Comparison of Oral Morphine Versus Nasal Ketamine Spray With Chitosan in Cancer Pain Outpatients

34 adult (\>18 years) cancer pain outpatients with Opioid base therapy because of pain and breakthrough pain or extreme pain on movement will be included in this prospective, randomized, double-blind crossover study. Over a period of 3 weeks patients will go through 3 treatment arms, each one lasting one week: Group A receives morphine drops and Placebo spray, Group B receives ketamine/chitosan spray nasal and Placebo drops and Group C receives morphine drops and ketamine/chitosan spray nasal. Primary endpoint is time to onset of action of intranasal ketamine compared with morphine drops. Secondary endpoint is the median numeric rating scale (NRS) improvement after using the spray or morphine or the combination of ketamine spray and morphine drops.