I t has been said that “a young physician has 10 medications for one disease, while a seasoned physician has one medication for 10 diseases.” Such is the case for me. After a number of years in practice, I typically stick with medications that consistently work best with the fewest side effects or complications. Doxycycline is one such medication. 

Take, for example, the patient with a persistent red eye response who has labored through a diagnostic odyssey with several practitioners and multiple medications, to no avail. Chances are this patient is not going to show improvement unless they stop the topical medications and start using an oral medication instead. If seemingly appropriate treatment has been rendered, this patient may have adult inclusion conjunctivitis or an undetected case of rosacea. So, what to do?

Enter Doxycycline
Doctors have used doxycycline, an antibiotic in the tetracycline class first approved in 1967, to treat a number of medical afflictions over the last several decades, including sexually transmitted disease, respiratory and ophthalmic infections. In substantial doses, it has been shown to have an anti-inflammatory effect on MMP-9. One study found that doxycycline inhibits TGF-1–induced MMP-9 production and activity.¹ These inhibitory effects may explain the reported efficacy of doxycycline in treating MMP-9–mediated ocular surface diseases, and why it has been proposed for recalcitrant recurrent corneal erosion. 

In light of doxycycline’s multiple roles, however, questions remain: Does a daily dose of only 50mg lead to significant MMP-9 reduction? Are there untapped indications for this medication?¹ 

Curious, I visited an online clinical trial archive—and found roughly 112 studies involving doxycycline either actively accepting participants, ongoing or recently completed.² Recent trials ranged from evaluating doxycycline for treatment of diabetic retinopathy to multiple sclerosis used in tandem with interferon-β, with the most cited trials covering use of the drug for Graves’ orbitopathy, meibomian gland dysfunction/ocular surface disease and optic atrophy progression.² Of course, not all will pan out as an effective treatment modality. 

One interesting report showed doxy to elicit some improvement in foveal sensitivity, as measured by frequency doubling perimetry in diabetic patients. While the study does have limitations (e.g., sample size, attrition rate), the authors conclude that oral doxycycline might help prevent or delay the late complications of retinopathy that require more invasive treatments.³ 

Keep In Mind
As with any drug, caveats in prescribing are always worth noting. Side effects for doxycycline can be significant, and are similar to other medications listed under the tetracycline group. A photosensitivity reaction (including an erythematous rash) is possible with sun exposure.^4-6 Anorexia, heartburn, nausea, vomiting, flatulence and diarrhea may commonly occur.⁶ Bone growth depression and tooth discoloration are also possible; thus, practitioners should abstain from prescribing any tetracycline group medication for any patient under the age of eight years.^5,6 As a class D drug, doxycycline use is contraindicated during pregnancy.⁵ Vestibular toxicity is rare in doxycycline, and more common with minocycline use.⁶ Blood dyscrasias have been cited and its potentiated effect on Coumadin-type anticoagulants is well known.⁶  

Nevertheless, the next time a patient presents with that persistent, unexplained red eye, doxycycline might just be your wonder drug. Also, pay attention to the side effects and contraindications for sure when considering doxycycline. Overall, however, while the spectrum of activity of this medication is somewhat limited, its extra value in reducing inflammation often justifies its use. I believe it’s still a marvel due to its great versatility, and just might be the mythical drug to prescribe for 10 different diseases.  

1. Kim HS, Luo L, Pflugfelder SC and Li, D:  Doxycycline inhibition of TGF-B 1 induced MMP-9 via Smad and Mapk pathways in human corneal epithelial cells. Invest. Ophthalmol. Vis. Sci. 2005; 46(3):840-8.
2. DrugLib. Doxycycline. Available at: www.druglib.com/ratingsreviews/doxycycline/. Accessed January 18, 2015. 
3. Scott IU, Jackson GR, Quillen DA, et al. Effect of doxycycline on retinal function and diabetic retinopathy progression in patients with severe nonproliferative or non-high risk proliferative retinopathy: A randomized clinical trial. JAMA Opththalmol 2014; 132: 535-543.
4. Medical News Today. Adding Antibiotics To Medication May Slow MS. Available at:www.medicalnewstoday.com/articles/91379.php. Accessed January 18, 2015.
5. Medline Plus. Doxycycline. Available at: www.nlm.nih.gov/medlineplus/druginfo/meds/a682063.html. Accessed January 18, 2015.
6. Bartlett JD and Jaanus SD. Clinical Ocular Pharmacology. Butterworth-Heinemann, 1995. pp. 269-270.