- Drug with ↓ solubility in blood = rapid induction and rapid recovery (NO ↓ solubility; Halothane ↑ solubility)
- Arteriovenous gradient = solubility in blood
- Drug with ↑ solubility in lipids = ↑ potency = 1/MAC
- MAC = Minimum Alveolar Concentration required to prevent 50% of subjects from moving in response to a noxious stimulus
- High blood:gas coefficient = high solubility
One-Compartment Model
- Remifentanyl is so rapidly metabolized by ester hydrolysis that significant depot storage does not occur, and a one-compartment model of pharmacokinetics is approximated, causing rapid emergence from its effects after cessation of administration. Meperidine, morphine, and fentanyl undergo more slow hepatic degradation and follow a two-compartment model.
- Alfentanil has a potency 1/10th that of fentanyl and is relatively rapidly metabolized by hepatic degradation. These two properties allow relative safety in intermittent bolus administration in a sedation technique, and have made this drug popular as an agent in an outpatient general anesthetic technique. Sufentanil has a shorter alpha half-life (by redistribution) and a shorter beta half life (by hepatic and renal metabolism) than does fentanyl. However, its potency is 10 times that of fentanyl and it is recommended for continuous intravenous infusion only, since a bolus administration of this extremely potent opioid can yield very high peaks of pharmacologic effect and side-effect. Remifentanil is equipotent to fentanyl. However, its rapid onset is associated with bradypnea, trunchal rigidity and bradycardia. Although it has been used as a bolus administration for procedures such as a retrobulbar block it is generally recommended for continuous infusion. Meperidine undergoes slower metabolization and repetitive administration can prolong recovery.
