What is it?
Verteporfin, sold under the brand name Visudyne, is a light activated drug used in photodynamic therapy (PDT) for the treatment of wet age-related macular degeneration (AMD). Wet AMD is an advanced form of AMD that occurs when abnormal blood vessels grow underneath the macula, the central area of the retina. These new blood vessels are usually fragile and leak blood and fluid, which causes rapid damage to the macula and vision loss. Visudyne works by selectively accumulating in these new, leaky blood vessels when administered intravenously and activated by low-power laser light directed at the diseased portion of the retina. When activated by the laser, Visudyne produces a light-activated chemical that causes the abnormal blood vessels to close off, reducing fluid leakage and preventing further damage to the macula.

How Does it Work?
Verteporfin itself does not have any biological activity in the body. It is a light-activated drug that accumulates more in the new, leaky blood vessels found in wet AMD compared to normal vessels. About 15 minutes after an intravenous injection of Visudyne, the retinal area containing the new blood vessels is treated with low-intensity nonthermal laser light from a special light delivery device called a photoactivator. The laser light activates the Visudyne molecules, which then produce highly reactive, short-lived oxygen radicals upon exposure to light in the presence of oxygen. These oxygen radicals are toxic only to the immediate area of activation, which is confined to the new blood vessels containing the Visudyne. The activated Visudyne causes temporary damage to these diseased blood vessels, making them collapse and close off. This helps to reduce further fluid leakage and prevent additional damage to the macula.

Benefits of Visudyne Therapy
Several large clinical studies have demonstrated the benefits of Visudyne PDT compared to no treatment or placebo control for wet AMD. Some of the key benefits include:
- Slows progression of vision loss - Visudyne PDT has been shown to significantly reduce and slow further vision loss compared to no treatment over 2 years.
- Preserves and sometimes improves vision - Some patients have stable or even improved vision following Visudyne therapy. Vision is preserved better than with no treatment.
- Closes abnormal new blood vessels - The photochemical reaction of Visudyne helps collapse and seal off the leaky new blood vessels, reducing further fluid leakage and damage.
- Individualized treatment - Visudyne PDT allows targeting the area of active lesion only and avoids damage to surrounding normal retinal tissues.
- Minimal invasiveness - Visudyne requires only an IV injection and non-damaging laser treatment at the diseased site, avoiding major intraocular surgeries.
- Well tolerated - Visudyne is generally well tolerated with minimal side effects like transient visual disturbances in a small percentage of patients.

How is Verteporfin Administered?
Visudyne therapy involves an intravenous injection of the drug, followed by non-thermal laser light application to activate the Visudyne molecules local to the diseased lesion site.
- Drug administration: Visudyne is given as a 10-minute intravenous infusion at a standard dose of 6mg/m2 body surface area.
- Laser treatment: About 15 minutes after the infusion ends, low-intensity laser light at 689nm wavelength is applied via a specialized photoactivator directly to the abnormal new blood vessels in the retina. Very low power (50mW/cm2) is used for 83 seconds to activate the Visudyne locally.
- Single session: In most cases, Visudyne PDT involves a single session of drug injection and laser treatment only. Further retreatments are done only if needed based on disease recurrence.
- Outpatient procedure: Visudyne administration and laser treatment can typically be performed on an outpatient basis without hospitalization.

Safety Considerations with Verteporfin Use
Visudyne therapy is generally well tolerated with very few serious adverse reactions. However, some safety considerations need to be kept in mind:

- Photosensitivity issues: Patients continue to have increased skin sensitivity to light for 48-72 hours after Visudyne injection. They are advised to avoid direct sunlight or bright indoor lights and wear protective clothing/eyegear during this period.

- Vision side effects: Transient visual symptoms like blurring, lights, flashes or shadows may occur right after laser treatment in up to 25% patients but resolve within hours.

- Infusion related reactions: Rare minor infusion reactions like nausea, vomiting, dizziness or pain may occur. More serious allergic reactions are very uncommon.

- Retinal damage risks: While minimal, there remains a small risk of collateral damage to adjacent normal retina if laser is misapplied beyond the new vessels or with incorrect dosage.

- Long term effects unknown: As Visudyne has only been studied up to 3 years so far, very long term risks beyond 5-10 years cannot be completely ruled out yet.

So in summary, verteporfin therapy offers an effective option to minimize vision loss from wet AMD, when administered accurately following recommended guidelines by a retinal specialist. With proper counseling on precautions, it presents a favorable benefit-risk profile for eligible patients.

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