Metronidazole

Metronidazole Vaginal Gel is indicated in the treatment of bacterial vaginosis (formerly referred to as

•  
  NOTE   
  For purposes of this indication, a clinical diagnosis of bacterial vaginosis is usually defined by the presence of a homogeneous vaginal discharge that (a) has a pH of greater than 4.5, (b) emits a “fishy” amine odor when mixed with a 10% KOH solution, and (c) contains clue cells on microscopic examination. Gram’s stain results consistent with a diagnosis of bacterial vaginosis include (a) markedly reduced or absent
  Lactobacillus
  morphology, (b) predominance of
  Gardnerella
  morphotype, and (c) absent or few white blood cells.

Other pathogens commonly associated with vulvovaginitis, e.g.,

The recommended dose is one applicator full of Metronidazole Vaginal Gel (approximately 5 grams containing approximately 37.5 mg of metronidazole) intravaginally once or twice a day for 5 days. For once-a-day dosing, Metronidazole Vaginal Gel should be administered at bedtime.

There were no deaths or serious adverse events related to drug therapy in clinical trials involving 800 non-pregnant women who received Metronidazole Vaginal Gel.

In a randomized, single-blind clinical trial of 505 non-pregnant women who received Metronidazole Vaginal Gel once or twice a day, 2 patients (one from each regimen) discontinued therapy early due to drug-related adverse events. One patient discontinued drug because of moderate abdominal cramping and loose stools, while the other patient discontinued drug because of mild vaginal burning. These symptoms resolved after discontinuation of drug.

Medical events judged to be related, probably related, or possibly related to administration of Metronidazole Vaginal Gel once or twice a day were reported for 195/505 (39%) patients. The incidence of individual adverse reactions were not significantly different between the two regimens. Unless percentages are otherwise stipulated, the incidence of individual adverse reactions listed below was less than 1%:

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  Reproductive:
  
  
  Vaginal discharge (12%),
  
  Symptomatic
  Candida
  cervicitis/vaginitis (10%),
  
  Vulva/vaginal irritative symptoms (9%),
  
  Pelvic discomfort (3%).
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  Gastrointestinal:
  
  
  Gastrointestinal discomfort (7%),
  
  Nausea and/or vomiting (4%),
  
  Unusual taste (2%),
  
  Diarrhea/loose stools (1%),
  
  Decreased appetite (1%),
  
  Abdominal bloating/gas; thirsty, dry mouth.
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  Neurologic:
  
  
  Headache (5%),
  
  Dizziness (2%),
  
  Depression.
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  Dermatologic:
  
  
  Generalized itching or rash.
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  Other:
  
  
  Unspecified cramping (1%),
  
  Fatigue,
  
  Darkened urine.

In previous clinical trials submitted for approved labeling of Metronidazole Vaginal Gel the following was also reported:

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  Laboratory:
  
  
  Increased/decreased white blood cell counts (1.7%).

Other effects that have been reported in association with the use of

Metronidazole Vaginal Gel affords minimal peak serum levels and systemic exposure (AUC) of metronidazole compared to 500 mg oral metronidazole dosing. Although these lower levels of exposure are less likely to produce the common reactions seen with oral metronidazole, the possibility of these and other reactions cannot be excluded presently.

The following adverse reactions and altered laboratory tests have been reported with the

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  Cardiovascular:
  Flattening of the T-wave may be seen in electrocardiographic tracings.
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  Central Nervous System:
  (See
  WARNINGS

  Convulsive Seizures and Peripheral Neuropathy

  Convulsive seizures and peripheral neuropathy, the latter characterized mainly by numbness or paresthesia of an extremity, have been reported in patients treated with oral or intravenous metronidazole. The appearance of abnormal neurologic signs demands the prompt discontinuation of metronidazole vaginal gel therapy. Metronidazole vaginal gel should be administered with caution to patients with central nervous system diseases.

  Psychotic Reactions

  Psychotic reactions have been reported in alcoholic patients who were using oral metronidazole and disulfiram concurrently. Metronidazole vaginal gel should not be administered to patients who have taken disulfiram within the last 2 weeks.
  .) Headache, dizziness, syncope, ataxia, confusion, convulsive seizures, peripheral neuropathy, vertigo, incoordination, irritability, depression, weakness, insomnia.
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  Gastrointestinal:
  Abdominal discomfort, nausea, vomiting, diarrhea, an unpleasant metallic taste, anorexia, epigastric distress, abdominal cramping, constipation, “furry” tongue, glossitis, stomatitis, pancreatitis, and modification of taste of alcoholic beverages.
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  Genitourinary:
  Overgrowth of
  Candida
   in the vagina, dyspareunia, decreased libido, proctitis.
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  Hematopoietic:
  Reversible neutropenia, reversible thrombocytopenia.
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  Hypersensitivity Reactions:
  Urticaria; erythematous rash; flushing; nasal congestion; dryness of the mouth, vagina, or vulva; fever; pruritus; fleeting joint pains.
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  Renal:
  Dysuria, cystitis, polyuria, incontinence, a sense of pelvic pressure, darkened urine.

Metronidazole Vaginal Gel is the intravaginal dosage form of the synthetic antibacterial agent, metronidazole, USP at a concentration of 0.75%. Metronidazole is a member of the imidazole class of antibacterial agents and is classified therapeutically as an antiprotozoal and antibacterial agent. Chemically, metronidazole is a 2-methyl-5-nitroimidazole-1-ethanol. It has a chemical formula of C₆H₉N₃O₃, a molecular weight of 171.16, and has the following structure:

Metronidazole Vaginal Gel is a gelled, purified water solution, containing metronidazole at a concentration of 7.5 mg/g (0.75%). The gel is formulated at pH 4.0. The gel also contains carbomer 934P, edetate disodium, methylparaben, propylparaben, propylene glycol, and sodium hydroxide.

Each applicator full of 5 grams of vaginal gel contains approximately 37.5 mg of metronidazole.

Following a single, intravaginal 5 g dose of metronidazole vaginal gel (equivalent to 37.5 mg of metronidazole) to 12 normal subjects, a mean maximum serum metronidazole concentration of 237 ng/mL was reported (range: 152 to 368 ng/mL). This is approximately 2% of the mean maximum serum metronidazole concentration reported in the same subjects administered a single, oral 500 mg dose of metronidazole (mean C_max = 12,785 ng/mL, range: 10,013 to 17,400 ng/mL). These peak concentrations were obtained in 6 to 12 hours after dosing with metronidazole vaginal gel and 1 to 3 hours after dosing with oral metronidazole.

The extent of exposure [area under the curve (AUC)] of metronidazole, when administered as a single intravaginal 5 g dose of metronidazole vaginal gel (equivalent to 37.5 mg of metronidazole), was approximately 4% of the AUC of a single oral 500 mg dose of metronidazole (4977 ng-hr/mL and approximately 125,000 ng-hr/mL, respectively).

Dose-adjusted comparisons of AUCs demonstrated that, on a mg to mg comparison basis, the absorption of metronidazole, when administered vaginally, was approximately half that of an equivalent oral dosage.

Following single and multiple 5 g doses of metronidazole vaginal gel to 4 patients with bacterial vaginosis, a mean maximum serum metronidazole concentration of 214 ng/mL on day 1 and 294 ng/mL (range: 228 to 349 ng/mL) on day five were reported. Steady-state metronidazole serum concentrations following oral dosages of 400 to 500 mg BID have been reported to range from 6,000 to 20,000 ng/mL.

The intracellular targets of action of metronidazole on anaerobes are largely unknown. The 5-nitro group of metronidazole is reduced by metabolically active anaerobes, and studies have demonstrated that the reduced form of the drug interacts with bacterial DNA. However, it is not clear whether interaction with DNA alone is an important component in the bactericidal action of metronidazole on anaerobic organisms.

Culture and sensitivity testing of bacteria are not routinely performed to establish the diagnosis of bacterial vaginosis. (See

Standard methodology for the susceptibility testing of the potential bacterial vaginosis pathogens,

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  Bacteroides
  spp
  .
  
  
  
  Gardnerella vaginalis
  
  
  
  Mobiluncus
  spp
  .
  
  
  
  Peptostreptococcus
  spp
  .