Medication Summary
The goal of therapy for postherpetic neuralgia (PHN) is to reduce morbidity through the use of tricyclic antidepressants, anticonvulsants, anesthetics, analgesics, corticosteroids, and antiviral agents. An approved vaccine is also effective for preventing herpes zoster (HZ) outbreaks and PHN. [12] One trial demonstrated that the combination of gabapentin and nortriptyline was more efficacious than either drug as monotherapy for neuropathic pain. [16] Another study found that a single 60-minute treatment with the high-concentration capsaicin patch NGX-4010 reduced PHN for up to 12 weeks regardless of concomitant systemic neuropathic pain medication use. [17]
Anesthetics
Class Summary
These agents stabilize the neuronal membrane so the neuron is less permeable to ions. This prevents the initiation and transmission of nerve impulses, thereby producing the local anesthetic action.
Tricyclic antidepressants
Class Summary
Complex group of drugs that have central and peripheral anticholinergic effects as well as sedative effects. They have central effects on pain transmission. They block the active reuptake of norepinephrine and serotonin.
Amitriptyline (Elavil)
By inhibiting reuptake of serotonin and/or norepinephrine by presynaptic neuronal membrane, may increase synaptic concentration in CNS. Useful as analgesic for certain types of chronic and neuropathic pain.
Nortriptyline (Pamelor, Aventyl HCl)
Has demonstrated effectiveness in treatment of chronic pain; by inhibiting reuptake of serotonin and/or norepinephrine by presynaptic neuronal membrane, may increase synaptic concentration in CNS; pharmacodynamic effects such as desensitization of adenyl cyclase and down-regulation of beta-adrenergic receptors and serotonin receptors also appear to play role in its mechanisms of action.
Antiviral agents
Class Summary
The goal of antivirals is to shorten the clinical course, prevent complications, prevent the development of latency and/or subsequent recurrences, decrease transmission, and eliminate established latency.
Famciclovir
Pro-drug that, when biotransformed into active metabolite penciclovir, may inhibit viral DNA synthesis/replication.
Anticonvulsants
Class Summary
These agents are used to manage severe muscle spasms and provide sedation in neuralgia. They have central effects on pain modulation. Prescribing information for gabapentin products (ie, Neurontin, Gralise, Horizant) describe a statistical improvement in pain scores (ie, a decrease by at least 50% from baseline) compared with placebo when treated for postherpetic neuralgia.
In October 2017, FDA approved Lyrica CR (pregabalin extended-release tablets), a once-daily treatment for the management of neuropathic pain associated with diabetic peripheral neuropathy (pDPN) and the management of postherpetic neuralgia (PHN). The approval was based on data from a randomized placebo-controlled trial conducted in 801 patients with PHN. The trial included a 6-week single-blind, dose optimization phase followed by a 13-week double-blind phase. Compared to placebo, more patients in the Lyrica CR group experienced at least a 50% improvement in pain intensity (73.6% vs. 54.6%).
Pregabalin (Lyrica, Lyrica CR)
Approved by FDA for use in PHN. Freynhagen et al describe a statistically significant reduction in mean pain score and in pain-related sleep interference compared with placebo. Pregabalin binds with high affinity to alpha2-delta subunit of voltage-gaited calcium channels, thereby reducing excitatory neurotransmitters. Has half-life of approximately 6 h and is eliminated by renal excretion. Decrease in creatinine clearance results in decrease elimination and, therefore, increase in plasma concentration. Peak plasma concentration occurs at one and one half hours after oral intake. Bioavailability is 90%. Following repeated dosing, steady state concentration is achieved at 24-48 h. Can be taken with or without food.
The extend-release formulation is available in 82.5mg, 165mg, and 330mg tablets strength. It is administered once daily after an evening.
Gabapentin (Neurontin, Gralise)
This medication has been approved by the FDA for the treatment of PHN. Has properties common to other anticonvulsants and antineuralgic effects. Exact mechanism of action is not known. Structurally, gabapentin is related to GABA, but it does not interact with GABA receptors. Believed to have a binding site at the alpha 2-delta protein, an auxiliary subunit of voltage-gaited calcium channels. In the rat brain, binding is localized on neuronal dendritic areas. Relevance of these observations to treatment of PHN is not known.
Gabapentin enacarbil (Horizant)
Gabapentin prodrug that provides a longer duration of action compared with gabapentin. Structurally related to neurotransmitter GABA, but has no effect on GABA binding, uptake, or degradation. The mechanism for analgesic activity is unknown. Approved by the FDA for PHN.
Corticosteroids
Class Summary
These agents have anti-inflammatory properties. Glucocorticoids cause profound and varied metabolic effects. In addition, they modify the body's immune response to diverse stimuli.
Dexamethasone
Used to treat various allergic and inflammatory diseases. Decreases inflammation by suppressing migration of polymorphonuclear leukocytes and by reversing increased capillary permeability.
Prednisone (Deltasone, Rayos)
Decreases inflammation by suppressing migration of polymorphonuclear leukocytes and by reversing increased capillary permeability.
Methylprednisolone (Solu-Medrol)
Decreases inflammation by suppression of migration of polymorphonuclear leukocytes and reversal of increased capillary permeability.
Analgesics, Topical
Class Summary
Pain control is essential to quality patient care; it ensures patient comfort and promotes pulmonary toilet. Most analgesics have sedating properties, which are beneficial for patients who experience pain.
Capsaicin topical
Natural chemical derived from plants of Solanaceae family. By depleting and preventing reaccumulation of substance P in peripheral sensory neurons, may render skin and joints insensitive to pain. Substance P thought to be chemomediator of pain transmission from periphery to CNS.
Capsaicin 8% transdermal patch (Qutenza)
Transient receptor potential vanilloid-1 (TRPV1) agonist indicated for neuropathic pain associated with postherpetic neuralgia. TRPV1 is an ion channel–receptor complex expressed on nociceptive skin nerve fibers. Topical capsaicin causes initial TRPV1 stimulation that may cause pain, followed by pain relief by reduction in TRPV1-expressing nociceptive nerve endings. Neuropathic pain may gradually recur over several months (thought to be caused by TRPV1 nerve fiber reinnervation of treated area).
Anesthetics, Topical
Class Summary
These agents stabilize the neuronal membrane so the neuron is less permeable to ions. This prevents the initiation and transmission of nerve impulses, thereby producing the local anesthetic action.
Lidocaine transdermal (Lidoderm, Ztlido)
Indicated for pain associated with postherpetic neuralgia. Lidoderm 5% transdermal patch contains 700 mg of lidocaine per patch. ZTlido 1.8% transdermal patch contains 36 mg per patch. Pharmacokinetic studies have demonstrated bioequivalence of the 2 patches. The ZTlido 1.8% patch is engineered to provide improved adhesion and flexibility to provide targeted transdermal absorption, so a lower amount of lidocaine can be used.
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Hypopigmented rash in thoracic dermatome of postherpetic lesion.
