Will sulfamethoxazole cause a false negative for blood in urinalysis or cause red blood cells to lyse for microscopic exam?

A rare side effect of this drug can be the lysis of red blood cells . Also it should be avoided in patient with G6Pd deficiency or with folic acid deficiency . For other side effects , some rare , you could go to drugs.com

This drug is unlikely to cause the side effects you listed. Visit this site for info: https://www.mayoclinic.org/drugs-supplements/sulfamethoxazole-and-trimethoprim-oral-route/side-effects/drg-20071899

No it does not.