Accepted for Publication in American Journal of Medicine
Post-herpetic neuralgia has the features of all neuropathic pain syndromes: sensory abnormalities, ongoing pain, allodynia, a well-defined pathogenesis and a well-defined onset (1). The effectiveness of neuropathic pain treatments is limited (2-6). Geranium oil is a steam distillate of the geranium plant (Pelargonium spp.), is generally regarded as safe (GRAS) by the US FDA and is used in flavors and fragrances (7-8).
The purpose of this trial was to verify observations of neuropathic pain relief with topical geranium oil, to confirm its safety, to define a dose-response relationship, and to define the timing of the onset of pain relief.
The study was a multi-center, double-blind crossover design using 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 with moderately or severely painful post-herpetic neuralgia (> 2 on a 0-4 pain intensity scale) for > 3 months.
Subjects signed informed consent, had a medical history, physical exam, vital signs and chemistry panel performed at baseline. Measures of spontaneous and evoked pain were made using a 100 mm visual analog scale (VAS) anchored by "least possible pain and "worst possible pain." Spontaneous and evoked pain intensity were assessed at 2, 10, 15, 20, 30, 45 and 60 minutes. Baseline laboratory tests were repeated 24 hours after each treatment.
Each treatment yielded nine VAS 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.
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Twenty-four of the 30 subjects completed the study. Mean values for the time-integral of spontaneous pain reduction were 21.3, 12.7, and 8.0 for 100%, 50%, and 10% geranium oil treatments respectively. For evoked pain reduction, these values were 15.8, 7.7, and 5.9 respectively. Thus, the geranium oil treatment produced a significant reduction in pain (p < .002, one tailed), for spontaneous (Figure) and evoked pain, compared to placebo (-4.3 for spontaneous pain, -1.7 for evoked pain). Pain reduction was dose dependent (p < ƒ~.003, one tailed) and similar for spontaneous pain and evoked pain (p < .008).
There were ten minor adverse reactions among seven patients for the five treatments, none of which were serious and all resolved in 1 hour. Four of these minor adverse events were in the geranium oil groups: burning in eye with facial application of 100% (2), skin rash with 100% (1) and light headedness with 10% (1). There were no laboratory abnormalities or abnormalities in clinical signs.
Post-herpetic neuralgia pain can be severe, disabling, and treatments are less than ideal. Topical capsaicin relieves pain gradually over two 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 the several high responder's experience illustrates the potential impact on quality of life. Mrs. S. was unable to leave home and spent most of the day in bed with a wet washcloth over her forehead due to the severity of her pain. The continued use of topical 100% geranium oil has given pain relief for years with resumption of a normal life outside her home.
Since pain relief was still increasing at the end of the 1-hour study, further trials will be necessary to define the time period of time over which geranium oil relieves pain and to define its mechanism of action.
Frank L. Greenway, M.D.
Pennington Biomedical Research Center, Baton Rouge, Louisiana
Bruce M. Frome, M.D.
Fromix Formulas, Inc., Beverly Hills, California
Thomas M. Engels III, B.S.
Guidant Corporation, San Jose, California
Alexander McLellan, N.D.
Origin Biomedicinals, Halifax, Nova Scotia
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7. Office of Health and Human Services, Code of Federal, Regulations 1990; Part 182.20; 295-396.
8. Flavoring Extract Manufacturer's Association.