PDE5 inhibitors can be only so effective

Phosphodiesterase type 5 (PDE5) inhibitors do not increase arginine levels from which nitric oxide is synthesized. Nitric oxide activates soluble guanylyl cyclase producing cyclic guanosine monophophate resulting in vasodilation. PDE5 inhibitors prevent the metabolism of cyclic guanosine monophosphate (cGMP).

For PDE5 inhibitors to work there has to be L-arginine from which nitric oxide is synthesized but where L-citrulline can not be synthesized appropriately nitric oxide can not be synthesized appropriately. PDE5 inhibitors would tend to lose effectiveness over time where carbonated drinks, other acidic drinks have been drunk and/or megadosages of vitamin C have been taken.

Supplementing L-arginine is not effective. L-arginine is metabolized by arginase.

Supplementing L-citrulline, branched-chain amino acids and creatine could be of assistances in increasing L-arginine levels. See this post. L-citrulline also inhibits arginase.

Where carbonated drinks, other acidic drinks have been drunk and/or megadosages of vitamin C has been supplemented a treatment to increase orotate levels, increase RNA synthesis and increase DNA synthesis could be required. See this post. For adults only water is safe to drink.