How long can one continue on a skin regimen of clindamycin and retin a (tretinoin) micro? used these for about 4 years. just want to make sure it's safe. thanks!

It's unclear: how long you can use these medications "safely". Most dermatologists feel that topical retinoids(like Retin A) are the best long term maintenance option. The issue with clindamycin use long term, is antibiotic resistance. Sometimes dermatologists will utilize benzyl peroxide to help reduce resistance emergence. Why not review your concerns with your dermatologist.