Acyclovir 400mg tablets (Ranbaxy) are indicated for the treatment of infections caused by certain types of viruses, such as herpes simplex and varicella zoster, contraindicated in patients with known hypersensitivity to acyclovir or valacyclovir, common side effects may include nausea, diarrhea, headache, and dizziness, and it may interact with drugs that affect renal function or other medications that are nephrotoxic.