Anesthetic pharmacokinetics, receptors and adverse effects
Pharmacology connects concentration, receptor action, time course and clinical response. Potency describes the concentration or dose associated with a specified effect; efficacy describes the maximum effect under the relevant conditions. A reversible competitive antagonist can shift an agonist concentration-response curve while preserving the maximum response in the idealized model. A partial agonist can have a lower maximal effect even at high receptor occupancy. Those models are useful only when the assumptions and the actual measured endpoint are clear.
Pharmacokinetics separates absorption, distribution, metabolism and elimination. Rapid recovery after a single intravenous bolus can reflect redistribution from the effect site rather than complete elimination from the body. Context-sensitive half-time describes a fall in plasma concentration after stopping an infusion of a specified duration; it is not interchangeable with terminal elimination half-life or the time required for safe recovery of every clinical function. Organ dysfunction, active metabolites, protein binding, body composition and interactions can alter the response. First-order elimination removes an approximately constant fraction per unit time within its applicable range, while saturation can produce a different relationship.
Volatile-agent reasoning distinguishes minimum alveolar concentration as a population movement endpoint from blood-gas partitioning and speed of equilibration. A lower blood-gas solubility generally favors a faster alveolar rise under comparable conditions, but delivery, ventilation, cardiac output and other factors also matter. Local anesthetics block voltage-gated sodium channels. Their ionization depends on pKa relative to tissue pH, and acidic tissue can reduce the unionized fraction available to cross membranes. The relative onset is not determined by pKa alone because concentration, dose, diffusion and anatomical conditions also affect it.
Neuromuscular blockers act at the motor end plate but have different mechanisms and reversal pathways. Depolarizing and nondepolarizing patterns must be distinguished, including the altered behavior possible after prolonged depolarizing exposure. Sugammadex binds susceptible steroidal neuromuscular blockers by encapsulation; it does not reverse every cause of weakness or replace quantitative assessment of recovery. Hofmann elimination is a temperature- and pH-dependent chemical pathway rather than ordinary renal excretion. Drug adverse effects require mechanistic interpretation: etomidate can inhibit adrenal steroid synthesis, opioids can depress ventilation, and several agents can cause bradycardia or hypotension. An association with a class does not establish an individual treatment order. Evaluate contraindications, monitoring, the intended endpoint and the actual clinical setting.