Sir,
Compliance with glaucoma treatment can be a significant challenge to successful management of the condition. We would like to suggest that the herbal preparation Hypericum perforatum, also known as St. John's wort, may affect intraocular pressure (IOP) control. Herbal preparations are considered by many users as “safe,” and it has been demonstrated that many herbal remedies consumers would not report the use of these medications.[1]
St. John's wort is commonly used for the treatment of minor-to-moderate depression.[2] It is known to interact with a number of drugs, including beta-blockers, as it induces the hepatic cytochrome P450 system and causes faster drug metabolism.[3] Little is known about the activity of P450 in ocular tissues, but the studies in bovine eyes have shown that the ciliary body has the highest activity of cytochrome P450-dependent monooxygenases.[4] We report the case of a primary open-angle glaucoma patient with suboptimal IOP control, which improved on discontinuation of St. John's wort.
A 58-year-old male was diagnosed with the primary open-angle glaucoma in 2007. His medical history included depression and sleep apnea. Presenting intraocular pressure (IOP) was 26 mmHg in the right eye and 24 mmHg in the left. Humphrey's visual fields test revealed a right superior paracentral defect and an inferior nasal step, while the left field was full.
The patient was started on topical treatment, initially a prostaglandin analog (Travoprost) and then a b-blocker and carbonic anhydrase inhibitor in various combinations due to suboptimal control. His IOPs remained above target range despite reported good compliance, proper instillation technique, and maximum topical treatment (which, after initial Travoprost, always included a b-blocker). As the visual fields continued to deteriorate, the patient was booked for serial IOP measurements in preparation for trabeculectomy surgery.
However, at the final preoperative appointment, his IOP was found to have decreased to 12–14 mmHg. The patient revealed that he had been on St. John's wort for a number of years and had discontinued treatment the month before. No other changes in treatment had occurred. Since then, his IOPs have remained within target range on a combination of timolol and latanoprost, with stabilization of visual fields.
The case highlights that the use of St. John's wort might be associated with suboptimal IOP control in patients on topical beta-blockers. St. John's wort is known to interact with systemic beta-blockers by increasing their metabolism through the P450 cytochrome system.[3] There is limited information on the activity of these enzymes in the eye, but the studies have confirmed cytochrome P450-dependent monooxygenase activity in the ciliary body and retinal pigment epithelium of bovine eyes.[4] High levels of P450 mRNA have previously been found in the human iris and ciliary body.[5] It is, therefore, possible that St. John's wort could have the same effect on these enzymes in the eye as it does elsewhere in the body.
Our case highlights a potential interaction of herbal remedies such as St. John's wort with patients' glaucoma treatment. The sudden decrease in IOP and long-term maintenance of pressures in target range after discontinuation of St. John's wort could indicate that the patient was previously experiencing a diminished effect of topical beta-blockers. More studies on the role of the cytochrome P450 system on ophthalmic drug pharmacokinetics are clearly required to investigate this relationship further. However, we recommend taking a complete and detailed drug history from glaucoma patients, including enquiries about herbal and nonpresription medication, particularly when IOP control is suboptimal.
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Conflicts of interest
There are no conflicts of interest.
References
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