What is Famvir and how is it used?
Famvir belongs to a class of drugs called Antivirals, Other.
It is not known if Famvir is safe and effective in children younger than 18 years of age.
What are the possible side effects of Famvir?
Famvir may cause serious side effects including:
- little or no urination,
- swelling in your feet or ankles,
- tiredness, and
- shortness of breath
Famciclovir is a white to pale yellow solid. It is freely soluble in acetone and methanol, and sparingly soluble in ethanol and isopropanol. At 25°C famciclovir is freely soluble (>25% w/v) in water initially, but rapidly precipitates as the sparingly soluble (2%-3% w/v) monohydrate. Famciclovir is not hygroscopic below 85% relative humidity. Partition coefficients are: octanol/water (pH 4.8) P=1.09 and octanol/phosphate buffer (pH 7.4) P=2.08.
FAMVIR tablets contain 125 mg, 250 mg, or 500 mg of famciclovir, together with the following inactive ingredients: hydroxypropyl cellulose, hydroxypropyl methylcellulose, lactose, magnesium stearate, polyethylene glycols, sodium starch glycolate and titanium dioxide.
Immunocompetent Adult Patients
Herpes Labialis (Cold Sores)
FAMVIR is indicated for the treatment of recurrent herpes labialis.
FAMVIR is indicated for the treatment of recurrent episodes of genital herpes. The efficacy of FAMVIR when initiated more than 6 hours after onset of symptoms or lesions has not been established.
FAMVIR is indicated for chronic suppressive therapy of recurrent episodes of genital herpes. The efficacy and safety of FAMVIR for the suppression of recurrent genital herpes beyond 1 year have not been established.
Herpes Zoster (Shingles)
FAMVIR is indicated for the treatment of herpes zoster. The efficacy of FAMVIR when initiated more than 72 hours after onset of rash has not been established.
HIV-Infected Adult Patients
Recurrent Orolabial Or Genital Herpes
FAMVIR is indicated for the treatment of recurrent episodes of orolabial or genital herpes in HIV-infected adults. The efficacy of FAMVIR when initiated more than 48 hours after onset of symptoms or lesions has not been established.
Limitation Of Use
The efficacy and safety of FAMVIR have not been established for:
DOSAGE AND ADMINISTRATION
FAMVIR may be taken with or without food.
Dosing Recommendation In Immunocompetent Adult Patients
Herpes Labialis (Cold Sores)
The recommended dosage of FAMVIR for the treatment of recurrent herpes labialis is 1500 mg as a single dose. Therapy should be initiated at the first sign or symptom of herpes labialis (e.g., tingling, itching, burning, pain, or lesion).
The recommended dosage of FAMVIR for the treatment of recurrent episodes of genital herpes is 1000 mg twice daily for 1 day. Therapy should be initiated at the first sign or symptom of a recurrent episode (e.g., tingling, itching, burning, pain, or lesion).
The recommended dosage of FAMVIR for chronic suppressive therapy of recurrent episodes of genital herpes is 250 mg twice daily.
Herpes Zoster (Shingles)
The recommended dosage of FAMVIR for the treatment of herpes zoster is 500 mg every 8 hours for 7 days. Therapy should be initiated as soon as herpes zoster is diagnosed.
The recommended dosage of FAMVIR for the treatment of recurrent orolabial or genital herpes in HIV-infected patients is 500 mg twice daily for 7 days. Therapy should be initiated at the first sign or symptom of a recurrent episode (e.g., tingling, itching, burning, pain, or lesion).
Because clinical trials are conducted under widely varying conditions, adverse reaction rates observed in the clinical trials of a drug cannot be directly compared with rates in the clinical trials of another drug and may not reflect the rates observed in practice.
The safety of FAMVIR has been evaluated in active-and placebo-controlled clinical studies involving 816 FAMVIR-treated patients with herpes zoster (FAMVIR, 250 mg three times daily to 750 mg three times daily); 163 FAMVIR-treated patients with recurrent genital herpes (FAMVIR, 1000 mg twice daily); 1,197 patients with recurrent genital herpes treated with FAMVIR as suppressive therapy (125 mg once daily to 250 mg three times daily) of which 570 patients received FAMVIR (open-labeled and/or double-blind) for at least 10 months; and 447 FAMVIR-treated patients with herpes labialis (FAMVIR, 1500 mg once daily or 750 mg twice daily). Table 2 lists selected adverse events.
In HIV-infected patients, the most frequently reported adverse events for FAMVIR (500 mg twice daily; n=150) and acyclovir (400 mg, 5x/day; n=143), respectively, were headache (17% vs. 15%), nausea (11% vs. 13%), diarrhea (7% vs. 11%), vomiting (5% vs. 4%), fatigue (4% vs. 2%), and abdominal pain (3% vs. 6%).
The adverse events listed below have been reported during postapproval use of FAMVIR. Because these events are reported voluntarily from a population of uncertain size, it is not always possible to reliably estimate their frequency or establish a causal relationship to drug exposure:
Blood and lymphatic system disorders: Thrombocytopenia
Hepatobiliary disorders: Abnormal liver function tests, cholestatic jaundice
Immune system disorders: Anaphylactic shock, anaphylactic reaction
Skin and subcutaneous tissue disorders: Urticaria, erythema multiforme, Stevens-Johnson syndrome, toxic epidermal necrolysis, angioedema (e.g., face, eyelid, periorbital, and pharyngeal edema), hypersensitivity vasculitis
Cardiac disorders: Palpitations
Potential For FAMVIR To Affect Other Drugs
The steady-state pharmacokinetics of digoxin were not altered by concomitant administration of multiple doses of famciclovir (500 mg three times daily). No clinically significant effect on the pharmacokinetics of zidovudine, its metabolite zidovudine glucuronide, or emtricitabine was observed following a single oral dose of 500 mg famciclovir coadministered with zidovudine or emtricitabine.
An in vitro study using human liver microsomes suggests that famciclovir is not an inhibitor of CYP3A4 enzymes.
No clinically significant alterations in penciclovir pharmacokinetics were observed following single-dose administration of 500 mg famciclovir after pretreatment with multiple doses of allopurinol, cimetidine, theophylline, zidovudine, promethazine, when given shortly after an antacid (magnesium and aluminum hydroxide), or concomitantly with emtricitabine. No clinically significant effect on penciclovir pharmacokinetics was observed following multiple-dose (three times daily) administration of famciclovir (500 mg) with multiple doses of digoxin.
Concurrent use with probenecid or other drugs significantly eliminated by active renal tubular secretion may result in increased plasma concentrations of penciclovir.
The conversion of 6-deoxy penciclovir to penciclovir is catalyzed by aldehyde oxidase. Interactions with other drugs metabolized by this enzyme and/or inhibiting this enzyme could potentially occur. Clinical interaction studies of famciclovir with cimetidine and promethazine, in vitro inhibitors of aldehyde oxidase, did not show relevant effects on the formation of penciclovir. Raloxifene, a potent aldehyde oxidase inhibitor in vitro, could decrease the formation of penciclovir. However, a clinical drug-drug interaction study to determine the magnitude of interaction between penciclovir and raloxifene has not been conducted.
Included as part of the "PRECAUTIONS" Section
Acute Renal Failure
Cases of acute renal failure have been reported in patients with underlying renal disease who have received inappropriately high doses of FAMVIR for their level of renal function. Dosage reduction is recommended when administering FAMVIR to patients with renal impairment [see DOSAGE AND ADMINISTRATION, Use In Specific Populations].
Patient Counseling Information
Advise the patient to read the FDA-approved patient labeling (Patient Information).
There is no evidence that FAMVIR will affect the ability of a patient to drive or to use machines. However, patients who experience dizziness, somnolence, confusion or other central nervous system disturbances while taking FAMVIR should refrain from driving or operating machinery.
Because FAMVIR contains lactose (FAMVIR 125 mg, 250 mg, and 500 mg tablets contain lactose 26.9 mg, 53.7 mg and 107.4 mg, respectively), patients with rare hereditary problems of galactose intolerance, a severe lactase deficiency or glucose-galactose malabsorption should be advised to discuss with their healthcare provider before taking FAMVIR.
Herpes Labialis (Cold Sores)
Patients should be advised to initiate treatment at the earliest sign or symptom of a recurrence of cold sores (e.g., tingling, itching, burning, pain, or lesion). Patients should be instructed that treatment for cold sores should not exceed 1 dose. Patients should be informed that FAMVIR is not a cure for cold sores.
Patients should be informed that FAMVIR is not a cure for genital herpes. There are no data evaluating whether FAMVIR will prevent transmission of infection to others. Because genital herpes is a sexually transmitted disease, patients should avoid contact with lesions or intercourse when lesions and/or symptoms are present to avoid infecting partners. Genital herpes is frequently transmitted in the absence of symptoms through asymptomatic viral shedding. Therefore, patients should be counseled to use safer sex practices.
If episodic therapy for recurrent genital herpes is indicated, patients should be advised to initiate therapy at the first sign or symptom of an episode.
There are no data on safety or effectiveness of chronic suppressive therapy of longer than 1-year duration.
Herpes Zoster (Shingles)
There are no data on treatment initiated more than 72 hours after onset of zoster rash. Patients should be advised to initiate treatment as soon as possible after a diagnosis of herpes zoster.
Carcinogenesis, Mutagenesis, Impairment Of Fertility
Two-year dietary carcinogenicity studies with famciclovir were conducted in rats and mice. An increase in the incidence of mammary adenocarcinoma (a common tumor in animals of this strain) was seen in female rats receiving the high dose of 600 mg/kg/day (1.1 to 4.5x the human systemic exposure at the recommended total daily oral dose ranging between 500 mg and 2000 mg, based on area under the plasma concentration curve comparisons [24 hr AUC] for penciclovir). No increases in tumor incidence were reported in male rats treated at doses up to 240 mg/kg/day (0.7 to 2.7x the human AUC), or in male and female mice at doses up to 600 mg/kg/day (0.3 to 1.2x the human AUC).
Famciclovir and penciclovir (the active metabolite of famciclovir) were tested for genotoxic potential in a battery of in vitro and in vivo assays. Famciclovir and penciclovir were negative in in vitro tests for gene mutations in bacteria (S. typhimurium and E. coli) and unscheduled DNA synthesis in mammalian HeLa 83 cells (at doses up to 10,000 and 5,000 mcg/plate, respectively). Famciclovir was also negative in the L5178Y mouse lymphoma assay (5000 mcg/mL), the in vivo mouse micronucleus test (4800 mg/kg), and rat dominant lethal study (5000 mg/kg). Famciclovir induced increases in polyploidy in human lymphocytes in vitro in the absence of chromosomal damage (1200 mcg/mL). Penciclovir was positive in the L5178Y mouse lymphoma assay for gene mutation/chromosomal aberrations, with and without metabolic activation (1000 mcg/mL). In human lymphocytes, penciclovir caused chromosomal aberrations in the absence of metabolic activation (250 mcg/mL). Penciclovir caused an increased incidence of micronuclei in mouse bone marrow in vivo when administered intravenously at doses highly toxic to bone marrow (500 mg/kg), but not when administered orally.
Impairment Of Fertility
Testicular toxicity was observed in rats, mice, and dogs following repeated administration of famciclovir or penciclovir. Testicular changes included atrophy of the seminiferous tubules, reduction in sperm count, and/or increased incidence of sperm with abnormal morphology or reduced motility. The degree of toxicity to male reproduction was related to dose and duration of exposure. In male rats, decreased fertility was observed after 10 weeks of dosing at 500 mg/kg/day (1.4 to 5.7x the human AUC). The no observable effect level for sperm and testicular toxicity in rats following chronic administration (26 weeks) was 50 mg/kg/day (0.15 to 0.6x the human systemic exposure based on AUC comparisons). Testicular toxicity was observed following chronic administration to mice (104 weeks) and dogs (26 weeks) at doses of 600 mg/kg/day (0.3 to 1.2x the human AUC) and 150 mg/kg/day (1.3 to 5.1x the human AUC), respectively.
Famciclovir had no effect on general reproductive performance or fertility in female rats at doses up to 1000 mg/kg/day (2.7 to 10.8x the human AUC).
Two placebo-controlled studies in a total of 130 otherwise healthy men with a normal sperm profile over an 8-week baseline period and recurrent genital herpes receiving oral FAMVIR (250 mg twice daily) (n=66) or placebo (n=64) therapy for 18 weeks showed no evidence of significant effects on sperm count, motility or morphology during treatment or during an 8-week follow-up.
Use In Specific Populations
Pregnancy Category B
After oral administration, famciclovir (prodrug) is converted to penciclovir (active drug). There are no adequate and well-controlled studies of famciclovir or penciclovir use in pregnant women. No adverse effects on embryofetal development were observed in animal reproduction studies using famciclovir and penciclovir at doses higher than the maximum recommended human dose (MRHD) and human exposure. Because animal reproduction studies are not always predictive of human response, famciclovir should be used during pregnancy only if needed.
In animal reproduction studies, pregnant rats and rabbits received oral famciclovir at doses (up to 1000 mg/kg/day) that provided 2.7 to 10.8 times (rats) and 1.4 to 5.4 times (rabbits) the human systemic exposure based on AUC. No adverse effects were observed on embryo-fetal development. In other studies, pregnant rats and rabbits received intravenous famciclovir at doses (360 mg/kg/day) 1.5 to 6 times (rats) and (120 mg/kg/day) 1.1 to 4.5 times (rabbits) or penciclovir at doses (80 mg/kg/day) 0.3 to 1.3 times (rats) and (60 mg/kg/day) 0.5 to 2.1 times (rabbits) the MRHD based on body surface area comparisons. No adverse effects were observed on embryo-fetal development.
Pregnancy Exposure Reporting
To monitor maternal-fetal outcomes of pregnant women exposed to FAMVIR, Novartis Pharmaceuticals Corporation maintains a FAMVIR Pregnancy Reporting system. Physicians are encouraged to report their patients by calling 1-888-NOW-NOVA (669-6682).
It is not known whether famciclovir (prodrug) or penciclovir (active drug) are excreted in human milk. Following oral administration of famciclovir to lactating rats, penciclovir was excreted in breast milk at concentrations higher than those seen in the plasma. There are no data on the safety of FAMVIR in infants. FAMVIR should not be used in nursing mothers unless the potential benefits are considered to outweigh the potential risks associated with treatment.
The efficacy of FAMVIR has not been established in pediatric patients. The pharmacokinetic profile and safety of famciclovir (experimental granules mixed with OraSweet® or tablets) were studied in 3 open-label studies.
Study 1 was a single-dose pharmacokinetic and safety study in infants 1 month to <1 year of age who had an active herpes simplex virus (HSV) infection or who were at risk for HSV infection. Eighteen subjects were enrolled and received a single dose of famciclovir experimental granules mixed with OraSweet based on the patient’s body weight (doses ranged from 25 mg to 175 mg). These doses were selected to provide penciclovir systemic exposures similar to the penciclovir systemic exposures observed in adults after administration of 500 mg famciclovir. The efficacy and safety of famciclovir have not been established as suppressive therapy in infants following neonatal HSV infections. In addition, the efficacy cannot be extrapolated from adults to infants because there is no similar disease in adults. Therefore, famciclovir is not recommended in infants.
Study 2 was an open-label, single-dose pharmacokinetic, multiple-dose safety study of famciclovir experimental granules mixed with OraSweet in children 1 to <12 years of age with clinically suspected HSV or varicella zoster virus (VZV) infection. Fifty-one subjects were enrolled in the pharmacokinetic part of the study and received a single body weight adjusted dose of famciclovir (doses ranged from 125 mg to 500 mg). These doses were selected to provide penciclovir systemic exposures similar to the penciclovir systemic exposures observed in adults after administration of 500 mg famciclovir. Based on the pharmacokinetic data observed with these doses in children, a new weight-based dosing algorithm was designed and used in the multiple-dose safety part of the study. Pharmacokinetic data were not obtained with the revised weight-based dosing algorithm.
A total of 100 patients were enrolled in the multiple-dose safety part of the study; 47 subjects with active or latent HSV infection and 53 subjects with chickenpox. Patients with active or latent HSV infection received famciclovir twice a day for 7 days. The daily dose of famciclovir ranged from 150 mg to 500 mg twice daily depending on the patient’s body weight. Patients with chickenpox received famciclovir three times daily for 7 days. The daily dose of famciclovir ranged from 150 mg to 500 mg three times daily depending on the patient’s body weight. The clinical adverse events and laboratory test abnormalities observed in this study were similar to these seen in adults. The available data are insufficient to support the use of famciclovir for the treatment of children 1 to <12 years of age with chickenpox or infections due to HSV for the following reasons:
The efficacy of famciclovir for the treatment of chickenpox has not been established in either pediatric or adult patients. Famciclovir is approved for the treatment of herpes zoster in adult patients. However, extrapolation of efficacy data from adults with herpes zoster to children with chickenpox would not be appropriate. Although chickenpox and herpes zoster are caused by the same virus, the diseases are different.
Clinical information on genital herpes in children is limited. Therefore, efficacy data from adults cannot be extrapolated to this population. Further, famciclovir has not been studied in children 1 to <12 years of age with recurrent genital herpes. None of the children in Study 2 had genital herpes.
There are no pharmacokinetic and safety data in children 1 to <12 years of age to support a famciclovir dose that provides penciclovir systemic exposures comparable to the penciclovir systemic exposures in adults after a single dose administration of 1500 mg. Moreover, no efficacy data have been obtained in children 1 to <12 years of age with recurrent herpes labialis.
Study 3 was an open-label, single-arm study to evaluate the pharmacokinetics, safety, and antiviral activity of a single 1500 mg dose (three 500 mg tablets) of famciclovir in children 12 to <18 years of age with recurrent herpes labialis. A total of 53 subjects were enrolled in the study; 10 subjects in the pharmacokinetic part of the study and 43 subjects in the non-pharmacokinetic part of the study. All enrolled subjects weighed ≥40 kg. The 43 subjects enrolled in the nonpharmacokinetic part of the study had active recurrent herpes labialis and received a single 1500 mg dose of famciclovir within 24 hours after the onset of symptoms (median time to treatment initiation was 21 hours). The safety profile of famciclovir observed in this study was similar to that seen in adults. The median time to healing of patients with non-aborted lesions was 5.9 days.
In a phase 3 trial in adults in which patients received a single 1500 mg dose of famciclovir or placebo, the median time to healing among patients with non-aborted lesions was 4.4 days in the famciclovir 1500 mg single-dose group and 6.2 days in the placebo group. Of note, in the adult study treatment was initiated by patients within 1 hour after the onset of symptoms [see Clinical Studies]. Based on the efficacy results in Study 3, famciclovir is not recommended in children 12 to <18 years of age with recurrent herpes labialis.
Of 816 patients with herpes zoster in clinical studies who were treated with FAMVIR, 248 (30.4%) were ≥65 years of age and 103 (13%) were ≥75 years of age. No overall differences were observed in the incidence or types of adverse events between younger and older patients. Of 610 patients with recurrent herpes simplex (type 1 or type 2) in clinical studies who were treated with FAMVIR, 26 (4.3%) were >65 years of age and 7 (1.1%) were >75 years of age. Clinical studies of FAMVIR in patients with recurrent genital herpes did not include sufficient numbers of subjects aged 65 and over to determine whether they respond differently compared to younger subjects.
No famciclovir dosage adjustment based on age is recommended unless renal function is impaired [see DOSAGE AND ADMINISTRATION, CLINICAL PHARMACOLOGY]. In general, appropriate caution should be exercised in the administration and monitoring of FAMVIR in elderly patients reflecting the greater frequency of decreased renal function and concomitant use of other drugs.
Patients With Renal Impairment
Apparent plasma clearance, renal clearance, and the plasma-elimination rate constant of penciclovir decreased linearly with reductions in renal function. After the administration of a single 500 mg famciclovir oral dose (n=27) to healthy volunteers and to volunteers with varying degrees of renal impairment (CLCR ranged from 6.4 to 138.8 mL/min), the following results were obtained (Table 4):
Table 4 Pharmacokinetic Parameters of Penciclovir in Subjects with Different Degrees of Renal Impairment
|Parameter (mean ± S.D.)||CLCR † ≥60
|CLCR (mL/min)||88.1 ± 20.6||49.3 ± 5.9||26.5 ± 5.3||12.7 ± 5.9|
|CLR (L/hr)||30.1 ± 10.6||13.0 ± 1.3‡||4.2 ± 0.9||1.6 ± 1.0|
|CL/F§ (L/hr)||66.9 ± 27.5||27.3 ± 2.8||12.8 ± 1.3||5.8 ± 2.8|
|Half-life (hr)||2.3 ± 0.5||3.4 ± 0.7||6.2 ± 1.6||13.4 ± 10.2|
|† CLCR is measured creatinine clearance.
§ CL/F consists of bioavailability factor and famciclovir to penciclovir conversion factor.
In a multiple-dose study of famciclovir conducted in subjects with varying degrees of renal impairment (n=18), the pharmacokinetics of penciclovir were comparable to those after single doses.
A dosage adjustment is recommended for patients with renal impairment [see DOSAGE AND ADMINISTRATION].
Patients With Hepatic Impairment
Mild or moderate hepatic impairment (chronic hepatitis [n=6], chronic ethanol abuse [n=8], or primary biliary cirrhosis [n=1]) had no effect on the extent of availability (AUC) of penciclovir following a single dose of 500 mg famciclovir. However, there was a 44% decrease in penciclovir mean maximum plasma concentration (Cmax) and the time to maximum plasma concentration (tmax) was increased by 0.75 hours in patients with hepatic impairment compared to normal volunteers. No dosage adjustment is recommended for patients with mild or moderate hepatic impairment. The pharmacokinetics of penciclovir has not been evaluated in patients with severe hepatic impairment. Conversion of famciclovir to the active metabolite penciclovir may be impaired in these patients resulting in a lower penciclovir plasma concentrations, and thus possibly a decrease of efficacy of famciclovir [see CLINICAL PHARMACOLOGY].
Black And African American Patients
In a randomized, double-blind, placebo-controlled trial conducted in 304 immunocompetent black and African American adults with recurrent genital herpes there was no difference in median time to healing between patients receiving FAMVIR or placebo. In general, the adverse reaction profile was similar to that observed in other FAMVIR clinical trials for adult patients [see ADVERSE REACTIONS]. The relevance of these study results to other indications in black and African American patients is unknown [see Clinical Studies].
Mechanism Of Action
Famciclovir is the diacetyl 6-deoxy analog of the active antiviral compound penciclovir. Following oral administration famciclovir undergoes rapid and extensive metabolism to penciclovir and little or no famciclovir is detected in plasma or urine. Penciclovir is predominantly eliminated unchanged by the kidney. Therefore, the dose of FAMVIR needs to be adjusted in patients with different degrees of renal impairment [see DOSAGE AND ADMINISTRATION].
Pharmacokinetics In Adults
Absorption and Bioavailability:
The absolute bioavailability of penciclovir is 77 ± 8% as determined following the administration of a 500 mg famciclovir oral dose and a 400 mg penciclovir intravenous dose to 12 healthy male subjects.
Penciclovir concentrations increased in proportion to dose over a famciclovir dose range of 125 mg to 1000 mg administered as a single dose. Table 5 shows the mean pharmacokinetic parameters of penciclovir after single administration of FAMVIR to healthy male volunteers.
Table 5 Mean Pharmacokinetic Parameters of Penciclovir in Healthy Adult Subjects*
|Dose||AUC (0-inf)† (mcg hr/mL)||Cmax ‡ (mcg/mL)||tmax § (h)|
|* Based on pharmacokinetic data from 17 studies
† AUC (0-inf) (mcg hr/mL)=area under the plasma concentration-time profile extrapolated to infinity.
‡ Cmax (mcg/mL)=maximum observed plasma concentration.
§ tmax (h)= time to Cmax.
Following oral single-dose administration of 500 mg famciclovir to 7 patients with herpes zoster, the AUC (mean ± SD), Cmax, and tmax were 12.1±1.7 mcg hr/mL, 4.0±0.7 mcg/mL, and 0.7±0.2 hours, respectively. The AUC of penciclovir was approximately 35% greater in patients with herpes zoster as compared to healthy volunteers. Some of this difference may be due to differences in renal function between the 2 groups.
There is no accumulation of penciclovir after the administration of 500 mg famciclovir three times daily for 7 days.
Penciclovir Cmax decreased approximately 50% and tmax was delayed by 1.5 hours when a capsule formulation of famciclovir was administered with food (nutritional content was approximately 910 Kcal and 26% fat). There was no effect on the extent of availability (AUC) of penciclovir. There was an 18% decrease in Cmax and a delay in tmax of about 1 hour when famciclovir was given 2 hours after a meal as compared to its administration 2 hours before a meal. Because there was no effect on the extent of systemic availability of penciclovir, FAMVIR can be taken without regard to meals.
The volume of distribution (Vdβ) was 1.08±0.17 L/kg in 12 healthy male subjects following a single intravenous dose of penciclovir at 400 mg administered as a 1-hour intravenous infusion. Penciclovir is <20% bound to plasma proteins over the concentration range of 0.1 to 20 mcg/mL. The blood/plasma ratio of penciclovir is approximately 1.
Following oral administration, famciclovir is deacetylated and oxidized to form penciclovir. Metabolites that are inactive include 6-deoxy penciclovir, monoacetylated penciclovir, and 6-deoxy monoacetylated penciclovir (5%, <0.5% and <0.5% of the dose in the urine, respectively). Little or no famciclovir is detected in plasma or urine. An in vitro study using human liver microsomes demonstrated that cytochrome P450 does not play an important role in famciclovir metabolism. The conversion of 6-deoxy penciclovir to penciclovir is catalyzed by aldehyde oxidase. Cimetidine and promethazine, in vitro inhibitors of aldehyde oxidase, did not show relevant effects on the formation of penciclovir in vivo [see DRUG INTERACTIONS].
Approximately 94% of administered radioactivity was recovered in urine over 24 hours (83% of the dose was excreted in the first 6 hours) after the administration of 5 mg/kg radiolabeled penciclovir as a 1-hour infusion to 3 healthy male volunteers. Penciclovir accounted for 91% of the radioactivity excreted in the urine.
Following the oral administration of a single 500 mg dose of radiolabeled famciclovir to 3 healthy male volunteers, 73% and 27% of administered radioactivity were recovered in urine and feces over 72 hours, respectively. Penciclovir accounted for 82% and 6-deoxy penciclovir accounted for 7% of the radioactivity excreted in the urine. Approximately 60% of the administered radiolabeled dose was collected in urine in the first 6 hours.
After intravenous administration of penciclovir in 48 healthy male volunteers, mean ± SD total plasma clearance of penciclovir was 36.6±6.3 L/hr (0.48±0.09 L/hr/kg). Penciclovir renal clearance accounted for 74.5±8.8% of total plasma clearance.
Renal clearance of penciclovir following the oral administration of a single 500 mg dose of famciclovir to 109 healthy male volunteers was 27.7±7.6 L/hr. Active tubular secretion contributes to the renal elimination of penciclovir.
The plasma elimination half-life of penciclovir was 2.0±0.3 hours after intravenous administration of penciclovir to 48 healthy male volunteers and 2.3±0.4 hours after oral administration of 500 mg famciclovir to 124 healthy male volunteers. The half-life in 17 patients with herpes zoster was 2.8±1.0 hours and 2.7±1.0 hours after single and repeated doses, respectively.
Based on cross study comparison, penciclovir AUC was 40% higher and penciclovir renal clearance was 22% lower in elderly subjects (n=18, age 65-79 years) as compared with younger subjects. Some of this difference may be due to differences in renal function between the 2 groups. No famciclovir dosage adjustment based on age is recommended unless renal function is impaired [see DOSAGE AND ADMINISTRATION, Use In Specific Populations]
Patients With Renal Impairment
In subjects with varying degrees of renal impairment, apparent plasma clearance, renal clearance, and the plasma-elimination rate constant of penciclovir decreased linearly with reductions in renal function, after both single and repeated dosing [see Use In Specific Populations]. A dosage adjustment is recommended for patients with renal impairment [see DOSAGE AND ADMINISTRATION].
Patients With Hepatic Impairment
Mild or moderate hepatic impairment had no effect on the extent of availability (AUC) of penciclovir [see Use In Specific Populations]. No dosage adjustment is recommended for patients with mild or moderate hepatic impairment. The effect of severe hepatic impairment on the pharmacokinetics of penciclovir has not been evaluated.
Following oral administration of a single dose of 500 mg famciclovir to HIV-positive patients, the pharmacokinetic parameters of penciclovir were comparable to those observed in healthy subjects.
The pharmacokinetics of penciclovir were evaluated in 18 healthy male and 18 healthy female volunteers after single-dose oral administration of 500 mg famciclovir. AUC of penciclovir was 9.3±1.9 mcg hr/mL and 11.1±2.1 mcg hr/mL in males and females, respectively. Penciclovir renal clearance was 28.5±8.9 L/hr and 21.8±4.3 L/hr, respectively. These differences were attributed to differences in renal function between the 2 groups. No famciclovir dosage adjustment based on gender is recommended.
A retrospective evaluation was performed to compare the pharmacokinetic parameters obtained in black and Caucasian subjects after single and repeat once-daily, twice-daily, or three times-daily administration of famciclovir 500 mg. Data from a study in healthy volunteers (single dose), a study in subjects with varying degrees of renal impairment (single and repeat dose) and a study in subjects with hepatic impairment (single dose) did not indicate any significant differences in the pharmacokinetics of penciclovir between black and Caucasian subjects.
Mechanism Of Action
Famciclovir is a prodrug of penciclovir, which has demonstrated inhibitory activity against herpes simplex virus types 1 (HSV-1) and 2 (HSV-2) and varicella zoster virus (VZV). In cells infected with HSV-1, HSV-2 or VZV, the viral thymidine kinase phosphorylates penciclovir to a monophosphate form that, in turn, is converted by cellular kinases to the active form penciclovir triphosphate. Biochemical studies demonstrate that penciclovir triphosphate inhibits HSV-2 DNA polymerase competitively with deoxyguanosine triphosphate. Consequently, herpes viral DNA synthesis and, therefore, replication are selectively inhibited. Penciclovir triphosphate has an intracellular half-life of 10 hours in HSV-1-, 20 hours in HSV-2-and 7 hours in VZV-infected cells grown in culture. However, the clinical significance of the intracellular half-life is unknown.
In cell culture studies, penciclovir is inhibitory to the following herpes viruses: HSV-1, HSV-2 and VZV. The antiviral activity of penciclovir against wild type strains grown on human foreskin fibroblasts was assessed with a plaque reduction assay and staining with crystal violet 3 days postinfection for HSV and 10 days postinfection for VZV. The median EC50 values of penciclovir against laboratory and clinical isolates of HSV-1, HSV-2, and VZV were 2 μM (range 1.2 to 2.4 μM, n=7), 2.6 μM (range 1.6 to 11 μM, n=6), and 34 μM (range 6.7 to 71 μM, n=6), respectively.
Penciclovir-resistant mutants of HSV and VZV can result from mutations in the viral thymidine kinase (TK) and DNA polymerase genes. Mutations in the viral TK gene may lead to complete loss of TK activity (TK negative), reduced levels of TK activity (TK partial), or alteration in the ability of viral TK to phosphorylate the drug without an equivalent loss in the ability to phosphorylate thymidine (TK altered). The median EC50 values observed in a plaque reduction assay with penciclovir resistant HSV-1, HSV-2, and VZV were 69 μM (range 14 to 115 μM, n=6), 46 μM (range 4 to >395 μM, n=9), and 92 μM (range 51 to 148 μM, n=4), respectively. The possibility of viral resistance to penciclovir should be considered in patients who fail to respond or experience recurrent viral shedding during therapy.
Cross-resistance has been observed among HSV DNA polymerase inhibitors. The most commonly encountered acyclovir resistant mutants that are TK negative are also resistant to penciclovir.
Herpes Labialis (Cold Sores)
A randomized, double-blind, placebo-controlled trial was conducted in 701 immunocompetent adults with recurrent herpes labialis. Patients self-initiated therapy within 1 hour of first onset of signs or symptoms of a recurrent herpes labialis episode with FAMVIR 1500 mg as a single dose (n=227), FAMVIR 750 mg twice daily (n=220) or placebo (n=254) for 1 day. The median time to healing among patients with non-aborted lesions (progressing beyond the papule stage) was 4.4 days in the FAMVIR 1500 mg single-dose group (n=152) as compared to 6.2 days in the placebo group (n=168). The median difference in time to healing between the placebo and FAMVIR 1500 mg treated groups was 1.3 days (95% CI: 0.6–2.0). No differences in proportion of patients with aborted lesions (not progressing beyond the papule stage) were observed between patients receiving FAMVIR or placebo: 33% for FAMVIR 1500 mg single dose and 34% for placebo. The median time to loss of pain and tenderness was 1.7 days in FAMVIR 1500 mg single dose-treated patients vs. 2.9 days in placebo-treated patients.
A randomized, double-blind, placebo-controlled trial was conducted in 329 immunocompetent adults with recurrent genital herpes. Patients self-initiated therapy within 6 hours of the first sign or symptom of a recurrent genital herpes episode with either FAMVIR 1000 mg twice daily (n=163) or placebo (n=166) for 1 day. The median time to healing among patients with non-aborted lesions (progressing beyond the papule stage) was 4.3 days in FAMVIR-treated patients (n=125) as compared to 6.1 days in placebo-treated patients (n=145). The median difference in time to healing between the placebo and FAMVIR-treated groups was 1.2 days (95% CI: 0.5 to 2.0). Twenty-three percent of FAMVIR-treated patients had aborted lesions (no lesion development beyond erythema) vs. 13% in placebo-treated patients. The median time to loss of all symptoms (e.g., tingling, itching, burning, pain, or tenderness) was 3.3 days in FAMVIR-treated patients vs. 5.4 days in placebo-treated patients.
A randomized (2:1), double-blind, placebo-controlled trial was conducted in 304 immunocompetent black and African American adults with recurrent genital herpes. Patients self-initiated therapy within 6 hours of the first sign or symptom of a recurrent genital herpes episode with either FAMVIR 1000 mg twice daily (n=206) or placebo (n=98) for 1 day. The median time to healing among patients with non-aborted lesions was 5.4 days in FAMVIR-treated patients (n=152) as compared to 4.8 days in placebo-treated patients (n=78). The median difference in time to healing between the placebo and FAMVIR-treated groups was -0.26 days (95% CI: -0.98 to 0.40).
Two randomized, double-blind, placebo-controlled, 12-month trials were conducted in 934 immunocompetent adults with a history of 6 or more recurrences of genital herpes episodes per year. Comparisons included FAMVIR 125 mg three times daily, 250 mg twice daily, 250 mg three times daily, and placebo. At 12 months, 60% to 65% of patients were still receiving FAMVIR and 25% were receiving placebo treatment. Recurrence rates at 6 and 12 months in patients treated with the 250 mg twice daily dose are shown in Table 6.
|Recurrence Rates at 6 Months||Recurrence Rates at 12 Months|
|Famvir 250 mg twice daily||Placebo||Famvir 250 mg twice daily||Placebo|
|Lost to follow-up‡||14%||16%||17%||16%|
|†Based on patient reported data; not necessarily confirmed by a physician.
‡Patients recurrence-free at time of last contact prior to withdrawal.
FAMVIR-treated patients had approximately 1/5 the median number of recurrences as compared to placebo-treated patients. Higher doses of FAMVIR were not associated with an increase in efficacy.
Recurrent Orolabial Or Genital Herpes In HIV-Infected Patients
A randomized, double-blind trial compared famciclovir 500 mg twice daily for 7 days (n=150) with oral acyclovir 400 mg 5 times daily for 7 days (n=143) in HIV-infected patients with recurrent orolabial or genital herpes treated within 48 hours of lesion onset. Approximately 40% of patients had a CD4 + count below 200 cells/mm3, 54% of patients had anogenital lesions and 35% had orolabial lesions. Famciclovir therapy was comparable to oral acyclovir in reducing new lesion formation and in time to complete healing.
Herpes Zoster (Shingles)
Two randomized, double-blind trials, 1 placebo-controlled and 1 active-controlled, were conducted in 964 immunocompetent adults with uncomplicated herpes zoster. Treatment was initiated within 72 hours of first lesion appearance and was continued for 7 days.
In the placebo-controlled trial, 419 patients were treated with either FAMVIR 500 mg three times daily (n=138), FAMVIR 750 mg three times daily (n=135) or placebo (n=146). The median time to full crusting was 5 days among FAMVIR 500 mg-treated patients as compared to 7 days in placebo-treated patients. The times to full crusting, loss of vesicles, loss of ulcers, and loss of crusts were shorter for FAMVIR 500 mg-treated patients than for placebo-treated patients in the overall study population. The effects of FAMVIR were greater when therapy was initiated within 48 hours of rash onset; it was also more profound in patients 50 years of age or older. Among the 65.2% of patients with at least 1 positive viral culture, FAMVIR treated patients had a shorter median duration of viral shedding than placebo-treated patients (1 day and 2 days, respectively).
There were no overall differences in the duration of pain before rash healing between FAMVIR-and placebo-treated groups. In addition, there was no difference in the incidence of pain after rash healing (postherpetic neuralgia) between the treatment groups. In the 186 patients (44.4% of total study population) who developed postherpetic neuralgia, the median duration of postherpetic neuralgia was shorter in patients treated with FAMVIR 500 mg than in those treated with placebo (63 days and 119 days, respectively). No additional efficacy was demonstrated with higher dose of FAMVIR.
In the active-controlled trial, 545 patients were treated with 1 of 3 doses of FAMVIR three times daily or with acyclovir 800 mg five times daily. Times to full lesion crusting and times to loss of acute pain were comparable for all groups and there were no statistically significant differences in the time to loss of postherpetic neuralgia between FAMVIR and acyclovir-treated groups.
FAMVIR is not a cure for herpes. It is not known if FAMVIR can stop the spread of herpes to others. If you are sexually active, you can pass herpes to your partner even if you are taking FAMVIR. Herpes can be transmitted even if you do not have active symptoms. You should continue to practice safer sex to lower the chances of spreading genital herpes to others. Do not have sexual contact with your partner during an outbreak of genital herpes or if you have any symptoms of genital herpes. Use a condom made of latex or polyurethane when you have a sexual contact. Ask your healthcare provider for more information about safer sex practices.
Who should not take FAMVIR?
Do not take FAMVIR if you are allergic to any of its ingredients or to Denavir® (penciclovir cream). See the end of this Patient Information leaflet for a complete list of ingredients in FAMVIR.
What should I tell my healthcare provider before taking FAMVIR?
Before you start taking FAMVIR, tell your healthcare provider if you:
- have kidney or liver problems
- have a rare genetic problem with galactose intolerance, a severe lactase deficiency or you do not absorb glucose-galactose (malabsorption)
- are pregnant or planning to become pregnant. It is not known if FAMVIR will harm your unborn baby
- Pregnancy Exposure Reporting: Novartis Pharmaceuticals Corporation collects pregnancy reports which are reported on a voluntary basis. In case of pregnancy, talk to your healthcare provider about reporting your pregnancy
- are breastfeeding or plan to breastfeed
Tell your healthcare provider about all the medicines you take, including prescription and nonprescription medicines, vitamins, and herbal supplements. Especially tell your healthcare provider if you take:
- any other medicines and products you use to treat herpes outbreaks
- probenecid (Probalan)
Know the medicines you take. Keep a list of them with you to show to your healthcare provider and pharmacist every time you get a new medicine.
How should I take FAMVIR?
- Take FAMVIR exactly as prescribed
- Your healthcare provider will tell you how many FAMVIR to take and when to take them. Your dose of FAMVIR and how often you take it may be different depending on your condition
- FAMVIR can be taken with or without food
- It is important for you to finish all of the medicine as prescribed, even if you begin to feel better
- Your symptoms may continue even after you finish all of your FAMVIR. This does not mean that you need more medicine, since you have already finished a full course of FAMVIR and it will continue to work in your body. Talk to your healthcare provider if you have any questions about your condition and your treatment