Metronidazole starts to work fairly quickly, usually within 1 to 2 hours after taking it, as it gets absorbed rapidly and reaches its maximum concentration in the blood within about 20 minutes to 3 hours. However, it typically takes a few days before noticeable improvement in symptoms occurs. For many infections, people start feeling better within a few days, but the full course should be completed to ensure the infection is fully treated. In some cases, it can take up to a week or longer for full effect, depending on the infection being treated. For example, bacterial vaginosis symptoms often improve within a few days, but the entire treatment course of about seven days should be completed. Dental infections and other serious infections may also show symptom relief within a few days but require a full course to prevent recurrence.
