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Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_5394_Библиотеки_им_академика_М_И_Перельмана

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19 Regulatory Considerations in Product Development for Back of the Eye
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these trials as needed. After the successful completion of Phase II clinical trials, a thorough evaluation of all the available data should be done to obtain crucial under­standing of the drug’s formulation feasibility and characteristics, safety profile and safety margins, dose–response relationships, and pharmacokinetics and metabo­lism. This evaluation also helps in choosing the correct doses that have the highest probability of success for potential future Phase III clinical trials. The decision to proceed with Phase III clinical trials that are generally long, expensive and involve a significantly higher number of patients should be made following this evaluation. The FDA requires at least two successful Phase III studies powered adequately to demonstrate statistically significant proof of the claimed therapeutic efficacy. Additional data from reproductive and developmental toxicity studies are needed before initiating Phase III clinical trials. Once Phase III clinical trials are complete and the sponsor has enough confidence in the statistical significance of the results, a NDA can be filed with the FDA for marketing authorization of the drug.
During the course of this regulatory process to obtain product approval, the FDA offers several mechanisms for the sponsor to consult with the agency before pro­ceeding with the clinical trials. These come in the form of Type A, Type B, or Type C meetings between the sponsor and the FDA. These meetings can be officially requested by the sponsor and are granted by the FDA based on urgency of the matter and resources available to the agency. A comprehensive description of the types of meetings, procedures for requesting these meetings, content and timing of submis­sion of information packages, and the procedures for the conduct of these meetings are detailed in the Guidance document prepared by the Review Management Working Group comprising individuals in the Centers for Drug Evaluation and Research (CDER) and Biologics Evaluation and Research (CBER) at the FDA in February 2000.
19.3 Considerations for Back of the Eye Treatments
None of the health agencies around the world have established a specific set of guidelines to assist in development of drug products for treatment of diseases of the back of the eye. However, assessing the quality of formulation development (chem­istry, manufacturing, and control – CMC), ensuring the safety and efficacy of the drug product via nonclinical testing, and obtaining clinical evidence of the safety and efficacy using a rigorous clinical development program are the cornerstones of any drug development program and apply to the development of drug products for treatment of back of the eye diseases as well. The overall drug product approval process is similar to that mentioned in the previous section. The CMC section is geared towards assuring the quality of the drug substance and the drug product and comprises, at a minimum, documents supporting the following:
1. Description of the synthetic process for manufacturing the drug substance.
2. Physicochemical properties of the drug substance.
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3. Development and validation of analytical methods for the drug and potential
impurities.
4. Details on the composition and characterization of the formulation (composition,
sterility testing, endotoxin testing, pH, etc.).
5. Proof of stability of the drug substance and the drug product.
6. In vitro release rates from the formulation.
All drug products designed for intraocular injection should be completely sterile and free of endotoxin to prevent any potential complications due to infections and/ or endophthalmitis. It is the responsibility of the sponsor to demonstrate that the sterilization procedures do not change the nature and composition of the drug prod­uct. The best way to avoid any complications from this is to treat the drug product used in nonclinical studies in the same way as the potential commercial product. This accounts for any chemical changes or residual by-products of sterilization and evaluates the corresponding safety risk in nonclinical species before progressing into clinical trials. Furthermore, since longer duration of action is preferred for drugs delivered to the posterior segment of the eye (to reduce the frequency of intraocular injection), most of the drug delivery systems need to demonstrate con­sistent release rates to ensure steady delivery of the drug to the target tissue over the intended duration. The FDA has stated that the release rates should be within
± 10% of nominal. If the release rates fall out of specification at a later stage in the develop­ment program, the initial preclinical and clinical study data could be rendered invalid (Gryziewicz and Whitcup 2005). The use of Good Manufacturing Practices (GMP) is critical during this phase.
The IND-enabling nonclinical studies are part of a standardized pharmacology, pharmacokinetics, and toxicology package required by the FDA (as well as other health agencies around the world). The aim of these studies is to demonstrate the safety and efficacy characteristics of the drug product in acceptable in vitro and in vivo models. The scope and nature of the studies should be based on sound sci­entific principles and astute scientific judgments based on all the available data.
The standard pharmacology, pharmacokinetics, and toxicology package required for any drug typically includes but is not limited to the following:
1. Pharmacology
(a) Primary pharmacodynamics
(b) Secondary pharmacodynamics
(c) Safety pharmacology
(d) Pharmacodynamic drug interactions
2. PKDM
(a) Analytical methods and validation
(b) Absorption (via the intended route of administration)
(c) Distribution
(d) Metabolism
(e) Excretion
(f) Pharmacokinetic Drug Interactions
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3. Toxicology
(a) Local tolerance
(b) Single dose toxicity
(c) Repeat dose toxicity
(d) Genotoxicity
(e) Carcinogenicity
(f) Reproductive and developmental toxicity
In addition to the nonclinical toxicology studies, the nonclinical pharmacokinetic studies are crucial during the development of drug products for back of the eye diseases since it is very difficult to obtain clinical ocular samples. Therefore a good understanding of the target tissue(s) and development of a good pharmacokinetic– pharmacodynamic (PKPD) model based on drug concentration in the target tissue(s) goes a long way in scaling up the findings from nonclinical species (most likely rabbit, dog, or monkey) to humans. For retinal diseases like macular degeneration, the drug concentration at the retinal pigment epithelium, or choroid is important while for retinal diseases like proliferative vitreoretinopathy, vitreous levels may be the target (Gryziewicz.
2005).
A detailed description of these nonclinical studies is provided in Section C (Preclinical Development) of this book and most of these studies are conducted under the auspices of Good Laboratory Practices (GLP). Depending on the nature and marketing status of the drug, a formal request to waive some of these studies can be made by the sponsor to the agency based on scientific justification. For example, if the drug has been previously marketed for nonocular indications (sys­temic use), a fair amount of systemic pharmacokinetics, metabolism, and toxicity data can possibly be obtained from the literature, providing the option of utilizing the 505(b)(2) approval route (FDA Draft Guidance). This data combined with the potential lack of significant systemic exposure following intraocular administration (high safety margins) could be used to justify a waiver for some of the nonclinical studies such as systemic distribution and metabolism studies, chronic systemic tox­icity studies, reproductive and developmental toxicity studies, and carcinogenicity studies. However, if the drug is a new chemical entity (NCE) with unknown safety characteristics, the full complement of studies may be needed for registration filing. These concerns can be discussed at Pre-IND or end of Phase II (EOP2) meetings between the sponsor and the agency. The approval of such requests is completely at the discretion of the agency. During the meeting, the sponsor may request a waiver of some studies. If granted, these waivers can save the sponsor a significant amount of time, money, and resources during the drug development process without jeopar­dizing the integrity of the overall submission package.
The clinical development of drug products is carried out in accordance with Good Clinical Practice (GCP) that set the standard for ethical and scientific quality for all aspects of clinical trial conduct and reporting. Typically, the sponsor pro­gresses through Phase I, Phase II, and then Phase III clinical trials in a logical sequential manner with the data from each trial guiding the design of the next larger and more definitive trial. But with increasing cost and time of clinical trials, some
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STAGE 1: Open Label Staggering Dose Escalation
Cohort 1
Microdose or
Sham
Cohort 2
Low dose
*Dose escalation may be stopped following review of the safety data from each cohort
Cohort 3
Mid dose
Primary
Endpoint
Stage 2
Sham
Optimized low dose
Optimized
Dose Levels
Based on
Stage 1
Results
Optimized high dose
Optimized mid dose
Cohort 4
High dose
STOP
ESCALATION*
STOP
ESCALATION*
STOP
ESCALATION*
STAGE 2: Masked Randomized Dose-Response
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Fig. 19.1 Example of a two-stage Phase I/II clinical trial design
sponsors prefer conducting Phase I/II trials in a multistage fashion. One example of such multistage trial is shown in Fig. 19.1. In addition, the initial multistage clinical trials can be designed as proof-of-concept trials to exhibit efficacy over a shorter period of time even though the ultimate goal is for a longer duration (ideally ³ 6 months to 1 year). If these shorter trials demonstrate the activity of the drug when administered via its intended route of administration, it provides the sponsor with confidence to proceed with larger, expensive, and longer trials (Phase III) aimed at demonstrating the efficacy for a longer duration.
Phase III clinical trials are designed to demonstrate one of the following outcomes:
1. The drug product is superior to a placebo.
2. The drug product is equivalent or noninferior to an approved marketed product
for similar indication.
3. The drug product has superior efficacy and/or safety compared to an approved
marketed product for similar indication.
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19.4 Adaptive Trial Design
The Office of Biostatistics and the Office of New Drugs in CDER in conjunction with CBER released a Draft Guidance document on “Adaptive Design Clinical Trials for Drugs and Biologics” in February 2010 that clearly underscores the grow- ing interest and push towards adaptive design clinical trials to make the studies more efficient and more informative. The Draft Guidance defines an adaptive design clinical study as a study that includes a prospectively planned opportunity for modi­fication of one or more specified aspects of the study design and hypotheses based on the analysis of data (usually interim data) from subjects in the study. Analyses of the accumulating data are performed at prospectively planned timepoints within the study, can be performed in a fully blinded manner or unblinded manner, and can occur with or without formal statistical hypotheses testing. In other words, adaptive clinical trials will empower the sponsors and investigators to change the design or analyses of clinical trials based on insights obtained by examination of the accumu­lated data at an interim point in the trial. Since this is a relatively new concept, the greatest interest in this approach has been in the adequate and well-controlled stud­ies intended to support marketing a drug. It is always in the best interest of the spon­sor to plan the adaptation in advance (being prospective) and discuss the details of this adaptation with the FDA in order to avoid any potential complications that may affect the validity of the interim analysis, the changes implemented the following interim analysis or the integrity of the entire clinical study itself. It would be devas­tating if the entire study is deemed invalid due to issues such as introduction of bias based on an unplanned action by the sponsor.
Adaptive Design clinical trials offer some key advantages over the conventional design clinical trials. Planning a well-designed study to support market registration of a drug requires adequate knowledge on a variety of parameters such as event rates, variance, discontinuation rates, etc., and these are generally incorporated in a conventional design clinical trial as assumptions or “best estimates.” If these assumptions are incorrect, the study may fail to achieve its goal. Therefore to increase the likelihood of success, the study may be designed with higher number of patients or duration resulting in increased cost and time. Additionally, it may also lead to instances where the patients in the suboptimal dose group continue to get dosed for the entire duration of the study providing no meaningful data and there­fore increasing the cost of the study and reducing the overall efficiency. An adaptive design clinical trial takes this into account and eliminates some of these issues by including an interim analysis at predetermined timepoints. Following interim anal­ysis of the dose response or other parameters, a decision can be made on whether the suboptimal dose group should continue to be dosed or discontinued (will dosing this group provide any additional value). Discontinuation may lead to a decrease in cost and time of the study without reducing the informativeness. This can lead to efficient allocation of resources and potentially the collection of more data on more parameters than would be possible with the conventional design.
Even though interactions by the sponsor with the FDA are commonplace during the course of a drug development program, these become even more crucial when
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the sponsor decides to use an adaptive design for conducting a clinical trial. Due to the increased complexity of the adaptive design, it is important that the sponsor has earlier and more extensive interactions with the FDA. If the study is an exploratory study, the FDA will focus upon the safety of the study participants and will consider the relevance of the parameters being examined (dose response, endpoints, bio­markers, etc.) to guide the design of later studies. The efficacy measurements are outside the realm of this review and will be focused on during the late stages of drug development. The assessment of the adaptive design features by the FDA gets more extensive during the late stages of drug development. This review still focuses on the safety of study participants and now includes evaluation of the assessment of safety and efficacy to ensure that the study data will be of sufficient quality and quantity to inform a regulatory decision. It is important to note that the FDA will generally not be involved in examining the interim data used for the adaptive decision making and will not provide comments on the adaptive decision while the study is ongoing. In addition, the acceptance of adaptive design at the protocol design stage does not imply its advance concurrence that the adaptively selected choices will be optimal choices. An overview of the regulatory mechanisms for obtaining formal approval, substantive, feedback from FDA on design of the later stage trials and their place in drug development program are described in the Sect.
19.3 of this chapter.
19.5 Drug-Device Combinations
Since local delivery of the drug to the posterior segment of the eye typically requires intraocular injections, devices such as needles and syringes play a prominent role in facilitating such delivery. As a result, the new therapeutic products may not be clas­sified exclusively as a drug or device but rather a “combination” product. OZURDEX™, a dexamethasone biodegradable Intravitreal implant marketed by Allergan Inc, is one such example of a combination product. The drug product is a rod-shaped intravitreal implant that comes preloaded into a standard 22-G thin wall hypodermic needle of a single-use applicator that delivers the implant directly to the posterior segment of the eye. CDER, CBER, and the Center for Devices and Radiological Health (CDRH) have entered into agreements clarifying the product jurisdictional issues per Part 3 of Title 21 of the Code of Federal Regulations (Product Jurisdiction). The sponsor of the drug application (IND, NDA, or any other premarket or investigational application) needs to contact the appropriate center in the agency to confirm coverage and discuss the application process. Even though the application is made to a single center in the agency, it does not preclude the center from requesting assistance from the other centers to evaluate the appropriate parts of the application, as needed.
According to 21 CFR Part 3, the primary mode of action of the product needs to be clarified in order to determine which center will take the lead role in reviewing the premarket application. Here are some examples:
1. If the primary mode of action of the product is that of a drug (other than biologi-
cal products), then CDER will have primary jurisdiction for the application
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review. A prefilled delivery system (e.g., OZURDEX™) is a good example of
this combination product where the implant is preloaded into a single-use delivery
applicator but the main purpose of this system is to deliver the implant into the
posterior segment of the eye.
2. If the primary mode of action of the product is that of a drug and the drug sub-
stance is a biological product, then CDER will have primary jurisdiction for the
application review. An example would be a solution of any biological product
(such as LUCENTIS™) provided with an unfilled syringe and needle, with the
intention of using the unfilled syringe and needle (device) for delivering the drug
(in this case LUCENTIS™). If the device has not been previously approved by
CDRH, then the jurisdiction will be divided between the two centers; CDRH for
the device and CDER for the drug.
3. If the product includes a drug–device combination that is intended primarily to
perform as a device, then CDRH will have primary jurisdiction for the applica-
tion review. A good example of this is a surgical draper coated with an antimicro-
bial agent, or bone cement containing an antimicrobial agent.
4. If the product includes a drug–device combination that is intended primarily to
perform as a drug, then CDER/CBER will have primary jurisdiction for the
application review based on whether the drug is a small molecule entity or a
biologic. For example, skin prep pads with antimicrobial agent.
19.6 Product Summary Basis of Approval Reviews
A better understanding of the regulatory programs for back of the eye treatments can be obtained by reviewing the summary basis of approvals (SBAs) for products that have been evaluated and approved by the FDA and/or other health agencies around the world. A review of these SBAs will help the reader understand the nature of CMC, nonclinical and clinical studies that form the template for a global development plan for the investi­gational new drug; and even though every drug is unique and may need some tweaking of plan (some additional studies may need to be conducted), the overall template will remain relatively similar. The SBA for MACUGEN™ (Pegaptanib sodium injection) has been discussed by Gryziewicz ( (Dexamethasone biodegradable intravitreal implant – a small molecule corticosteroid) and LUCENTIS™ (Ranibizumab injection – a humanized antibody). The reader is also encouraged to review the SBAs of other products on the FDA website.
2005). Here we review the SBAs for OZURDEX™
19.6.1 OZURDEX™
OZURDEX™ is a dexamethasone containing intraocular drug delivery system developed by Allergan Inc for treatment of macular edema following branch retinal
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vein occlusion (BRVO) or central retinal vein occlusion (CRVO). It is a biodegradable implant containing 0.7 mg dexamethasone that is injected into the vitreous humor using a specifically designed injector. On 10 January 2005, the agency granted Allergan with a Fast Track Designation for the dexamethasone Intravitreal implant stating that there were no approved drug products indicated for patients with macular edema secondary to BRVO or CRVO at that time. The drug product is a rod-shaped intravitreal implant loaded into a standard 22-G thin wall hypodermic needle of a single-use applicator that delivers the implant directly to the posterior segment of the eye. It contains the active drug in a biodegradable poly (d,l-lactide­co-glycolide) (PLGA) matrix. Consistent in
vitro release rates were demonstrated and these showed good correlation with the in vivo release rates in rabbits and mon­keys. Additionally, the sterility and endotoxin limits were specified and accepted by the agency.
Dexamethasone is a synthetic derivative of hydrocortisone that acts as a potent anti-inflammatory agent and inhibits the expression of VEGF leading to an inhibi­tion of VEGF-induced vascular leakage in a rabbit model of blood-retinal and blood-aqueous barrier breakdown (Edelman et al., 2005). This was confirmed in a 10-week study evaluating the primary pharmacodynamics of the dexamethasone intravitreal implant. A dose-dependent inhibition of VEGF-induced blood-retinal­barrier (BRB) breakdown was observed with 0.35 and 0.7 mg dexamethasone implants with the higher dose producing a more pronounced inhibitory effect com­pared to lower dose.
In addition to the pharmacology studies, the submission included a condensed nonclinical safety program (PKDM and toxicology studies) because dexametha­sone had been marketed in the United States for decades and its systemic ADME (absorption, distribution, metabolism, and excretion) and toxicology profile had been well established. Five single dose ocular absorption and distribution studies with the dexamethasone implant were conducted in rabbits and one single dose study was conducted in monkeys. Dexamethasone concentrations were generally lower in monkeys compared to rabbits and lasted for a longer period of time with the implant releasing >90% dexamethasone by 3 months and containing detectable levels in the vitreous humor up to 6 months. These concentrations were higher than the EC50 values obtained from cell-based potency assays supporting the 6-month clinical dosing interval. In vitro, dexamethasone did not bind to synthetic melanin suggesting that it does not accumulate in pigmented ocular tissues following repeated dosing. Tissue distribution studies using radiolabeled dexamethasone con­taining implants showed that the drug distribution in the posterior segment of the eye was relatively higher than its distribution in the anterior segment of the eye fol­lowing intravitreal injection. Dexamethasone also exhibited negligible metabolism in an in
vitro study using human ocular tissues and in in vivo ocular metabolism studies in rabbits and monkeys. Since the characteristics and metabolism of the matrix PLGA polymers had been extensively studied during the past few decades and these polymers had been approved by the FDA for human use, no additional studies were conducted to characterize the metabolism of these polymers. Since the
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systemic use of dexamethasone had been reported for several decades, systemic distribution, metabolism, and excretion studies were not conducted. In addition, the plasma concentrations of dexamethasone following intravitreal administration were minimal, alleviating any concerns of systemic side effects.
Ocular and systemic safety of the dexamethasone implant was evaluated in three single dose toxicity studies in rabbits and in repeat dose toxicity studies each (two injections, 3 months apart) in rabbits and monkeys. Even though some transient and expected dexamethasone-related systemic adverse effects in rabbits were observed, the repeat dose toxicity study in monkeys did not exhibit any significant ocular or systemic toxicity at doses up to two 0.7
mg implants, 3 months apart. The
0.7 mg dose was substantially lower than the maximal doses in animal studies reported without adverse ocular findings for single intravitreal injection (4.8 mg) or for implanted sustained release dexamethasone devices (5.0 mg). Furthermore, dexamethasone had been widely used in ophthalmology for many decades (Gordon
1959a, b). Since the plasma concentrations of dexamethasone following intravitreal
administration were minimal and the systemic use of dexamethasone had been well documented, additional toxicity studies via the systemic route of administration, genetic toxicology studies, reproductive toxicology studies, and carcinogenicity studies were not conducted because the data were either not needed (due to ade­quate systemic safety margins following intravitreal injection) or was available in the literature, resulting in significant savings of time, money, and resources. Furthermore, since the use of PLGA polymers was well documented in humans with no safety concerns, no toxicity studies were needed to prove the safety of the PLGA matrix alone.
The clinical development program included Phase I emergency and compassion­ate use studies, Phases I and II dose ranging trials and two Phase III multicenter, masked, randomized, sham-controlled, safety and efficacy studies in patients with macular edema following BRVO or CRVO. The clinical data showed that 0.7 mg implant had greater efficacy and longer duration of effect than the 0.35 mg implant suggesting a dose response. The safety endpoints (mostly class effects related to steroids) did not exhibit a dose response and the overall incidence of adverse events was significantly higher when compared to sham, but was not statistically signifi­cant between the two dose groups. Overall there was substantial evidence of safety and efficacy to file an NDA application with the FDA. Following the NDA applica­tion, OZURDEX™ was approved in June
2009.
In addition to these studies, the sponsor requested a Pediatric Waiver at one of the two pre-NDA meetings based on the justification that pediatric studies with dexamethasone implants are highly impractical due to the fact that macular edema associated with BRVO or CRVO is mainly found in adults and the number of pedi­atric patients with this indication is very small. This request was granted by the FDA. The sponsor also held additional meetings with the FDA that included a pre-IND meeting, an EOP2 clinical trial meeting , clinical meetings and discussions throughout the drug development program to obtain relevant guidance on the nonclinical and clinical plans.
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19.6.2 LUCENTIS™
LUCENTIS™ (Ranibizumab) is a recombinant, humanized monoclonal IgG1 anti­body antigen-binding fragment (Fab) designed to bind and inhibit all active forms of human VEGF and indicated for neovascular (wet) ARMD. It is approximately 48 kilodaltons (kDa) and is produced by an Escherichia coli expression system. It is administered as a 0.05-mL (0.5 mg) intravitreal injection of the sterile, colorless to pale yellow solution once a month. In pharmacology studies, ranibizumab showed high binding affinity to different isoforms of rhVEGF. This was confirmed in a guinea-pig skin model where ranibizumab significantly inhibited VEGF-induced vascular permeability in a dose-dependent manner.
Analytical methods including ELISA were developed to monitor the drug con­centrations as well as antibodies against ranibizumab in various tissues and blood. The nonclinical ADME studies included rabbit and monkey distribution studies following intravitreal administration of the drug and a distribution study in rabbits evaluating the pharmacokinetics of LUCENTIS™ following subconjunctival, intracameral, and intravitreal administration. Ranibizumab was absorbed in most of the ocular tissues (vitreous humor, retina, aqueous humor, ICB, corneal endothe­lium) and serum in both rabbits and monkeys with elimination half-life of 2–3 days. The serum concentration was minimal and the maximal separation between the vitreous humor concentrations and serum concentrations was observed with intravitreal administration compared to subconjunctival and intracameral adminis­tration suggesting that the intravitreal route is the better route of administration. Ranibizumab elicited an antibody response in the vitreous humor and serum in rabbits but not in monkeys. In an effort to extrapolate the results to humans, the sponsor developed a pharmacokinetic model to predict the retina and serum expo­sure of ranibizumab under simulated dosing regimens after intravitreal and intrave­nous administration. The nonclinical toxicology package consisted of local tolerance studies in rabbits and four repeat dose toxicology studies in monkeys ranging in doses from 0.25 to 2.0 were conducted following a single intravitreal injection of the drug at 2.0 or 2.5 mg/ eye followed by a 7-day observation. Ocular inflammation was observed in these animals. In the repeat dose toxicology studies in monkeys, dose-related inflamma­tory responses were observed in the anterior and posterior chambers at all doses, possibly due to the lyophilized nature of the test article and suggesting that monkey is the more sensitive model; however, these were transient and mostly reversible. None of the animals exhibited any drug-induced systemic toxicity. The antibody did not exhibit any cross reactivity to human tissues and was compatible at up to 20 mg/mL with human and monkey serum and plasma and human vitreal fluid. Since the serum concentrations of the drug following intravitreal administration were deemed negligible, genetic toxicity studies, carcinogenicity studies, and reproductive and developmental toxicity studies were not conducted at the time of BLA (Biological License Application) submission. Since the reproductive and develop­mental toxicity studies were not conducted, the review indicated that ranibizumab
mg/eye. The local tolerance studies in rabbits