Journal of clinical anesthesia
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The pharmacokinetic and pharmacodynamic interactions between opioids and propofol increasingly have been described and used in clinical practice. It is now known that propofol inhibits both alfentanil and sufentanil metabolism, thereby increasing the plasma concentrations of these opioids, while alfentanil also elevates propofol concentrations. ⋯ From the interaction data, the optimal propofol concentrations have been extracted that assure adequate anesthesia and the most rapid recovery possible. In the presence of fentanyl, sufentanil, and alfentanil, the optimal propofol concentration is approximately 3.5 microgram/ml, whereas in the presence of remifentanil, lower propofol concentrations of 2.5 to 3 microgram/ml are required.
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For more than 40 years, succinylcholine has been the traditional choice of muscle relaxant to facilitate tracheal intubation, particularly for anesthesia in the emergency patient with a full stomach. This presentation reviews factors that determine the onset of neuromuscular blockade, particularly with regard to tracheal intubation. Measurement of neuromuscular block, both clinical and via nerve stimulators, is described and compared, and correlations with intubating conditions are attempted. ⋯ None of the currently available drugs, or those undergoing clinical investigation, possesses the rapid onset and prompt recovery of succinylcholine. Despite the formidable side effect profile of succinylcholine, it has not been replaced by a nondepolarizing agent for use in emergency conditions. However, the alternatives, particularly rocuronium and mivacurium, are drugs with a greater safety profile that, in many circumstances, can substitute for succinylcholine.
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Multiple drugs are used to provide anesthesia. Volatile anesthetics are commonly combined with opioids. Several studies have demonstrated that small doses of opioid (i.e., within the analgesic range) result in a marked reduction in minimum alveolar concentration (MAC) of the volatile anesthetic that will prevent purposeful movement in 50% of patients at skin incision). ⋯ Recovery from anesthesia when an opioid is combined with a volatile anesthetic is dependent on the rate of decrease of both drugs to their respective concentrations that are associated with adequate spontaneous ventilation and awakening. Through an understanding of the pharmacodynamic interaction of volatile anesthetics with opioids and the pharmacokinetic processes responsible for the recovery from drug effect, optimal dosing schemes can thus be developed. A review of these pharmacodynamic and pharmacokinetic principles that will allow clinicians to administer drugs to provide a more optimal anesthetic is provided.
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Modern anesthetic techniques involve combinations of intravenous (i.v.) and inhaled anesthetic drugs that may produce synergistic (supraadditive), additive, or antagonistic interactions. Synergistic interaction is most likely to occur when two or more drugs produce similar effects by different mechanisms. ⋯ The usefulness of a drug interaction depends on whether it produces greater efficacy or reduced toxicity. Surprisingly, these outcomes have only been specifically measured for a handful of common drug combinations.
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Anesthesia often involves the administration of several drugs belonging to different classes. In addition, many patients will be taking a number of drugs related to their surgical condition or for other medical diseases. ⋯ Other important interactions involve monoamine oxidase inhibitors, some antibiotics, and the tricyclic and tetracyclic antidepressants. These adverse interactions are the subject of this review.