Propofol

MECHANISM OF ACTION

Propofol is a short-acting intravenous anesthetic that produces sedation and hypnosis primarily by potentiating the activity of GABA-A receptors in the central nervous system. By binding to these ligand-gated chloride channels, propofol increases the duration that the channels remain open when gamma-aminobutyric acid (GABA) is present, leading to hyperpolarization of neuronal membranes and a reduction in neuronal excitability.

PHARMACOKINETICS

Absorption

Propofol is administered exclusively by intravenous injection; it is not absorbed orally due to extensive first-pass metabolism in the liver. Following IV administration, propofol rapidly enters the systemic circulation and quickly crosses the blood-brain barrier because of its high lipid solubility. 

Distribution

After intravenous administration, propofol is rapidly distributed throughout the body due to its high lipid solubility. It quickly penetrates highly perfused organs such as the brain, heart, and lungs, which contributes to its rapid onset of anesthesia. Propofol has a large volume of distribution, approximately 2–10 L/kg, reflecting its extensive uptake into peripheral tissues, including muscle and fat.

Metabolism

Propofol undergoes extensive hepatic metabolism, primarily through glucuronidation and sulfation, producing inactive water-soluble metabolites. A smaller proportion is metabolized by cytochrome P450 enzymes in the liver. These metabolites are pharmacologically inactive and are efficiently cleared from the body. Extrahepatic metabolism also occurs, particularly in the lungs, contributing to the rapid clearance of the drug.

Elimination

Propofol and its inactive metabolites are primarily excreted by the kidneys. Less than 1% of unchanged propofol appears in the urine. The elimination half-life is approximately 1–3 hours, though the clinical effect wears off much sooner due to rapid redistribution from the brain to peripheral tissues.

PHARMACODYNAMICS

Propofol is a short-acting intravenous anesthetic and sedative-hypnotic that produces its effects by enhancing inhibitory neurotransmission in the central nervous system. Its primary action is potentiation of GABA-A receptors, which increases chloride ion influx into neurons, leading to hyperpolarization and decreased neuronal excitability. This results in rapid onset of sedation, hypnosis, and amnesia, typically within 30–60 seconds of IV administration. Propofol also exhibits modest inhibition of excitatory NMDA receptors, further contributing to its CNS depressant effects.

ADMINISTRATION

Propofol is administered exclusively by intravenous (IV) injection due to poor oral bioavailability. It can be given as a bolus for rapid induction of anesthesia or as a continuous infusion for maintenance of anesthesia or sedation in the operating room or intensive care unit. Dosing is weight-based and adjusted according to the patient’s age, clinical condition, and procedure type. Propofol should be administered by trained healthcare professionals with immediate access to airway management and resuscitation equipment, as it can cause respiratory depression, hypotension, and apnea.

DOSAGE AND STRENGTH

Propofol is available as a sterile intravenous lipid emulsion, typically in concentrations of 1% (10 mg/mL) or 2% (20 mg/mL). The dosage varies depending on the patient’s age, weight, clinical condition, and intended use. For induction of anesthesia in adults, a bolus of 1.5–2.5 mg/kg is usually administered over 20–30 seconds, producing rapid onset within 30–60 seconds and a short duration of action. Maintenance of anesthesia is achieved with a continuous infusion of 4–12 mg/kg/hr or intermittent boluses, while sedation for procedures or in intensive care typically requires 0.3–4 mg/kg/hr, titrated to effect.

DRUG INTERACTIONS

Propofol’s effects can be significantly influenced by other medications, particularly those that depress the central nervous system or affect cardiovascular function. Concomitant use with benzodiazepines, opioids, barbiturates, or other anesthetics can potentiate sedation, hypnosis, and respiratory depression, increasing the risk of apnea and hypotension. Drugs such as beta-blockers, calcium channel blockers, and other vasodilators may enhance propofol-induced hypotension, necessitating careful hemodynamic monitoring.

FOOD INTERACTIONS

Propofol is administered exclusively by intravenous injection, so it does not interact directly with food. Its absorption and effect are unaffected by meals, unlike oral medications that undergo first-pass metabolism. However, in clinical practice, patients are usually instructed to fast before anesthesia to reduce the risk of aspiration during sedation or surgery, which is a precaution related to anesthesia rather than a pharmacokinetic interaction.

CONTRAINDICATIONS

Propofol is contraindicated in patients with a known hypersensitivity to propofol or any of its components, including soybean oil, egg lecithin, or glycerol. It should also be avoided in individuals with disorders of lipid metabolism, such as familial hypertriglyceridemia, due to the lipid emulsion formulation. Propofol is contraindicated in patients with severe hypotension or shock, as its vasodilatory effects can exacerbate hemodynamic instability.

SIDE EFFECTS

• Hypotension – dose-dependent decrease in blood pressure due to vasodilation 

• Respiratory depression – including apnea, especially after rapid bolus 

Dizziness, headache, or lightheadedness.

OVER DOSAGE

Overdosage of Proguanil is uncommon but may cause symptoms such as nausea, vomiting, dizziness, abdominal discomfort, and general weakness. Treatment is mainly supportive, including hydration and symptom management, as serious toxicity is rare.

TOXICITY

Propofol toxicity is uncommon at standard clinical doses but can occur with overdose or prolonged high-dose infusion, particularly in critically ill patients. Toxicity primarily affects the cardiovascular and metabolic systems, manifesting as severe hypotension, bradycardia, and, in extreme cases, cardiovascular collapse.