uniform through out the body, including mother's milk.
Liver metabolism of metronidazole leads to two major metabolites: hydroxylation of the 2-methyl group to 2-hydroxymethylmetronidazole (HM), and oxidation to metronidazole acetic acid. Both compounds possess biological activity. Additionally, HM is found in the urine as glucuronide and sulfate conjugates. In addition, a small amount of metronidazole is oxidized to acetamide, a known carcinogen in rats but not in humans.

Перевозки

UN3249 Medicine, solid, toxic, n.o.s., Hazard Class: 6.1; Labels: 6.1-Poisonous materials.

Несовместимости

Incompatible with oxidizers (chlorates, nitrates, peroxides, permanganates, perchlorates, chlorine, bromine, fluorine, etc.); contact may cause fires or explosions. Keep away from alkaline materials, strong bases, strong acids, oxoacids, epoxides.

Утилизация отходов

Dispose of contents and container to an approved waste disposal plant. All federal, state, and local environmental regulations must be observed. It is inappropriate and possibly dangerous to the environment to dispose of expired or waste drugs and pharmaceuticals by flushing them down the toilet or discarding them to the trash. Household quantities of expired or waste pharmaceuticals may be mixed with wet cat litter or coffee grounds, doublebagged in plastic, discard in trash. Larger quantities shall carefully take into consideration applicable DEA, EPA, and FDA regulations. If possible return the pharmaceutical to the manufacturer for proper disposal being careful to properly label and securely package the material. Alternatively, the waste pharmaceutical shall be labeled, securely packaged, and transported by a state licensed medical waste contractor to dispose by burial in a licensed hazardous or toxic waste landfill or incinerator.