Pharmacology in the elderly


With aging, decreased muscle mass and increased body fat result in overall decrease in total body water. Thus, lipid-soluble drugs have higher plasma concentrations and water-soluble drugs have lower concentrations. Also, GFR and hepatic function decline resulting in increased duration of action of several common anesthetics (see below). Protein binding via albumin is usually decreased (targeting drugs such as barbiturates, benzodiazepines, opioids), resulting in increased action of those specific drugs. The action of local anesthetics, however, is usually decreased (this is not generally the case for neuraxial use of local) because they are bound by alpha-1 acid glycoprotein, which increases with age. MAC declines by approximately 4-6% per decade over 40. Volatile anesthetic agents’ myocardial depressant effect is augmented in elderly patients. Recovery from volatile anesthesia is prolonged for reasons outlined above. Propofol is more likely to cause apnea and hypotension; requirement in the elderly population is reduced by as much as 50%. Dose requirements for fentanyl, alfentanil, and sufentanil are all reduced by as much as 50%. Clearance is a factor for remifentanil – thus dosing requirements for remifentanil in particular may be even further reduced. Dosing requirements are reduced by 50% for Midazolam as well and half-life is prolonged up to 4 hours. The perioperative use of Midazolam (and other benzodiazepines) is also associated with an increased risk of postoperative delirium. Aging does not significantly change the response to succinylcholine or NMDBs. Those drugs that depend on renal clearance (pancuronium) may produce prolonged block due to diminished GFR in the elderly. Renally excreted drugs (rocuronium and vecuronium) may also have prolonged action if hepatic function is diminished in an elderly patient as well. Be aware of the generally greater number of home meds elderly patients are taking and possible drug-drug interactions pertinent to our practice.


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