The Netherlands Pharmacovigilance Centre Lareb received five reports concerning photo-onycholysis associated with the use of doxycycline (table). All five patients used 200 mg of doxycycline a day for the prophylactic treatment of Lyme disease after tick bite. In all cases the affected nails had been exposed to the sun during the summer. All patients showed (partial) recovery after several months. To our knowledge, no other factors (either specific physical disorders or concomitant drug use) were responsible for the onycholysis in these patients.
Table 1.
Reports of photo-onycholysis associated with the use of doxycycline*
| Patient | Sex | Age (years) | Duration of treatment (weeks) | Sun exposure | Concomitant medication | Reported adverse drug reactions | Time to onset of onycholysis (days) | Outcome |
|---|---|---|---|---|---|---|---|---|
| 1 | M | 12 | 2 | Sunbathing (August), feet were protected | None | Photosensitivity reaction | 35 | Partly recovered after 1 month |
| Skin discolouration | ||||||||
| Onycholysis (all fingernails affected) | ||||||||
| 2 | F | 38 | 4 | Sunbathing (holiday in France in June), foot protection unknown | Citalopram, 20 mg once a day | Onycholysis (3 fingernails affected) | 3 | Partly recovered after 2 months |
| 3 | F | 38 | 2 | Sunbathing (sunny weather on holiday in August), toes unprotected | None | Onycholysis (all fingernails and 4 toenails affected) | 14 | Fully recovered after 5 months |
| 4 | F | 8 | 1 | Sun exposure (August), foot protection unknown | None | Onycholysis (all fingernails affected) | 25 | Partly recovered after 3 weeks |
| 5 | F | 58 | 2 | Sun exposure (holiday on a sailing boat in July), feet were protected | None | Abdominal discomfort | 21 | Partly recovered after 3 months |
| Photosensitivity reaction | ||||||||
| Onycholysis (all fingernails affected) |
All patients used 200 mg a day of doxycycline for the prophylaxis of Lyme disease after probable tick bite (erythema migrans was seen in patients 3 to 5).
Although the association between doxycyline and onycholysis has been sparsely reported,1-3 the circumstances of the patients we report differ from those described elsewhere. All five patients used doxycycline exclusively for the prophylactic treatment of Lyme disease; we did not find any studies that suggested a possible connection between Lyme disease and onycholysis.
The mechanism of this phototoxic reaction is not fully understood. The nail bed is relatively unprotected from sunlight and contains less melanin (implicating less ultraviolet protection) than other skin sites. Onycholysis may, therefore, be the sole expression of a photosensitivity reaction.4 Photosensitisation to doxycycline may be mediated by excited state oxygen singlets and free radicals, which arise because ofirradiation with ultraviolet A. This may cause selective injury to mitochondria, the preferential intracellular site of localisation of doxycycline.5
Borrelia burgdorferi—which causes Lyme disease—is becoming a more common coinfecting pathogen, and doctors are developing an increased knowledge and awareness concerning the potential risks of tick bites. Due to these developments, more high dosages of doxycycline may be prescribed more often. Considering the relatively good health of the patients using doxycycline for the given indication, exposure to sunlight is the likely cause of onycholysis. These patients should avoid exposure of their nails to the sun shortly after using doxycycline.
Funding: None.
Competing interests: None declared.
References
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