The numbness your wife is experiencing is a known side effect of long-term metronidazole use, called peripheral neuropathy. Do not start any new medication on your own. The most important step is to contact her prescribing doctor immediately. They will likely need to stop or change the metronidazole, which is the key treatment to prevent permanent nerve damage and allow the nerves to heal. Her doctor may also recommend specific nerve-supportive supplements, such as Vitamin B complex, or other prescription therapies to help manage the symptoms during her recovery.