I want to start using Triluma cream. Can I use it with a vitamin C serum that contains vitamins C, E and ferulic acid?

Hi Sofia, Using Vitamin C to help control Melasma is a great idea! Vitamin C works to help regulate our pigment producing cells. You want to make sure you are using CE Ferulic in the morning and TriLuma at night. You do not want to use them at the same time. Vitamin C and Retin A counteract each other. Also, you do not want to use TriLuma long term. When you are coming towards the end of your TriLuma treatment, start to alternate days with a NonHQ skin lightening agent. If you just stop TriLuma cold turkey, you will experience a rebound effect and the pigment will come back right away. -Megan Asp LME

Yes you can. Triluma has a good formulation with stability. You can add Vitamin C, E and ferulic acid as tolerated. Start off 2-3 times a week, increase if you do not have any skin irritation. Melasma can not be completely cured, however effective treatment are possible. Melasma patients have skin that is very sensitive to UV light. Even the smallest amount can stimulate your pigment cells to produce colour. The mainstay of treatment is strict UV protection- hats, sunglasses and SPF every 4 hours. 
I prefer to use a combination of creams and laser for melasma. My most frequently prescribed topicals include hydroquinone, along with vitamin A creams and botanical extracts. The exact percentages will depend on your skin sensitivity, clinical presentation and your current skin care routine. 
I usually start my patients on a series of lasers (low dose Q switch or Picosure), along with medical therapy. Another laser I use is the Clear and Brilliant in the Permea setting. In some cases I combine glycolic AHAs, TCA low strength single coat peels, and in other cases I use a tablet called Tranexamic acid to help modulate the blood vessels that are associated with melanocytes (pigment cells). Melasma treatments should be tailored to each patient. 
All the best, Dr Davin Lim. Laser, surgical and aesthetic dermatologist. Brisbane, Australia. Cutis International