Because of the low plasma concentration after local application of the dental gel, the risk of systemic side effects is low.
The following adverse experiences have been reported with the topical use of Metronidazole-Chlorhexidine combination: burning, irritation, dryness, transient redness, metallic taste, staining of teeth, tingling or numbness of extremities and nausea.
Adverse effects, caused by metronidazole
The most common are local and are related to the application, namely a bitter taste and temporary local tenderness. Headache has been reported.
Adverse effects, caused by chlorhexidine
Irritative skin reactions: irritative skin reactions to chlorhexidine preparations can occasionally occur.
Generalised reactions: allergic reactions, hypersensitivity & anaphylaxis to chlorhexidine have also been reported but are extremely rare.
A superficial discoloration of the dorsum of the tongue may occur. This disappears after treatment is discontinued. Discoloration of the teeth and silicate or composite restorations may also occur. The stain is not permanent and can largely be prevented by reducing the consumption of tea, coffee and red wine and brushing with a conventional toothpaste daily before using the gel. However, in certain cases a professional prophylaxis (scaling and polishing) may be required to remove the stain completely. Stained anterior tooth coloured restorations with poor margins or rough surfaces which are not adequately cleaned by professional prophylaxis may require replacement.
Transient disturbance of taste sensation and a burning sensation of the tongue may occur on initial use of the gel. These effects usually diminish with continued use.