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`PA I N M E D I C I N E
`Volume 5 • Number S1 • 2004
`
`Pharmacologic Management Part 1: Better-Studied Neuropathic
`Pain Diseases
`
`Misha-Miroslav Backonja, MD,* Jordi Serra, MD†
`*University of Wisconsin Hospital and Clinics, Madison, Wisconsin; †Neuropathic Pain Unit, Hospital General de
`Catalunya, Barcelona, Spain
`
`A B S T R A C T
`
`Neuropathic pain impacts millions of people in the United States and around the world. Patients
`experience one of many symptoms, such as pain, paresthesia, dysesthesia, hyperalgesia, and allo-
`dynia, for many years because of unavailable or inadequate treatment. One of the major challenges
`in treating patients with neuropathic pain syndromes is a lack of consensus concerning the appro-
`priate first-line treatment options for conditions associated with neuropathic pain, including post-
`herpetic neuralgia, diabetic peripheral neuropathy, and trigeminal neuralgia.
`This review summarizes the published results of randomized trials involving treatment for neu-
`ropathic pain conditions. Anticonvulsants, such as gabapentin, carbamazepine, and lamotrigine, and
`tricyclic antidepressants, including amitriptyline and desipramine, have demonstrated efficacy in
`relieving pain associated with postherpetic neuralgia, diabetic peripheral neuropathy, and trigemi-
`nal neuralgia, in several studies. However, the lack of head-to-head comparison studies of these
`agents limits the conclusions that can be reached. Clinicians who must make decisions regarding
`the care of individual patients may find some guidance from the number of randomized trials with
`a positive outcome for each agent. Using quality-of-life study outcomes, treatment strategies must
`encompass the impact of therapeutic agents on the comorbid conditions of sleep disturbance and
`mood and anxiety disorders associated with neuropathic pain.
`Looking to the future, emerging therapies, such as pregabalin and newer N-methyl-D-aspartate–
`receptor blockers, may provide physicians and patients with new treatment options for more effec-
`tive relief of pain.
`
`Key Words. Neuropathic Pain; Diabetic Peripheral Neuropathy (DPN); Postherpetic Neuralgia
`(PHN); Trigeminal Neuralgia (TGN); Anticonvulsants; Tricyclic Antidepressants.
`
`Introduction
`
`It is estimated that over 4 million people in the
`
`United States suffer from neuropathic pain [1],
`which is defined as “pain initiated or caused by
`a primary lesion or dysfunction in the nervous
`system” by the International Association for the
`Study of Pain [2]. A more specific definition calls
`for pain that is the result of injury to the nervous
`system, peripheral, central, or both, and manifests
`with positive and negative sensory phenomena [3].
`Lesions that originate in the peripheral or central
`
`Reprint requests to: Dr. Jordi Serra, Neuropathic Pain Unit,
`Hospital General de Catalunya, c. Gomera s/n, 08190 Sant
`Cugat del Vallès, Barcelona, Spain. Tel: +34-93-565-6000;
`Fax: +34-93-589-2618; E-mail: jserrac@meditex.es.
`© American Academy of Pain Medicine 1526-2375/04/$15.00/S28 S28–S47
`
`nervous system may manifest as different neuro-
`pathic pain syndromes, depending on the anatomic
`location and type of impairment. Noncancer neu-
`ropathic pain syndromes are listed in Table 1.
`Patients with neuropathic pain experience a
`combination of positive and negative sensory,
`motor, and autonomic signs and symptoms. Posi-
`tive sensory symptoms include pain, paresthesia
`(abnormal sensation, either evoked or sponta-
`neous), dysesthesia
`(evoked or
`spontaneous
`unpleasant, abnormal sensation), hyperalgesia
`(increased response to a normally painful stimu-
`lus), and allodynia (painful response to a non-
`noxious stimulus). Negative sensory symptoms
`involve a loss of sensitivity to stimulation in
`general and painful stimuli in particular (hypoes-
`
`ARGENTUM Exhibit 1145
` Argentum Pharmaceuticals LLC v. Research Corporation Technologies, Inc.
`IPR2016-00204
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`Pharmacologic Management Part 1
`
`Table 1 Noncancer neuropathic pain syndromes
`
`Peripheral
`
`Central
`
`Complex regional pain syndrome (type I and II)
`Posttraumatic nerve injury
`Radiculopathy
`HIV sensory neuropathy
`Diabetic peripheral neuropathy
`Phantom limb pain
`Postherpetic neuralgia
`Trigeminal neuralgia
`Central poststroke pain
`Multiple sclerosis pain
`Spinal cord injury pain
`
`Adapted with permission from Dworkin [90].
`
`thesia and hypoalgesia, respectively) [4]. Often,
`these symptoms of neuropathic pain are chronic
`and endure for many years with either no treat-
`ment or inadequate treatment [5]. A survey con-
`ducted by the American Pain Society in 1998
`found that most people with chronic pain had been
`experiencing pain for over 5 years, that approxi-
`mately one third of chronic pain sufferers rated
`their pain as “the worst pain one can possibly
`imagine,” and that many chronic pain sufferers
`had to visit more than one doctor in an effort to
`gain relief from their pain [6].
`Despite the large number of people who are
`affected by neuropathic pain and the degree of suf-
`fering they endure, there does not appear to be
`consensus regarding the best way to treat the more
`commonly encountered neuropathic pain condi-
`tions [7]. No one therapeutic drug class or agent
`has been proven to be effective for all patients with
`neuropathic pain from a given etiology. Identifi-
`cation of an effective pharmacologic regimen for
`a specific patient is further complicated by the fact
`that a particular pain symptom may be produced
`by different mechanisms and that one underlying
`mechanism may manifest as several different
`symptoms [8,9]. Theoretically, the ability to iden-
`tify the mechanism(s) underlying a patient’s pain
`would enable the clinician to target pharmacologic
`treatment based on a drug’s mechanism of action
`[10]. Currently, patients with neuropathic pain
`are often treated with agents such as nonsteroidal
`anti-inflammatory drugs, which do not have
`proven efficacy in relieving neuropathic pain, or
`are treated with inappropriately low doses of
`agents that have demonstrated efficacy.
`In addition, as Nicholson and Verma discuss
`elsewhere in this issue, an understanding of the
`impact of comorbid conditions on pain and the
`effect of pain treatment on comorbidities is a
`key component in the successful management of
`patients with neuropathic pain [11].
`
`S29
`
`In this first part of our review of the pharma-
`cologic management of neuropathic pain, we
`discuss three of the better-studied neuropathic
`pain conditions—postherpetic neuralgia (PHN),
`diabetic peripheral neuropathy
`(DPN), and
`trigeminal neuralgia (TGN)—by examining pub-
`lished reports of clinical trials to draw conclusions
`from the available data.
`
`Methods
`This review is not intended to be a complete, sys-
`tematic analysis of all available data concerning the
`treatment of these three neuropathic pain condi-
`tions. Rather, it provides a summary of published
`data from well-designed, randomized trials. We
`discuss several selected studies within the context
`of each specific neuropathic pain syndrome, high-
`lighting those that have a quantitatively measured
`effect on the treatment of specific neuropathic
`pain symptoms or quality-of-life parameters. We
`have excluded open-label studies, case studies,
`unpublished data, and study results reported only
`in abstracts or poster presentations.
`
`Postherpetic Neuralgia
`Disease Overview
`The varicella zoster virus that causes chicken pox
`can remain latent in sensory ganglia for many years
`following the original infection [12]. Each year in
`the United States, reactivation of this virus mani-
`fests as herpes zoster (i.e., shingles) in an estimated
`800,000 people [13]. During the acute phase of
`herpes zoster, a painful rash usually forms along a
`single dermatome related to the affected dorsal
`root or cranial nerve ganglion [12]. The rash and
`severe pain associated with herpes zoster usually
`lasts less than 4 weeks [14]. However, a common
`sequela of herpes zoster is PHN, a condition in
`which pain along the involved nerve territory per-
`sists for a prolonged period after the acute rash
`resolves. Evidence suggests that the pathogenesis
`of PHN involves both peripheral and central mech-
`anisms that change over time, such as irritable pe-
`ripheral nociceptors and central sensitization [9,15].
`People 50 years of age and older are most likely
`to develop PHN following herpes zoster, and this
`painful condition can severely impact all aspects
`of life, including mood, sleep, physical activity,
`appetite, social activity, and the performance of
`necessary functions of daily living [13]. Therefore,
`the identification of an appropriate treatment to
`optimize outcome is essential.
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`S30
`
`Treatment Options
`Published data from randomized trials assessing
`the effect of various pharmacotherapeutic agents
`on pain in patients with PHN are summarized in
`Table 2 and discussed briefly below. The most
`commonly studied therapeutic classes in PHN are
`anticonvulsants and antidepressants; however,
`many other systemic and topical agents, including
`vincristine and magnesium sulfate, have also been
`investigated.
`Anticonvulsants
`The efficacy of anticonvulsants in relieving the
`pain associated with PHN has been demonstrated
`in several randomized, placebo-controlled trials.
`For example, Rice et al. [16] and Rowbotham
`et al. [17] demonstrated that gabapentin, at doses
`of 1,800mg/day, 2,400mg/day, and 3,600mg/day,
`was significantly better than placebo at reducing
`pain in patients with PHN (P < 0.01 for 1,800-mg
`and 2,400-mg doses [16]; P < 0.001 for 3,600-mg
`dose) [17]. In both of those studies, improvements
`in quality-of-life parameters were significantly
`greater in gabapentin-treated patients compared
`with patients who received placebo, including
`vitality (P < 0.05), mental health (P < 0.05) [16],
`sleep interference (P < 0.001) [17], mood, depres-
`sion, anger, fatigue (P < 0.001 for each), and con-
`fusion (P = 0.01) [17].
`The mechanisms by which gabapentin allevi-
`ates neuropathic pain have not been fully eluci-
`dated. Gabapentin binds to the a2d subunit of
`neurotransmitter-gated calcium ion channels [18];
`however, ongoing research suggests other mecha-
`nisms may be involved [19].
`Tricyclic Antidepressants
`Tricyclic antidepressants (TCAs) are prescribed
`frequently for the treatment of PHN. In 1982,
`Watson et al. demonstrated the efficacy of amitrip-
`tyline, versus placebo, in significantly (P £ 0.0001)
`reducing pain in patients with PHN, specifically
`paroxysmal, lancinating pain [20]. Subsequent
`studies found that amitriptyline was more effective
`in relieving PHN-related pain than lorazepam [21],
`fluphenazine [22], and maprotiline [23]. However,
`nortriptyline was as effective as amitriptyline in
`ameliorating neuropathic pain in patients with
`PHN [24], and other TCAs, such as desipramine,
`also have demonstrated efficacy [25]. Indeed, Raja
`et al. found no significant difference between pain
`relief with nortriptyline or desipramine and that
`seen with opioids in patients with PHN [26].
`Inhibiting the reuptake of norepinephrine and
`serotonin is how TCAs exert their effect. In gen-
`
`Backonja and Serra
`
`eral, the most common adverse events observed
`during treatment with these agents include seda-
`tion, anticholinergic effects (i.e., dry mouth, con-
`stipation), and hypotension. However, amitriptyline,
`clomipramine, and imipramine, which inhibit
`both norepinephrine and serotonin reuptake, have
`worse side-effect profiles than agents such as de-
`sipramine and nortriptyline that act on serotonin
`only [27].
`Opioids
`Controversy exists concerning the use of opioids to
`treat neuropathic pain. Although some pain spe-
`cialists believe that opioids are either ineffective or
`effective only at doses that cause intolerable side
`effects, others feel that it is possible to achieve pain
`relief while maintaining an acceptable side-effect
`profile [28]. Significant decreases in pain scores
`have been noted in patients with PHN during
`treatment with opioids [26,29]. Oxycodone in
`extended-release form was significantly more
`effective than placebo at relieving allodynia (P =
`0.0004) and paroxysmal pain (P = 0.0001) in
`patients with PHN [29]. However, oxycodone had
`no effect on mood and depression, and adverse
`events included constipation, nausea, and sedation.
`Extended-release morphine was associated with
`less cognitive side effects than nortriptyline, and
`it was preferred by patients over nortriptyline [26].
`Tramadol, a centrally acting analgesic, although
`chemically different from the opioids, has been
`shown to be effective in relieving the pain associ-
`ated with PHN. Tramadol was also shown to be
`more effective than placebo in decreasing visual
`analog scale (VAS) pain scores (P < 0.05), and
`patients in the tramadol group in that study
`required less rescue medication (P < 0.05) than
`those given placebo [30].
`Topical Agents
`The 5% lidocaine patch, a local anesthetic, has
`been shown to reduce the pain and allodynia asso-
`ciated with PHN in several randomized studies
`[31–33], possibly by reducing ectopic activity in
`the involved sensory nerves, and by providing a
`physical barrier to mechanical stimulation from
`contact with clothing, etc. [31,32]. In one study,
`involving 96 patients with PHN, the lidocaine
`patch was significantly more effective in relieving
`neuropathic pain than a vehicle patch (P = 0.043),
`and significant benefits were experienced by
`patients with nonallodynic pain (P = 0.022) and
`patients with “sharp,” “hot,” “dull,” and “deep”
`pain (P = 0.013) [33]. In a similar study, the only
`side effect reported was a mild redness at the
`
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`Pharmacologic Management Part 1
`
`Table 2 Pharmacotherapy of PHN
`
`S31
`
`Study
`
`Patients
`
`Treatment
`
`Outcomes
`
`Adverse events/withdrawals
`
`Randomized, double-blind, placebo-controlled trials
`Tramadol £400 mg/d (N = 63)
`Boureau et al.,
`Pts with PHN
`(N = 125)
`(£300 mg/d if 75 y or older)
`2003 [30]
`or placebo (N = 62) ¥6 wks
`
`Dowd et al.,
`1999 [91]
`
`Dworkin et al.,
`2003 [37]
`
`Pts with PHN Vincristine 0.01% (N = 11) or
`(N = 20)
`placebo (saline, N = 9)
`administered by
`iontophoresis over 1 h daily
`¥20 days
`
`Pts with PHN Pregabalin, 600 mg/d (N = 59)
`(N = 173)
`if creatinine clearance
`>60 mL/min or 300 mg/d
`(N = 30) if creatinine
`clearance 30–60 mL/min, or
`placebo (N = 84) ¥8 wks
`
`Mean pain intensity was
`significantly lower in the
`tramadol group than in the
`placebo group (P < 0.05) and
`required less rescue medication
`(P < 0.05)
`Pain scores were significantly
`lower in both groups on Day 20
`vs baseline. Pain relief was
`moderate or greater in 40% of
`vincristine-treated patients and
`55% of placebo-treated pts
`Pregabalin vs placebo
`demonstrated significantly
`greater decreases in pain (end
`point mean pain scores 3.60 vs
`5.29, P = 0.0001) and sleep
`interference (P = 0.0001)
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`No difference in rates of AEs,
`tramadol (29.7%) vs placebo
`(31.8%) or total AEs,
`tramadol (31) vs placebo
`(28)
`
`No neurological deficits or
`changes in blood profiles
`were detected in either
`group
`
`Withdrawals due to AEs:
`pregabalin 32% vs placebo
`5%; AEs, pregabalin vs
`placebo: dizziness, 28% vs
`12%; somnolence, 25% vs
`7%; peripheral edema, 19%
`vs 2%; amblyopia, 11% vs
`1%; dry mouth, 11% vs 2%;
`abnormal gait, 8% vs 1%;
`headache, 8% vs 8%; ataxia,
`7% vs 0%; confusion, 7% vs
`0%; diarrhea, 7% vs 5%;
`speech disorder, 6% vs 0%
`NA
`
`G2 (amitriptyline and
`fluphenazine) had the
`highest incidence of
`sleepiness and G1
`(amitriptyline) had the highest
`incidence of dry mouth
`AEs: dizziness and
`somnolence, particularly
`during titration phase
`
`Withdrawals: 13.3% with
`gabapentin; 9.5% with
`placebo; AEs: somnolence,
`dizziness, ataxia, peripheral
`edema, and infections were
`more frequent with
`gabapentin than placebo
`Withdrawals: gabapentin,
`32 pts; placebo, 41 pts; AEs,
`gabapentin vs placebo:
`dizziness, 24% vs 8%;
`somnolence, 14% vs 5%;
`infection, 9% vs 13%;
`headache, 9% vs 14%;
`nausea, 9% vs 9%; flu
`syndrome, 7% vs 5%;
`abdominal pain, 7% vs 4%;
`accidental injury, 6% vs
`5%; diarrhea, 5% vs 4%
`AEs: burning and stinging at
`application site in 60% of
`pts using capsaicin and
`33% using placebo
`
`Galer et al.,
`2002 [33]
`
`Pts with PHN
`(N = 96)
`
`5% lidocaine patch vs vehicle
`patch ¥3 wks
`
`Pts with PHN Pts randomly assigned to 1 of
`(N = 49)
`4 groups: G1, amitriptyline;
`G2, amitriptyline and
`fluphenazine; G3,
`fluphenazine; G4, active
`placebo, ¥8 wks
`Pts with PHN Gabapentin, 1,800 mg/d
`(N = 334)
`(N = 115), gabapentin,
`2,400 mg/d (N = 108), or
`placebo (N = 111) ¥7 wks
`(with dose titration during
`first 2 wks)
`
`Pts with PHN Gabapentin maximum dose:
`(N = 229)
`3,600 mg/d (range: 1,200–
`3,600 mg/d, N = 113) or
`placebo (N = 116) ¥8 wks;
`dose titration during first
`4 wks
`
`Graff-Radford
`et al., 2000
`[22]
`
`Rice et al.,
`2001 [16]
`
`Rowbotham
`et al., 1998
`[17]
`
`Serpell et al.,
`2002 [39]
`
`Lidocaine patch improved pain
`qualities as measured by NPS
`to a greater extent than vehicle
`patch (P = 0.043)
`Statistically significant decrease
`in pain (measured by VAS)
`compared with baseline
`occurred in G1 and G2
`(P < 0.001 and P = 0.04,
`respectively)
`Differences in pain scores vs
`baseline were -34.5% (1,800-mg
`dose), -34.4% (2,400-mg dose),
`and -15.7% (placebo). Both
`gabapentin doses were
`significantly better than placebo
`(P < 0.01 for each dose)
`Reduction in pain scores
`significantly greater with
`gabapentin vs placebo (from
`6.3 to 4.2 points vs 6.5 to 6.0
`points, respectively, P < 0.001)
`
`Pts with
`various
`symptoms
`(N = 307),
`PHN
`(43/307)
`
`Gabapentin, 900 mg/d (titrated Gabapentin demonstrated
`over 3 days), with escalation
`greater improvement in pain
`to 1,800 mg/d or 2,400 mg/d,
`score than placebo (21% vs
`for a total of 8 wks (N = 153),
`14%, P = 0.048)
`or placebo (N = 152)
`
`Watson et al.,
`1993 [35]
`
`Pts with PHN Capsaicin 0.075% cream vs
`(N = 143)
`placebo (vehicle) cream
`
`Capsaicin resulted in greater
`decrease in pain than placebo
`(measured by VAS) at 2 wks
`(19% vs 0.4%, P < 0.05) and
`6 wks (P = 0.032). Long-term
`follow up (£2 years, N = 77)
`showed clinical benefit in
`86% of patients
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`
`S32
`
`Table 2 Continued
`
`Backonja and Serra
`
`Study
`
`Patients
`
`Treatment
`
`Outcomes
`
`Adverse events/withdrawals
`
`Randomized, double-blind, placebo-controlled, crossover trials
`Baranowski
`Pts with PHN Pts received each of the
`(N = 24)
`et al., 1999
`following IV infusions over
`2 h ≥1 wk apart: placebo
`[92]
`(normal saline), lidocaine
`1 mg/kg, and lidocaine
`5 mg/kg
`
`Brill et al.,
`2002 [93]
`
`Pts with PHN Magnesium sulphate, 30 mg/kg,
`(N = 7)
`IV, or saline
`
`De Benedittis
`and
`Lorenzetti,
`1996 [94]
`
`Galer et al.,
`1999 [31]
`
`Pts with PHN Pts had 1 of 4 suspension/
`(N = 22)
`diethyl ether solutions
`AHN
`applied to affected areas in
`(N = 15)
`a randomized order on 4
`different days. Median
`doses of active suspensions:
`aspirin 1,000 mg;
`indomethacin 75 mg;
`diclofenac 100 mg; lactose
`was used for placebo
`Topical 5% lidocaine patch vs
`placebo (vehicle) patch for
`2–14 days, depending on
`increase in pain; then
`patients crossed over to
`alternative treatment
`
`Pts with PHN
`(N = 33)
`
`Ongoing pain (measured by VAS)
`was significantly reduced after
`all infusions (P < 0.05); dynamic
`pressure-evoked pain was
`significantly reduced by both
`lidocaine infusions (P < 0.05,
`for each dosage level); area of
`allodynia declined with lidocaine
`1 and 5 mg/kg (P < 0.05 and
`P < 0.001, respectively)
`Mean pain score decreased from
`6.7 to 1.9 at 30 minutes
`posttreatment with magnesium
`sulphate. Pain scores were
`significantly lower with
`magnesium sulphate than with
`placebo at 20 and 30 minutes
`(P = 0.016)
`Only aspirin was significantly
`superior to placebo for reduction
`in pain (based on VAS score)
`from baseline (P < 0.05) and
`duration of pain (P < 0.01).
`Good-to-excellent results were
`reported in >81% of PHN pts
`with topical aspirin suspension
`
`Primary end point was “time to
`exit,” i.e., pts were allowed
`to discontinue treatment if pain
`relief diminished. Median time
`to exit was significantly better
`with lidocaine than placebo
`(14 d vs 3.8 d, P < 0.001).
`Lidocaine patch was preferred
`by 78.1% of pts vs 9.4% for
`placebo (P < 0.001)
`
`Kishore-
`Kumar et al.,
`1990 [25]
`
`Pts with PHN Desipramine (mean dose:
`(N = 26)
`167 mg/d) or placebo
`¥6 wks; then pts crossed
`over to alternative treatment
`
`Pain relief with desipramine was
`significantly greater from weeks
`3 to 6 than with placebo
`(P < 0.001)
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`No pts at the lower dose
`reached toxic plasma levels;
`however, several pts at the
`higher dose did reach toxic
`levels. Thus, the lower doses
`may be considered safe
`
`No side effects were
`reported during treatment
`with magnesium sulphate
`
`Mild cutaneous rash in 1 pt
`each with indomethacin and
`diclofenac
`
`Withdrawals: 1 pt suffered a
`stroke prior to receiving
`study medication; 1 pt
`withdrew during placebo
`period because of increased
`pain and insomnia; 1 pt
`stopped placebo because
`of red, irritated skin; AEs
`were mild or moderate;
`application site reaction
`redness/rash reported in
`9 pts with lidocaine patch
`and 11 pts with placebo
`patch
`Withdrawals: 8 pts because of
`AEs or intercurrent medical
`illnesses; AEs: desipramine:
`syncope, 1 pt; left bundle
`branch block, 1 pt; jitteriness
`and atypical chest pain, 1 pt;
`fever, 1 pt; and vertigo, 1 pt;
`placebo: vertigo and nausea,
`1 pt; skin rash, 1 pt;
`unsteadiness + mental
`fogginess, 1 pt
`AEs: dry mouth, sedation,
`dizziness; occurred with
`both active treatments
`
`Max et al.,
`1988 [21]
`
`Nelson et al.,
`1997 [95]
`
`Pts with PHN Amitriptyline (12.5–150 mg/d),
`(N = 58)
`lorazepam (0.5–6 mg/d), or
`placebo (lactose) ¥2 wks;
`followed by 1-wk washout;
`then crossed to alternative
`treatment
`Pts with DPN Oral dextromethorphan (mean
`(N = 14)
`dose in PHN: 439 mg/d) or
`placebo ¥6 wks followed by
`and with
`PHN
`1-wk washout; then crossed
`(N = 18)
`over to alternative treatment
`
`Moderate or greater pain relief
`was reported by 47% of pts
`with amitriptyline, 16% of pts
`with placebo, and 15% of
`pts with lorazepam
`
`Dextromethorphan did not reduce Withdrawals: 5 PHN pts due
`pain in pts with PHN to a
`to sedation, ataxia and
`greater extent than placebo
`confusion, and (unrelated)
`(P = 0.72)
`6th cranial nerve palsy
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`S33
`
`Adverse events/withdrawals
`
`Withdrawals: opioids, 20 pts;
`TCA = 6 pts; placebo, 1 pt
`(P < 0.01); AEs:
`constipation, nausea,
`dizziness, drowsiness, loss
`of appetite, and dry mouth
`
`AEs: bruising and pain upon
`patch removal, 1 pt; mild
`skin reddening, 2 pts (1 pt
`each with lidocaine and
`vehicle patch)
`
`AEs included sedation (71%,
`63%, and 38%), dry mouth
`(30%, 21%, and 25%), and
`GI distress (17%, 0%, and
`0%) for dextromethorphan,
`memantine, and lorazepam,
`respectively
`AEs resulting in withdrawal:
`amitriptyline: dry mouth
`combined with constipation,
`sedation, dizziness, lethargy,
`mouth ulcers, and nausea
`(1 pt each); maprotiline: dry
`mouth and nausea, nausea
`and vomiting, restless legs
`(1 pt each)
`Withdrawal: 1 pt because
`of erythema multiforme;
`AEs: dry mouth, 16 pts;
`drowsiness, 4 pts;
`constipation, 2 pts; increased
`breast size, 1 pt; rash, 1 pt
`
`Pts with PHN Pts randomly assigned to
`(N = 35)
`amitriptyline or maprotiline.
`Median dose of both agents
`was 100 mg/d ¥ 5 wks;
`followed by 2-wk washout
`then crossed over to
`alternative treatment
`
`Pts with PHN Amitriptyline, 12.5–25 mg/d,
`(N = 24)
`increased to median dose
`of 75 mg, or placebo ¥3 wk;
`followed by a 1- to 2-wk
`washout, then pts crossed
`over to alternative
`treatment
`Pts with PHN Oxycodone, 10 mg (increased
`(N = 50)
`to a maximum of 30 mg), or
`placebo every 12 h ¥ 4 wks,
`followed by crossover to the
`alternative treatment
`
`Pts with PHN Amitriptyline or nortriptyline,
`(N = 33)
`10 mg (≥65 y of age), or
`20 mg (<65 y of age), with
`dosage increases ¥5 wks;
`followed by 2-wk washout,
`then crossed over to
`alternative treatment
`
`Amitriptyline was significantly
`better than maprotiline at
`relieving pain as measured by
`VAS score (P < 0.01)
`
`Changes in VAS scores
`demonstrated that amitriptyline
`was superior to placebo in
`relieving pain (P £ 0.0001)
`
`Reduction in pain was significantly Withdrawals: 6 pts with
`better with oxycodone than with
`oxycodone; 5 pts with
`placebo (P = 0.0001)
`placebo; AEs with
`oxycodone: constipation,
`5 pts; nausea, 4 pts;
`sedation, 3 pts
`Withdrawals: 2 pts left due to
`AEs (1 pt taking nortriptyline
`experienced increased pain
`fever, epigastric pain, bad
`dreams, and perspiration;
`1 pt taking amitriptyline
`experienced slurred speech
`and urinary retention)
`
`No difference between the two
`drugs in any pain parameter
`
`Abbreviations: AEs = adverse events; AHN = acute herpetic neuralgia; d = day; GI = gastrointestinal; h = hour; min = minute; NA = not available; NPS = Neuro-
`pathic Pain Scale; pts = patients; wk = week; y = year.
`
`Pharmacologic Management Part 1
`
`Table 2 Continued
`
`Study
`
`Patients
`
`Treatment
`
`Outcomes
`
`Greater mean decreases in pain
`ratings on a 0–10 scale were
`achieved with TCAs (1.4) and
`with opioids (1.9) than with
`placebo (0.2, P < 0.001)
`
`Pts with PHN Each pt was scheduled to
`(N = 76)
`undergo three treatment
`periods (8 wks each) in
`random order: opioid (mean
`dose: morphine 91 mg or
`methadone 15 mg); TCA
`(mean dose nortriptyline
`89 mg or desipramine
`63 mg); and placebo
`Pts with PHN Pts randomly assigned (as to
`(N = 35)
`session order) to four 12-h
`long treatment sessions:
`5% lidocaine patch (2
`sessions), vehicle patch,
`and observations only
`
`Pain intensity reductions
`significantly greater with
`lidocaine patch than with vehicle
`patch (P < 0.001 to P = 0.038 at
`individual time points) and with
`observation only (P = 0.0001 to
`P = 0.021 at individual time
`points); pain reductions
`significantly greater with
`vehicle patch than with
`observation only at 2-h
`(P = 0.016) and 6-h (P = 0.041)
`time points
`Pts with DPN Median doses for pts with PHN Mean reductions in pain intensity
`(N = 23)
`were: dextromethorphan
`in pts with PHN were 6% with
`and with
`400 mg/d, memantine
`dextromethorphan, 2% with
`PHN
`35 mg/d, or lorazepam
`memantine, and 0%
`(N = 21)
`(active placebo) 1.2 mg/d
`with lorazepam
`
`Raja et al.,
`2002 [26]
`
`Rowbotham
`et al., 1996
`[32]
`
`Sang et al.,
`2002 [38]
`
`Watson et al.,
`1992 [23]
`
`Watson et al.,
`1982 [20]
`
`Watson and
`Babul, 1998
`[29]
`
`Watson et al.,
`1998 [24]
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`S34
`
`application site of the patch in patients who
`used either the lidocaine patch or the vehicle
`patch [31].
`Reduction in pain, as measured on a VAS, has
`also been observed with the topical agent capsaicin.
`Capsaicin binds to receptors (VR1/TRPV1) on
`subpopulations of sensory nociceptive C or Ad
`fibers. Initially, capsaicin causes pain by initiating
`nociceptor firing, resulting in increased sensitivity
`to painful thermal and mechanical stimuli. An
`analgesic effect follows the painful experience as
`prolonged exposure to capsaicin desensitizes noci-
`ceptive terminals through partial or complete
`degeneration of axon terminals or the neuron [34].
`However, the initial burning and stinging at the
`application site may be intolerable to some
`patients [35].
`
`Emerging Treatment Regimens
`Pregabalin, a new a2d ligand with analgesic, anxi-
`olytic, and anticonvulsant activities, is currently
`being investigated for use in the treatment of neu-
`ropathic pain [36]. Dworkin et al. reported the
`results of a randomized, double-blind study involv-
`ing 173 patients with PHN [37]. Patients treated
`with pregabalin (600mg/day or 300mg/day based
`on creatinine clearances of >60mL/minute or
`30–60mL/minute, respectively) had a significantly
`lower mean pain score than patients who received
`placebo (3.60 vs 5.29, P = 0.0001), and 50% of
`the pregabalin-treated patients reported a ≥50%
`reduction in mean pain scores, compared with only
`20% of patients who received placebo (P = 0.001).
`Compared with patients in the placebo group, pre-
`gabalin-treated patients also experienced signifi-
`cantly greater improvements in sleep (P = 0.0001).
`Side effects associated with pregabalin included
`dizziness, somnolence, peripheral edema, and dry
`mouth. In most cases, side effects were of mild to
`moderate intensity.
`Sang et al.
`investigated the use of dex-
`tromethorphan and memantine, low-affinity N-
`methyl-d-aspartate (NMDA) antagonists, in the
`treatment of neuropathic pain in patients with
`DPN and PHN [38]. In patients with PHN, the
`mean reduction in pain intensity from baseline was
`7% with dextromethorphan, 2% with memantine,
`and 0% with lorazepam (active placebo). Although
`these results were not statistically significant, 29%
`of patients with PHN had moderate or better pain
`relief with dextromethorphan, as did 12% with
`memantine. Adverse events with dextromethor-
`phan and memantine included sedation, dry
`mouth, and gastrointestinal distress.
`
`Backonja and Serra
`
`Non–Disease-Specific Trials: Anticonvulsant
`Serpell et al. [39] conducted a study designed to
`assess the impact of gabapentin on specific neuro-
`pathic pain symptoms in patients with various neu-
`ropathic pain conditions. Evidence suggests that
`neuropathic pain symptoms reflect an underlying
`pathophysiology and, therefore, may respond to
`the same pharmacologic agents regardless of eti-
`ology. Of the 307 patients enrolled in that study,
`43 had PHN. Although data for patients with
`PHN were not reported specifically, overall,
`higher percentages of gabapentin-treated patients,
`than patients in the placebo group, experienced
`improvements in allodynia (23% vs 15%), shoot-
`ing pain (32% vs 24%), burning pain (23% vs
`15%), and hyperalgesia (26% vs 17%), although
`no clear inference on specific mechanisms that
`responded better to gabapentin could be estab-
`lished. The most common adverse events observed
`with gabapentin treatment in those studies were
`somnolence, dizziness, ataxia, peripheral edema,
`and infections.
`
`Number Needed to Treat
`The importance of data generated from clinical
`studies is that the knowledge gained can be trans-
`lated to clinical practice. Thus, clinicians who are
`making decisions about the management of indi-
`vidual patients need to have a measurement of
`treatment effect. This enables clinicians to evalu-
`ate the results of various clinical trials that have
`different end points and use different statistical
`analytic methods. The number needed to treat
`(NNT), which indicates the number of patients
`that would have to be treated in order to obtain a
`positive therapeutic response, or to prevent one
`untoward event, is calculated as the reciprocal of
`the absolute risk reduction, that is, the difference
`between event rates in the treatment and placebo
`groups [40]; for example NNT = 1/(response
`rate to treatment)–(response rate to placebo).
`However, when making clinical decisions based on
`NNT values, certain caveats should be consid-
`ered—pooled NNT values are not adjusted for
`study quality or size; different studies use different
`outcome measures; there can be differences in
`clinical settings or patient characteristics; and
`there may be secular trends in incidence or
`morality [41].
`Collins et al. analyzed data from randomized
`trials to calculate NNT values for anticonvulsants
`and antidepressants used to treat neuropathic pain
`in patients with PHN [42]. They determined that
`the NNT to obtain a ≥50% pain relief in one
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`Pharmacologic Management Part 1
`
`patient is 3.2 for anticonvulsants and 2.1 for anti-
`depressants. Sindrup and Jensen reported NNT
`values of 2.3 for TCAs, 2.5 for oxycodone, and 5.3
`for capsaicin in PHN [43].
`
`Number Needed to Harm
`The number needed to harm (NNH) indicates the
`number of patients that would need to be treated
`in order for one patient to have an adverse event.
`Calculation of the NNH uses the same basic equa-
`tion as for the NNT, that is, NNH = 1/(adverse
`event rate to treatment)–(adverse event rate of
`placebo). In a report by Collins et al. [42], NNH
`data were pooled for both PHN and DPN in a
`comparison of antidepressants (TCAs and selec-
`tive serotonin reuptake inhibitors [SSRIs]) with
`placebo. TCAs were found to have an NNH value
`of 14 for major adverse events while SSRIs were
`shown to be no different than placebo. Although
`there were no NNH anticonvulsant data available
`for major adverse events, for m