There is a scroll "restoration scroll", that cures level drain. You can also get rid of it at a temple, or with a priest spell minor restoration or restoration. If you want to protect yourself against leveldrain, then the spell negative plane protection is good. Otherwise there are items out there, that protect against leveldrain.
Also, if you have a berserker, barbarian or Minsc (ranger??) then you can rage/enrage him/her and he/she will be immune to leveldrain for a while.
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