Taking cephalexin for paronychia,no condoms w husband bc i've been on nexplanon since last august.should i be worried it can make it less effective?

Yes: There is a drug interaction listed which states that the efficacy of the contraceptive is decreased. The other issue is why are you taking cephalexin to treat a paronychia. You might switch to a penicillin. Discuss it with your doc.

Not likely rendering: Nexplanon implant useless, but antibiotics certainly can affect the hormone levels, which are normally consistent through an implant. I would use protection during that time frame, or just abstain until after whatever the condition requiring antibiotics has improved.

No interaction: There are no minor, moderate or major drug interactions reported with these 2 medicines. This should not be a problem in terms of birth control efficacy.