Usage
Capsaicin is prescribed for the management of neuropathic pain, including postherpetic neuralgia (PHN), painful diabetic neuropathy, and osteoarthritis. It is also used for temporary relief of minor aches and pains of muscles and joints associated with arthritis, simple backache, strains, and sprains.
Its pharmacological classification is as a topical analgesic, counterirritant, and TRPV1 agonist.
Capsaicin’s mechanism of action involves activating the transient receptor potential vanilloid 1 (TRPV1) receptor, a heat-activated ion channel. This initial activation leads to a sensation of heat and pain. However, repeated or prolonged capsaicin application causes desensitization of TRPV1 receptors and depletion of substance P, a neurotransmitter involved in pain transmission, resulting in pain relief.
Alternate Names
Capsaicin is also known as 8-methyl-N-vanillyl-6-nonenamide. Popular brand names include Qutenza, Zostrix, Capzasin-HP, and Axsain. Numerous other brand names exist, especially for over-the-counter formulations.
How It Works
Pharmacodynamics: Capsaicin binds to and activates TRPV1 receptors located on sensory neurons, primarily C-fibers and A-delta fibers responsible for transmitting pain and heat sensations. TRPV1 activation causes an influx of calcium and sodium ions, leading to depolarization and initiation of nerve impulses. Repeated exposure to capsaicin desensitizes TRPV1, resulting in decreased responsiveness to noxious stimuli and depletion of substance P.
Pharmacokinetics: Topical capsaicin is poorly absorbed through intact skin. Systemic absorption is minimal with topical use, especially with lower concentrations (0.025% to 0.075%). Higher concentrations (8% patch) may lead to slightly greater systemic absorption. The extent of metabolism and elimination pathways after topical application are not fully elucidated. With oral administration, capsaicin is well-absorbed and metabolized in the liver, primarily by CYP enzymes. Elimination occurs via renal and fecal routes.
Dosage
Standard Dosage
Adults:
- Topical cream/lotion (0.025% - 0.075%): Apply to the affected area 3 to 4 times daily.
- Topical patch (8% - Qutenza): Applied by a healthcare professional for 30-60 minutes, depending on the indication, and repeated no more frequently than every 3 months.
Children:
Safety and efficacy in children under 2 years old have not been established. For children 2 years and older, use of lower concentration topical formulations (0.025%) should be done cautiously under medical supervision. The 0.075% strength and 8% patch are generally not recommended for pediatric use.
Special Cases:
- Elderly Patients: No specific dose adjustment is usually needed.
- Patients with Renal Impairment: No specific dose adjustment is typically required due to low systemic absorption with topical use.
- Patients with Hepatic Dysfunction: No specific dose adjustment is typically required with topical use.
- Patients with Comorbid Conditions: Caution is advised in patients with asthma or respiratory conditions, as capsaicin can cause bronchospasm.
Clinical Use Cases:
Capsaicin is not typically used in the clinical settings of intubation, surgical procedures, mechanical ventilation, ICU use, or emergency situations. It is primarily indicated for chronic neuropathic pain management.
Dosage Adjustments:
Dosage adjustments are usually not necessary for topical capsaicin due to its limited systemic absorption.
Side Effects
Common Side Effects:
Burning, stinging, or pain at the application site, redness, itching, cough, sneezing, throat irritation.
Rare but Serious Side Effects:
Severe burning or blistering at the application site, allergic reactions, eye pain or irritation (avoid contact with eyes).
Long-Term Effects:
Long-term use of topical capsaicin is generally considered safe. Some patients might experience persistent skin irritation with chronic use.
Adverse Drug Reactions (ADR):
Severe skin reactions, bronchospasm (in susceptible individuals).
Contraindications
Hypersensitivity to capsaicin or any component of the formulation. Broken or irritated skin at the application site. Avoid application near the eyes, mucous membranes, or open wounds.
Drug Interactions
Limited information is available regarding drug interactions with topical capsaicin due to its minimal systemic absorption. No clinically significant interactions have been consistently reported with topical use. However, concurrent use of other topical agents on the same area might increase the risk of skin irritation. Ace inhibitors are known to interact with capsaicin. Systemic capsaicin might potentially interact with medications metabolized by CYP enzymes.
Pregnancy and Breastfeeding
Topical capsaicin is considered relatively safe during pregnancy and breastfeeding, especially at lower concentrations. However, it is recommended to use the lowest effective dose for the shortest duration necessary. Avoid applying capsaicin directly to the nipple area during breastfeeding. Limited data are available on the effects of high-dose capsaicin (8% patch) during pregnancy and breastfeeding.
Drug Profile Summary
- Mechanism of Action: Activates TRPV1 receptors, leading to desensitization and depletion of substance P.
- Side Effects: Burning, stinging, redness at application site; rare allergic reactions.
- Contraindications: Hypersensitivity, broken skin, application near eyes or mucous membranes.
- Drug Interactions: Limited information available; potential for interaction with ACE inhibitors.
- Pregnancy & Breastfeeding: Generally safe with topical use, particularly at lower concentrations.
- Dosage: Creams/lotions (0.025% - 0.075%): 3-4 times daily; patch (8%): 30-60 minutes every 3 months.
- Monitoring Parameters: Observe for local skin reactions and effectiveness in pain reduction.
Popular Combinations:
Topical capsaicin is sometimes combined with other topical analgesics like menthol or methyl salicylate in over-the-counter products.
Precautions
Wash hands thoroughly after application. Avoid contact with eyes, mucous membranes, and broken skin. Caution in patients with respiratory conditions. Use the lowest effective dose for the shortest duration.
FAQs (Frequently Asked Questions)
Q1: What is the recommended dosage for Capsaicin?
A: For adults, topical creams or lotions (0.025% - 0.075%) can be applied 3-4 times daily. The 8% patch (Qutenza) is applied by a healthcare professional for 30-60 minutes and repeated no more frequently than every 3 months. For children over 2 years old, lower concentrations (0.025%) should be used cautiously under medical supervision.
Q2: How long does it take for capsaicin to work?
A: Initial pain relief might be noticed within the first week of regular use, but maximum effect might take several weeks (4-6 weeks) of consistent application.
Q3: Can I use capsaicin with other pain medications?
A: Consult with a physician before combining capsaicin with other topical analgesics on the same area to avoid skin irritation. For systemic pain medications, consult a physician to assess potential drug interactions.
Q4: What should I do if I experience severe burning with capsaicin?
A: Discontinue use and consult a doctor immediately. Severe burning or blistering indicates a potential adverse reaction.
Q5: Can I use capsaicin if I am pregnant or breastfeeding?
A: Topical capsaicin, especially in lower concentrations, is considered relatively safe during pregnancy and breastfeeding. However, it is essential to consult a healthcare professional for guidance. Avoid applying it directly to the nipple area during breastfeeding.
Q6: Are there any long-term side effects of using capsaicin?
A: Long-term topical use of capsaicin is generally well-tolerated. Some patients might experience persistent, mild skin irritation.
Q7: How should I store capsaicin products?
A: Store capsaicin products at room temperature, away from excess heat and moisture, and out of reach of children.
Q8: Can capsaicin be used for nerve pain other than PHN or diabetic neuropathy?
A: Capsaicin is sometimes used off-label for other types of neuropathic pain. Consult a doctor for advice.
Q9: Can I apply a heating pad after applying capsaicin cream?
A: No. Applying external heat sources after applying capsaicin can intensify the burning sensation and may cause skin damage.
Q10: What is the difference between the various concentrations of capsaicin creams?
A: Lower concentrations (0.025%-0.075%) are available over-the-counter for minor aches and pains. The 8% patch (Qutenza) is a prescription medication for more severe neuropathic pain and requires administration by a healthcare professional.
