Effect of rofecoxib on the pharmacokinetics of chronically administered oral contraceptives in healthy female volunteers

Concomitant Administration of Lumiracoxib and a Triphasic Oral Contraceptive Does Not Affect Contraceptive Activity or Pharmacokinetic Profile

This study evaluated the effect of lumiracoxib on the pharmacokinetics and pharmacodynamics of ethinyl estradiol (EE) and levonorgestrel (LN) in Triphasil-28 (a triphasic oral contraceptive). Females stabilized on Triphasil-28 continued on Triphasil-28 alone for another month (Treatment Period 1), then also received lumiracoxib (400 mg daily) or placebo for 28 days each (Periods 2 and 3) in a double-blind crossover design. Plasma pharmacokinetic profiles were assessed on Day 21 of Periods 2 and 3. Progesterone and plasma sex hormone binding globulin (SHBG) concentrations were measured before and 2 hours after Triphasil-28 administration on Day 21 of all three treatment periods. Lumiracoxib had no significant effect on EE or LN pharmacokinetics or on progesterone or SHBG concentrations, indicating that anovulation and Triphasil-28 effectiveness was maintained. Adverse events were similar for lumiracoxib and placebo. Therefore, no clinically important consequences are anticipated if lumiracoxib is coadministered with oral contraceptives containing EE or LN.

Effect of vicriviroc with or without ritonavir on oral contraceptive pharmacokinetics: a randomized, open-label, parallel-group, fixed-sequence crossover trial in healthy women

BACKGROUND

Because women of childbearing potential represent 20% to 25% of the HIV population, it is important to determine any potential drug interactions between vicriviroc, an antiretroviral agent, and an oral contraceptive (OC) to provide guidance on any potential dose adjustments.

OBJECTIVE

The primary study objective was to determine the effect of vicriviroc, a C-C chemokine receptor type 5 inhibitor, alone or in the presence of ritonavir, on the pharmacokinetics (AUC and C(max)) of the study OC (ethinyl estradiol [EE] 0.035 mg + norethindrone [NET] 1 mg). A secondary objective was to monitor the safety and tolerability of vicriviroc plus an OC with and without ritonavir.

METHODS

This was a randomized, open-label, parallel-group, single-center study with a fixed-sequence crossover design. Female subjects were randomized into 2 groups and treated for 2 menstrual cycles. In cycle 1, all received the OC alone, per standard 28-day pack instructions. On the first 10 days of cycle 2, group 1 received OC + vicriviroc and group 2 received OC + ritonavir; on the following 11 days, both groups received OC + vicriviroc + ritonavir. Blood samples were collected up to 24 hours after dosing on prespecified days. Pharmacokinetic parameters, including AUC(0-24), C(max), and C(min), were calculated using noncompartmental methods, and drug interactions were evaluated using an ANOVA model by treatment group. Adverse events were collected using physical examination, vital sign measurements, clinical laboratory analysis, electrocardiography, and questioning at predefined time points throughout the study to assess the safety profile.

RESULTS

Twenty-seven subjects were enrolled (26 white, 1 black). The median age and body mass index were 21 years (range, 18-36 years) and 24.5 kg/m(2) (range, 19.1-31.3 kg/m(2)), respectively. Twenty-one subjects completed the study and were included in the pharmacokinetic analysis; 4 discontinued for reasons unrelated to study drug and 2 discontinued because of adverse events. Vicriviroc had little effect on the pharmacokinetics of the OC. EE mean ratio estimates for C(max) and AUC(0-24) compared with OC administered alone were 91% and 97%, respectively, and for NET were 106% and 93%. Subjects receiving ritonavir, alone or with vicriviroc, experienced decreases in exposure of EE (C(max) mean ratio estimates, 89% and 76%; AUC(0-24) mean ratio estimates, 71% each, for ritonavir alone and ritonavir with vicriviroc, respectively) and, to a lesser extent, decreases in NET (C(max) mean ratio estimates 89% each; AUC(0-24) mean ratio estimates: 93% and 83%, for ritonavir alone and ritonavir with vicriviroc, respectively). Twenty-two of 27 (81%) subjects reported ≥1 treatment-emergent adverse event (TEAE). During cycle 1, TEAEs were reported for 18 of 27 (67%) subjects while receiving OC alone and for 3 of 24 (13%) subjects while receiving placebo OC. During cycle 2, TEAEs were reported for 8 of 12 (67%) subjects while receiving vicriviroc with OC, 4 of 12 (33%) subjects while receiving ritonavir with OC, 7 of 22 (32%) subjects while receiving vicriviroc + ritonavir with OC, and 2 of 22 (9%) subjects while receiving placebo OC. The most commonly reported TEAE was headache (vicriviroc + OC, n = 1; ritonavir + OC, n = 3; vicriviroc + ritonavir + OC, n = 2; OC alone, n = 12; placebo OC, n = 2). No TEAEs were considered severe.

CONCLUSIONS

In this population of healthy female subjects, vicriviroc had little effect on the pharmacokinetics of EE or NET, whereas ritonavir, alone or with vicriviroc, was associated with consistent decrease in exposure of EE and a lesser decrease in NET.

Pharmacokinetics of rofecoxib: a specific cyclo-oxygenase-2 inhibitor

Rofecoxib is a commonly used specific cyclo-oxygenase-2 (COX-2) inhibitor. Rofecoxib has high bioavailability, poor aqueous solubility, an elimination half-life suitable for daily administration and a volume of distribution approximating body mass. Species-specific, predominantly hepatic, metabolism occurs, with novel enterohepatic circulation in rats and O-glucuronidation by uridine diphosphate-glucuronosyl transferase (UGT) 2B7 and 2B15 in human liver microsomes. Discrepancies in studies of postoperative analgesia can be putatively explained by known pharmacokinetics. Changes in rofecoxib disposition and pharmacokinetics are evident between races, in elderly patients, in patients with chronic renal insufficiency and in patients with mild to moderate hepatic impairment. Despite the selective action of COX-2 inhibitors, there remains the potential for significant drug interactions. Rofecoxib has been shown to have interactions with rifampicin (rifampin), warfarin, lithium and angiotensin converting enzyme (ACE) inhibitors and theophylline. COX-2 inhibitors represent a major therapeutic advance in terms of gastrointestinal safety; however, long-term safety in other organ systems and with concomitant drug administration still remain to be proven.

Rofecoxib: an update on physicochemical, pharmaceutical, pharmacodynamic and pharmacokinetic aspects

Rofecoxib (MK-966) is a new generation non-steroidal anti-inflammatory agent (NSAID) that exhibits promising anti-inflammatory, analgesic and antipyretic activity. It selectively inhibits cyclooxygenase (COX)-2 isoenzyme in a dose-dependent manner in man. No significant inhibition of COX-1 is observed with rofecoxib up to doses of 1000 mg. The pharmacokinetics of rofecoxib has been found to be complex and variable. Mean oral bioavailability after single dose of rofecoxib (12.5, 25 or 50 mg) is 93% with t(max) varying widely between 2 and 9 h. It is highly plasma-protein bound and is metabolized primarily by cytosolic reductases to inactive metabolites. Rofecoxib is eliminated predominantly by hepatic metabolism with a terminal half-life of approximately 17 h during steady state. Various experimental models and clinical studies have demonstrated rofecoxib to be superior, or at least equivalent, in anti-inflammatory, analgesic and antipyretic efficacy to comparator nonselective NSAIDs in osteoarthritis, rheumatoid arthritis and other pain models. Emerging evidence suggests that rofecoxib may also find potential use as supportive therapy in various pathophysiologic conditions like Alzheimer's disease, and in various malignant tumours and polyps, where COX-2 is overly expressed. Rofecoxib is generally well-tolerated. Analysis of data pooled from several trials suggests that rofecoxib is associated with fewer incidences of clinically symptomatic gastrointestinal ulcers and ulcer complications vis-à-vis conventional NSAIDs. However, this gastropreserving effect may be negated by concurrent use of low-dose aspirin for cardiovascular risk reduction. Rofecoxib tends to show similar tolerability for renal and cardiothrombotic events as compared with nonnaproxen nonselective NSAIDs. No clinically significant drug interaction has been reported for rofecoxib except with diuretics, where it reverses their salt-wasting effect and thus can be clinically exploited in electrolyte-wasting disorders. There is only modest information about the physicochemical and pharmaceutical aspects of rofecoxib. Being poorly water soluble, its drug delivery has been improved using varied formulation approaches. Although it is stable in solid state, rofecoxib is photosensitive and base-sensitive in solution form with its degradation mechanistics elucidated. Analytical determinations of rofecoxib and its metabolites in biological fluids employing HPLC with varied types of detectors have been reported. Isolated studies have also been published on the chromatographic and spectrophotometric assay of rofecoxib and its degradants in bulk samples and pharmaceutical dosage forms. The current article provides an updated overview on the physicochemical, pharmaceutical, pharmacokinetic and pharmacodynamic vistas of rofecoxib.

COX-2 inhibitors and their role in gynecology

This review summarizes current knowledge about the roles of cyclooxygenases and prostaglandins in reproductive medicine. With the development of COX-2 specific inhibitors, new therapeutic options are available to obstetricians and gynecologists, offering better-tolerated alternatives to conventional NSAIDs. The analgesic effectiveness of COX-2 specific inhibitors is well established, and they are already in use in a range of painful conditions. Both celecoxib and valdecoxib are indicated for the treatment of primary dysmenorrhea, and may be effective in postoperative pain, including hysterectomy, and pain associated with endometriosis. There is also speculation that COX-2 specific inhibitors may be effective tocolytic agents without the risks to the fetus seen with conventional NSAIDs. The role of COX-2 in oncogenesis is also under investigation, and COX-2 specific inhibitors may eventually be used in the prevention and treatment of gynecologic malignancies.

TARGET AUDIENCE

Obstetricians & Gynecologists, Family Physicians Learning Objectives: After completion of this article, the reader will be able to describe the two types of cylooxygenase enzymes (COX), to list the effects and side effects of NSAIDs and COX-2 medications, and to outline the various changes in COX expression during pregnancy.