Varicose Veins – Superficial Thrombophlebitis Management

A 45-year-old man with a 10-year history of varicose veins in the left lower limb presents with sudden onset of pain, swelling, and erythema over the medial calf. On examination, a tender, palpable cord is felt along the greater saphenous vein. Duplex ultrasound confirms thrombosis of the greater saphenous vein with no involvement of the deep venous system. What is the most appropriate next step in management?