This is just copied and pasted from the MSDS and Product Insert. I didn’t write much except I think two lines in parenthesis. I deleted a lot to shorten it. In summary, this drug shouldn’t be overused… shouldn’t be given when the doctor/vet is not SURE that it will work on that PARTICULAR problem before starting the treatment… it does cause cancer as well as birth defects, potentially seizures, overgrowth of candida yeast, joint pain, rashes, intestinal distress and, in rare cases, pancreatitis … so there ya go… you hear about this medication more often than almost any other so it’s important to read through this:
Metronidazole / Flagyl
MSDS and Product Insert information
MSDS (Material Safety Data Sheet):
Section 11: Toxicological Information p. 4
…Toxicity to Animals: Acute oral toxicity (LD50): 3000 mg/kg [Rat].
Chronic Effects on Humans:
CARCINOGENIC EFFECTS: Classified 2 (Reasonably anticipated.) by NTP. The substance is toxic to mucous membranes.
Other Toxic Effects on Humans:
Very hazardous in case of skin contact (irritant, permeator), of inhalation.
Hazardous in case of ingestion.
Special Remarks on Toxicity to Animals: Not available.
Special Remarks on Chronic Effects on Humans: Not available.
Special Remarks on other Toxic Effects on Humans: Not available.
Section 15: Other Regulatory Information p. 5
Federal and State Regulations:
California prop. 65: This product contains the following ingredients for which the State of California has found to cause cancer, birth defects or other reproductive harm, which would require a warning under the statute: Metronidazole California prop. 65: This product contains the following ingredients for which the State of California has found to cause cancer which would require a warning under the statute: Metronidazole Pennsylvania RTK: Metronidazole Massachusetts RTK: Metronidazole
Other Regulations: OSHA: Hazardous by definition of Hazard Communication Standard (29 CFR 1910.1200).
WHMIS (Canada): CLASS D-2B: Material causing other toxic effects (TOXIC).
R38- Irritating to skin. R41- Risk of serious damage to eyes. R45- May cause cancer.
FLAGYL- metronidazole tablet, film coated
G.D. Searle LLC Division of Pfizer Inc
To reduce the development of drug-resistant bacteria and maintain the effectiveness of FLAGYL® and other antibacterial drugs, FLAGYL® should be used only to treat or prevent infections that are proven or strongly suspected to be caused by bacteria.
Metronidazole has been shown to be carcinogenic in mice and rats (see PRECAUTIONS). Unnecessary use of the drug should be avoided. Its use should be reserved for the conditions described in the INDICATIONS AND USAGE section below.
FLAGYL (metronidazole) tablets, 250 mg or 500 mg is an oral formulation of the synthetic nitroimidazole antimicrobial, 2-methyl-5-nitro-1H-imidazole-1-ethanol…
FLAGYL (metronidazole) tablets contain 250 mg or 500 mg of metronidazole. Inactive ingredients include cellulose, FD&C Blue No. 2 Lake, hydroxypropyl cellulose, hypromellose, polyethylene glycol, stearic acid, and titanium dioxide.
Metronidazole is the major component appearing in the plasma, with lesser quantities of metabolites also being present. Less than 20% of the circulating metronidazole is bound to plasma proteins. Metronidazole appears in cerebrospinal fluid, saliva, and breast milk in concentrations similar to those found in plasma. Bactericidal concentrations of metronidazole have also been detected in pus from hepatic abscesses.
Mechanism of Action
Metronidazole, a nitroimidazole, exerts antibacterial effects in an anaerobic environment against most obligate anaerobes. Once metronidazole enters the organism by passive diffusion and activated in the cytoplasm of susceptible anaerobic bacteria, it is reduced; this process includes intracellular electron transport proteins such as ferredoxin, transfer of an electron to the nitro group of the metronidazole, and formation of a short-lived nitroso free radical. Because of this alteration of the metronidazole molecule, a concentration gradient is created and maintained which promotes the drug’s intracellular transport. The reduced form of metronidazole and free radicals can interact with DNA leading to inhibition of DNA synthesis and DNA degradation leading to death of the bacteria. (No comment is made on the effect on the DNA of the person pet that is CONSUMING the metronidazole. It seems unlikely that the ONLY DNA that is damaged is that of the bacteria.) The precise mechanism of action of metronidazole is unclear.
A potential for development of resistance exists against metronidazole.
Resistance may be due to multiple mechanisms that include decreased uptake of the drug, altered reduction efficiency, overexpression of the efflux pumps, inactivation of the drug, and/or increased DNA damage repair (This implies the DNA of the one taking the drug may be damaged and therefore unable to repair itself, leading to resistance).
Activity In Vitro and in Clinical Infections
Metronidazole has been shown to be active against most isolates of the following bacteria both in vitro and in clinical infections as described in the INDICATIONS AND USAGE section.
Clostridium species, Eubacterium species, Peptococcus species, Peptostreptococcus species, Gram-negative anaerobes
Bacteroides fragilis group (B. fragilis, B. distasonis, B. ovatus, B. thetaiotaomicron, B.vulgatus), Fusobacterium species, Protozoal parasites, Entamoeba histolytica, Trichomonas vaginalis
The following in vitro data are available, but their clinical significance is unknown:
Metronidazole exhibits in vitro minimal inhibitory concentrations (MIC’s) of 8 mcg/mL or less against most (≥ 90%) isolates of the following bacteria; however, the safety and effectiveness of metronidazole in treating clinical infections due to these bacteria have not been established in adequate and well-controlled clinical trials.
INDICATIONS AND USAGE
FLAGYL is indicated for the treatment of T. vaginalis infection in females and males when the presence of the trichomonad has been confirmed by appropriate laboratory procedures (wet smears and/or cultures).
FLAGYL is indicated in the treatment of acute intestinal amebiasis (amebic dysentery) and amebic liver abscess.
In amebic liver abscess, FLAGYL therapy does not obviate the need for aspiration or drainage of pus.
Anaerobic Bacterial Infections
FLAGYL is indicated in the treatment of serious infections caused by susceptible anaerobic bacteria. Indicated surgical procedures should be performed in conjunction with FLAGYL therapy. In a mixed aerobic and anaerobic infection, antimicrobials appropriate for the treatment of the aerobic infection should be used in addition to FLAGYL.
INTRA-ABDOMINAL INFECTIONS, including peritonitis, intra-abdominal abscess, and liver abscess, caused by Bacteroides species including the B. fragilis group (B. fragilis, B. distasonis, B. ovatus, B. thetaiotaomicron, B. vulgatus), Clostridium species, Eubacterium species, Peptococcus species,and Peptostreptococcus species.
SKIN AND SKIN STRUCTURE INFECTIONS caused by Bacteroides species including the B. fragilis group, Clostridium species, Peptococcus species, Peptostreptococcus species, and Fusobacterium species.
GYNECOLOGIC INFECTIONS, including endometritis, endomyometritis, tubo-ovarian abscess, and postsurgical vaginal cuff infection, caused byBacteroides species including the B. fragilis group, Clostridium species, Peptococcus species, Peptostreptococcus species, and Fusobacteriumspecies.
BACTERIAL SEPTICEMIA caused by Bacteroides species including the B. fragilis group and Clostridium species.
BONE AND JOINT INFECTIONS, (as adjunctive therapy), caused by Bacteroides species including the B. fragilis group.
CENTRAL NERVOUS SYSTEM (CNS) INFECTIONS, including meningitis and brain abscess, caused by Bacteroides species including the B. fragilisgroup.
LOWER RESPIRATORY TRACT INFECTIONS, including pneumonia, empyema, and lung abscess, caused by Bacteroides species including the B. fragilis group.
ENDOCARDITIS caused by Bacteroides species including the B. fragilis group.
To reduce the development of drug-resistant bacteria and maintain the effectiveness of FLAGYL and other antibacterial drugs, FLAGYL should be used only to treat or prevent infections that are proven or strongly suspected to be caused by susceptible bacteria. When culture and susceptibility information are available, they should be considered in selecting or modifying antibacterial therapy. In the absence of such data, local epidemiology and susceptibility patterns may contribute to the empiric selection of therapy.
Central and Peripheral Nervous System Effects
Encephalopathy and peripheral neuropathy
Cases of encephalopathy and peripheral neuropathy (including optic neuropathy) have been reported with metronidazole.
Encephalopathy has been reported in association with cerebellar toxicity characterized by ataxia, dizziness, and dysarthria. CNS lesions seen on MRI have been described in reports of encephalopathy. CNS symptoms are generally reversible within days to weeks upon discontinuation of metronidazole. CNS lesions seen on MRI have also been described as reversible.
Peripheral neuropathy, mainly of sensory type has been reported and is characterized by numbness or paresthesia of an extremity.
Convulsive seizures have been reported in patients treated with metronidazole.
Cases of aseptic meningitis have been reported with metronidazole. Symptoms can occur within hours of dose administration and generally resolve after metronidazole therapy is discontinued.
The appearance of abnormal neurologic signs and symptoms demands the prompt evaluation of the benefit/risk ratio of the continuation of therapy (see ADVERSE REACTIONS).
Patients with hepatic impairment metabolize metronidazole slowly, with resultant accumulation of metronidazole in the plasma. …
Patients with end-stage renal disease may excrete metronidazole and metabolites slowly in the urine, resulting in significant accumulation of metronidazole metabolites…
Known or previously unrecognized candidiasis may present more prominent symptoms during therapy with FLAGYL and requires treatment with a candidacidal agent.
Use in Patients with Blood Dyscrasias
Metronidazole is a nitroimidazole and should be used with caution in patients with evidence of or history of blood dyscrasia. A mild leukopenia has been observed during its administration; however, no persistent hematologic abnormalities attributable to metronidazole have been observed in clinical studies. Total and differential leukocyte counts are recommended before and after therapy.
Drug-Resistant Bacteria and Parasites
Prescribing FLAGYL in the absence of a proven or strongly suspected bacterial or parasitic infection or a prophylactic indication is unlikely to provide benefit to the patient and increases the risk of the development of drug-resistant bacteria and parasites.
Treatment of Bacterial and Parasitic Infections
Patients should be counseled that FLAGYL should only be used to treat bacterial and parasitic infections. FLAGYL does not treat viral infections (e.g., the common cold). When FLAGYL is prescribed to treat a bacterial infection, patients should be told that although it is common to feel better early in the course of therapy, the medication should be taken exactly as directed. Skipping doses or not completing the full course of therapy may (1) decrease the effectiveness of the immediate treatment and (2) increase the likelihood that bacteria will develop resistance and will not be treatable by FLAGYL in the future.
Drug/Laboratory Test Interactions
Metronidazole may interfere with certain types of determinations of serum chemistry values, such as aspartate aminotransferase (AST, SGOT), alanine aminotransferase (ALT, SGPT), lactate dehydrogenase (LDH), triglycerides, and glucose hexokinase. Values of zero may be observed. All of the assays in which interference has been reported involve enzymatic coupling of the assay to oxidation-reduction of nicotinamide adenine dinucleotide (NAD+ NADH). Interference is due to the similarity in absorbance peaks of NADH (340 nm) and metronidazole (322 nm) at pH 7.
Carcinogenesis, Mutagenesis, Impairment of Fertility
Tumors affecting the liver, lungs, mammary, and lymphatic tissues have been detected in several studies of metronidazole in rats and mice,but not hamsters.
Pulmonary tumors have been observed in all six reported studies in the mouse, including one study in which the animals were dosed on an intermittent schedule (administration during every fourth week only). Malignant liver tumors were increased in male mice treated at approximately 1500 mg/m2 (similar to the maximum recommended daily dose, based on body surface area comparisons). Malignant lymphomas and pulmonary neoplasms were also increased with lifetime feeding of the drug to mice. Mammary and hepatic tumors were increased among female rats administered oral metronidazole compared to concurrent controls. Two lifetime tumorigenicity studies in hamsters have been performed and reported to be negative.
Metronidazole has shown mutagenic activity in in vitro assay systems including the Ames test. Studies in mammals in vivo have failed to demonstrate a potential for genetic damage.
Metronidazole failed to produce any adverse effects on fertility or testicular function in male rats at doses up at 400 mg/kg/day (similar to the maximum recommended clinical dose, based on body surface area comparisons) for 28 days. However, rats treated at the same dose for 6 weeks or longer were infertile and showed severe degeneration of the seminiferous epithelium in the testes as well as marked decreases in testicular spermatid counts and epididymal sperm counts. Fertility was restored in most rats after an eight week, drug-free recovery period.
Safety and effectiveness in pediatric patients have not been established, except for the treatment of amebiasis.
The following reactions have been reported during treatment with metronidazole:
Central Nervous System
The most serious adverse reactions reported in patients treated with metronidazole have been convulsive seizures, encephalopathy, aseptic meningitis, optic and peripheral neuropathy, the latter characterized mainly by numbness or paresthesia of an extremity. Since persistent peripheral neuropathy has been reported in some patients receiving prolonged administration of metronidazole, patients should be specifically warned about these reactions and should be told to stop the drug and report immediately to their physicians if any neurologic symptoms occur. In addition, patients have reported headache, syncope, dizziness, vertigo, incoordination, ataxia, confusion, dysarthria, irritability, depression, weakness, and insomnia(see WARNINGS).
The most common adverse reactions reported have been referable to the gastrointestinal tract, particularly nausea, sometimes accompanied byheadache, anorexia, and occasionally vomiting; diarrhea; epigastric distress; and abdominal cramping and constipation.
A sharp, unpleasant metallic taste is not unusual. Furry tongue, glossitis, and stomatitis have occurred; these may be associated with a sudden overgrowth of Candida which may occur during therapy.
Erythematous rash and pruritus.
Reversible neutropenia (leukopenia); rarely, reversible thrombocytopenia.
Flattening of the T-wave may be seen in electrocardiographic tracings.
Urticaria, erythematous rash, Stevens-Johnson Syndrome, toxic epidermal necrolysis, flushing, nasal congestion, dryness of the mouth (or vagina or vulva), and fever.
Dysuria, cystitis, polyuria, incontinence, and a sense of pelvic pressure. Instances of darkened urine have been reported by approximately one patient in 100,000. Although the pigment which is probably responsible for this phenomenon has not been positively identified, it is almost certainly a metabolite of metronidazole and seems to have no clinical significance.
Proliferation of Candida in the vagina, dyspareunia, decrease of libido, proctitis, and fleeting joint pains sometimes resembling “serum sickness.” Rare cases of pancreatitis, which generally abated on withdrawal of the drug, have been reported.
Patients with Crohn’s disease are known to have an increased incidence of gastrointestinal and certain extraintestinal cancers. There have been some reports in the medical literature of breast and colon cancer in Crohn’s disease patients who have been treated with metronidazole at high doses for extended periods of time. A cause and effect relationship has not been established. Crohn’s disease is not an approved indication for FLAGYL tablets.
Clinical and Laboratory Standards Institute (CLSI). Methods for Antimicrobial Susceptibility Testing of Anaerobic Bacteria; Approved Standard – Eighth Edition. CLSI document M11-A8. Clinical and Laboratory Standards Institute, 950 West Valley Road, Suite 2500, Wayne, PA 19087 USA, 2012.
Clinical and Laboratory Standards Institute (CLSI). Performance Standards for Antimicrobial Susceptibility Testing; Twenty-fifth Informational Supplement, CLSI document M100-S25. CLSI, 950 West Valley Road, Suite 2500, Wayne, Pennsylvania 19087, USA, 2015.
Section 11: Toxicological Information Routes of Entry: Inhalation. Ingestion.
Eye: Dust may cause eye irritation Inhalation: Dust may cause respiratory tract distress