Do intravenous and intramuscular injections taken for medicinal or nutritional reasons invalidate fasting?

Fasting is not invalidated by intravenous and intramuscular injections taken for medicinal or nutritional purposes because fasting is nullified by anything that enters the body cavity through a visible external natural body orifice. The injected fluid does not reach the stomach in the first place and does not enter the body through a visible external natural body orifice but through the pores; therefore, it does not nullify fasting.