Latanoprost – A Lasting Glaucoma Breakthrough

Glaucoma eye drop therapies have faced many triumphs and setbacks over the decades, but for pharmaceutical companies the quest for a ‘Holy Grail’ treatment has always boiled down to three factors: universal effectiveness, reduced side effects and compliance.

Intraocular pressure (IOP)-lowering medications can be traced back to the 1870s with a cholinergic agonist derived from the West African calabar bean initially used for miosis in iridectomy cases, then later found to lower IOP and address angle-closure attacks. During the course of the 20th century, however, beta blockers, adrenergics, miotics and systemic carbonic anhydrase inhibitors emerged as the four main families of anti- glaucoma drugs.

But as Professor John Grigg – an academic ophthalmologist and specialist within the Sydney Eye Hospital’s glaucoma unit – explains, up until the 1990s ophthalmologists were eager for a breakthrough first line therapy that was as effective as existing products, but required less effort for patients and fewer side effects.

“At that time, timolol was the gold standard and was a twice daily medication, but that was prohibited in people with asthma and respiratory illnesses,” Grigg, who is also head of clinical ophthalmology and eye health at the University of Sydney’s Save Sight Institute, explains.

“We also had betaxolol which is a selective beta-blocker but it wasn’t as effective as timolol. Other than that, there was pilocarpine which needed to be given four times a day, so compliance was difficult, and then there was epinephrine, an adrenalin compound but it caused allergic eye disease – there were a lot of eye drops, but they all had drawbacks.”

That was until a new compound – latanoprost– shot to prominence after its performance in clinical trials in the mid-1990s. After two decades of development, the once-a-day eye drop represented a major leap forward in terms of effectiveness, safety and tolerability.

Latanoprost was the first in a new class of prostaglandin analogs. Grigg says it still remains one of the most-prescribed glaucoma drops among Australian ophthalmologists. Other well-known therapies to later join this group were travoprost and bimatoprost, which now provide more alternative treatment options for ophthalmologists.

As one of his first jobs as a young academic in 1996, Grigg was an investigator in a Phase 3 trial under prominent Australian ophthalmologist Clinical Professor Ivan Goldberg comparing latanoprost with timolol. They followed approximately 30 patients at the Sydney Eye Hospital for several years, forming part of a global trial that paved the way for regulatory approval in Australia in 1997.

“Suddenly we had a drug that had less side effects and only needed to be used once a day – it was a breath of fresh air. Patients with latanoprost often had a 25% IOP reduction at first and then this would flatten out to be a 20% reduction over two years, whereas timolol would have about a 10% reduction, it was quite a dramatic difference,” he says.

“Latanoprost’s main side effects were it causes your eye lashes to grow longer and darker, and if you have hazel-coloured eyes it can turn them brown because it increases melanin production. You do get some irritation, there can be some red eye, but it still causes the least amount of side effects compared with other drops.” Grigg says a defining feature of latanoprost at the time was its mechanism of action.

“In glaucoma medications you have drops that inhibit inflow and some that increase outflow. Latanoprost works by increasing outflow through the uveoscleral pathway, so it doesn’t go through the trabecular meshwork, it actually increases space in the ciliary body to drain through that into the suprachoroidal space, so it’s exploiting a mechanism that was used to deal with trauma in the eye as we’ve evolved.”

Sixteen years later in a 2012 update of latanoprost’s use in glaucoma and ocular hypertension in the journal SpringLink, the authors wrote that latanoprost monotherapy reduced IOP levels by 22% to 39% over one to 12 months’ treatment. It was significantly more effective than timolol twice daily in three of four large randomised, double-blind trials. Latanoprost also demonstrated a stable long-term IOP-lowering effect, with no sign of diminishing effect during prolonged treatment.

Following the success of the clinical trials, latanoprost was commercialised and first approved in Sweden in 1996 and then in Australia in 1997.

The treatment landscape

While glaucoma eye drops have typically been a first line treatment, Grigg says selective laser trabeculoplasty (SLT) – traditionally a second line treatment – has begun to increase into the realm of initial treatment options.

The flashpoint for this was a study out of the Moorfields Eye Hospital in the UK. Published in The Lancet, the researchers found at 36 months, 74% of SLT patients required no drops to maintain their IOP target and were within target IOP at 93% visits compared with 91% in the eye drops group. No glaucoma surgery was required to lower IOP in the SLT group compared to 11 in eye drop group requiring glaucoma surgery in the study timeframe. 

“There’s been a changing pattern as a result of the Moorfields study where more people are considering SLT as a first line treatment whereas previously it had always been eye drops first then SLT second – and that’s happening in Australia,” Grigg explains.

“Now I think they hold equal place and so that’s where patient factors come into play. People may be hesitant to have surgery in general, and you’re more wary of offering SLT to patients with inflammation. For people with uveitic glaucoma – it’s not an absolute contra-indication – but perhaps SLT’s not the best first line therapy. There’s also angle closure where after laser iridotomy, people still need drops to keep the pressure down; so there are secondary types of glaucoma where SLT isn’t appropriate, and the eye drops still are.”

He continues: “Precision medicine is the key. Until you know that patient you don’t know what their fears or concerns are; whether they’d prefer to put a drop in every night or have laser and not be aware [of their glaucoma]. You can only know as you understand their health needs and issues, and so then you can tailor the treatment to their lifestyle or medical conditions.”

In terms of compliance, Grigg says latanoprost’s once-a-day application overcame major barriers compared with its competitors, and the latanaprost/timolol  combined formulation – removing the need for two sets of eye drops – was also a welcome advance.

However, correct drop installation remains as “a never-ending conversation” with many patients who wrongly attempt to blink the drop into their eye or use more than one drop. Dexterity issues for patients with conditions like arthritis also create problems.

Published with permission from www.insightnews.com.au

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