Chloroprocaine

Usage

• Chloroprocaine is prescribed for local anesthesia, including infiltration, peripheral nerve block, and spinal anesthesia. It is frequently used in surgical procedures, particularly for short-duration operations, and in obstetrics for labor analgesia. It can also be used for diagnostic and therapeutic nerve blocks. Specifically, it’s indicated for intrathecal injection in adults for subarachnoid block (spinal anesthesia).

• Pharmacological Classification: Local anesthetic, ester type.

• Mechanism of Action: Chloroprocaine blocks the generation and conduction of nerve impulses, primarily by inhibiting sodium influx through voltage-gated sodium channels in nerve axons. This reversible blockade prevents depolarization and subsequent propagation of nerve impulses, leading to a localized loss of sensation.

Alternate Names

• International Nonproprietary Name (INN): chloroprocaine hydrochloride

• Brand Names: Nesacaine, Nesacaine-MPF, Clorotekal, Ampres

How It Works

• Pharmacodynamics: Chloroprocaine acts locally by binding to sodium channels in nerve cell membranes, blocking nerve impulse transmission. It has a rapid onset of action and a relatively short duration of effect compared to other local anesthetics due to its rapid metabolism.
• Pharmacokinetics:
  • Absorption: When administered intrathecally, chloroprocaine has direct access to the cerebrospinal fluid and the spinal cord, resulting in rapid onset. Absorption from other administration sites varies depending on factors like vascularity, concentration, and the presence of vasoconstrictors.
  • Metabolism: Chloroprocaine is rapidly metabolized in the plasma by pseudocholinesterase, an enzyme found in the liver. This rapid hydrolysis is the primary reason for its short duration of action. Its metabolites include 2-chloro-4-aminobenzoic acid and diethylaminoethanol.
  • Elimination: The primary elimination pathway is renal excretion of metabolites.

Dosage

Standard Dosage

Adults:

• Intrathecal (Spinal Anesthesia): 40-50 mg (4-5 mL of a 10 mg/mL solution) as a single injection. The recommended dose for an effective block to the T10 level is 50 mg in an adult weighing approximately 70 kg. Doses above 50 mg have not been adequately tested.

Children:

• Not recommended for use in children younger than 3 years.
• Children 3 years and older: For infiltration anesthesia: 0.5% - 1% solution; for nerve block: 1% - 1.5% solution, not exceeding 11 mg/kg.

Special Cases:

• Elderly Patients: Start with lower doses and titrate carefully, monitoring for signs of toxicity. Elderly patients may be more prone to hypotension.
• Patients with Renal Impairment: Reduced doses might be needed. Close monitoring of renal function is recommended.
• Patients with Hepatic Dysfunction: Use with caution due to potential for reduced metabolism. Monitor closely for signs of prolonged anesthetic effects or toxicity.
• Patients with Comorbid Conditions: Adjust dosage based on the specific comorbidity and the patient’s overall health status.

Clinical Use Cases

• Intubation: Not routinely recommended due to short duration of action.
• Surgical Procedures: Used for short duration surgeries, particularly in ambulatory settings.
• Mechanical Ventilation: Not typically used for prolonged analgesia or sedation related to mechanical ventilation.
• Intensive Care Unit (ICU) Use: Limited use in ICU due to short duration of action.
• Emergency Situations: Not ideal for most emergencies due to short duration.

Dosage Adjustments:

• Adjust dosage based on patient response, body weight, age, and concomitant medications.

Side Effects

Common Side Effects:

• Restlessness, anxiety, dizziness, blurred vision, tremors, nausea, vomiting, backache, headache.

Rare but Serious Side Effects:

• Hypotension, bradycardia, respiratory depression, seizures, allergic reactions (including anaphylaxis), methemoglobinemia, cardiac arrest. Cauda equina syndrome and permanent neurological injury have been reported with neuraxial administration.

Long-Term Effects:

• Chronic complications are rare but may include persistent neurological deficits with improper administration or in susceptible individuals.

Adverse Drug Reactions (ADR):

• Severe allergic reactions, methemoglobinemia, and cardiovascular collapse.

Contraindications

• Known hypersensitivity to chloroprocaine, para-aminobenzoic acid (PABA), or other ester-type local anesthetics.
• General contraindications to spinal anesthesia (e.g., severe hypovolemia, coagulopathy, infection at the injection site, increased intracranial pressure).

Drug Interactions

• Other local anesthetics: Additive toxicity.
• Cholinesterase inhibitors: Prolonged duration of action.
• Beta-blockers: May potentiate bradycardia and hypotension.
• CYP450 interactions: Limited data suggests minimal involvement with CYP enzymes.
• Medications that cause methemoglobinemia: Increased risk of methemoglobinemia. Examples include nitrates, sulfonamides, dapsone.
• Bupivacaine liposome or implant: Contraindicated.

Pregnancy and Breastfeeding

• Pregnancy Safety Category: C. Limited data available, use with caution. While considered Pregnancy Category C, Chloroprocaine is regularly used in labor and delivery units throughout the world due to its rapid metabolism and minimal fetal exposure.
• Breastfeeding: Limited data suggests low risk to infants due to rapid metabolism; however, caution is advised.

Drug Profile Summary

• Mechanism of Action: Blocks sodium channels in nerve axons, inhibiting impulse conduction.
• Side Effects: Common: Restlessness, anxiety, dizziness. Serious: Hypotension, bradycardia, respiratory depression, allergic reactions.
• Contraindications: Hypersensitivity, general contraindications to spinal anesthesia.
• Drug Interactions: Other local anesthetics, cholinesterase inhibitors, beta-blockers.
• Pregnancy & Breastfeeding: Category C, use with caution. Limited data suggests low risk during breastfeeding.
• Dosage: Adults (spinal): 40-50mg. Pediatrics (over 3 years): Not to exceed 11 mg/kg.
• Monitoring Parameters: Heart rate, blood pressure, respiratory rate, oxygen saturation, level of consciousness.

Popular Combinations

• Often combined with epinephrine to prolong duration of action and reduce systemic absorption, though not in spinal anesthesia.

Precautions

• Standard precautions for local anesthetic administration. Careful aspiration before injection to avoid intravascular injection. Monitor for signs of toxicity.

FAQs (Frequently Asked Questions)

Q1: What is the recommended dosage for Chloroprocaine for spinal anesthesia?

A: The recommended dosage for spinal anesthesia in adults is 40-50mg.

Q2: Can Chloroprocaine be used in children?

A: It is not recommended for children under 3 years of age. For children over 3, the dose should not exceed 11mg/kg.

Q3: What are the serious side effects of Chloroprocaine?

A: Serious side effects include hypotension, bradycardia, respiratory depression, seizures, allergic reactions, and methemoglobinemia.

Q4: What are the contraindications to using Chloroprocaine?

A: Contraindications include hypersensitivity to chloroprocaine, PABA, or other ester anesthetics, as well as general contraindications to spinal anesthesia.

Q5: Can Chloroprocaine be used during pregnancy?

A: It’s a Pregnancy Category C drug; use with caution. It is often used during labor and delivery due to its short half-life and minimal fetal exposure.

Q6: How is Chloroprocaine metabolized?

A: Chloroprocaine is rapidly metabolized by plasma cholinesterase.

Q7: What are the drug interactions I should be aware of with Chloroprocaine?

A: Significant interactions can occur with other local anesthetics, cholinesterase inhibitors, and beta-blockers. Concomitant use with medications that cause methemoglobinemia increase that risk. Bupivacaine liposome or implant is contraindicated with Chloroprocaine.

Q8: What is the duration of action of Chloroprocaine?

A: Chloroprocaine has a short duration of action, typically 30-60 minutes, which may be extended with epinephrine (though epinephrine is not used with spinal anesthesia).

Q9: How should I monitor patients receiving Chloroprocaine?

A: Closely monitor vital signs, including heart rate, blood pressure, respiratory rate, and oxygen saturation. Assess level of consciousness and monitor for signs of local anesthetic systemic toxicity.