Hi!
Penicillin G is acid labile and thus poorly absorbed when administered
orally.  Pen G is mainly administered via the intravenous route, since
the intramuscular injection is very
painful.
Pen VK  has a good oral absorption and is more stable than Pen G,
therefore Pen VK can be administered orally. The absorption of Pen VK
is optimal if taken on an empty stomach - one hour before meals or
three hours after meals.

Kind Regards