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Ribavirin Interferon alfa 2b, recombinant
REBETOL ® REBETOL is Schering Corporation’s brand name for ribavirin, a nucleoside analog with antiviral activity. The chemical name of ribavirin is 1-J-D-ribofuranosyl-1H-1,2,4-triazole-3-carboxamide. Ribavirin is a white, crystalline powder. It is freely soluble in water and slightly soluble in anhydrous alcohol. The empirical formula is C8H12N4O5 and the molecular weight is 244.21. REBETOL Capsules consist of a white powder in a white, opaque, gelatin capsule. Each capsule contains 200 mg ribavirin and the inactive ingredients microcrystalline cellulose, lactose monohydrate, croscarmellose sodium, and magnesium stearate. The capsule shell consists of gelatin, sodium lauryl sulfate, silicon dioxide, and titanium dioxide. The capsule is printed with edible blue pharmaceutical ink which is made of shellac, anhydrous ethyl alcohol, isopropyl alcohol, n-butyl alcohol, propylene glycol, ammonium hydroxide, and FD& C Blue #2 aluminum lake. INTRON ® A INTRON A is Schering Corporation’s brand name for interferon alfa-2b, recombinant, a purified, sterile, recombinant interferon product. Interferon alfa-2b, recombinant has been classified as an alpha interferon and is a water-soluble protein composed of 165 amino acids with a molecular weight of 19,271 daltons produced by recombinant DNA techniques. It is obtained from the bacterial fermentation of a strain of Escherichia coli bearing a genetically engineered plasmid containing an interferon alfa-2b gene from human leukocytes. The fermentation is carried out in a defined nutrient medium containing the antibiotic tetracycline hydrochloride at a concentration of 5 to 10 mg/L; the presence of this antibiotic is not detectable in the final product. INTRON A Injection is a clear, colorless solution. The 3 million IU vial of INTRON A Injection contains 3 million IU of interferon alfa-2b, recombinant per 0.5 mL. The 18 million IU multidose vial of INTRON A Injection contains a total of 22.8 million IU of interferon alfa-2b, recombinant per 3.8 mL (3 million IU/0.5 mL) in order to provide the delivery of six 0.5 mL doses, each containing 3 million IU of INTRON A (for a label strength of 18 million IU). The 18 million IU INTRON A Injection multidose pen contains a total of 22.5 million IU of interferon alfa-2b, recombinant per 1.5 mL (3 million IU/0.2 mL) in order to provide the delivery of six 0.2 mL doses, each containing 3 million IU of Intron A (for a label strength of 18 million IU). Each mL also contains 7.5 mg sodium chloride, 1.8 mg sodium phosphate dibasic, 1.3 mg sodium phosphate monobasic, 0.1 mg edetate disodium, 0.1 mg polysorbate 80, and 1.5 mg m-cresol as a preservative. Based on the specific activity of approximately 2.6 x 10 IU/mg protein as measured by HPLC assay, the corresponding quantities of interferon alfa-2b, recombinant in the vials and pen described above are approximately 0.012 mg, 0.088 mg, and 0.087 mg protein, respectively. Mechanism of Action Ribavirin/Interferon alfa-2b, recombinant The mechanism
of inhibition of hepatitis
C virus (HCV) RNA
by combination therapy
with REBETOL and INTRON A has not been established.
Pharmacokinetics Interferon alfa-2b, recombinant Single and multiple dose pharmacokinetic properties of INTRON A (interferon alfa-2b, recombinant) are summarized in Table 1 . Following a single 3 million IU (MIU) subcutaneous dose in 12 patients with chronic hepatitis C, mean (% CV*) serum concentrations peaked at 7 (44%) hours. Following 4 weeks of subcutaneous dosing with 3 MIU three times a week (TIW), interferon serum concentrations were undetectable predose. However, a twofold increase in bioavailability was noted upon multiple dosing of interferon; the reason for this is unknown. Mean half-life values following single- and multiple- dose administrations were 6.8 (24%) hours and 6.5 (29%) hours, respectively. Ribavirin Single- and multiple- dose pharmacokinetic properties in adults with chronic hepatitis C are summarized in Table 1 . Ribavirin was rapidly and extensively absorbed following oral administration. However, due to first-pass metabolism, the absolute bioavailability averaged 64% (44%). There was a linear relationship between dose and AUCtf (AUC from time zero to last measurable concentration) following single doses of 200-1200 mg ribavirin. The relationship between dose and Cmax was curvilinear, tending to asymptote above single doses of 400-600 mg. Upon multiple oral dosing, based on AUC12 hr , a sixfold accumulation of ribavirin was observed in plasma. Following oral dosing with 600 mg BID, steady-state was reached by approximately 4 weeks, with mean steady-state plasma concentrations of 2200 (37%) ng/mL. Upon discontinuation of dosing, the mean half-life was 298 (30%) hours, which probably reflects slow elimination from nonplasma compartments. Effect of Food on Absorption of Ribavirin Both AUC tf and Cmax increased by 70% when Rebetol Capsules were administered with a high-fat meal (841 kcal, 53.8 g fat, 31.6 g protein, and 57.4 g carbohydrate) in a single-dose pharmacokinetic study. There are insufficient data to address the clinical relevance of these results. Clinical efficacy studies were conducted without instructions with respect to food consumption. (See DOSAGE AND ADMINISTRATION .) Effect of Antacid on Absorption of Ribavirin Coadministration with an antacid containing magnesium, aluminum, and simethicone (Mylanta®) resulted in a 14% decrease in mean ribavirin AUCtf. The clinical relevance of results from this single-dose study is unknown.
** IU. hr/mL for Intron A and ng. hr/mL for Rebetol † data obtained from a single-dose pharmacokinetic study using 14C labeled ribavirin; N = 5 †† N = 6 *** n = 11 Ribavirin transport into nonplasma compartments has been most extensively studied in red blood cells, and has been identified to be primarily via an es-type equilibrative nucleoside transporter. This type of transporter is present on virtually all cell types and may account for the extensive volume of distribution. Ribavirin does not bind to plasma proteins. Ribavirin has two pathways of metabolism: (i) a reversible phosphorylation pathway in nucleated cells; and (ii) a degradative pathway involving deribosylation and amide hydrolysis to yield a triazole carboxylic acid metabolite. Ribavirin and its triazole carboxamide and triazole carboxylic acid metabolites are excreted renally. After oral administration of 600 mg of 14 C-ribavirin, approximately 61% and 12% of the radioactivity was eliminated in the urine and feces, respectively, in 336 hours. Unchanged ribavirin accounted for 17% of the administered dose. Results of in vitro studies using both human and rat liver microsome preparations indicated little or no cytochrome P450 enzyme mediated metabolism of ribavirin, with minimal potential for P450 enzyme-based drug interactions. No pharmacokinetic interactions were noted between INTRON A Injection and REBETOL Capsules in a multiple-dose pharmacokinetic study. Special Populations Renal Dysfunction The pharmacokinetics of ribavirin were assessed after administration of a single oral dose (400 mg) of ribavirin to subjects with varying degrees of renal dysfunction. The mean AUCtf value was threefold greater in subjects with creatinine clearance values between 10 to 30 mL/min when compared to control subjects (creatinine clearance >90 mL/min). This appears to be due to reduction of apparent clearance in these patients. Ribavirin was not removed by hemodialysis. Rebetol is not recommended for patients with severe renal impairment (see WARNINGS ). Hepatic Dysfunction The effect of hepatic dysfunction was assessed after a single oral dose of ribavirin (600 mg). The mean AUC tf values were not significantly different in subjects with mild, moderate, or severe hepatic dysfunction (Child- Pugh Classification A, B, or C), when compared to control subjects. However, the mean C max values increased with severity of hepatic dysfunction and was twofold greater in subjects with severe hepatic dysfunction when compared to control subjects. Pediatric Patients Pharmacokinetic evaluations for pediatric subjects have not been performed. Elderly Patients Pharmacokinetic evaluations for elderly subjects have not been performed. Gender There were no clinically significant pharmacokinetic differences noted in a single-dose study of eighteen male and eighteen female subjects. * In this section
of the label, numbers in parenthesis indicate % coefficient
of variation.
REBETOL (ribavirin, USP) Capsules is indicated in combination with INTRON A (interferon alfa-2b, recombinant) Injection for the treatment of chronic hepatitis C in patients with compensated liver disease previously untreated with alpha interferon or who have relapsed following alpha interferon therapy. Description of Clinical Studies Previously Untreated Patients Adults with compensated chronic hepatitis C and detectable HCV RNA (assessed by a central laboratory using a research based RT-PCR assay) who were previously untreated with alpha interferon therapy were enrolled into two multicenter, double-blind trials (US and International) and randomized to receive REBETOL Capsules 1200 mg/day (1000 mg/day for patients weighing £75kg) plus INTRON A Injection 3 MIU TIW or INTRON A Injection plus placebo for 24 or 48 weeks followed by 24 weeks of off-therapy follow-up. The International study did not contain a 24 week INTRON A plus placebo treatment arm. The US study enrolled 912 patients who, at baseline, were 67% male, 89% caucasian with a mean Knodell HAI score (I+II+III) of 7.5, and 72% genotype 1. The International study, conducted in Europe, Israel, Canada, and Australia, enrolled 799 patients (65% male, 95% caucasian, mean Knodell score 6.8, and 58% genotype 1). Study results are summarized in Table 2 . Table 2. Virologic and Histologic Responses: Previously Untreated Patients*
1. Defined as HCV RNA below limit of detection using a research based RT-PCR assay at end of treatment and during follow-up period. 2. Defined as posttreatment (end of follow-up) minus pretreatment liver biopsy Knodell HAI score (I+II+III) improvement of ³2 points. Of patients who had not achieved HCV RNA below the limit of detection of the research based assay by week 24 of REBETOL/INTRON A treatment, less than 5% responded to an additional 24 weeks of combination treatment. Among patients with HCV Genotype 1 treated with REBETOL/INTRON A therapy who achieved HCV RNA below the detection limit of the research based assay by 24 weeks, those randomized to 48 weeks of treatment had higher virologic responses compared to those in the 24 week treatment group. There was no observed increase in response rates for patients with HCV non-genotype 1 randomized to REBETOL/INTRON A therapy for 48 weeks compared to 24 weeks. Relapse Patients Patients with compensated chronic hepatitis C and detectable HCV RNA (assessed by a central laboratory using a research based RT-PCR assay) who had relapsed following one or two courses of interferon therapy (defined as abnormal serum ALT levels) were enrolled into two multicenter, double-blind trials (US and International) and randomized to receive REBETOL 1200 mg/day (1000 mg/day for patients weighing £75 kg) plus INTRON A 3 MIU TIW or INTRON A plus placebo for 24 weeks followed by 24 weeks of off-therapy follow-up. The US study enrolled 153 patients who, at baseline, were 67% male, 92% caucasian with a mean Knodell HAI score (I+II+III) of 6.8, and 58% genotype 1. The International study, conducted in Europe, Israel, Canada, and Australia, enrolled 192 patients (64% male, 95% caucasian, mean Knodell score 6.6, and 56% genotype 1). Study results are summarized in table 3 . Table 3. Virologic and Histologic Responses: Relapse Patients*
1. Defined as HCV RNA below limit of detection using a research based RT-PCR assay at end of treatment and during follow-up period. 2. Defined as post treatment (end of follow-up) minus pretreatment liver biopsy Knodell HAI score (I+II+III) improvement of ³2 points. Virologic and histologic responses were similar among male and female patients in both the previously untreated and relapse studies.
INTRON A Injection should be administered subcutaneously and Rebetol Capsules should be administered orally (see Table 6). The recommended dose of REBETOL Capsules depends on the patient’s body weight. The recommended doses of Rebetol and INTRON A are given in Table 6. The recommended duration
of treatment for patients
previously untreated with interferon
is 24 to 48 weeks. The duration
of treatment should
be individualized to the patient
depending on baseline
disease characteristics,
response to therapy,
and tolerability of the regimen
(see In patients who relapse following interferon therapy, the recommended duration of treatment is 24 weeks. There are no safety and efficacy data on treatment for longer than 24 weeks in the relapse patient population. Table 6. Recommended Dosing
Dose Modifications ( TABLE 7 ) In clinical trials, approximately 26% of patients required modification of their dose of REBETOL Capsules, INTRON A Injection, or both agents. If severe adverse reactions or laboratory abnormalities develop during combination REBETOL/INTRON A therapy the dose should be modified, or discontinued if appropriate, until the adverse reactions abate. If intolerance persists after dose adjustment, REBETOL/INTRON A therapy should be discontinued. REBETOL/INTRON A therapy should be administered with caution to patients with pre-existing cardiac disease. Patients should be assessed before commencement of therapy and should be appropriately monitored during therapy. If there is any deterioration of cardiovascular status, therapy should be stopped. (See WARNINGS. ) For patients with a history of stable cardiovascular disease, a permanent dose reduction is required if the hemoglobin decreases by ³2 g/dL during any 4-week period. In addition, for these cardiac history patients, if the hemoglobin remains <12 g/dL after 4 weeks on a reduced dose, the patient should discontinue combination REBETOL/INTRON A therapy. It is recommended that a patient whose hemoglobin level falls below 10 g/dL have his/her REBETOL dose reduced to 600 mg daily (1 x 200 mg capsule AM , 2 x 200 mg capsules PM ). A patient whose hemoglobin level falls below 8.5 g/dL should be permanently discontinued from REBETOL/INTRON A therapy. (See WARNINGS.) It is recommended that a patient who experiences moderate depression (persistent low mood, loss of interest, p.o. self image, and/or hopelessness) have his/her INTRON A dose temporarily reduced and/or be considered for medical therapy. A patient experiencing severe depression or suicidal ideation/attempt should be discontinued from REBETOL/INTRON A therapy and followed closely with appropriate medical management. (See WARNINGS.) TABLE 7. Guidelines for Dose Modifications
Administration of INTRON A Injection At the discretion of the physician, the patient may self-administer the INTRON A. (See illustrated MEDICATION GUIDE for instructions.) The Intron A Injection is supplied as a clear and colorless solution. The appropriate INTRON A dose should be withdrawn from the vial or set on the multidose pen and injected subcutaneously. After administration of INTRON A Injection, it is essential to follow the procedure for proper disposal of syringes and needles. (See MEDICATION GUIDE for detailed instructions.)
†† This is a multidose pen which contains a total of 22.5 million IU of interferon alfa-2b, recombinant per 1.5 mL in order to provide the delivery of six 0.2-mL doses, each containing 3 million IU of interferon alfa-2b, recombinant (for a label strength of 18 million IU). Parenteral drug products should be inspected visually for particulate matter and discoloration prior to administration, whenever solution and container permit. INTRON A Injection may be administered using either sterilized glass or plastic disposable syringes. Stability INTRON A Injection provided in vials is stable at 35o C(95o F) for up to 7 days and at 30o C (86o F) for up to 14 days. INTRON A Injection provided in a multidose pen is stable at 30o C (86o F) for up to 2 days. The solution is clear and colorless. HOW SUPPLIED REBETOL 200-mg Capsules are white, opaque capsules with REBETOL, 200 mg, and the Schering Corporation logo imprinted on the capsule shell; the capsules are packaged in blisters. INTRON A Injection is a clear, colorless solution packaged in single dose and multidose vials, and a multidose pen. INTRON A Injection and REBETOL Capsules are available in the following combination package presentations:
Storage Conditions Store the REBETOL Capsules plus INTRON A Injection combination package refrigerated between 2ºC and 8ºC (36ºF and 46º F). When separated, the individual carton of REBETOL Capsules should be stored refrigerated between 2º C; and 8ºC (36ºand 46ºF) or at 25ºC (77ºF); excursions are permitted between 15 and 30ºC (59º and 86ºF). When separated, the individual carton or vial
of INTRON A Injection and the INTRON A Multidose Pen should be stored
refrigerated between 2º and 8ºC
(36º and 46ºF).
The safety of combination REBETOL/INTRON A therapy was evaluated in controlled trials of 1010 HCV-infected adults who were previously untreated with interferon therapy and were subsequently treated for 24 or 48 weeks with combination REBETOL/INTRON A therapy and in 173 HCV-infected patients who had relapsed after interferon therapy and were subsequently treated for 24 weeks with combination REBETOL/INTRON A therapy. (See INDICATIONS, Description of Clinical Studies) Overall, 19% and 6% of previously untreated and relapse patients, respectively, discontinued therapy due to adverse events in the combination arms compared to 13% and 3% in the interferon arms. The primary toxicity of ribavirin is hemolytic anemia. Reductions in hemoglobin levels occurred within the first 1-2 weeks of therapy (see WARNINGS). Cardiac and pulmonary events associated with anemia occurred in approximately 10% of patients treated with REBETOL/INTRONA therapy. (See WARNINGS.) The most common psychiatric events occurring in US studies of previously untreated and relapse patients treated with REBETOL/INTRON A therapy, respectively, were insomnia (39%, 26%), depression (34%, 23%), and irritability (27%, 25%). Suicidal behavior (ideation, attempts, and suicides) occurred in 1% of patients. (See WARNINGS.) Selected treatment-emergent adverse events that occurred in the US studies with ³5% incidence are provided in TABLE 4 by treatment group. In general, the selected treatment-emergent adverse events reported with lower incidence in the international studies as compared to the US studies with the exception of asthenia, influenza-like symptoms, nervousness, and pruritus. Table 4. Selected Treatment-Emergent Adverse Events: Previously Untreated and Relapse Patients
Laboratory Values Changes in selected hematologic values (hemoglobin, white blood cells, neutrophils, and platelets) during combination REBETOL/INTRON A treatment are described below (see TABLE 5 ). Hemoglobin Hemoglobin decreases among patients on combination therapy began at Week 1, with stabilization by Week 4. In previously untreated patients treated for 48 weeks the mean maximum decrease from baseline was 3.1 g/dL in the US study and 2.9 g/dL in the International study. In relapse patients the mean maximum decrease from baseline was 2.8 g/dL in the US study and 2.6 g/dL in the International study. Hemoglobin values returned to pretreatment levels within 4 -8 weeks of cessation of therapy in most patients. Neutrophils There were decreases in neutrophil counts in both the combination REBETOL/INTRON A and INTRON A plus placebo dose groups. In previously untreated patients treated for 48 weeks the mean maximum decrease in neutrophil count in the US study was 1.3 x 109/L and in the International study was 1.59 x 109/L. In relapse patients the mean maximum decrease in neutrophil count in the US study was 1.3 x 109/L and in the International study was 1.6 x 109/L. Neutrophil counts returned to pretreatment levels within 4 weeks of cessation of therapy in most patients. Platelets In both previously untreated and relapse patients mean platelet counts generally remained in the normal range in all treatment groups, however, mean platelet counts were 10% to 15% lower in the INTRON A plus placebo group than the REBETOL/INTRON A group. Mean platelet counts returned to baseline levels within 4 weeks after treatment discontinuation. Thyroid Function Of patients who entered the previously untreated (24 and 48 week treatment) and relapse (24 week treatment) studies without thyroid abnormalities, approximately 3% to 6% and 1% to 2%, respectively, developed thyroid abnormalities requiring clinical intervention. Bilirubin and Uric Acid Increases in both bilirubin and uric acid, associated with hemolysis, were noted in clinical trials. Most were moderate biochemical changes and were reversed within 4 weeks after treatment discontinuation. This observation occurs most frequently in patients with a previous diagnosis of Gilbert’s syndrome. This has not been associated with hepatic dysfunction or clinical morbidity. TABLE 5. Selected Hematologic Values During Treatment with REBETOL plus INTRON A: Previously Untreated and Relapse Patients
Pregnancy Category X, may cause
birth defects. See
CONTRAINDICATIONS boxed CONTRAINDICATIONS
AND Anemia HEMOLYTIC Anemia (hemoglobin <10 g/dl) was observed in APPROXIMATELY 10% of REBETOL/INTRON A- treated patients in clinical trials (see adverse reactions laboratory values - hemoglobin ). anemia occurred within 1-2 weeks of initiation of ribavirin therapy. because of this initial acute drop in hemoglobin, it is advised that complete blood counts (cbc) should be obtained pretreatment and at week 2 and week 4 of therapy or more frequently if clinically indicated. Patients should then be followed as clinically appropriate. The anemia associated with REBETOL/INTRON A therapy may result in deterioration of cardiac function and/or exacerbation of the symptoms of coronary disease. Patients should be assessed before initiation of therapy and should be appropriately monitored during therapy. If there is any deterioration of cardiovascular status, therapy should be suspended or discontinued. (See DOSAGE AND ADMINISTRATION. ) Because cardiac disease may be worsened by drug induced anemia, patients with a history of significant or unstable cardiac disease should not use combination REBETOL/INTRON A therapy. (See ADVERSE REACTIONS. ) Similarly, patients with hemoglobinopathies (eg, thalassemia, sickle-cell anemia) should not be treated with combination REBETOL/INTRON A therapy. Psychiatric SEVERE PSYCHIATRIC ADVERSE EVENTS, INCLUDING DEPRESSION AND SUICIDAL BEHAVIOR (SUICIDAL IDEATION, SUICIDAL ATTEMPTS, AND SUICIDES) HAVE OCCURRED DURING COMBINATION REBETOL/INTRON A THERAPY AND WITH INTERFERON ALPHA MONOTHERAPY (including INTRON A therapy), BOTH IN PATIENTS WITH AND WITHOUT A PREVIOUS PSYCHIATRIC ILLNESS. REBETOL/INTRON A therapy should be used with extreme caution in patients with a history of pre-existing psychiatric disorders who report a history of severe depression, and physicians should monitor all patients for evidence of depression. In severe cases, therapy should be stopped and psychiatric intervention sought. In general, the adverse events resolve on cessation of therapy; however, adjunctive psychiatric medications may be required. (See ADVERSE REACTIONS.) Pulmonary Pulmonary symptoms, including dyspnea, pulmonary infiltrates, pneumonitis and pneumonia, including fatality, have been reported during therapy with REBETOL/INTRON A. If there is evidence of pulmonary infiltrates or pulmonary function impairment, the patient should be closely monitored, and if appropriate, combination REBETOL/INTRON A treatment should be discontinued. Other
Exacerbation of autoimmune disease has been reported in patients receiving alpha interferon therapy (including INTRON A therapy). REBETOL/INTRON A therapy should be used with caution in patients with other autoimmune disorders. There have been reports of interferon, including INTRON A (interferon alfa-2b, recombinant), exacerbating pre-existing psoriasis; therefore, combination REBETOL/INTRON A therapy should be used in these patients only if the potential benefit justifies the potential risk. The safety and efficacy of REBETOL/INTRON A therapy has not been established in liver or other organ transplant patients, decompensated hepatitis C patients, patients who are nonresponders to interferon therapy, or patients coinfected with HBV or HIV. The safety and efficacy of REBETOL Capsule monotherapy for the treatment of HIV infection, adenovirus, early RSV infection, parainfluenza, or influenza have not been established and REBETOL Capsules should not be used for these indications. There is no information regarding the use of REBETOL Capsules with other interferons. Information for Patients See PATIENT INFORMATION section. Laboratory Tests The following laboratory tests are recommended for all patients on combination REBETOL/INTRON A therapy, prior to beginning treatment and then periodically thereafter. •Standard hematologic tests - including hemoglobin
(pretreatment, week 2 and week 4 of therapy,
and as clinically appropriate
[see •Blood chemistries - liver function tests and TSH. •Pregnancy - including monthly monitoring for women of childbearing potential. Carcinogenesis and Mutagenesis Carcinogenicity studies with interferon alfa-2b, recombinant have not been performed because neutralizing activity appears in the serum after multiple dosing in all of the animal species tested. Adequate studies to assess the carcinogenic potential of ribavirin in animals have not been conducted. However, ribavirin is a nucleoside analog that has produced positive findings in multiple in vitro and animal in vivo genotoxicity assays, and should be considered a potential carcinogen. Further studies to assess the carcinogenic potential of ribavirin in animals are ongoing. Mutagenicity studies have demonstrated that interferon alfa-2b, recombinant is not mutagenic. Ribavirin demonstrated increased incidences of mutation and cell transformation in multiple genotoxicity assays. Ribavirin was active in the Balb/3T3 In Vitro Cell Transformation Assay. Mutagenic activity was observed in the mouse lymphoma assay, and at doses of 20-200 mg/kg (estimated human equivalent of 1.67-16.7 mg/kg, based on body surface area adjustment for a 60 kg adult; 0.1 - 1 X the maximum recommended human 24-hour dose of ribavirin) in a mouse micronucleus assay. A dominant lethal assay in rats was negative, indicating that if mutations occurred in rats they were not transmitted through male gametes. Impairment of Fertility No reproductive toxicology studies have been performed using interferon alfa-2b, recombinant in combination with ribavirin. However, evidence provided below for interferon alfa-2b, recombinant and ribavirin when administered alone indicate that both agents have adverse effects on reproduction. It should be assumed that the effects produced by either agent alone will also be caused by the combination of the two agents. Interferons may impair human fertility. In studies of interferon alfa- 2b recombinant administration in nonhuman primates, menstrual cycle abnormalities have been observed. Decreases in serum estradiol and progesterone concentrations have been reported in women treated with human leukocyte interferon. In addition, ribavirin demonstrated significant embryocidal and/or teratogenic effects at doses well below the recommended human dose in all animal species in which adequate studies have been conducted. Fertile women and partners of fertile women should not receive combination REBETOL/INTRON A therapy unless the patient and his/her partner are using effective contraception (two reliable forms). Based on a multiple dose half- life (t 1/2 ) of ribavirin of 12 days, effective contraception must be utilized for 6 months posttherapy (eg, 15 half-lives of clearance for ribavirin). Combination REBETOL/INTRON A therapy should be used with caution in fertile men. In studies in mice to evaluate the time course and reversibility of ribavirin- induced testicular degeneration at doses of 15 to 150 mg/kg/day (estimated human equivalent of 1.25 - 12.5 mg/kg/day, based on body surface area adjustment for a 60 kg adult; 0.1 - 0.8 X the maximum human 24- hour dose of ribavirin) administered for 3 or 6 months, abnormalities in sperm occurred. Upon cessation of treatment, essentially total recovery from ribavirin- induced testicular toxicity was apparent within 1 or 2 spermatogenesis cycles. Animal Toxicology Long- term studies in the mouse and rat (18-24 months; doses of 20-75 and 10 - 40 mg/kg/day, respectively estimated human equivalent doses of 1.67-6.25 and 1.43-5.71 mg/kg/day, respectively, based on body surface area adjustment for a 60 kg adult; approximately 0.1 - 0.4 X the maximum human 24-hour dose of ribavirin) have demonstrated a relationship between chronic ribavirin exposure and increased incidences of vascular lesions (microscopic hemorrhages) in mice. In rats, retinal degeneration occurred in controls, but the incidence was increased in ribavirin- treated rats. Pregnancy Category X (see CONTRAINDICATIONS) Interferon alfa-2b, recombinant has been shown to have abortifacient effects in Macaca mulatta (rhesus monkeys) at 15 and 30 million IU/kg (estimated human equivalent of 5 and 10 million IU/kg, based on body surface area adjustment for a 60 kg adult). There are no adequate and well-controlled studies in pregnant women. Ribavirin produced significant embryocidal and/or teratogenic effects in all animal species in which adequate studies have been conducted. Malformations of the skull, palate, eye, jaw, limbs, skeleton, and gastrointestinal tract were noted. The incidence and severity of teratogenic effects increased with escalation of the drug dose. Survival of fetuses and offspring was reduced. In conventional embryotoxicity/teratogenicity studies in rats and rabbits, observed no effect dose levels were well below those for proposed clinical use (0.3 mg/kg/day for both the rat and rabbit; approximately 0.06 X the recommended human 24-hour dose of ribavirin). No maternal toxicity or effects on offspring were observed in a peri/postnatal toxicity study in rats dosed orally at up to 1 mg/kg/day (estimated human equivalent dose of 0.17 mg/kg based on body surface area adjustment for a 60 kg adult; approximately 0.01 X the maximum recommended human 24-hour dose of ribavirin). Treatment and Posttreatment Potential Risk to the Fetus Ribavirin is known to accumulate in intracellular components from where it is cleared very slowly. It is not known whether ribavirin contained in sperm will exert a potential teratogenic effect upon fertilization of the ova. In a study in rats, it was concluded that dominant lethality was not induced by ribavirin at doses up to 200 mg/kg for 5 days (estimated human equivalent doses of 7.14-28.6 mg/kg, based on body surface area adjustment for a 60 kg adult; up to 1.7 X the maximum recommended human dose of ribavirin). However, because of the potential human teratogenic effects of ribavirin, male patients should be advised to take every precaution to avoid risk of pregnancy for their female partners. Women of childbearing potential should not receive combination REBETOL/INTRON A therapy unless they are using effective contraception (two reliable forms) during the therapy period. In addition, effective contraception should be utilized for 6 months posttherapy based on a multiple dose half-life (t 1/2 ) of ribavirin of 12 days. Male patients and their female partners must practice effective contraception (two reliable forms) during treatment with combination REBETOL/INTRON A therapy and for the 6-month posttherapy period (eg, 15 half-lives for ribavirin clearance from the body). If pregnancy occurs in a patient or partner of a patient during treatment or during the 6 months after treatment cessation, physicians are encouraged to report such cases by calling (800) 727-7064. Nursing Mothers It is not known whether REBETOL and INTRON A are excreted in human milk. However, studies in mice have shown that mouse interferons are excreted into the milk. Because of the potential for nursing or to discontinue combination REBETOL/INTRON A therapy, taking into account the importance of the therapy to the mother. Pediatric Use Safety and effectiveness
in pediatric patients
below the age of 18 years
have not been established.
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