Tetracaine Hydrochloride

Tetracaine hydrochloride is administered by subarachnoid injection for spinal anesthesia. Partially used solutions that do not contain preservatives should be discarded. Dosage of tetracaine hydrochloride varies with the anesthetic procedure, the degree of anesthesia required, and individual patient response. Debilitated, geriatric, acutely ill, obstetric patients, and patients with increased intra-abdominal pressure should generally be given low doses. The drug should be administered cautiously to patients with abnormal or low plasma esterase concentrations. The smallest dose and lowest concentration required to produce the desired effect should be used. The patient's blood pressure should be monitored during spinal anesthesia. Resuscitative equipment and drugs which may be required for treatment of adverse reactions should be immediately available when tetracaine is administered. Proper positioning of the patient is extremely important in spinal anesthesia. For specific procedures and techniques of administration, specialized references should be consulted.

For spinal anesthesia, a 1% solution of tetracaine hydrochloride is diluted with an equal volume of CSF immediately prior to administration. Alternatively, each 5 mg of tetracaine hydrochloride powder is dissolved in 1 mL of CSF. The resulting solutions are administered slowly at a rate of approximately 1 mL/5 seconds. When CSF is added to the powder or the 1% solution, some turbidity may result, depending on the pH of the CSF, the amount of drug and diluent, and the temperature of the solution. The cloudiness results from the release of the free base and this process (which is completed within the spinal canal) is essential for activity of the anesthetic.

For anesthesia of the perineum, the usual adult dose of tetracaine hydrochloride is 5 mg. For anesthesia of the perineum and lower extremities, the usual adult dose is 10 mg. For spinal anesthesia extending up to the costal margin, the usual adult dose is 15-20 mg. For low spinal (saddle block) anesthesia in vaginal delivery, 2-5 mg of tetracaine hydrochloride is administered as a hyperbaric solution. Doses greater than 15 mg are rarely required and should be used only in exceptional cases.

Cautions ⬆ ⬇

Tetracaine hydrochloride shares the toxic potentials of the local anesthetics, and the usual precautions of local anesthetic therapy should be observed. (See Cautions in the Local Anesthetics, Parenteral, General Statement 72:00.)

Some commercially available formulations of tetracaine hydrochloride contain acetone sodium bisulfite, a sulfite that may cause allergic-type reactions, including anaphylaxis and life-threatening or less severe asthmatic episodes, in certain susceptible individuals. The overall prevalence of sulfite sensitivity in the general population is unknown but probably low; such sensitivity appears to occur more frequently in asthmatic than in nonasthmatic individuals.

Life-threatening adverse effects (e.g., irregular heart beat, seizures, breathing difficulties, coma, death) may occur when topical anesthetics are applied to a large area of skin, when the area of application is covered with an occlusive dressing, if a large amount of topical anesthetic is applied, if the anesthetic is applied to irritated or broken skin, or if the skin temperature increases (from exercise or use of a heating pad).101,102 When applied in such a manner, the amount of anesthetic that is absorbed systemically is unpredictable and the plasma concentrations achieved may be high enough to cause life-threatening adverse effects.101,102 Use of lidocaine gel has been investigated to reduce discomfort during mammography.101,103 During the study, the topical anesthetic was spread over a wide area of the chest and covered with an occlusive dressing.101,103 Whether such use could result in serious reactions has not been determined.101,103 Patients should speak with their clinician if they are considering using a topical anesthetic before obtaining a mammogram.101

When a topical anesthetic is needed for a procedure, use of an FDA-approved preparation has been recommended.101 A preparation containing the lowest concentration of anesthetic likely to be effective should be used; a small amount of topical anesthetic should be applied to the affected area for the shortest period necessary for the desired effect.101 When the topical anesthetic will be applied by the patient, the patient should apply the topical preparation as directed by a clinician, and should not apply the topical preparation to broken or irritated skin.101

Drug Interactions ⬆ ⬇

Since the aminobenzoic acid metabolite of tetracaine may antagonize the activity of aminosalicylic acid and sulfonamides, some clinicians have suggested that tetracaine should not be used in patients receiving these drugs.

Other Information ⬆ ⬇

[Section Outline]

Chemistry
Stability

Pharmacokinetics

Tetracaine hydrochloride has a delayed onset of action, often up to 15 minutes in large nerve trunks. Duration of action during spinal anesthesia is about 1.5-3 hours.

Tetracaine is hydrolyzed to p -aminobenzoic acid by plasma pseudocholinesterase. The drug has the slowest rate of hydrolysis of the ester type local anesthetics. Tetracaine metabolites are excreted mainly by the kidneys. In animals, biliary excretion of tetracaine also occurs.

Chemistry and Stability

Chemistry

Tetracaine hydrochloride is a local anesthetic of the ester type with a long duration of action. Tetracaine hydrochloride occurs as a fine, white crystalline powder that has a slightly bitter taste. The drug is very soluble in water and soluble in alcohol. The pK_a of tetracaine hydrochloride is 8.39.

Commercially available solutions of tetracaine hydrochloride have a pH of 3.2-6. After reconstitution of sterile tetracaine hydrochloride powder for injection with sterile water for injection, a 1% solution has a pH of 5-6. Commercially available 1% tetracaine hydrochloride solution is isobaric, having a specific gravity of 1.0060-1.0074 at 25°C. A solution of tetracaine hydrochloride powder in spinal fluid has a specific gravity slightly greater than CSF. A hypobaric solution, having a specific gravity of 1.000 at 25°C, may be prepared by dissolving tetracaine hydrochloride powder for injection in sterile water for injection to provide a 0.1% solution. Hyperbaric solutions are commercially available as 0.2 or 0.3% tetracaine hydrochloride in 6% dextrose. A hyperbaric solution may also be prepared by mixing the commercially available 1% solution with an equal volume of 10% dextrose injection. Alternatively, a hyperbaric solution may be prepared by dissolving tetracaine hydrochloride powder for injection in 10% dextrose injection using 1 mL of 10% dextrose injection for each 10 mg of tetracaine hydrochloride. The resulting solution is further diluted with an equal volume of CSF to provide a solution containing 5 mg of tetracaine hydrochloride and 5 mg of dextrose per mL.

Stability

Tetracaine hydrochloride preparations should be protected from light and stored at 2-8°C; freezing should be avoided.

Solutions of tetracaine hydrochloride undergo slow hydrolysis resulting in precipitation of p -butylaminobenzoic acid crystals. Ampuls containing tetracaine hydrochloride should be examined closely before use; cloudy or discolored solutions or those containing crystals must not be used. Tetracaine hydrochloride ampuls may be sterilized once by autoclaving at 15 PSI and 121°C for 15 minutes. Since autoclaving increases the likelihood of crystal formation, unused autoclaved ampuls must be discarded. Ampuls containing tetracaine hydrochloride powder may also be autoclaved at 15 PSI and 121°C for 15 minutes, but the drug may lose its snowlike appearance and cling to the sides of the ampul. Although this may decrease the dissolution rate of the drug, anesthetic potency is not affected.

Addition of alkali hydroxides or carbonates to tetracaine hydrochloride solutions precipitates tetracaine base as an oily liquid.

Additional Information

For further information on chemistry and stability, pharmacology, pharmacokinetics, uses, cautions, and dosage and administration of tetracaine hydrochloride, see the Local Anesthetics, Parenteral, General Statement 72:00.

Preparations ⬆ ⬇

Excipients in commercially available drug preparations may have clinically important effects in some individuals; consult specific product labeling for details.

Please refer to the ASHP Drug Shortages Resource Center for information on shortages of one or more of these preparations.