This article is more than 5 years old. Information may no longer be current.
Patient adherence, drug response keys to selecting glaucoma therapy
An expert in the field reviews ‘anchor’ and ‘adjunct’ regimens and discusses the right time to switch therapies.
 Thomas W. Samuelson |
OTTAWA, Canada — When choosing glaucoma therapy, clinicians must consider several factors, including patient adherence and their response to the drug.
“It’s important that we make it a manageable regimen for patients,” said Thomas W. Samuelson, MD, OSN Glaucoma Section Editor, at the annual Sally Letson Symposium. “It’s about deciding on treatment efficiency and looking at the mechanisms of action and, in some cases, the feasibility of making a change to more effective therapy by changing classes or switching within a class of drugs.”
Dr. Samuelson described drug regimens to treat glaucoma as consisting of “anchors” and “adjuncts.” He said anchors include drugs such as prostaglandin analogs and combination medications, whereas adjuncts include drugs such as beta-blockers.
Prostaglandin analogs
Prostaglandins dominate medical therapy for glaucoma because they are efficacious and well-tolerated. They also have a favorable dosing schedule because they have to be taken only once in a 24-hour period.
“I tell patients that they can leave these medications on their nightstands beside the alarm clock and just remember to take them at night,” Dr. Samuelson said. “The drugs produce minimal systemic side effects and possess a favorable mechanism of action.”
Medical therapy for glaucoma is aimed at keeping IOP low and stable, Dr. Samuelson said. Consequently, clinicians should consider the mechanism of action of pharmacological agents they select for therapy.
He said research has shown that glaucoma is characterized by reduced pressure-sensitive outflow through the trabecular meshwork. It is this impaired outflow that causes high IOP and diurnal IOP fluctuations. Normal eyes do not experience prolonged pressure spikes, but glaucomatous eyes do experience pressure spikes that can be sustained for several hours or longer. Pressure-sensitive aqueous outflow assists in preventing and alleviating pressure spikes. Drugs that augment outflow facility are conducive to stabilizing and reducing IOP, as well as restoring the ability of IOP to self-regulate.
Dr. Samuelson said older drugs such as cholinergic agents processed excellent mechanism of action, primarily targeting outflow facility, but they were not favorable in their side effect profile, making them a less attractive therapy choice than the prostaglandins, which also improve outflow facility.
‘Under-responding’ to treatment
There is no hard or fast rule on when a clinician should decide to alter drug therapy for a patient with glaucoma, Dr. Samuelson said.
“If patients are ‘under-responding’ to therapy, I would tend to switch the therapy,” he said. “There are reasons to think that there may be individual differences between drugs within a class.”
Dr. Samuelson said under-responding is not the same as no response to therapy. He cited a study published in 2006 that found the majority of subjects on latanoprost (326 of 340) responded with at least a 15% reduction in IOP. Those who did not adequately respond were then put on other agents to lower IOP.
“I would look for at least a 20% reduction in pressure and preferably a 30% drop with ‘anchor’-type drugs such as prostaglandin analogs,” he said, adding that clinicians should assess the impact of the medications after a month of treatment. “If I don’t see that response, I would switch [therapies].”
For more information:
- Thomas W. Samuelson, MD, can be reached at Minnesota Eye Consultants, 710 E. 24th St., Suite 106, Minneapolis, MN 55404; 612-813-3600; fax: 612-813-3636; e-mail: twsamuelson@mneye.com.
Reference:
- Rossetti L, Gandolfi S, et al. An evaluation of the rate of nonresponders to latanoprost therapy. J Glaucoma. 2006;15(3):238-243.
- Louise Gagnon is an OSN correspondent based in Whitby, Ontario, Canada.