PDGFRB and Respiratory insufficiency due to muscle weakness: Since tolerance to unpleasant or potentially life-threatening side effects of opioids such as respiratory depression, constipation, urinary retention and delirium, does not occur as rapidly as analgesic tolerance [3], PDGFR-β antagonism could potentially reduce the risks associated with chronic opioid treatment [16] and the suffering that results when opioids lose effectiveness.