For complete healing of a chronic anal fissure, you should continue applying Nitrogesic ointment for 6 to 8 weeks, even if your pain disappears within 5 days. Stopping too early can cause the fissure to reopen. To prevent recurrence, the key is keeping stools soft. You can take daily fiber supplements like Psyllium husk (Isabgol) and occasional osmotic laxatives like Lactulose if you experience constipation. Additionally, drink 2-3 liters of water daily, maintain a high-fiber diet, and avoid straining during bowel movements. If symptoms persist after 8 weeks, consult your doctor to discuss further treatment options.