Pronunciation of กระเพรา

Hi everybody! I'm a bit confused about the pronunciation of this word in the basil stir fry. Based on my knowledge of the script, I would pronounce it as 'kra prao'. However I'm hearing it pronounced as 'ka prao' or 'kra pao'. Some places I'm also seeing it spelled as กะเพรา. Is this one of those variations that just exists?