The Answer is Yes, but with Extreme Caution
Yes, tetracaine can be injected, but its use is restricted to specialized medical procedures performed by trained professionals. The most common injectable application is for spinal anesthesia, which requires precise administration into the subarachnoid space surrounding the spinal cord. Because tetracaine is highly potent and carries a high risk of systemic toxicity if administered incorrectly, it is never used for routine, superficial local injections like those for dental work or minor skin procedures.
How and where is injectable tetracaine used?
The primary indication for injectable tetracaine is to provide prolonged spinal anesthesia, with effects lasting two to three hours or more, especially when combined with epinephrine. It is often used in the following contexts:
- Spinal Anesthesia: Used for procedures on the lower abdomen, perineum, and lower extremities. Doses are carefully calculated based on the area of desired numbness, the patient's weight and health, and the injection site.
- Labor and Delivery: Administered as a "saddle block" to numb the perineum during vaginal delivery.
- Historical Intravenous Use: While not a current standard for routine anesthesia, an older study documented the use of intravenous tetracaine for treating pain, muscle spasms, and neuromuscular tension. However, this method is associated with high risk and is not commonly practiced for general anesthesia today.
- Important distinction: Topical forms of tetracaine, such as eye drops or creams, are never for injection. For example, ophthalmic tetracaine is for surface-level numbing of the eye, and injecting it could cause severe, permanent damage.
Critical risks associated with tetracaine injections
The potency and pharmacology of tetracaine mean that inappropriate administration, such as an accidental intravascular injection, can have severe consequences. All tetracaine injections must be done in a medically controlled environment where monitoring and resuscitative equipment are immediately available.
Local Anesthetic Systemic Toxicity (LAST)
LAST is a life-threatening complication that can occur if a local anesthetic is accidentally injected into the bloodstream or an excessive dose is used. Symptoms can affect the central nervous and cardiovascular systems.
Signs of LAST include:
- Central Nervous System Effects: Dizziness, tremors, blurred vision, numbness, severe drowsiness, convulsions, and even unconsciousness.
- Cardiovascular Effects: Myocardial depression, low blood pressure (hypotension), cardiac arrhythmias, and potentially cardiac arrest.
- Methemoglobinemia: A rare but potentially deadly blood disorder where the skin, lips, and nails turn a pale, blue, or gray color.
Allergic Reactions and Contraindications
Some individuals may have allergic-type reactions to tetracaine due to its classification as an ester-type local anesthetic. Allergic signs can include rash, hives, swelling, and, in severe cases, anaphylaxis. Tetracaine is contraindicated in patients with known hypersensitivity to ester-type local anesthetics or sulfonamide drugs.
Comparison: Injectable vs. Topical Tetracaine
| Feature | Injectable Tetracaine (Spinal) | Topical Tetracaine (Eye Drops) |
|---|---|---|
| Primary Use | Prolonged spinal anesthesia for surgery | Short-acting surface anesthesia for eye procedures |
| Route of Administration | Subarachnoid space in the spine | Applied directly to the eye's surface |
| Medical Supervision | Required, administered by an anesthesiologist | Required, administered by a healthcare provider |
| Onset of Action | Rapid (3-5 minutes) | Rapid (15-20 seconds) |
| Duration of Action | Long (2-3 hours), longer with additives | Short (10-20 minutes) |
| Potency | Highly potent | Less potent, only affects surface |
| Risk of Systemic Toxicity | High if administered incorrectly | Low, but long-term or misuse can cause corneal damage |
The takeaway
Injectable tetracaine is a potent, long-acting local anesthetic used exclusively for specific procedures like spinal anesthesia under expert medical supervision. It is not suitable for routine surface-level injections due to a significant risk of systemic toxicity. In contrast, topical formulations are used safely for surface numbing, but ophthalmic preparations must never be injected. Patients should always receive tetracaine from a trained healthcare professional in the appropriate formulation and setting, ensuring careful monitoring to prevent serious side effects.
For more in-depth professional information on tetracaine's various uses, including injectable forms, refer to the detailed monograph on Drugs.com.
