The Barbiturate Family 😴

Barbiturates are a class of central nervous system (CNS) depressants once widely used for everything from sleep induction to seizure control. Today, their primary clinical role has shifted to specific anesthetic purposes, particularly those with ultra-short duration of action.

This article explores the spectrum of barbiturate activity, focusing on their use in anesthesia, their mechanism, and the profiles of key examples like Methohexital sodium, Thiamylal sodium, and Thiopental sodium.

⚡ The Spectrum of Barbiturate Action

Barbiturates are classified based on how quickly they take effect and how long their effects last. This classification dictates their primary medical use.

1. Ultra-Short Acting Barbiturates

Action: Act very rapidly, typically within minutes.
Use: Ideal for anesthesia induction (putting a patient to sleep quickly) and for short-term, rapid procedures like intubation.

2. Short-Acting Barbiturates

Action: Act relatively quickly, typically within an hour.
Use: Employed for general anesthesia and more lengthy surgical or procedural needs. Pentobarbital is a classic example.

Mode of Action

Barbiturates work by depressing the central nervous system. They enhance the activity of GABA ( $\gamma$ -aminobutyric acid), the main inhibitory neurotransmitter in the brain. This enhancement slows brain and nervous system activity, producing general anesthesia (sleep, amnesia, and unawareness of pain).

🔑 Key Ultra-Short Acting Barbiturates

These agents are crucial in modern anesthesiology for their swift onset.

Methohexital Sodium (Brevital Sodium)

Methohexital sodium, also known by the trade name Brevital Sodium, is a prime example of an ultra-short-acting agent.

Onset and Duration: It has a rapid onset of action (within minutes) and a very short duration of action, typically lasting about 30 minutes.
Spectrum of Action: It is a potent CNS depressant with sedative and hypnotic effects.
Unique Side Effect: Methohexital can sometimes cause paradoxical excitement, a state of increased energy and activity, rather than sedation.
Interactions: It interacts significantly with other CNS depressants like alcohol, opioids, and sedatives, and can be complicated by conditions like sleep apnea.

Thiamylal Sodium

Administration: It is typically administered intravenously as a bolus or an infusion, with a dose range of 2.5 to 10 mg/kg.
Precautions: It is generally not recommended for nursing mothers as it is excreted in breast milk.

Thiopental Sodium (Pentothal)

Thiopental sodium (formerly marketed as Pentothal) is historically significant as one of the first anesthetics developed in the 1930s.

Clinical Status: While use of Pentothal has ceased in the United States, it remains available and used for general anesthesia in many other countries.
Administration: Given by injection into a muscle or vein, it begins to work within minutes, with effects lasting about half an hour.
Uses: Used for general anesthesia induction, sometimes to relieve pain and anxiety, or to calm a patient experiencing a seizure.
Absolute Contraindications: Porphyria and liver disease preclude the use of Thiopental. It should also be avoided in pregnant women and children.

⚠️ Important Drug Interactions

Barbiturates have a broad spectrum of action that necessitates extreme caution when combined with other medications. The CNS depressant effects of Thiopental (Pentothal) and other barbiturates are greatly enhanced when taken with: