How Long Does Avastin Eye Injection Stay in Your System?

Avastin (bevacizumab) is commonly used off-label as an eye injection to treat conditions like age-related macular degeneration and diabetic retinopathy. Patients often wonder how long the drug remains in their system, particularly regarding its effects and potential side effects.

Understanding this requires examining how Avastin is administered, distributed, metabolized, and cleared from the body.

Route Of Administration And Absorption

Avastin is given as an intravitreal injection, meaning it is injected directly into the vitreous humor of the eye. This method ensures the drug reaches the retina and choroid, where it inhibits vascular endothelial growth factor (VEGF), preventing abnormal blood vessel growth and leakage. Unlike systemic administration, intravitreal injection bypasses the gastrointestinal tract and bloodstream, delivering a high concentration directly to ocular tissues.

Once injected, bevacizumab remains in the vitreous, gradually diffusing into surrounding structures. Its absorption rate depends on molecular size, VEGF binding affinity, and ocular barrier permeability. As a full-length monoclonal antibody with a molecular weight of approximately 149 kDa, bevacizumab diffuses more slowly than smaller molecules like ranibizumab (Lucentis). Studies suggest its vitreous half-life ranges from 4.32 to 6.7 days, allowing for sustained VEGF inhibition and reducing injection frequency compared to some alternatives.

Absorption into systemic circulation occurs mainly through two pathways: anterior elimination via aqueous humor outflow and posterior diffusion into the choroidal circulation. The anterior route clears the drug through the trabecular meshwork and Schlemm’s canal, while the posterior route allows entry into the bloodstream via choroidal vasculature. Though systemic absorption is lower than with intravenous administration, detectable levels appear in plasma, with systemic VEGF suppression lasting for weeks. This raises considerations for patients with cardiovascular risk factors.

Distribution In Ocular And Systemic Tissues

After injection, Avastin disperses within the eye, concentrating in structures critical to its function. The retina, particularly its outer layers and the retinal pigment epithelium (RPE), absorbs a significant portion due to its vascularization and proximity to the choroid. Bevacizumab binds to VEGF, preventing pathological neovascularization and vascular leakage, which characterize conditions like AMD and diabetic retinopathy. The choroid, one of the body’s most vascularized tissues, also accumulates the drug, prolonging its anti-angiogenic effects.

Bevacizumab gradually moves into the anterior chamber, where it can be detected in the aqueous humor for several weeks post-injection. Its large molecular size limits permeability through ocular barriers compared to smaller anti-VEGF agents like ranibizumab and aflibercept. The sclera may also contribute to drug movement, but its role remains under study.

As bevacizumab exits ocular compartments, it enters systemic circulation at much lower levels than with intravenous administration. Plasma concentrations peak within days and decline over several weeks. Though lower than levels from intravenous dosing, they are sufficient to suppress circulating VEGF, raising concerns about systemic effects, particularly in patients with cardiovascular conditions.

Metabolism And Clearance

Once in systemic circulation, bevacizumab follows the metabolism and clearance patterns of other monoclonal antibodies. Unlike small-molecule drugs metabolized by liver enzymes, bevacizumab undergoes proteolytic degradation via cellular uptake and lysosomal breakdown. Endothelial and immune cells internalize the antibody, breaking it down into amino acids recycled for protein synthesis. Since bevacizumab does not generate active metabolites, concerns about prolonged bioactivity from metabolic byproducts are minimal.

Clearance is governed by molecular size and VEGF interactions. At 149 kDa, bevacizumab is too large for efficient renal filtration, so receptor-mediated endocytosis removes it instead. Endothelial and immune cells engulf the antibody for degradation. The systemic half-life after intravitreal injection is estimated at around 20 days, though individual factors like systemic VEGF levels and overall protein catabolism can influence this.

Duration Of Detectable Levels In The Body

Following intravitreal injection, bevacizumab remains detectable in ocular tissues and systemic circulation for weeks. In the eye, concentrations decline gradually, with measurable levels in aqueous humor up to 30 days post-injection. Its prolonged intraocular presence supports sustained VEGF inhibition, which is why dosing intervals typically range from four to eight weeks, depending on patient response and disease severity.

In systemic circulation, bevacizumab peaks within a few days and declines slowly. While systemic exposure is lower than with intravenous administration, trace amounts remain in plasma for weeks. Some studies report systemic VEGF suppression lasting up to 28 days after a single injection, which is relevant for patients with conditions influenced by VEGF signaling, such as cardiovascular disease or wound healing disorders. The persistence of systemic bevacizumab highlights the need for individualized treatment plans, particularly for patients with preexisting health concerns.