Hemolysis and thrombocytopenia.
+Central or peripheral loss of visual field.
+Muscle fasciculations and rhabdomyolysis.
+Photodermatitis.
+Hepatitis.
Hepatitis is the most severe potential side effect of isoniazid and may be fatal. Its incidence increases in older patients. Peripheral neuropathy is the most common toxic reaction; vitamin B6 is often given to ameliorate this effect. Skin reactions do occur, but photodermatitis is not particularly associated with isoniazid.