Polocaine (mepivacaine Hcl)

Mepivacaine is a potent amide-type local anesthetic used for infiltration, nerve block, and epidural anesthesia. It provides rapid onset and intermediate duration of action by blocking sodium ion channels in nerve fibers.

The dosage of Mepivacaine must be individualized based on the patient's age, weight, physical status, and the specific procedure being performed. Healthcare providers follow the principle of using the lowest effective dose to achieve the desired level of anesthesia.

• Local Infiltration: For minor procedures, doses typically range from 5 mL to 40 mL of a 1% solution (50 mg to 400 mg). The total dose should generally not exceed 400 mg in a single administration.
• Peripheral Nerve Blocks: For major nerve blocks (e.g., brachial plexus), 15 mL to 40 mL of a 1% or 2% solution (150 mg to 800 mg) may be used, though the upper limit is strictly monitored.
• Epidural Anesthesia: Dosages vary significantly based on the level of the spine. Typically, 15 mL to 30 mL of a 1.5% or 2% solution is administered in increments to reach the desired sensory level.
• Dental Procedures: The standard dose for dental infiltration or nerve block is 1.8 mL to 3.6 mL (one to two cartridges) of a 3% solution. The maximum recommended dose for a healthy adult in dentistry is 6.6 mg/kg (3 mg/lb), not to exceed a total of 400 mg.

Mepivacaine is used in pediatric patients, but the dosage must be calculated with extreme caution based on the child's weight and physical condition.

• General Guidelines: The maximum dose for children should generally not exceed 5 mg/kg to 6 mg/kg of body weight. In children under 3 years of age or weighing less than 13 kg (30 lbs), Mepivacaine 3% is often the preferred concentration in dental settings.
• Safety Note: Pediatric patients are at a higher risk for systemic toxicity if the dose is not precisely calculated. Healthcare providers will use the smallest volume necessary to achieve adequate anesthesia.

Renal Impairment

While Mepivacaine is primarily metabolized by the liver, its metabolites are excreted by the kidneys. In patients with severe renal impairment, there is a theoretical risk of metabolite accumulation. However, because the parent drug is rapidly metabolized, dose adjustments are usually not required for single-dose procedures, though caution is advised in repeated dosing.

Hepatic Impairment

Patients with significant liver disease (e.g., cirrhosis, hepatitis) require careful dose reduction. Since the liver is the primary organ responsible for breaking down Mepivacaine, impaired function can lead to toxic plasma levels. Healthcare providers may reduce the total dose by 25% to 50% in patients with severe hepatic dysfunction.

Elderly Patients

Geriatric patients often have reduced physiological reserves and may have undiagnosed cardiovascular or hepatic issues. Lower doses are generally recommended for the elderly to minimize the risk of systemic toxicity and cardiovascular depression. Clinical data suggests that the volume of distribution and clearance may be altered in patients over 65.

Mepivacaine is administered only by healthcare professionals trained in the management of regional anesthesia.

• Administration Route: It is given via subcutaneous infiltration, intramuscular injection near nerves, or epidural injection. It must never be injected directly into a vein (intravenously), as this can cause immediate and severe toxicity.
• Monitoring: During administration, the provider will perform 'aspiration' (pulling back on the syringe) to ensure the needle is not inside a blood vessel.
• Storage: Mepivacaine should be stored at controlled room temperature (20°C to 25°C). Solutions that are discolored or contain particulate matter should not be used.

Since Mepivacaine is administered by a healthcare professional in a clinical or surgical setting for a specific procedure, the concept of a 'missed dose' by a patient does not apply. If a procedure is delayed, the medical team will determine the appropriate timing for the injection.

An overdose of Mepivacaine leads to Local Anesthetic Systemic Toxicity (LAST). This is a medical emergency.

• Signs of Overdose: Initial symptoms include a metallic taste, ringing in the ears (tinnitus), lightheadedness, and numbness around the mouth. This can progress to tremors, seizures, loss of consciousness, and respiratory arrest. Cardiovascular signs include low blood pressure, slow heart rate, and cardiac arrest.
• Emergency Measures: If an overdose is suspected, the administration must be stopped immediately. Treatment involves maintaining the airway, providing 100% oxygen, and administering intravenous lipid emulsion (Intralipid) to 'soak up' the anesthetic from the bloodstream, along with medications to control seizures.

> Important: Follow your healthcare provider's dosing instructions. Do not adjust your dose without medical guidance. If you feel any unusual symptoms during or after the injection, notify your medical team immediately.

Most patients tolerate Mepivacaine well, but some local reactions are common due to the nature of the injection and the anesthetic effect.

• Localized Numbness: The primary intended effect is numbness, but this can feel like a heavy, 'dead' sensation in the affected limb or area. This typically resolves within 2 to 4 hours.
• Tingling or 'Pins and Needles': As the medication begins to wear off, patients frequently experience paresthesia (tingling) in the area. This is a normal sign that nerve function is returning.
• Mild Injection Site Pain: Slight soreness or bruising at the site where the needle entered the skin is common and usually fades within 24 to 48 hours.

Mepivacaine should only be administered by clinicians who are well-versed in the diagnosis and management of dose-related toxicity and other acute emergencies that might arise from the block to be employed. Resuscitative equipment, including oxygen, intravenous fluids, and medications for seizure control, must be immediately available. The safety and effectiveness of Mepivacaine depend on proper dosage, correct technique, adequate precautions, and readiness for emergencies.

No FDA black box warnings for Mepivacaine. While it lacks a specific black box warning, it shares the general class warnings for all local anesthetics regarding the risk of systemic toxicity and the need for immediate access to resuscitation equipment.

• Allergic Reactions / Anaphylaxis Risk: While rare with amide anesthetics, hypersensitivity reactions can occur. Patients with a known allergy to other amide-type anesthetics (like lidocaine or bupivacaine) may exhibit cross-sensitivity. Some formulations contain methylparaben as a preservative, which can also trigger allergic reactions.

There are few absolute contraindications for drug combinations with Mepivacaine, but the following should be avoided:

• Other Amide Local Anesthetics: Using Mepivacaine in combination with other amides (e.g., lidocaine, bupivacaine) is generally avoided unless the total dose is carefully calculated to be below toxic thresholds. Their toxic effects are additive.
• Specific Antiarrhythmics: Drugs like tocainide or mexiletine, which are structurally related to local anesthetics, should not be used concurrently as they can significantly increase the risk of systemic toxicity.

• CNS Depressants: Medications such as benzodiazepines (Valium, Xanax), opioids, and barbiturates can increase the risk of respiratory depression and enhance the CNS effects of Mepivacaine. While often used together in surgical settings, they require expert monitoring.

Mepivacaine must NEVER be used in the following circumstances:

• Known Hypersensitivity: Patients with a documented allergy to Mepivacaine or any other amide-type local anesthetic (e.g., lidocaine, prilocaine, bupivacaine, ropivacaine) must not receive this drug. Anaphylaxis, though rare, can be fatal.
• Hypersensitivity to Parabens: Some multi-dose vials contain methylparaben. Patients with a known allergy to parabens should only receive preservative-free formulations.
• Severe Heart Block: Because Mepivacaine can slow electrical conduction in the heart, it is absolutely contraindicated in patients with second or third-degree heart block without a functioning pacemaker.
• Obstetric Paracervical Block: Mepivacaine is specifically contraindicated for paracervical block anesthesia in obstetrics due to a high risk of fetal bradycardia and death.

Mepivacaine is classified as FDA Pregnancy Category C. This means that animal reproduction studies have shown an adverse effect on the fetus, but there are no adequate and well-controlled studies in humans.

• Teratogenicity: There is no clear evidence that Mepivacaine causes birth defects when used for short-term anesthesia.
• Labor and Delivery: Mepivacaine is widely used for epidural anesthesia during labor. However, it readily crosses the placenta. If high doses are used, it can cause fetal bradycardia (slow heart rate), acidosis, and neurological depression in the newborn.
• Obstetric Warning: As noted in contraindications, it should not be used for paracervical blocks due to fetal risk.

It is not known whether Mepivacaine is excreted in human milk. However, because most local anesthetics are excreted in very small amounts and Mepivacaine has a relatively short half-life, it is generally considered safe to resume breastfeeding once the mother has fully recovered from the anesthetic effects. Healthcare providers often suggest waiting 4 to 6 hours after the procedure as a precaution.

Mepivacaine is an amide-type local anesthetic that acts by inhibiting the ionic fluxes required for the initiation and conduction of nerve impulses. Its primary target is the voltage-gated sodium channel (Nav1.5 and other subtypes) located in the neuronal cell membrane.

When Mepivacaine is injected near a nerve, the uncharged (base) form of the molecule diffuses across the lipid-rich nerve sheath and membrane. Once inside the axoplasm, the molecule becomes protonated (charged). This charged form binds to the S6 segment of domain IV of the alpha-subunit of the sodium channel. By binding to the internal pore, Mepivacaine prevents the channel from transitioning to its 'open' state, thereby blocking the influx of sodium ions. Without sodium influx, the threshold potential is not reached, and the nerve cannot fire an action potential.

• Onset of Action: Rapid (typically 3 to 5 minutes for infiltration and 10 to 15 minutes for major nerve blocks).
• Duration: Intermediate. Without epinephrine, it lasts 1.5 to 2 hours. With epinephrine, the duration can extend to 3 hours or more.