Short acting opioids for the elderly: What's the point?

Alfentanil and Remifentanil are two short acting opioids that have been known for several years and used for short procedures.[12] Remifentanil is a synthetic opioid with direct action on mu-opioid receptors. It has a rapid onset and short latency to peak effect. It is rapidly inactivated by esterases in both blood and tissues, resulting in a very short duration of action. The context-sensitive half-life remains very short (three to four minutes), independent of the duration of infusion. The rapid effect-site equilibration characteristic of alfentanil is a result of the low pK of this opioid, so that nearly 90% of the drug exists in the non-ionized form at physiologic pH. The non-ionized fraction readily crosses the blood-brain barrier. Alfentanil, depends on its small volume of distribution for rapid termination of its effect, but still possesses the potential to accumulate because of its relatively long terminal elimination half-life.

When comparing pharmacokinetics and pharmacodynamics of both drugs, Egan et al. concluded that with the exception of remifentanil's nearly 20-times greater potency, the drugs are pharmacodynamically similar.[3] Pharmacological characteristics of both drugs seem interesting for old people having short procedures.

Alfentanil and remifentanil have been compared in both children and adults. The speed of recovery is controversial.[4-7] No data was found concerning old people. In this current issue, Entezariasl et al.,[8] in a prospective, randomized and blinded study compared recovery time after alfentanil or remifentanil administration for cataract surgery in elderly patients. Although time to respiration, eyes opening, verbal response and stay in the post anesthesia care unit were not statistically different between the two groups, incidence of postoperative nausea and vomiting (PONV) was higher after remifentanil infusion. Although, the authors did not evaluate the incidence of nausea and its severity, the frequency of antiemetics use and the incidence of retching and vomiting alone, it remains a very important issue, particularly vomiting after eye surgeries in elderly patients. We think it deserves a more detailed and structured study. Postoperative nausea and vomiting is one of the major concerns of patients. They are willing to pay more money to avoid PONV than postoperative pain.[9]

Remifentanil is known to induce postoperative hyperalgesia and this particular criterion was not evaluated, although it is part of postoperative recovery.[5] The authors did not mention if local or regional anesthesia were used.

After all, what really matters is the economic impact of these results. How long will the patient stay in the post anesthesia care unit? Will he/she need an antiemetic drug? Will vomiting have a negative impact on cataract surgery? Which opioid is more expensive: remifentanil or alfentanil?