Management of Nerve Injuries

Kiran Panesar, BPharmS (Hons), MRPharmS, RPh, CPh

US Pharmacist. 2012;37(10):HS-12-HS-16.

Treatment of Nerve Injuries

The treatment of nerve injuries is traced to William A. Hammond, surgeon general of the U.S. Army during the American Civil War.^[3] The goal of treatment is to restore function to the damaged nerve, improve quality of life, and reduce neuropathic pain.^[8] It is important to treat not only the nerve, but also exogenous sources of injury.

In severe pain syndrome, which is perhaps the most pressing consideration in early stages, the nerve injury leads to axonal sprouting and neuroma formation.^[9] Nerve pain, a combination of somatosensory, cognitive, and emotional alterations, is characterized by a burning sensation and dysesthesias.^[10] Typically neuropathic, this pain is relatively difficult to treat. Severe pain syndrome requires medications that specifically treat neuropathic pain.^[6] Although a number of options for reducing nerve pain exist, only about 70% of patients are adequately managed; in some patients, combination therapy provides better control.^[11] A typical strategy is to use short-acting medications that provide relief until longer-acting medications, such as antiepileptics or antidepressants, take effect.^[5] Refractory pain may require the further addition of an antidepressant or antiepileptic whose mechanism of action (MOA) differs from the MOA of the one already being used. Narcotics are reserved for more aggressive pain control.^[5]

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Table 1. Classification of Nerve Injury
Seddon's Classification	Sunderland's Classification	Tissues Injured
Neurapraxia	Grade I	Myelin
Axonotmesis	Grade II	Myelin, axon
Neurotmesis	Grade III: Axon continuity is disrupted by loss of endoneurial tubes, but perineurium is protected	Myelin, axon, endoneurium
	Grade IV: Nerve fascicle is damaged, but sheath continuity is maintained	Myelin, axon, endoneurium, perineurium
	Grade V: Substantial perineural hemorrhage and scarring occur	Myelin, axon, endoneurium, perineurium, epineurium

Source: References 3, 5.

Table 2. Analgesics and Anesthetics Used to Treat Neuropathic Pain
Class	Agent	Dosage
Analgesics	Tramadol	150 mg/day in 2–3 divided doses, increase by 50 mg/wk, max 200–400 mg/day
	Morphine (oral)	15–30 mg q8h
	Oxycodone	20 mg q12h, increase by 10 mg/wk, max 40–160 mg/day
	Fentanyl patch	25–100 mcg TD q3d
Anesthetics	Lidocaine patch	5% patch, apply to area of pain, max 3 patches q12h
Antidepressants (TCAs)	Amitriptyline	50–100 mg qd, starting at 10 mg qd and increasing by 10 mg/wk
	Imipramine	0.2–3 mg/kg/day to max 300 mg qd (adults) or 100 mg qd (elderly)
	Desipramine	50–150 mg qd, starting at 25 mg qd and increasing by 25 mg/wk
	Nortriptyline	50–100 mg qd, starting at 10–25 mg qd and increasing by 10–25 mg/wk
Antidepressants (SSRIs)	Paroxetine	10 mg once daily, increase by 10 mg/wk to max 60 mg qd
	Fluoxetine	0 mg once daily, increased by 20 mg q1–2w to max 60 mg/day
Antidepressants (SNRIs)	Duloxetine	30 mg qd, increase to 60–120 mg qd as single dose or 2 divided doses, qd or bid
	Venlafaxine	37.5 mg once daily, increased by 37.5 mg qw to max 225–375 mg/day

max: maximum; SNRI: serotonin-norepinephrine reuptake inhibitor; SSRI: selective serotonin reuptake inhibitor; TCA: tricyclic antidepressant; TD: transdermal.
Source: References 5, 12.

Table 3. Antiepileptics Used in the Management of Nerve Pain
Drug	Dosage	Side Effects
Carbamazepine	400 mg po bid, increase to tid if necessary	Risk of aplastic anemia and hyponatremia (monitor CBC and chemistries), somnolence, ataxia, blurred vision
Gabapentin	Begin 300 mg po qd, advance to 300 mg po tid by end of 1st wk. Effective dose: 900–3,600 mg in 3 divided doses	Somnolence, peripheral edema, dry mouth, ataxia, weight gain
Pregabalin	Begin 50 mg po tid, increase slowly to 100–200 mg po tid	Somnolence, peripheral edema, ataxia
Lamotrigine	Begin 25 mg po bid, increase slowly by 100 mg biwkly to max effective dose of 200–300 mg po bid	Somnolence, dizziness, aplastic anemia, nausea/vomiting, toxic epidermal necrosis, Stevens-Johnson syndrome