A review of the use of topical analgesics for myofascial pain

Pharmacological Topical Therapy for Intra-Oral Post Traumatic Trigeminal Neuropathic Pain: A Comprehensive Review

Background: The efficacy of topical treatments in alleviating neuropathic pain is well-established. However, there is a paucity of research on topical interventions designed specifically for intra-oral application, where the tissue composition differs from that of exposed skin. Methods: This comprehensive review endeavors to assess the extant evidence regarding the efficacy of topical treatments in addressing neuropathic pain within the oral cavity. Utilizing combinations of search terms, we conducted a thorough search across standard electronic bibliographic databases-MEDLINE (via PubMed), Embase, Google Scholar, and Up to Date. The variables under scrutiny encompassed topical treatment, local intervention, chronic oral and orofacial pain, and neuropathic pain. All pertinent studies published in the English language between 1992 and 2022 were included in our analysis. Results: Fourteen relevant manuscripts were identified, primarily consisting of expert opinions and case reports. The comprehensive review suggests that topical treatments, especially when applied under a stent, could be effective in mitigating neuropathic pain in the oral area. However, it is crucial to conduct further studies to confirm these preliminary results. The limitations of the reviewed studies, mainly the reliance on expert opinions, small sample sizes, inconsistent study designs, and a lack of long-term follow-up data, highlight the need for more rigorous research. Conclusions: Although initial findings indicate topical treatments may be effective for oral neuropathic pain, the limitations of current studies call for more thorough research. Further comprehensive studies are essential to validate the efficacy of these treatments, standardize procedures, and determine long-term results. This will provide clearer guidance for treating chronic neuropathic pain in the oral cavity.

Capsaicin topical cream (8%) for the treatment of myofascial pain syndrome

Background

Myofascial pain syndrome is a common cause of musculoskeletal pain. The objective of this study was to evaluate the potential analgesic action of 8% capsaicin cream for topical use in patients with myofascial pain syndrome.

Methods

Initially, cream formulations of PLA (Placebo) and CPS (Capsaicin 8%) were developed and approved according to the current requirements of the health authority agency. The 40 participating patients were randomly assigned to the PLA and CPS groups in a double-blind fashion. Before the creams were topically administered, according to the allocation group, the local anesthetic was used for a period of 50 minutes directly in the area of interest. The cream was applied to the area of the skin over the trigger point, represented by the area with pain at palpation, in an amount of 10 g for 30 minutes in a circular area of 24 mm diameter. Subsequently, the cream was removed and the skin tolerability parameters were evaluated. The pain was measured before and during the formulation application, as well as at 1 hour, 7 days, 30 days, and 60 days after the procedure, evaluated using a verbal numerical scale (from 0 to 10: with 0 = no pain and 10 = worst pain imaginable).

Results

No patient in PLA Group had hyperemia or burning sensation at the site of application, while 85% of patients in CPS Group had hyperemia or burning sensation at 15 minutes. These complaints disappeared 24 hours after the cream was removed. The pain score in CPS Group decreased steadily up to the 60^th day of evaluation (p < 0.0001).

Conclusion

Application of the formulations did not cause macroscopic acute or chronic skin lesions in patients, and the 8% capsaicin formulation was beneficial and well tolerated.

Pharmacokinetics of intravenous, subcutaneous, and topical administration of lidocaine hydrochloride and metabolites 3-hydroxylidocaine, monoethylglycinexylidide, and 4-hydroxylidocaine in horse

Intravenous (iv), subcutaneous (sq), and topical (tp) lidocaine was administered to six horses in a cross-over, randomized design study. Samples were collected for up to 72 hr. Compartmental models were used to investigate the pharmacokinetics of (LD) and its metabolites 3-hydroxylidocaine (3-OH), 4-hydroxylidocaine (4-OH), and monoethylglycinexylidide (MEGX). Metabolites 3-OH and 4-OH were present in conjugated forms, whereas LD and metabolite MEXG were present primarily in the un-conjugated form. Plasma concentrations of LD after iv administration (100 mg) were described by three-compartment model with an additional three compartments to describe the elimination of metabolites. Median (range) elimination micro-constants (K_e ) for LD, 3-OH, 4-OH, and MEXG were 4.12 (2.62-6.23), 1.25 (1.10-2.15), 1.79 (1.22-2.39), and 1.69 (1.03-1.99)/hr, respectively. Median (range) values of alpha (t_½α ), beta (t_½β ), and gamma (t_½γ ) half-lives were 0.08 (0.07-0.13), 0.57 (0.15-1.25), and 4.11 (0.52-7.36) hr. Plasma concentrations of LD after sq (200 mg) administration were described by absorption and two-compartment elimination model. The median (range) of the LD absorption half-life (t_½ab ) was 0.47 (0.29-0.61) hr. The K_e for LD, 3-OH, 4-OH, and MEXG was 3.91 (1.48-9.25), 1.00 (0.78-1.08), 1.76 (0.96-2.11), and 1.13 (0.69-1.33)/hr. The median (range) of t_½α and t_½β was 0.15 (0.06-0.27) and 3.04 (2.53-6.39) hr. Plasma concentrations of LD after tp (400 mg) application were described by one-compartment model with a t_½ab of 8.49 (5.16-11.80) hr. The K_e for LD, 3-OH, and MEXG was 0.24 (0.10-0.81), 0.41 (0.08-0.93), and 0.38 (0.26-1.14)/hr.

A randomized, placebo-controlled double-blinded comparative clinical study of five over-the-counter non-pharmacological topical analgesics for myofascial pain: single session findings

OBJECTIVES

To investigate the effects of topical agents for the treatment of Myofascial Pain Syndrome (MPS) and Myofascial Trigger Point (MTRP).

METHODS

Subjects with an identifiable trigger point in the trapezius muscle, age 18-80 were recruited for a single-session randomized, placebo-blinded clinical study. Baseline measurements of trapezius muscle pressure pain threshold (PPT: by pressure algometer) along with right and left cervical lateral flexion (rangiometer) were obtained by a blinded examiner. An assessor blinded to the outcomes assessments applied one of 6 topical formulations which had been placed in identical plastic containers. Five of these topicals were proposed active formulations; the control group was given a non-active formulation (PLA). Five minutes after the application of the formula the outcome measures were re-tested. Data were analyzed with a 5-way ANOVA and Holms-adjusted t-tests with an alpha level of 0.05.

RESULTS

120 subjects were entered into the study (63 females; ages 16-82); 20 subjects randomly allocated into each group. The pre- and post-treatment results for pressure threshold did show significant intra-group increases for the Ben-Gay Ultra Strength Muscle Pain Ointment (BG), the Professional Therapy MuscleCare Roll-on (PTMC roll-on) and Motion Medicine Cream (MM) with an increased threshold of 0.5 kg/cm2 (+/-0.15), 0.72 kg/cm2 (+/-0.17) and 0.47 Kg/cm2 (+/-0.19) respectively. With respect to the inter-group comparisons, PTMC roll-on showed significant increases in pressure threshold compared with Placebo (PLA) (p = 0.002) and Icy Hot Extra Strength Cream (IH) (p = 0.006). In addition, BG demonstrated significant increases in pressure threshold compared with PLA (p = 0.0003).

CONCLUSIONS

With regards to pressure threshold, PTMC roll-on, BG and MM showed significant increases in pain threshold tolerance after a short-term application on a trigger points located in the trapezius muscle. PTMC roll-on and BG were both shown to be superior vs placebo while PTMC was also shown to be superior to IH in patients with trigger points located in the trapezius muscle on a single application.CMCC Research Ethics Board Approval # 1012X01, 2011.

The effect of cetylated fatty esters and physical therapy on myofascial pain syndrome of the neck

Participants with Myofascial Pain Syndrome (MPS) of the neck were randomly assigned into 2 groups of the double-blinded study: topical cetylated fatty ester complex (CFEC) cream application plus physical therapy (CF-PT; n=37), and placebo cream application plus physical therapy (PL-PT; n=35). There were 3 visits during 4 weeks of treatment. Physical Therapy (PT), given twice/week, included Ischaemic Compression, Deep Pressure Trigger Point Massage and Myofascial Releases. Topical cream [CFEC cream (5.6%) and 1.5% menthol] or placebo cream [1.5% menthol, in a cream base] was applied twice/day. CF-PT provided the fastest and most effective study treatment modality. The addition of CFEC cream to PT resulted in statistically significant improvements, compared to PL-PT, for reduction of pain, neck disability and life quality indicators. Our results indicate that cetylated derivatives of fatty acids can effectively reduce pain and symptoms associated with neck MPS, when combined with physical therapy.

Fibromyalgia: A Review of Its Pathophysiology and Drug Treatment

The objective of this article is to review the literature related to the pathophysiology of fibromyalgia and the drug therapy used to treat this disease. Fibromyalgia, the second most frequently diagnosed rheumatological disorder, has complex interrelated pathologies that must be addressed to achieve effective symptom control. Central and peripheral sensitization along with neurotransmitter abnormalities play a major role in defining the symptoms associated with this disease. Drug therapy must be multifaceted because no single drug addresses all pathologies. Drug and nondrug therapies showing strong-to-moderate effectiveness should be used to obtain the most benefit.

Safety and tolerability of the lidocaine patch 5%, a targeted peripheral analgesic: a review of the literature

The safety, tolerability, and efficacy of the lidocaine patch 5% (Lidoderm), a targeted peripheral analgesic with an FDA-approved indication for the treatment of postherpetic neuralgia, has been well established. Recent case reports and studies have suggested potential efficacy in other neuropathic and nonneuropathic pain conditions. Several pharmacokinetic studies have demonstrated minimal systemic absorption with 12-, 18-, and 24-hour/day dosing. Mean maximum plasma concentrations have shown the lidocaine patch to possess a minimal risk for systemic toxicities or drug-drug interactions. The most common adverse events generally involve mild skin reactions. There have been no drug-drug interactions noted in clinical trials. Recent evidence suggests that extended application does not result in A-beta-mediated sensory loss at the application site, which is particularly important in patients who already have a degree of sensory loss due to their underlying condition. The lidocaine patch provides a treatment option that carries a relatively low systemic adverse event and drug-drug interaction risk burden, even with continuous application of up to four patches per day.