Original:  The greater affinity of these substances for the -opioid receptor causes less naloxoneto bind to receptors, increasing the dosage necessary to counteract the resulting respiratory depression.
Revised:  The greater affinity of these substances for the -opioid receptor impedes the activity of naloxone, which is an antagonist at the receptor. Increasing the dosage of naloxone or its frequency of administration may be required to counteract respiratory depression.
Edit intent: clarity