Presentation on theme: "Background and Controversies in Dosing and Adjustment of Chemotherapy Agents Dana Cole, BScPharm, PharmD Oncology Drug Information Specialist BC Cancer."— Presentation transcript:
Background and Controversies in Dosing and Adjustment of Chemotherapy Agents Dana Cole, BScPharm, PharmD Oncology Drug Information Specialist BC Cancer Agency Partners in Cancer Care Conference November 30, 2002
Outline How Doses are Established BSA Dose Intensity Dose Scheduling How Doses are Adjusted Hematologic toxicity Hepatic dysfunction Renal dysfunction Other toxicities
BCCA Protocol Summary for Palliative Therapy for Advanced Breast Cancer using Cyclophosphamide, Methotrexate and Fluorouracil BRAVCMF ELIGIBILITY: Palliative treatment for advanced breast cancer. TESTS: Baseline: CBC & diff, bilirubin, creatinine Before each treatment: CBC & diff If clinically indicated: bilirubin, creatinine TREATMENT: DrugDoseBCCA Administration Guideline cyclophosphamide600 mg/m 2 IV in 100-250 mL NS or D5W over 20-60 min methotrexate40 mg/m 2 IV push fluorouracil (5-FU)600 mg/m 2 IV push Repeat every 21 days x 6-8 cycles.
Body Surface Area - History Pinkel in 1958 examined literature found conventional doses in animals and humans for 5 cytotoxic drugs correlation between animal/human dose and BSA recommended BSA be used in future for dosing No pharmacokinetic or efficacy studies Retrospective look at handful of cases
Body Surface Area - History In 1966, established as means of estimating dose to be used in Phase I trials from animal data Phase II and III trials adopted this convention
Body Surface Area (m 2 ) DuBois & DuBois 1916 BSA = 0.20247 x Ht (m) 0.725 x Wt (kg) 0.425 Boyd 1935 BSA = 0.0003207 x Ht (cm) 0.3 x Wt (g) 0.7285-(0.0188 x log(g) Gehan & George 1970 BSA = 0.0235 x Ht (cm) 0.42246 x Wt (kg) 0.51456 Haycock et al. 1978 BSA = 0.024265 x Ht (cm) 0.3964 x Wt (kg) 0.5378 Mosteller 1987 BSA = Ht (cm) x Wt (kg) 3600
Advantages of Mosteller Formula Easy to remember No error if Wt and Ht are accidentally interchanged Validated against other formulas, 10kg body weight children - use Wt
Disadvantages of BSA Risk of arithmetic error (small) Increases time Increases drug wastage False sense of accuracy (precise but NOT accurate) Suggested that level of inaccuracy may equal magnitude of benefit of adjuvant chemo in a breast cancer patient
Interpatient Variability Activity of CYP 3A4 varies 50-fold add in interactions… Dihydropyrimidine Dehydrogenase (DPD) activity varies 8-fold trial of 5FU treated patients - 80% had ineffective plasma concentrations Biliary excretion affected by multidrug resistance efflux pumps
Conservative estimate Drug elimination varies at least 4-fold between individuals.
Good Correlation with BSA Gemcitabine Clearance and Vd sensitive to BSA Docetaxel Variability in Cl correlates to BSA
Gurney H. Br J Cancer 2002;86:1297-1302 Suggested Guidelines for Dose Calculation Do not use BSA solely. Consider other parameters. Avoid extremes in BSA. Round liberally. Know how drug is eliminated. Check for drug interactions. Consider factors affecting tissue sensitivity. Know that 40% of time BSA calc dose is incorrect. Measure a biological endpoint. Always have doses checked.
Gurney H. Br J Cancer 2002;86:1297-1302. An Alternative Dosing Scheme 1. Determine standard dose 2. Modify pretreatment known differences in metabolism or elimination 3. Adjust next dose according to presence or absence of toxicity.
Assessing for Interactions – Active Metabolites Cyclophosphamide Doxorubicin Epirubicin Irinotecan Methotrexate Tamoxifen
Potential Problems with TDM Drugs often in combination Cost of assays Inconvenience, personnel Skills required for interpretation Errors in sampling, etc Sample every cycle or just first? Blood samples may not reflect action in tissues
The Case of Carboplatin Cleared 70% by glomerular filtration Linear correlation: Cl and GFR AUC correlates with thrombocytopenic nadir
Calvert et al J Clin Oncol 1989;7:1748-56 Derived formula based on renal function Constant used to represent nonrenal Cl Used 51 CrEDTA clearance Better correlation to AUC than with BSA dosing Dose (mg) = target AUC x (GFR + 25)
Challenges in Applying Calvert Formula in Practice 51 CrEDTA assessments not usually done Cockcroft-Gault and Jeliffe equations underestimate GFR, resulting in potential underdosing In patients without “normal” renal function, nonrenal Cl may be higher
Hematological Considerations for Dose Scheduling Lifespan Platelet - 7-10 days Red blood cell - 120 days Neutrophils - 6-12 hours Time from Stem Cell to Mature Neutrophil ~7-10 days
Deciding on Treatment Intervals As short as possible Recovery of bone marrow Supplies mature cells for 8-10 days Onset 9-10th days Lowest (nadir) 14-18 th days Recovery by day 21-28. Usual schedule is q21-28 days.
Dose Intensity Dose Intensity: Amount of drug delivered per unit of time Relative Dose Intensity: Amount relative to an arbitrarily chosen standard Positive relationship between dose intensity and tumour response
CMF for Adjuvant Breast Cancer Bonadonna et al N Engl J Med 1995;332:901-6 386 women with node + breast cancer CMF vs placebo (20 yr F/U) Overall Survival ≥ 85% dose - 55% alive at 20 years 65-84% dose – only 35% alive at 20 years <65% of dose was same as giving placebo!
Dose Intensity of CMF Wood et al. N Engl J Med 1994;330:1253-9. 1572 women with node + breast cancer 3 dose regimens of CMF Standard (6 cycles) 50% higher dose for 4 cycles (equal total dose) 50% less total dose over 6 cycles Significantly longer DFS in standard or high dose No survival advantage of higher dose (plateau effect?)
Dose Adjustment Based on Prognostics? Muss HB, et al. N Engl J Med 1994;330:1260-6. Analyzed 442 women from the Wood trial for HER2-neu status Longer DFS and Overall Survival in high dose group if HER2 positive. Illustrates added importance of dose intensity if higher risk
Organ Systems & Effect of Chemotherapy Rapidly Dividing Gut Mucosa Bone Marrow Ovaries Testes Hair Follicles Slowly Dividing Lung Liver Kidney Endocrine Glands Vascular Endothelium Very Slow/ No Division Muscle Bone Cartilage Nerve
Pharmacokinetic Determinants of Toxicity Genetics Diet Other medications Smoking Alcohol consumption Age Renal Function Hepatic function Pleural Effusion Obesity Amputations Performance Status
Pharmacodynamic Determinants of Toxicity Prior Therapy Age Performance Status Genetics Other medications Comorbidities
Adjustments for Toxicity Due to pharmacokinetics? Adjustment reasonable as similar drug levels achieved Due to pharmacodynamics? Adjustment may only lessen response Often significant dose reduction will have small effect on toxicity and great effect on efficacy
The Challenge: True Hepatic Function Tests Metabolic Capacity Microsomal function Functional hepatic perfusion Galactose elimination capacity Max removal of indocyanine green Aminopyrine demethylation Caffeine Cl Antipyrine Cl Erythromycin breath test Galactose Cl Sorbitol Cl Indocyanine green Cl Sulfobromophthalein Cl
What We Currently Measure Bilirubin marker of impaired excretion, not metabolism AST/ALT hepatocellular damage only, mets Alk Phos bone disease, mets INR/Albumin measures of synthetic ability may be better estimate of metabolic function need to have significant decrease before affected
Challenges in Renal Dosage Adjustments Serum creatinine vs Creatinine Clearance SCr 135 - 185 = 30-65 mL/min protocol states 66% literature 50 or 75% SCr >185 = <30-50 mL/min protocol states alternative drug literature alternative drug or 50% Significant Variability amongst protocols
Take Home Points Consider other factors in addition to BSA Dose Intensity is importance to long term efficacy Significant variability in adjustments for renal dysfunction. Consider INR/albumin in addition to bilirubin to evaluate hepatic dysfunction.
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