What Is Terrell (Isoflurane)? Uses, Dosage, and What You Need to Know in 2026

Terrell is a brand name for isoflurane USP — a clear, colorless liquid that's vaporized and inhaled to put patients under general anesthesia for surgery. If you're scheduled for a procedure that requires general anesthesia, there's a reasonable chance Terrell or another isoflurane product could be part of your care. Understanding what this medication is and how it works can help ease pre-surgical anxiety.

What Is Terrell (Isoflurane)?

Terrell (isoflurane, USP) is a general inhalation anesthetic manufactured by Piramal Critical Care, Inc. It belongs to the class of halogenated ether anesthetics — drugs that produce general anesthesia when inhaled. Isoflurane has been FDA-approved since 1979 and remains one of the most widely used general anesthetics in the world.

It is a nonflammable, colorless liquid with a mildly pungent odor. Terrell is available in 100 mL and 250 mL amber glass bottles and contains 99.9% isoflurane with no additives or chemical stabilizers.

What Is Terrell Used For?

Terrell's FDA-approved indication is: induction and maintenance of general anesthesia in adult and pediatric patients. In practical terms, this means:

• Induction: Starting the anesthetic — bringing the patient from consciousness to unconsciousness. (Note: isoflurane's pungency makes it less popular for mask induction than sevoflurane; it is often used after IV induction with propofol.)
• Maintenance: Keeping the patient unconscious and pain-free throughout a surgical procedure.

Terrell may be used in a wide range of surgeries including orthopedic, abdominal, cardiac, and general surgical procedures. The prescribing information notes that adequate data have not been developed to establish its application in obstetrical anesthesia.

How Is Terrell Administered?

Terrell is not taken as a pill or injection. It is a liquid that is placed in a calibrated vaporizer specifically designed for isoflurane. The vaporizer converts the liquid into a gas, which is then delivered to the patient through an anesthesia mask or breathing tube as part of a controlled gas mixture with oxygen.

The anesthesia team adjusts the concentration in real time based on the patient's vital signs, surgical stimulation, and depth of anesthesia monitoring.

Dosage: How Much Terrell Is Used?

Isoflurane dosing is measured as a percentage concentration in the inhaled gas mixture (MAC — minimum alveolar concentration):

• Induction: Inspired concentrations of 1.5–3.0% isoflurane typically produce surgical anesthesia in 7–10 minutes.
• Maintenance with nitrous oxide: 1.0–2.5% isoflurane is typically sufficient.
• Maintenance with oxygen alone: An additional 0.5–1.0% concentration is typically needed.

The MAC of isoflurane decreases with increasing age, so elderly patients typically require lower concentrations to achieve the same anesthetic depth. Concomitant use of nitrous oxide or opioids also reduces the required isoflurane concentration. All dosing is individualized by the anesthesia provider based on the patient's clinical status.

Who Can Prescribe and Administer Terrell?

Terrell must be administered only by trained anesthesia professionals: anesthesiologists (MD/DO), certified registered nurse anesthetists (CRNAs), and anesthesiologist assistants (AAs). It is not a controlled substance and has no DEA schedule, but it is a prescription drug requiring trained administration.

Is Terrell a Controlled Substance?

No. Isoflurane (Terrell) is not scheduled under the DEA Controlled Substances Act. It does not have abuse or addiction potential in the same way that opioids or sedative-hypnotics do. However, its use is strictly limited to clinical/procedural settings due to the specialized equipment and monitoring required for safe administration.

Key Facts to Know Before Your Surgery

• Tell your anesthesiologist about any personal or family history of malignant hyperthermia.
• Report any prior liver problems or unexplained reactions following previous anesthesia.
• You may feel confused, groggy, or emotionally fragile for 2–6 days after receiving general anesthesia. This is normal.
• Do not drive or make important decisions for at least 24 hours after surgery.

For other prescription medications you need around your surgery, medfinder can help you find them at pharmacies near you.

Want to understand the science? Read: How does Terrell (isoflurane) work? Mechanism of action explained.