What are the advantages and disadvantages of intramuscular opioid therapy?

What are the advantages and disadvantages of intramuscular opioid therapy?

For years, intramuscular (IM) opioids were the main-stay of postoperative pain management. An order such as “meperidine 75 mg IM q4H prn pain” was the gold standard by which other analgesic regimens were judged.

Advantages of the use of IM opioids include ease of administration, familiarity with the technique, and low cost. Disadvantages include long delays from a patient’s complaint of pain to actual time of drug administration, long onset of action, as well as variable and unreliable absorption. When IM opioids are administered every 3–4 hours, bolus doses lead to alternating periods of analgesic-induced over-sedation and painful under-medication. During IM administration, only during one third to one half of the time is the patient’s blood opioid concentration in the “analgesic therapeutic window”, where they are com-fortable but not having side-effects. Standard IM opioid orders do not take into account the variability seen between patients with regard to dosing of opioids to achieve analgesia. Individual variability may account for up to a sevenfold difference in the plasma opioid concentra-tion required to achieve analgesia. Each patient possesses particular plasma opioid concentration at which analgesia becomes adequate and only by individual titration can this be achieved.