Is glutathione injection a permanent solution for skin whitening?

No, the results are not permanent.   You must continue with monthly maintenance treatments. 
Glutathione is poorly absorbed orally when taken by mouth, therefore, intravenous therapy is recommended when treating medical conditions.  IV glutathione should only be administered by a license medical professional. The skin  effects of IV glutathione vary from person to person.  The number  of treatments needed to see improvement in skin texture and tone range from 15 to 30 treatments. It can take up to six months to see the benefits of IV glutathione combined with IV vitamin C and the results vary for each individual. The effects are not permanent since the skin is constantly changing and aging.  IV glutathione for skin brightening  is a off label use of  glutathione but it is used to improve many medical illnesses.  The dose may range from 1000mg to 5000mg. 

Glutathione  is a powerful anti-oxidant has many health benefits.  Antioxidants are our body’s solution for dealing with oxidative stress. Oxidative stress occurs when there is an  disruption of the balance  between the production of free radicals and the ability of naturally occurring antioxidants like glutathione  in our bodies  to  neutralize and detoxify their harmful effects. A free radical  is an oxygen containing molecule that has  unpaired electrons that makes it highly reactive with  other molecules in the body. This reaction can be good but it can also be bad for the body because it can damage cells and their components i.e DNA, cell walls,  protein and lipids, which makes cells unstable.  This instability can lead to neurodegenerative diseases, Alzheimer’s disease,  cancer, chronic fatigue, cardiovascular disease and inflammatory diseases.  Glutathione plays essential  roles in the immune response, DNA repair, and the detoxification process that neutralizes drugs, chemicals, metabolic wastes  and other toxins.   Its  depletion is associated with disease and  premature aging. The benefits of glutathione far outweigh any potential side effects that only occur with extremely high doses of glutathione.
 Glutathione also appears to work  by  ridding the body of toxins and free radicals that lead to hyper-pigmentation, age spots, sun spots, wrinkles, fine lines  and conditions such as melasma  or post inflammatory hyper-pigmentation.   It can help with  cystic acne, acne-prone skin,  red spots and  skin roughness  while improving the overall texture, tone, elasticity  and smoothness of the skin.