The Effects of Oral Contraceptive Pills vs Hormonal Patch on Coagulation Parameters

Twenty-four non-pregnant women 18-35 years of age, who had not been on hormonal contraception for at least 2 months prior to the study or who were least 3 months postpartum and non-lactating, were enrolled in this study between October 2003 and February 2005. The study protocol was approved by the University of Vermont Institutional Review Board, and all participants gave written informed consent. Exclusion criteria for participation were personal or family history of venous thromboembolism or coagulation disorders, pregnancy, uncontrolled hypertension, cardiovascular disease, complicated migraine headaches, breast cancer, diabetes, abnormal uterine bleeding, liver disease, or desire for pregnancy in less than 6 months.

This study was a randomized investigator-blind, cross-over clinical trial. The daily oral contraceptive contained 35 micrograms ethinyl estradiol and 250 micrograms norgestimate (Ortho Cylen®). The weekly transdermal hormonal contraceptive contained 0.75 milligrams ethinyl estradiol and 6.0 milligrams norelgestromin (Ortho Evra®). Norelgestromin is the active progestin metabolite of orally administered norgestimate. For the oral form the average steady state plasma concentration (Css) of ethinyl estradiol was 49.3 picograms/milliliter and of norelgestromin 0.73 nanograms/milliliter and for the transdermal form these concentrations were 80.0 picograms/milliliter and 0.888 nanograms/milliliter, respectively at the end of the second month of use.17 The average weekly exposure, calculated as area under the curve (AUC0-168pg.h/mL) for ethinyl estradiol was 55% higher with transdermal than with the oral contraceptive. The maximum ethinyl estradiol and norelgestromin levels (Cmax) were 133 pg/ml and 2.16 ng/ml for the oral form and 97.4 pg/ml and 1.12 ng/ml for the transdermal form.17 The application location of the patch does not alter the Css or Cmax.18 Medications were supplied to the patients by a research nurse and the completed packets were returned to document compliance. The contraceptives and the funding for the study were supplied by research grants from the University of Vermont Department of Obstetrics and Gynecology.

Prior to enrollment, participants underwent a physical examination including gynecologic examination. Women on hormonal contraceptives at recruitment were given barrier contraceptives for two months prior to starting the study. Participants were assigned a random identification number which indicated the sequence in which transdermal or oral contraceptives would be given. The daily oral contraceptive or weekly transdermal contraceptive was given with the typical dosing of three weeks active treatment followed by one week without hormone use. Following the first two months of hormonal contraceptive, each participated returned to barrier contraceptive for a two month washout period, then received two months of the alternative hormonal contraceptive. The investigators were blind to the order of contraceptive assigned for each participant.

There were four phlebotomies performed for each subject. Blood was drawn on menstrual cycle day 18 to 21 prior to the study, within 4 days of either the last pill or removal of the last patch, and on cycle day 18 to 21 in the second month of the washout period. Blood was collected using standardized methods with minimal stasis into vacutainer tubes, immediately placed on ice and centrifuged at 4oC. Plasma and serum was stored at -70oC until completion of the study.

Laboratory assays were performed in batch with each participant's serial samples analyzed in the same run. D-dimer, von Willebrand factor and antithrombin were measured using immuno-turbidometric assays on the STA-R analyzer (Liatest D-Di, Liatest vWF, Liatest ATIII, Diagnostica Stago, Parsippany, NJ) with coefficients of variation (CVs) of 3.0%, 3.85%, and 4.0-8.0% respectively. Factor VIII was determined by measuring the clotting time of the sample in factor VIII deficient plasma (STA-Deficient VIII; Diagnostica Stago, Parsippany, NJ) with a CV of 3.5%. Free and total protein S were measured by immunoassay (Asserachrom Free and Total Protein S, Diagnostica Stago, Parsippany, NJ) with CVs of 14.0% and 4.0% respectively. Fibrinogen and C-reactive protein were measured by immunonephelometry using the BNII instrument (N Antiserum to Human Fibrinogen, N High Sensitivity CRP, Dade-Behring, Deerfield, IL) with CVs of 2.3-4% and 2.6% respectively.