Metronidazole is most commonly taken twice a day, 12 hours apart, for 7 days. That’s the standard schedule for the immediate-release tablet, which is the version most people are prescribed. But the exact frequency depends on your condition, the form of the medication, and whether you’re taking the standard or extended-release version.
Twice Daily Is the Most Common Schedule
For most infections treated with oral metronidazole, the typical regimen is 500 mg taken every 12 hours for 7 days. This applies to bacterial vaginosis, trichomoniasis in women, and many other bacterial infections. The goal of twice-daily dosing is to keep the drug at effective levels in your body throughout the day, since the immediate-release version is processed relatively quickly.
There are exceptions. For trichomoniasis in men, the CDC recommends a single 2-gram dose taken all at once, rather than a week-long course. A one-time 2-gram dose is also sometimes prescribed for bacterial vaginosis, though the 7-day course is more standard. Your prescriber chooses between these based on the infection type, your sex, and how reliably you’re likely to complete a longer course.
Extended-Release Tablets: Once a Day
The extended-release version of metronidazole is taken once daily instead of twice. Each tablet contains 750 mg and is designed to release the drug gradually. A typical course is once a day for 7 days.
One important difference: the extended-release tablet must be taken on an empty stomach, either 1 hour before or 2 hours after eating. The standard immediate-release capsules and tablets don’t have this restriction. If your stomach gets upset, you can take the regular version with food or a snack. Mixing up these instructions between versions can affect how well the drug works.
Vaginal Gel Has Its Own Schedule
If you’ve been prescribed metronidazole as a vaginal gel (0.75%), the frequency is different from the oral tablets. The standard schedule is one full applicator inserted once a day for 5 days. This is a common alternative for bacterial vaginosis when someone wants to avoid oral medication or has trouble tolerating the side effects of the pills.
Spacing Your Doses Evenly
When taking metronidazole twice a day, try to space your doses as close to 12 hours apart as possible. If you take your first dose at 8 a.m., aim for the second around 8 p.m. Consistent spacing keeps steady levels of the drug in your system, which matters for clearing the infection completely.
If you miss a dose, take it as soon as you remember. But if it’s nearly time for your next scheduled dose, skip the missed one and continue your regular schedule. Don’t double up to compensate. Missing doses or stopping early can reduce the drug’s effectiveness and allow the infection to come back. The 7-day multidose regimen cuts reinfection rates significantly compared to single-dose treatment. In studies of trichomoniasis, for instance, women who completed the full 7-day course were half as likely to test positive at a follow-up visit compared to those given just one large dose.
Common Side Effects During Treatment
Metronidazole works by damaging the DNA of bacteria and certain parasites, and it’s effective against infections that thrive in low-oxygen environments. That potency comes with some predictable side effects. Nausea, stomach cramps, diarrhea, headache, and dizziness are the most frequently reported. About 1 in 6 people (15.5%) experience a metallic taste in their mouth during treatment, which is one of the drug’s signature complaints. These side effects are generally manageable and resolve after the course ends.
In rare cases, longer or high-dose courses can cause numbness or tingling in the hands and feet, a sign of nerve irritation. If you notice this, it’s worth flagging to your prescriber promptly, as stopping the medication early can prevent it from worsening.
Alcohol and Metronidazole Don’t Mix
You need to avoid alcohol entirely while taking metronidazole and for at least 48 to 72 hours after your last dose. The interaction can trigger severe nausea, vomiting, flushing, and rapid heartbeat. This isn’t limited to drinks: watch for alcohol in mouthwash, cooking extracts, and certain liquid medications. Some products containing propylene glycol can also cause a reaction. The package labeling advises waiting at least 48 hours after your final dose, though many clinicians recommend 72 hours to be safe.