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BEE 2600 Fall 2016 Case Study #1
Diffusion and Pharmacokinetics of Anti-VEGF Drugs Written by Sachiye Koide
Due Date: 09/27/2016 Macular degeneration is the leading cause of age-related vision loss and affects more than 10 million Americans today. Considered an incurable disease, macular degeneration is caused by deterioration in the macula, the central portion of the retina, and is the consequence of overexpression of vascular endothelial growth factor (VEGF). VEGF is a signal protein that stimulates vasculogenesis and angiogenesis, and helps restore oxygen supply to tissues as part of the cardiovascular system when circulation is inadequate. When functioning normally, VEGF creates new blood vessels, such as during embryonic development, after injury, and when bypassing blocked vessels. However, overexpression of VEGF can have harmful consequences such as macular degeneration and cancer metastasis.
Anti-VEGF drugs currently being used to treat macular degeneration include Bevacizumab and Ranibizumab, which can be administered straight to the eyes. However, direct injection of the anti-VEGF drugs into the eyes may cause an uneven drug concentration profile and require frequent eye injections for long-term treatment. Recently, coatings of hydrophilic gels (commonly referred to as hydrogels) have been used as drug delivery vehicles and have the advantage of time-controlled drug release [4]. Hydrogels are extensive polymer networks whose hydrophilic structure of chemical and physical crosslinks (entanglements, crystallites, and hydrogen-bonded structures) allows them to absorb copious amounts of biological fluid ten to twenty times their molecular weight without dissolving [1]. Hydrogels have proved to be extremely useful in biomedical and pharmaceutical applications due to their high water content, similarity to natural tissue, and biocompatibility [10]. Drugs can be concentrated within the polymer and released through a diffusion mechanism that allows for reduced dosing frequency. The physical properties of the hydrogel, drug-polymer interactions, drug concentration and drug solubility determine the diffusion kinetics, duration, and rate of drug release from the hydrogel [15]. There are several types of controlled-delivery hydrogel systems, including: diffusion-controlled, swelling-controlled, chemically-controlled, and environmentally-controlled [15]. In part 1 of this case study, we will focus on diffusion-based drug delivery hydrogels in the distribution of Bevacizumab and Ranibizumab to patients with macular degeneration. Part 1:
In treating macular degeneration, the hydrogel containing the drugs is injected into the vitreous humor of the eye where the anti-VEGF drugs diffuse into the surrounding eye tissue. The hydrogel has a spherical shape with the drugs concentrated in the center of the gel (Fig. 2). The outer radius of the hydrogel sphere is 0.72 mm. The drug concentration at the center is 12.351 !!
!". After a certain time, the hydrogel reaches a steady state where the concentration of the
drug at the interface of the hydrogel and eye tissue is zero (the drug is immediately absorbed by the tissue), while the concentration of the drug in the center of the gel continues to be constant. In
Fig. 1:Physiology of macular degeneration in the eye.
this study, we will model the drug diffusion through the hydrogel by only considering a small section (the rectangle section illustrated in Figure 2). We will assume there is no curve in this small section, and model it as a slab of drug and hydrogel. Assume that the hydrogel is in direct contact with the tissue throughout this section.
Bevacizumab has a diffusion coefficient of 4.1Γ10β7 cm2/s and a degradation rate of 7.943 x 10-Ββ7 Β΅g/mm3/s. Ranibizumab has a diffusion coefficient of 6.7Γ10β7 cm2/s and a degradation rate of Ξ± + Ξ²z where Ξ± = 3.972 x 10-Ββ4 Β΅g/mm3/s and Ξ² = -Ββ5.516 x 10-Ββ4 Β΅g/mm4/s. For this exercise, assume the anti-VEGF drug diffuses directly from the center of the hydrogel into the eye tissue in one dimension only, and the porosity of the hydrogel is 1. We are only concerned with diffusion from the center of the hydrogel into the eye tissue. Ignore any diffusion into the vitreous liquid.
Figure 2: Structure of the hydrogel containing the drug in the center.
1. Perform a literature search on the two drugs to determine the underlying mechanism of
using anti-VEGF drugs in treating macular degeneration (this will be included in your introduction)
2. Draw a schematic diagram modeling the diffusion of Bevacizumab and Ranibizumab through the hydrogel. Be sure to include all boundary conditions and list all variables (including definition and units for each variable) and assumptions.
3. Separately derive the steady-state concentration for Bevacizumab and Ranibizumab through the hydrogel using Fickβs Second Law of Diffusion in terms of the variables only.(You need to solve for k1 and k2 constants)
4. Graph both drug concentration profiles with respect to the depth of the hydrogel on the same plot.
5. Find the expressions for the flux of Bevacizumab and Ranibizumab at the hydrogel-eye tissue interface, first in terms of variables, and then substitute the values and units into the expressions. Leave final answers in units of [Β΅g/mm2/s].
6. How long does it take for a small molecule of each drug to diffuse from the hydrogel into the eye tissue [hours]?
7. Which drug is more suitable for the time-controlled released delivery for macular degeneration from a transport point of view (considering the flux and time of diffusion)? Remember that your aim is to minimize the need for frequent injections by choosing a method that releases drug slowly over time.
Part II:
Besides being a treatment for macular degeneration, Bevacizumab is the first anti-angiogenic antibody approved by the FDA for metastatic cancers [4]. However, the doses are much higher than the amount given to treat macular degeneration, at around 100 mg per dose via intravenous injection [8]. The higher dosage of Bevacizumab in healthy organs would result in a number of side effects. In Part II of the assignment, we will evaluate the toxicity of Bevacizumab and its pharmacokinetics.
Typically, cancer patients receive an injection of Bevacizumab every three weeks, or when Bevacizumab levels in the blood go down to lower than 0.008 mg/mL. For an adult patient, assume the volume of blood in the entire body is 5.5L. The elimination half-life of bevacizumab is 20 days.
In the treatment of metastatic cancers with Bevacizumab, consider an IV to be the reservoir for the drug and can hold 1000 mL of fluid. The elution rate of the fluid into the blood is 7.72 mL/min [3]. Bevacizumab subsequently moves into the tissue at a rate of Kt=0.082 βπ!! and the kidney at a rate of Kk= 0.041 βπ!!. From the kidney, the drug is excreted at a rate of Ke= 0.056 βπ!!. From the tissue, some of the drug moves back into the bloodstream at a rate Kb= 0.00025 mg/hr and some gets metabolized at a rate Km= 0.02 βπ!!. Assume that all the Bevacizumab is eventually either metabolized by the tissue or excreted from the body by the kidney.
1. Draw a pharmacokinetic model for the process of transport and excretion of
Bevacizumab in the body using Word or PowerPoint. Include the IV reservoir, blood, tissue, kidney, and all the appropriate rate constants. List all variables and assumptions.
2. Derive the rate equations for the mass of the Bevacizumab in the IV reservoir, blood, tissue, and kidney at time t. Start with a word equation and mass balance for each. Write all expressions in terms of variables and do not solve the equations.
3. Use the rate equation for blood to find an expression in terms of variables for the mass of Bevacizumab in the blood with respect to time.
4. If the patient is given a 100 mg dose through the IV, calculate the time it takes to deliver all of the contents of the IV bag containing the Bevacizumab. What is the concentration of drug in the blood once the entire contents of the IV has been delivered (considering absorption and elimination processes of the drug)?
5. How long until the patient can receive another dose? Hint: use the elimination half-life of Bevacizumab for your calculation.
References:
1. Ahmed, EM. 2015. Hydrogel: preparation, characterization, and applications: a review. Journal of Advanced Research. 6(2):105-121. doi:10.1016/j.jare.2013.07.006
2. Bhattarai N, Gunn J, Zhang M. 2010. Chitosan-based hydrogels for controlled, localized drug delivery. Advanced Drug Delivery Reviews. 62(1): 83-99. doi:10.1016/j.addr.2009.07.019
3. Fournier RL. 1998. Basic transport phenomena in biomedical engineering. CRC Press. 4. Li SK, Liddell MR, Wen H. 2011. Effective electrophoretic mobilities and charges of
anti-VEGF proteins determined by capillary zone electrophoresis, J of Pharmaceutical and Biomedical Analysis. 55(3):603-607. doi:10.1016/j.jpba.2010.12.027
5. Lin C, Metters AT. 2006. Hydrogels in controlled release formulations: network design and mathematical modeling. Advanced Drug Delivery Reviews. 58: 1379-1408. doi:10.1016/j.addr.2006.09.004
6. Marcarelli R. 2015. Injectable βself-healingβ hydrogel could target cancer cells, treat macular degeneration. HNGN [Internet]. [cited 2016 March]. Available from: http://www.hngn.com/articles/71174/20150220/
7. Medscape: drugs and diseases [Internet]. c1994-2016. WebMD LLC: [cited 2016 March]. Available from: http://reference.medscape.com/drug/avastin-bevacizumab-342257 [H]
8. Michels S. 2006. Is intravitreal bevacizumab (Avastin) safe? BMJ. 90(11):1333-1334 9. Peppas NA, Colombo P. 1997. Analysis of drug release behavior from swellable polymer
carriers using the dimensionality index. Journal of Controlled Release. 45(1): 35-40. doi:10.1016/S0168-3659(96)01542-8
10. Peppas, NA. 1997. Hydrogels and drug delivery. Current Opinion in Colloid & Interface Science. 2(5):531-537. doi:10.1016/j.addr.2009.07.019
11. Pike DB, Cai S, Pomraning KR, Firpo MA, Fisher RJ, Shu XZ, Prestwich GD, Peattie RA. 2006. Heparin-regulated release of growth factors in vitro and angiogenic response in vivo to implanted hyaluronan hydrogels containing VEGF and bFGF. Biomaterials. 27(30):5242-5251
12. Porter TL, Stewart R, Reed J, Morton K. 2007. Models of hydrogel swelling with applications to hydration sensing. PMC. 7(9):1980-1991
13. RxList: the internet drug index [Internet]. c2016. RxList Inc.: [cited 2016 March]. Available from: http://www.rxlist.com/lucentis-drug.htm
14. Salter JT, Miller KD. 2006. Targeting VEGF for breast cancer: safety and toxicity data with bevacizumab. Medscape CME and Education [Internet]. C1994-2016. WebMD LLC:[cited 2016 March].
15. Wei C, Kim C, Kim H, Limsakul P. 2012. Hydrogel drug delivery: diffusion models. [cited 2016 March].
SOLUTIONS 1.) Literature Search 2.) Variables
Given: L = 0.72 mm Concentration of Bevacizumab/Ranibizumab inside the hydrogel = 12.351 !!
!"
Ξ΅ = porosity = 1
Variables: CB(z)= concentration of Bevacizumab at a given depth of z CB,hydrogel = CB(0) = concentration of Bevacizumab at center of hydrogel (z=0) = 12.351 Β΅g/uL
CB,vitreous = CB(L) = concentration of Bevacizumab at vitreous-hydrogel boundary DS,B= Bevacizumab diffusion coefficient = 4.1Γ10β7 cm2/s = 4.1Γ10β5 mm2/s RB = Bevacizumab degradation rate = 7.943 x 10-7 Β΅g/mm3/s
CR(z)= concentration of Ranibizumab at a given depth of z CR,hydrogel = CR(0) = concentration of Ranibizumab at center of hydrogel (z=0) = 12.351 ug/uL
CR,tissue = CR(L) = concentration of Ranibizumab at vitreous-hydrogel boundary DS,R = Ranibizumab diffusion coefficient = 6.7Γ10β7 cm2/s = 6.7 x 10-5 mm2/s RR = Ranibizumab degradation rate = Ξ± + Ξ²z
Ξ± = 3.972 x 10-4 Β΅g/mm3/s
Ξ² = -5.516 x 10-4 Β΅g/mm4/s
Assumptions: β’ Drug diffuses directly from the center of the hydrogel into the eye tissue in one direction. β’ Only consider drug diffusion in one small section and model it as a slab of the hydrogel with uniform thickness. β’ Porosity of the hydrogel is 1 β’ Concentration of Bevacizumab / Ranibizumab in the hydrogel is the same as at z = 0 (the center of the gel), and is assumed to be constant throughout the diffusion process
Eye Tissue
z = 0, πΆ!,!!"#$%&' = 12.351 !!!"
πΆ!,!!"#$%&' = 12.351¡μππ’πΏ
z = L, CB, tissue = C(L) = 0 !!!"
Hydrogel
Bevacizumab/ ranibizumab diffusion
L
β’ The eye tissue absorbs the drug instantly, so that the concentration at the interface of hydrogel and eye tissue is zero. β’ Bevacizumab is degraded at a rate of R in the hydrogel wall and Ranibizumab is degraded at a rate R = Ξ± + Ξ²z that decreases with increasing depth
β’ The mass of Bevacizumab/ Ranibizumab is conserved β’ Diffusion rate, porosity, and thickness are constant throughout the hydrogel. β’ The concentrations of Bevacizumab/ Ranibizumab are homogeneous throughout the center of the hydrogel at time = 0
β’ System is in steady state
3.) Derivation of Concentration Bevacizumab
ππΏπΆ!πΏπ‘ = π·!,!
πΏ!πΆ!πΏπ§! β π !
π !!!
!"= 0 π π‘ππππ¦ π π‘ππ‘π πππ π = 1
π·!,!πΏ!πΆ!πΏπ§! = π !
πΏ!πΆ!πΏπ§! ππ§ =
π !π·!,!
ππ§
πΏπΆ!πΏπ§ ππ§ = (
π !π·!,!
π§ + π!)ππ§
πΆ! π§ = π !2π·!,!
π§! + π!π§ + π!
At z = 0, CB (0) = CB,hydrogel
π !2π·!,!
(0)! + π!(0)+ π! = πΆ!,!!"#$%&'
π! = πΆ!,!!"#$%&'
At z = L, CB(L) = CB,tissue
π !2π·!,!
(πΏ)! + π!πΏ + πΆ!,!!"#$%&' = 0
π! = βπΆ!,!!"#$%&' β
π !2π·!,!
(πΏ)!
πΏ
π! = βπΆ!,!!"#$%&'
πΏ β π !2π·!,!
πΏ
πͺπ© π =πΉπ©ππ«π,π©
ππ βπͺπ©,πππ πππππ
π³ + πΉπ©ππ«π,π©
π³ π+ πͺπ©,πππ πππππ
Derivation for Ranibizumab:
ππΏπΆ!πΏπ‘ = π·!,!
πΏ!πΆ!πΏπ§! β π !
πΏπΆ!πΏπ‘ = 0 π π‘ππππ¦ π π‘ππ‘π πππ π = 1
π·!,!πΏ!πΆ!πΏπ§! = πΌ + π½π§
πΏ!πΆ!πΏπ§! ππ§ =
πΌ + π½π§π·!,!
ππ§
πΏπΆ!πΏπ§ ππ§ =
πΌπ§π·!,!
+π½π§!
2π·!,!+ π! ππ§
πΆ! π§ = πΌπ§!
2π·!,!+
π½π§!
6π·!,!+ π!π§ + π!
Determining constants at the boundary conditions: At z = 0, CR (0) = CR,hydrogel
πΆ!,!!"#$%&' = πΌ(0)!
2π·!,!+ π½(0)!
6π·!,!+ π!(0)+ π!
π! = πΆ!,!!"#$%&'
At z = L, CR (L) = CR,tissue = 0
0 = πΌπΏ!
2π·!,!+
π½πΏ!
6π·!,!+ π!πΏ + πΆ!,!!"#$%&'
βπ!πΏ = πΌπΏ!
2π·!,!+
π½πΏ!
6π·!,!+ πΆ!,!!"#$%&'
π! = βπΌπΏ2π·!,!
β π½πΏ!
6π·!,!β πΆ!,!!"#$%&'
πΏ
πͺπΉ π = πΆππ
ππ«π,πΉ+
π·ππ
ππ«π,πΉβ
πΆπ³ππ«π,πΉ
+ π·π³π
ππ«π,πΉ+ πͺ!,!!"#$%&'
π³ π+ πͺ!,!!"#$%&'
4.) Matlab Code and Graph Figure 1: Concentration profiles with respect to the depth of the hydrogel wall for Bevacizumab and Ranibizumab
5. Bevacizumab Flux:
πΉππ’π₯ = βπ·!,!πΏπΆ!πΏπ§
πΏπΆ!πΏπ§ =
π !π·!,!
π§ + βπΆ!,!!"#$%&'
πΏ β π !2π·!,!
πΏ
πΉππ’π₯ = βπ·!,!π !π·!,!
π§ + βπΆ!,!!"#$%&'
πΏ β π !2π·!,!
πΏ
At z = L, (this part can be substitute later)
πΉππ’π₯ = βπ !πΏ + π·!,! β πΆ!,!!"#$%&'
πΏ + π !πΏ2
ππππ = βπΉπ©π³π +
π«π,π© β πͺ!,!!"#$%&'π³
πΉππ’π₯ = β(7.943 x 10β7 ¡μg
ππ!π )(0.72 mm)
2 + 4.1Γ10!!mm
!
s β 12.351 ¡μπ/ππ!
0.72 ππ
πΉππ’π₯ = π.ππ π±ππ!π¡μπ
πππ β π Ranibizumab Flux
πΉππ’π₯ = βπ·!,!πΏπΆ!πΏπ§
πΏπΆ!πΏπ§ =
πΌπ§π·!,!
+π½π§!
2π·!,! β
πΌπΏ2π·!,!
β π½πΏ!
6π·!,!β πΆ!,!!"#$%&'
πΏ
πΉππ’π₯ = βπ·!,!πΌπ§π·!,!
+π½π§!
2π·!,! β
πΌπΏ2π·!,!
β π½πΏ!
6π·!,!β πΆ!,!!"#$%&'
πΏ
At z = L,
πΉππ’π₯ = βπΌπΏ βπ½πΏ!
2 +πΌπΏ2 +
π½πΏ!
6 + π·!,! β πΆ!,!!"#$%&'
πΏ
ππππ = βπ·π³π
π βπΆπ³π +
π«π,πΉ β πͺπΉ,πππ ππππππ³
πΉππ’π₯ =
ββ 5.516 x 10β4 ¡μg
ππ4βπ !.!"!! 2
!β
3.972 x 10β4 ¡μgππ3βπ
!.!" !!
!+
(6.7 x 10β5mm2
s )(!".!"# !"!!!)
!.!" !!
ππππ = π.πππ π ππ!π ¡μπ/πππ/π
6. Time of Diffusion
π₯! = 2ππ·!π‘
t = !!
!!!!
For Bevacizumab: π‘ = (!.!"# !")!
!β!β(!.!"!"!! !"!/!) = 6321 s = 1.76 hours
For Ranibizumab: π‘ = (!.!"# !")!
!β!β(!.!"!"!!!!!/!) = 3867 s = 1.07 hours
7.
Compared to Ranibizumab, Bevacizumab takes longer time to diffuse and has a smaller flux at the interface of the hydrogel and the vitreous fluid. Therefore, Bevacizumab is a better drug for this macular degeneration treatment.
Part 2.
1.) Pharmacokinetic model
IV
U K
T
kb
RV
kk
kt
ke
L = mass of Bevacizumab in IV [mg] = 100 mg B = mass of Bevacizumab in blood [mg] T = mass of Bevacizumab in tissue [mg] K = mass of Bevacizumab in kidney [mg] U = mass of Bevacizumab excreted [mg] D* = mass of Bevacizumab metabolized [mg] r = elution rate = 7.72 mL/min v = volume of IV bag = 1000 mL c = concentration of drug in IV = L/v = 100 mg/1000 mL = 0.1 mg/mL RV = rc =7.72 mL/min x 0.1 mg/mLx 60min/1h = 46.32[mg/h] kb = rate of movement of drug from tissue back into bloodstream = 0.00025 [mg/s] kt = rate of movement of drug into tissue = 0.082 [1/hr] kk = rate of movement of drug into kidney = 0.041 [1/hr] ke = rate of excretion of drug from kidney = 0.056 [1/hr] km = rate of metabolism of drug in tissue = 0.02 [1/hr] t = time since administration of dose [hr] VB = volume of blood = 5.5 L
thalf=drug elimination half life= 20 days Bthreshold= maximum mass of drug in blood for additional dose = 0.008mg/mL
Assumptions: β’ The concentration of Bevacizumab in the IV reservoir and in the blood is constant β’ No new dose is needed if concentration of drug is above 0.008 mg/mL in the
blood. β’ There are 5.5 L of blood in the patientβs bloodstream. β’ The IV reservoir has a 1000 mL volume. β’ Flow rates are constant and unaffected by other bodily functions. β’ Bevacizumab only enters through the IV. β’ Bevacizumab diffuses completely into the bloodstream. β’ Diffusion rate and porosity are constant across the bloodstream. β’ The presence of Bevacizumab does not affect metabolism of Bevacizumab. β’ Temperature and pH of the system are uniform and thus do not affect rates.
D* km
B
β’ There is no drug in the blood initially (at t = 0). IV: πΆβππππ ππ πππ π ππ
Bevacizumabππ πΌπ
= πππ π ππ Bevacizumabπππ‘πππππ πΌπ β πππ π ππ π΅ππ£ππππ§π’ππππππ‘πππππ ππππππ π‘ππππ
βπΏ = βπ! !" !βπ‘ β
β!β!= βπ !
π π³π π = βπΉπ½
Blood: πΆβππππ ππ πππ π ππ
Bevacizumab ππ πππππ
=
πππ π ππ Bevacizumabπππ‘πππππ ππππππ π‘ππππ β πππ π ππ Bevacizumabπππ‘πππππ π‘ππ π π’π β
πππ π ππ Bevacizumabπππ‘πππππ ππππππ¦ + πππ π ππ Bevacizumabππ β πππ‘πππππ ππππππ π‘ππππ
βπ΅ = π! !" !βπ‘ βπ! !" !βπ‘ βπ! !" !βπ‘ +π! !" !βπ‘ β βπ΅βπ‘
= π ! β π!π΅ β π!π΅ + π!
π π©π π = πΉπ½ β πππ©β πππ©+ ππ
Tissue: πΆβππππ ππ πππ π ππ Bevacizumabππ π‘ππ π π’π
= πππ π ππ Bevacizumabπππ‘πππππ π‘ππ π π’π β πππ π ππ Bevacizumabππ β πππ‘πππππ ππππππ π‘ππππ
β πππ π ππ Bevacizumabπππ‘ππππππ§ππ ππ π‘ππ π π’π
βπ = π! !" !βπ‘ βπ! !" !βπ‘ βπ!"#$%&'()"*βπ‘ β βπβπ‘ = π!π΅ β π! β π!π
π π»π π = πππ©β ππ β πππ»
Kidney:
πΆβππππ ππ πππ π ππ Bevacizumabππ ππ ππππππ¦
= πππ π ππ Bevacizumabπππ‘πππππ ππππππ¦ β πππ π ππ Bevacizumabππ₯ππππ‘πππ
βπΎ = π! !" !βπ‘ βπ!"#$!%!&βπ‘ β βπΎβπ‘ = π!π΅ β π!πΎ
π π²π π = πππ©β πππ²
3. Mass of Bevacizumab in the blood
ππ΅ππ‘ = π ! β π!π΅ β π!π΅ + π!
ππ΅
π ! β π!π΅ β π!π΅ + π!= ππ‘
ππ΅
π ! β π!π΅ β π!π΅ + π!= ππ‘
(β1
π! + π!) ln π ! β π!π΅ β π!π΅ + π! = π‘ + π
ππ π ! β π΅ π! + π! + π! = β(π! + π!)(π‘ + π)
π!(!!!!!)(!!!) = π ! β π΅ π! + π! + π!
*simplify left side
π!(!!!!!)(!!!) = π!!(!!!!!) π!!(!!!!!)
π!!(!!!!!) = π!
π!(!!!!!)(!!!) = π!π!!(!!!!!)
π!π!!(!!!!!) = π ! β π΅ π! + π! + π!
π΅ = π ! + π! β π!π!! !!!!!
π! + π!
*Apply boundary conditions: when t=0, B=0
0 = π ! + π! β π!π!
π! + π!
0 = π ! + π! β π!
π! + π!
π! = π ! + π!
*Plug c1 back in
π΅ = π ! + π! β π ! + π! π!! !!!!!
π! + π!
π© = (πΉπ½ + ππ)πβ π!π ππ!ππππ + ππ
4.
t = v/r = 1000 mL/7.72 mL/min = 130 min = 2.17 hr 100 mg dose gives a drug mass flow rate of:
π ! = 46.32[mg/h]
Since π΅ = (π ! + π!)!!!!! !!!!!
!!!!!
π΅ = (46.32 ππ/β + 0.00025 ππ/β)1β π!!.!"#! 0.041 !!!!! !.!"#!!!!
0.041 βπ!! + 0.082 βπ!!
π© = ππ.π ππ
π΅ππ£ππππ§π’πππ πππππππ‘πππ‘πππ ππ πππππ = 88.2 ππ5500 ππ = π.πππ
ππππ
5.
π‘!!"# = 20 πππ¦π π΅!"#$ = 0.008ππππ β 5500 ππ = 44.0 ππ
ππ’ππππ ππ βπππ ππππ ππ¦ππππ = π‘
π‘!!"#
πππππ‘πππ ππ ππππππππ πππππππ‘πππ‘πππ πππππππππ =π΅!"#$π΅
Therefore:
Bsafe = B !!
! = B !
!
!!!!"# where x is the number of half life cycles
π΅ β12
!!!!"#
= π΅!"#$
12
!!!!"#
=π΅!"#$ π΅
π‘
π‘!!"#ln
12 = ln
π΅!"#$ π΅
π‘ = lnπ΅!"#$ π΅ β
π‘!!"#
ln 12
π‘ = ln 44.0ππ 88.2 ππ β
20 πππ¦π
ln 12
π = ππ π πππ
Appendix: code for generating graphs for Part I problem 4 part 1 %graph concentrations of becvacizumab and ranibizumab vs depth of hydrogel wall close all
figure hold on %variables L = .72; %thickness of hydrogel wall Dsb = 4.1e-Ββ5; % bevacizumab diffusion constant Rb = 7.943e-Ββ7; % bevacizumab degradation rate Dsr = 6.7e-Ββ5; %ranibizumab diffusion constant alpha = 3.972e-Ββ4; %constant for ranibizumab degradation rate beta = -Ββ5.516e-Ββ4; %constant for ranibizumab degredation rate Cl = 12.351; %drug concentration in hydrogel %%%%%plotting z = linspace(0,.72,100); k1b = (-ΒβCl/L)-Ββ((Rb*L)/(2*Dsb)); Cb = (Rb/(2*Dsb))*(z.^2) + k1b*z + Cl; plot(z,Cb,'r') k1r = ((-Ββalpha*L)/(2*Dsr))-Ββ((beta*(L^2))/(6*Dsr))-Ββ(Cl/L); Cr = ((alpha/(2*Dsr))*(z.^2))+((beta/(6*Dsr))*(z.^3)) + (k1r*z) + Cl; plot(z,Cr,'b') axis([0 0.72 0 12.3531]) title('Concentration of Bevacizumab and Ranibizumab vs depth in hydrogel') xlabel('depth into hydrogel wall [mm]') ylabel('drug concentration [ug/mm^3]') legend('Bevacizumab','Ranibizumab') grid on hold off %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%