JEADV ISSN 1468-3083
High in vitro efficacy of Nyda® L, a pediculicide containing
FAS Oliveira,† R Speare,‡ J Heukelbach*†‡
† Department of Community Health, School of Medicine, Federal University of Ceará, Fortaleza, Brazil‡ School of Public Health, Tropical Medicine and Rehabilitation Sciences, James Cook University, Townsville, Queensland, Australia Keywords
dimeticone, efficacy, head lice, in vitro testing, Background The therapy of pediculosis remains a common problem in clinical
practice. As resistance to commonly used chemical pediculicides is constantly increasing, there is a need for new effective compounds.
Saúde Comunitária, Faculdade de Medicina, Uni- Study design The efficacy of Nyda® L, a new pediculicide containing a high
versidade Federal do Ceará, Rua Prof. Costa concentration of dimeticone, was assessed in an in vitro trial and compared with Mendes 1608, 5. andar, Fortaleza CE 60430-140, three reference products (Hedrin® containing 4% dimeticone, Lyclear® contain- Brazil, tel. +55 85 33668045; fax + 55 85 ing 1% permethrin, and Prioderm® containing 1% malathion) and a negative control group. Head lice were collected from heavily infested patients in a resource-poor community in Northeast Brazil, where no resistance against pediculicides Received: 12 December 2006, accepted 20 December 2006 has been reported thus far. In each of the five groups, 50 adult fully vital licewere tested. We used a dip test (immersing head lice in the undiluted products for 3 min, washing off products after 20 min). Using predefined criteria for
mortality, the lice were monitored at different points in time, for a period of 24 h.
Results Nyda® L and Prioderm® killed all head lice already after 5 min. The
efficacy of Nyda® L was better than of Lyclear®. Lice treated with Hedrin®
resurrected after several hours and did not show a significantly higher mortality
compared with the control group after 24 h.
Conclusion Nyda® L can be regarded as a very efficacious pediculicidal
compound, killing all lice in vitro within 5 min.
(lindane), organophosphates (malathion), carbamates Introduction
(carbaryl), and benzyl benzoate, as well as formulations Head lice (Pediculus humanus var. capitis) are insects that have parasitized human beings for many thousands of In the last decades, as a result of extensive use, resist- years.1 In spite of therapeutic advances, pediculosis remains ance to pediculicides with a neurotoxic mode of action has a problem throughout the world, particularly in developed increased, particularly to permethrin.8,10–13 Permethrin is countries. Although the clinical effects of head lice seem used in many countries as first-line therapy, and resist- to be minor,2–4 pediculosis has been considered an important ance is frequent. This pertains not only to industrialised cause of impetigo in developing countries and may result countries, such as the USA, UK, France, Denmark, Israel, in stigmatization.3,5 Possibly, head lice play a role in the and Australia, but also to less developed countries, such as transmission of vector-borne diseases, such as bartonellosis Argentina. Where resistance will develop in the future Chemical pediculicides have been used extensively for Additional reasons to investigate alternative products the treatment of infestations since the early 20th century.
are failure of current chemical treatments to kill embryos Today, topical chemical insecticides still remain the main- in eggs, environmental and food safety, and potential stay of head lice treatment, such as pyrethrins and syn- toxicity of the chemical pediculicides, particularly organ- thetic pyrethroids (permethrin and allethrin), organochlorines ophosphates and organochlorines. Thus, there is a clear JEADV 2007, 21, 1325–1329 Journal compilation 2007 European Academy of Dermatology and Venereology
Dimeticone-based product against head lice need for compounds effectively killing adult lice and eggs filter paper was moistened by 200 μL tap water. Control lice were placed directly on moistened filter paper without Recently, Burgess et al.14 published a clinical trial com- any treatment. After lice were placed on the filter paper; paring Hedrin®, a 4% dimeticone lotion, with Full Marks obvious pools of the product were wiped from the lice Liquid® (0.5% phenothrin). The cure rate was similar in with a jeweller’s forceps directed under a dissecting both groups (70% and 75%, respectively).
microscope. Head lice were washed after 20 min by Here, we show in an in vitro study that the product immersing the hair strands in tap water for 1 min and Nyda® L (G. Pohl-Boskamp GmbH & Co. KG, Hohenlock- then placing them on unused filter paper in unused Petri stedt, Germany), which has a high concentration of dimeticone, is highly effective in killing head lice.
We tested lice in batches of 10 for each treatment and control group, repeating the tests five times to give a totalof 50 lice in each group. The relative frequencies of mor- tality were compared using the chi-squared test.
The lice were examined after 5, 10, 20, 30, 60, 120, and Head lice
180 min as well as after 6 and 24 h. Pre-defined criteria Adult head lice were obtained by dry combing from for evaluation of the survival of lice were used, based on individuals living in the township Vicente Pinzón in the activity, ataxic signs, ability to stay on hair, as well as gut outskirts of Fortaleza, the capital city of Ceará State in and leg movements.15 The vital state of each louse was Northeast Brazil. Resistance to commonly used pediculicidal classified according to the following categories: vital lice, agents has never been reported in the area, but formal fully active lice with normal movements; lice with major susceptibility testing has not been done.
vital signs, walking, but unable to walk in a progressive The individuals participated in a head lice control cam- fashion or no righting reflex when rolled onto the back; lice paign based on combing, and we used the lice that were with minor vital signs, not walking, but presence of internal obtained during this campaign. Only lice were used from (gut) movements, movements of antennae, or leg movements individuals who had not applied chemical pediculicides (with or without stimulation by a forceps); lice with no nor received ivermectin during the previous 4 weeks. All vital signs at all, even after stimulation by a forceps.
lice were examined for activity and morphological inte- For the calculation of mortality, highly stringent criteria grity under a dissecting microscope, and only fully active were used: head lice were only judged as ‘dead’ if they lice were tested within 60 min after collection. We used were in categories 3 or 4 (i.e. no or minor vital signs female and male adult lice and did not blood-feed the All lice were examined under a dissecting microscope by the same observer to prevent interobserver variation.
Lice were maintained at 27 °C to 29 °C during the tests.
The following products were tested: Nyda® L (G. Pohl- Boskamp GmbH & Co. KG, containing a high concentrationof dimeticone, as well as medium-chained triglycerides, All four commercial products killed lice, but efficacy jojoba oil, and fragrances); Hedrin® lotion (Thornton & differed, with Nyda® L and Prioderm® having 100% mortality Ross Ltd, UK, containing dimeticone 4%); Lyclear® at all test times (fig. 1). After 5 min, 100% of test lice had Creme Rinse (Chefaro Ltd, UK, containing permethrin no or minor vital signs, irrespective of the product applied, 1%); and Prioderm® Shampoo (Norpharma A/S, Denmark, compared with 0% in the negative control group. However, recovery of lice occurred over time in the Lyclear® andHedrin® groups. The detailed vital states of the tested headlice in the five groups over time are depicted in Table 1.
In vitro testing
Despite showing no major vital signs during the first To allow a direct comparison, all products were tested hour, lice treated with Hedrin® recovered after several according to a standard procedure. We used a dip technique hours, with a mortality of only 74% (95% confidence in which lice attached to strands of human hair were interval, 59.7–85.4) after 6 h, which is significantly lower immersed completely in the undiluted products for 3 min.
than the mortality for lice treated with Nyda® L The hair strands with lice were held with a forceps under (P < 0.001). After 24 h, the mortality of Hedrin®-treated the solution. We checked for the presence of air bubbles.
lice (78%; 95% confidence interval, 64.0–88.5) was not Then, the lice were placed with hairs on Whatman filter statistically different from the control lice (68%; 95% paper in 5-cm Petri dishes. To prevent lice desiccating, the confidence interval, 53.3–80.5; P = 0.3).
JEADV 2007, 21, 1325–1329 Journal compilation 2007 European Academy of Dermatology and Venereology
Dimeticone-based product against head lice Table 1 Vital state of head lice in four test groups and a negative control group over time (n = 50 in each group)
Negative control
At all points in time, Nyda® L, Lyclear®, and Prioderm® showed significantly higher mortality than the negativecontrol lice receiving no treatment (P < 0.001 in all cases).
In the control group, mortality due to desiccation started after 6 h and was high after 24 h.
Our data show that Nyda® L, based on a highconcentration of dimeticone, is highly effective in vitroagainst head lice. Other components of the product aremedium-chained triglycerides and jojoba oil. However,the exact concentration of dimeticone and the otheringredients is not publicly available, as the composition ofNyda® L, a medical device in the European Union, is a fig. 1 Mortality of head lice in four test groups and a negative control group
corporate secret of the manufacturer G. Pohl-Boskamp over time. Results of Nyda® L and Prioderm® are identical at all times of The mortality of lice treated with this product was similar to Prioderm® (1% malathion) and higher than Nyda® L performed slightly better than Lyclear®. This Lyclear® (1% permethrin). In the first hour, mortality was difference was statistically significant after 10 min (P = 0.04), similar to Hedrin® (4% dimeticone). However, lice resur- 30 min (P = 0.02), 60 min (P = 0.006), 120 min (P = 0.02), rected after several hours in the Hedrin® group and did 180 min (P = 0.02), and 6 h (P = 0.04).
not show a significantly higher mortality compared with JEADV 2007, 21, 1325–1329 Journal compilation 2007 European Academy of Dermatology and Venereology
Dimeticone-based product against head lice the negative control after 24 h, although mortality in con- Commonly, less stringent criteria are used for the defini- trol lice was high due to desiccation.
tion of ‘mortality’ of head lice: a state of reduced activity Burgess et al.14 reported a cure rate of about 70% after judged by the inability of the insect to walk in a progressive treating head lice infestation with Hedrin®, a 4% dimeti- fashion or to show a righting reflex when rolled onto its cone lotion. The lotion was left to dry naturally and not back.22,23 Such outcome measures are prone to overestimate washed out; thus, the contact time was prolonged.
mortality. Therefore, Burkhart and Burkhart18 suggested We immersed the lice only for 3 min in the respective to apply indicators of irreversible morbidity for the assessment solutions and washed the substances away after 20 min, of efficacy. In this study, we defined death as the absence simulating a standard treatment with an insecticide- of any vital signs or merely the presence of minor vital signs.
based pediculicide. The differences in contact time could It has been suggested that in vitro testing done in a manner be the reason why Hedrin® lotion was effective in a resembling the clinical application of a pediculicide may clinical trial but did not perform well after several hours be a proxy for the results of clinical trials.24 In this case, Nyda® L should be highly effective in vivo particularly As the instructions of the producers for the in vivo use because the usual contact time will be considerably longer of pediculicides vary considerably, our approach allowed than in our in vitro study. Albeit, clinical trials are warranted the comparison of different products in a standardized to corroborate our findings, and future studies will also manner. In addition, we could detect the products with have to test the efficacy of the product on head lice eggs.
the highest efficacy (i.e. killing most lice after a short In conclusion, our data show that Nyda® L is highly effective in killing head lice in vitro. Such products that An approach of killing head lice by suffocation has been probably kill head lice by physical means may prevent the described recently by Pearlman.16 He reported excellent clinical results with a so-called ‘dry-on suffocation-basedpediculicide’ (DSP). The DSP lotion seems to coat the lice Acknowledgments
with a film layer after drying, consequently blocking theinsect’s spiracles and suffocating the lice.
We thank the community leaders and inhabitants of Pearlman’s clinical study has been criticized due to the Morro do Sandra’s/Vicente Pinzón II for collaboration. J.
uncontrolled and open design, the outcome measures Heukelbach was supported by an Endeavour Australia used, and a putative conflict of interest of the author.17,18 Research Fellowship. F.A.S. Oliveira received a postgradu- In addition, there are no in vitro data available to corrob- ate scholarship from Coordenação de Aperfeiçoamento de Pes- orate the clinical findings. However, the strategy to kill soal de Nível Superior, Brazil.
head lice by physical measures is a promising approachbecause the compounds used for this purpose are consid- Conflicts of interest
ered non-toxic if applied topically, and resistance probablycannot develop.
J. Heukelbach has been a scientific consultant to G. Pohl- A possible mode of action of lowly viscous dimeticones Boskamp GmbH & Co KG. The company had no role in the is the penetration into the spiracles of the lice, causing design, execution, or interpretation of the study. R. Speare asphyxia and death. The substance group of dimeticones has been a consultant to an Australian producer of (polydimethylsiloxane) are silicon oils also used in cos- pediculicides in the past, but currently has no links to the metic products (e.g. to facilitate the use of a comb and to make the hair silky and soft).19 In addition, oral dimeti-cone is used as an anti-flatulent to alleviate gastrointesti-nal discomfort. Dimeticone is physiologically inert and References
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