Re:Temporary relief of postherpetic neuralgia pain with topical geranium oil

[문형철]

beyond reason

To the Editor:

Postherpetic neuralgia has the features of neuropathic pain syndromes: sensory abnormalities, ongoing pain, allodynia, and a well-defined pathogenesis and onset (

1

). The effectiveness of neuropathic pain treatments is limited (

2

, 

3

, 

4

, 

5

, 

6

). Geranium oil, a steam distillate of the geranium plant (Pelargonium spp) that is used in flavors and fragrances, is generally regarded as safe by the U.S. Food and Drug Administration (

7

, 

8

). We conducted a study to assess neuropathic pain relief with topical geranium oil, to confirm‎ its safety, to define a dose-response relation, and to define the timing of the onset of pain relief.

The multicenter, double-blind crossover study involved five groups (100% geranium oil, 50% geranium oil in mineral oil, and 10% geranium oil in mineral oil, versus a mineral oil USP 100% placebo and a capsaicin 0.025% control) in a balanced random order in subjects who had moderately or severely painful postherpetic neuralgia (≥2 on a 0 to 4 pain intensity scale) for ≥3 months. Participants signed informed consent, and had a medical history, physical examination, vital signs, and chemistry panel performed at baseline. Spontaneous and evoked pain were measured using a 100-mm visual analog scale (range, “least possible pain” to “worst possible pain”) at 2, 10, 15, 20, 30, 45, and 60 minutes. Baseline laboratory tests were repeated 24 hours after each treatment. Each treatment yielded nine ratings of pain intensity that were combined into the time-integral of pain reduction or the area under the curve, with positive time-integrals indicating pain relief over the hour of observation.

Twenty-four of the 30 subjects completed the study. Mean values for the time-integral of spontaneous pain reduction were 21.3 for 100% geranium oil treatment, 12.7 for 50% treatment, and 8.0 for 10% treatment. For evoked pain reduction, the values were 15.8 for 100% geranium oil treatment, 7.7 for 50% treatment, and 5.9 for 10% treatment. Thus, geranium oil treatment was associated with a significant reduction in pain (P ≤0.002, one-tailed) for spontaneous (Figure) and evoked pain, as compared with placebo (–4.3 for spontaneous pain, –1.7 for evoked pain). Pain reduction was dose dependent (P ≤.003) and similar for spontaneous pain and evoked pain (P ≤0.008).

FigureSpontaneous pain relief over 1 hour. Negative pain integrals indicate increased pain.

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There were 10 minor adverse reactions among 7 patients for the five treatments, none of which were serious and all resolved in 1 hour. Four of these events were in the geranium oil groups: burning in eye with facial application of 100% geranium oil (n = 2), skin rash with 100% geranium oil (n = 1), and light headedness with 10% geranium oil (n = 1). There were no abnormalities in laboratory tests and clinical signs.

Postherpetic neuralgia pain can be severe and disabling, and treatments are less than ideal. Topical capsaicin relieves pain gradually over 2 weeks. Geranium oil relieves pain in minutes and is well tolerated. Six patients (25%) had dramatic pain relief of spontaneous pain suggesting a high-responder group. One of these patients' experience illustrates the potential effect on quality of life. This patient was unable to leave home and spent most of the day in bed with a wet washcloth over her forehead because of the severity of her pain. Continued use of topical 100% geranium oil has given pain relief for years with resumption of a normal life outside her home. Because pain relief was still increasing at the end of the 1-hour study, further trials will be necessary to define the time over which geranium oil relieves pain and to define its mechanism of action.

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