Dose preparation procedures may help explain IOP fluctuations after anti-VEGF injections

Large-size aggregates found in samples from some compounding pharmacies may affect the trabecular meshwork and produce IOP spikes.

Malik Y. Kahook

As isolated reports of IOP spikes after administration of anti-VEGF agents begin to surface, controversy remains surrounding the exact cause of the glaucoma-like changes.

At the 2009 joint meeting of the American Academy of Ophthalmology and Pan-American Association of Ophthalmology, Malik Y. Kahook, MD, reported on six cases referred to his clinic for sudden ocular hypertension following one or multiple injections of Avastin (bevacizumab, Genentech). Three of the patients had a history of glaucoma or were glaucoma suspects, but they had a long history of stable IOP. The other three patients had no known history of pressure changes.

While the report of a small number of patients with an atypical reaction to intravitreal injection of an anti-VEGF agent would constitute an anomaly, Dr. Kahook said during his presentation that similar case reports had already been presented at previous meetings or published in the literature. In addition, he has heard anecdotal evidence of other cases that have not been published.

The largest case series reported to date was presented at Retina Congress 2009. A poster presented by John A. Carver, MD, of Provo, Utah, noted 42 instances of “dramatic intraocular pressure elevation and progressive ocular nerve changes” among 512 eyes of 438 patients who were treated with a 1.25-mg dose of bevacizumab for neovascular AMD.

In the series, topical medications were largely unsuccessful in lowering pressure; eight eyes required laser trabeculectomy, and an additional eight eyes required filtration surgery.

Reported cases

Similar to the patients in Dr. Carver’s series, Dr. Kahook noted that IOP spikes in his patients often did not respond well to medical management. When elevated pressure developed, it rose from 30 mm Hg to 50 mm Hg, and even two or three medications were ineffective in normalizing pressure.

In what may have been the first report of a sudden IOP spike following bevacizumab injection, Jalil and colleagues reported on a 75-year-old patient treated with a 1.75-mg dose who developed blurred vision, corneal edema and IOP of 56 mm Hg 3 days after a fourth injection. The patient required the addition of two topical medications and oral carbonic anhydrase inhibitor to control IOP.

In that study, the authors speculated that the high molecular weight of bevacizumab — about 148 kD — might have blocked the trabecular meshwork, thus inhibiting aqueous outflow and explaining why draining medications were of minimal benefit. Dr. Carver, in his poster, offered a similar hypothesis.

A study by Bakri and colleagues published in 2009 investigating IOP rise after injections of triamcinolone, bevacizumab or Macugen (pegaptanib, Eyetech/Pfizer) found that roughly one-third of patients in each group had an IOP elevation greater than 10 mm Hg within 30 minutes of injection. Eyes with glaucoma were more likely to have an IOP greater than 35 mm Hg, but the difference dissipated with time.

In a separate study, Bakri and colleagues reported on four cases of persistent “severe and sustained hypertension” after intravitreal Lucentis (ranibizumab, Genentech) injection. The exact cause was unknown, but patients were well-controlled on medication.

Other studies have provided evidence that IOP can be expected to rise shortly after intravitreal injection of bevacizumab but spontaneously resolve about 30 minutes after injection.

Individually, each report constitutes a small number of patients. In addition, each of these studies considers different variables. However, according to Dr. Kahook, the existence of multiple reports may signal an issue worthy of further investigation.

“Jointly, that makes up a lot of patients,” Dr. Kahook said.

Dose preparation protocols

According to Dr. Kahook, the clinical profile of some of these cases, and particularly the ones seen in his clinic, suggests that something may be blocking the trabecular meshwork or leading to outflow dysfunction, thus limiting the success of medical therapy. However, the drug component itself may not be the cause of IOP elevation.

In laboratory testing, Dr. Kahook discovered the presence of high molecular weight aggregates, some larger than 20 µm, in samples taken from bevacizumab doses acquired from different compounding pharmacies. The concentration of protein in those sampled lots also varied between doses acquired from different compounding pharmacies, as did the level of the bevacizumab IgG monomer.

Samples from certain compounding pharmacies showed the presence of aggregated material beyond the level of what might be expected from the formation of dimers and trimers from degraded drug proteins. The bevacizumab IgG monomer measured in the nanometer range, and formed dimers and trimers would hypothetically be not much larger. But the aggregated material from some sampled lots was of such a size that the likelihood of trabecular meshwork plugging is entirely plausible, Dr. Kahook said. It is unclear if these aggregates are made of protein or other materials such as silicone.

“When that happens, you are not going to improve the pressure by one or two medicines, and the mechanism is really resistant to therapy,” he said.

Dr. Kahook performed a study comparing protein and IgG levels in bevacizumab straight from the vial and from doses from two compounding pharmacies. Protein levels were consistent at about 30 mg/mL for all three, whereas IgG was about 25 mg/mL from the bottle, but 21 mg/mL from one pharmacy and 18.5 mg/mL from the other.

In a sample taken from syringes that were prepared by a pharmacy known to have supplied medication to practices with cases of IOP spikes, the overall protein level was again 30 mg/mL, but the IgG level measured 12.5 mg/mL.

Microflow imaging, looking specifically at the number of particles greater than 1 µm in diameter, also showed disparate results. A sample of bevacizumab straight from the vial showed 61,000 large molecules/mL, and a sample from the vehicle showed 37,000 molecules/mL. However, a third sample, again taken from a sample acquired from the pharmacy with the lowest concentration of IgG monomers, showed 510,000 molecules/mL, with some high molecular weight aggregates as large as 20 µm.

The exact nature of those aggregates and the reason for their formation is unknown, although ongoing studies should help provide some answers, Dr. Kahook said. But there is at least some suggestive evidence that varying practices at the compounding pharmacies may contribute.

Lack of universal protocols

Dr. Kahook is quick to point out that the reason that the number of such cases is currently small is that most compounding pharmacies follow strict sterility protocols, and so IgG levels as well as potential contaminants such as silicone are fairly consistent in most doses from pharmacy to pharmacy.

“This likely explains why we are not seeing thousands of cases across the country because, for the most part, most physicians use the same two or three compounding pharmacies throughout the country, and for the most part, most compounding pharmacies have good practices,” he said.

However, there is no universal protocol in how bevacizumab doses are prepared. The package insert for bevacizumab specifies that the drug “must be refrigerated at 2-8°C (36-46°F). Avastin must be protected from light.” However, the package insert is designed for bevacizumab’s approved use — treatment of metastatic colon or rectal cancer — and, therefore, does not specify how individual doses should be prepared or stored.

According to Dr. Kahook, under chapter 797 of the United States Pharmacopeia, which outlines regulations for compounding pharmacies, storage of proteins should not last longer than 14 days. However, he said, storage sometimes goes beyond 90 days at some pharmacies.

“We’re not seeing tons of this because most compounding pharmacies are actually doing things correctly. It’s just that we need to pay attention to those who aren’t and try to eliminate what they are doing so that we aren’t hurting patients,” Dr. Kahook said.

Studies by Bakri and colleagues that looked specifically at degradation of bevacizumab in individual syringes and unpierced and pierced multidose vials stored at 4°C showed “minimal change in the concentration of bevacizumab in the samples at 3 months and minimal further change from 3 months to 6 months.” In the study, unpierced vials exhibited the least degradation.

According to Dr. Kahook, some compounding pharmacies will draw down individual doses and store them for an indeterminate time period, while other pharmacies wait for an order before preparing the dose. Thus, the date of dose shipment may not accurately depict when it was prepared.

Compounding pharmacies also use different syringe types made of various materials and quality. It is possible, according to Dr. Kahook, that the bevacizumab IgG monomer reacts to the different materials used in the manufacture of syringes or syringe components. Likewise, these materials may react differently in storage situations and may contribute to aggregated large molecules in some doses.

“I think every physician, because of what we found and reported, should really become familiar with how their compounding pharmacy is doing things,” Dr. Kahook said. “It’s the physician’s right to call the compounding pharmacy and say, ‘Send us your protocol.’ And each individual physician is going to have to make a determination on their own as to whether they think the compounding pharmacy’s practice is appropriate.” – by Bryan Bechtel

References:

• Bakri SJ, McCannel CA, Edwards AO, Moshfeghi DM. Persistent ocular hypertension following intravitreal ranibizumab. Graefes Arch Clin Exp Ophthalmol. 2008;246(7):955-958.
• Bakri SJ, Pulido JS, McCannel CA, Hodge DO, Diehl N, Hillemeier J. Immediate intraocular pressure changes following intravitreal injections of triamcinolone, pegaptanib, and bevacizumab. Eye (Lond). 2009;23(1):181-185.
• Bakri SJ, Snyder MR, Pulido JS, McCannel CA, Weiss WT, Singh RJ. Six-month stability of bevacizumab (Avastin) binding to vascular endothelial growth factor after withdrawal into a syringe and refrigeration or freezing. Retina. 2006;26(5):519-522.
• Carver JA, Bouska CP, Corey RP. Avastin and risk of glaucoma. Poster presented at: Retina Congress 2009; Sept. 30 to Oct. 4, 2009; New York.
• Falkenstein IA, Cheng L, Freeman WR. Changes of intraocular pressure after intravitreal injection of bevacizumab (avastin). Retina. 2007;27(8):1044-1047.
• Hollands H, Wong J, Bruen R, Campbell RJ, Sharma S, Gale J. Short-term intraocular pressure changes after intravitreal injection of bevacizumab. Can J Ophthalmol. 2007;42(6):807-811.
• Jalil A, Fenerty C, Charles S. Intravitreal bevacizumab (Avastin) causing acute glaucoma: an unreported complication. Eye (Lond). 2007;21(12):1541.
• Kahook MY, Kimura AE, Wong LJ, Ammar DA, Maycotte MA, Mandava N. Sustained elevation in intraocular pressure associated with intravitreal bevacizumab injections. Ophthalmic Surg Lasers Imaging. 2009;40(3):293-295.

• Malik Y. Kahook, MD, can be reached at Department of Ophthalmology, University of Colorado School of Medicine, Rocky Mountain Lions Eye Institute, 1675 Aurora Court, P.O. Box 6510, Mailstop F73, Aurora, CO 80045, U.S.A.; +1-720-848-2500; fax: +1-720-848-5014; e-mail: malik.kahook@ucdenver.edu. Dr. Kahook has received research support from Genentech, Allergan, Alcon, Merck, Actelion and Pfizer. He is a consultant to Alcon, Allergan, Merck and VRT and a founding member of Shape Ophthalmics LLC.