Valacyclovir hydrochloride is contraindicated in patients who have had a demonstrated clinically significant hypersensitivity reaction (e.g., anaphylaxis) to valacyclovir, acyclovir, or any component of the formulation
[see
Adverse Reactions (6.3)]
.
The following serious adverse reactions are discussed in greater detail in other sections of the labeling:
- Thrombotic Thrombocytopenic Purpura/Hemolytic Uremic Syndrome
[
see Warnings and Precautions (5.1)].
- Acute Renal Failure
[see
Warnings and Precautions (5.2)]
.
- Central Nervous System Effects
[see
Warnings and Precautions (5.3)]
.
The most common adverse reactions reported in at least 1 indication by >10% of adult patients treated with valacyclovir hydrochloride and observed more frequently with valacyclovir hydrochloride compared to placebo are headache, nausea, and abdominal pain. The only adverse reaction reported in >10% of pediatric patients <18 years of age was headache.
No clinically significant drug-drug or drug-food interactions with valacyclovir hydrochloride are known
[see
Clinical Pharmacology (12.3)]
.
The pharmacokinetic profile and safety of valacyclovir oral suspension in children <12 years of age were studied in 3 open-label studies. No efficacy evaluations were conducted in any of the 3 studies.
Study 1 was a single-dose pharmacokinetic, multiple-dose safety study in 27 pediatric patients 1 to <12 years of age with clinically suspected varicella-zoster virus (VZV) infection
[see
Dosage and Administration (2.2), 64
Adverse Reactions (6.2),
Clinical Pharmacology (12.3),
Clinical Studies (14.4)].
Study 2 was a single-dose pharmacokinetic and safety study in pediatric patients 1 month to <6 years of age who had an active herpes virus infection or who were at risk for herpes virus infection. Fifty-seven subjects were enrolled and received a single dose of 25 mg/kg valacyclovir oral suspension. In infants and children 3 months to <6 years of age, this dose provided comparable systemic acyclovir exposures to that from a 1 gram dose of valacyclovir in adults (historical data). In infants 1 month to <3 months of age, mean acyclovir exposures resulting from a 25 mg/kg dose were higher (C
max: ↑30%, AUC: ↑60%) than acyclovir exposures following a 1 gram dose of valacyclovir in adults. Acyclovir is not approved for suppressive therapy in infants and children following neonatal HSV infections; therefore valacyclovir is not recommended for this indication because efficacy cannot be extrapolated from acyclovir.
Study 3 was a single-dose pharmacokinetic, multiple-dose safety study in 28 pediatric patients 1 to <12 years of age with clinically suspected HSV infection. None of the children enrolled in this study had genital herpes. Each subject was dosed with valacyclovir oral suspension, 10 mg/kg twice daily for 3 to 5 days. Acyclovir systemic exposures in pediatric patients following valacyclovir oral suspension were compared with historical acyclovir systemic exposures in immunocompetent adults receiving the solid oral dosage form of valacyclovir or acyclovir for the treatment of recurrent genital herpes. The mean projected daily acyclovir systemic exposures in pediatric patients across all age-groups (1 to <12 years of age) were lower (C
max: ↓20%, AUC: ↓33%) compared with the acyclovir systemic exposures in adults receiving valacyclovir 500 mg twice daily, but were higher (daily AUC: ↑16%) than systemic exposures in adults receiving acyclovir 200 mg 5 times daily. Insufficient data are available to support valacyclovir for the treatment of recurrent genital herpes in this age-group because clinical information on recurrent genital herpes in young children is limited; therefore, extrapolating efficacy data from adults to this population is not possible. Moreover, valacyclovir has not been studied in children 1 to <12 years of age with recurrent genital herpes.
Valacyclovir hydrochloride USP is a white to off-white powder with the molecular formula C
13H
20N
6O
4•HCl and a molecular weight of 360.80. The maximum solubility in water at 25°C is 174 mg/mL. The pk
as for valacyclovir hydrochloride are 1.90, 7.47, and 9.43.
Distribution: The binding of valacyclovir to human plasma proteins ranges from 13.5% to 17.9%. The binding of acyclovir to human plasma proteins ranges from 9% to 33%.
Metabolism: Valacyclovir is converted to acyclovir and
L-valine by first-pass intestinal and/or hepatic metabolism. Acyclovir is converted to a small extent to inactive metabolites by aldehyde oxidase and by alcohol and aldehyde dehydrogenase. Neither valacyclovir nor acyclovir is metabolized by cytochrome P450 enzymes. Plasma concentrations of unconverted valacyclovir are low and transient, generally becoming non-quantifiable by 3 hours after administration. Peak plasma valacyclovir concentrations are generally less than 0.5 mcg/mL at all doses. After single-dose administration of 1 gram of valacyclovir hydrochloride, average plasma valacyclovir concentrations observed were 0.5, 0.4, and 0.8 mcg/mL in patients with hepatic dysfunction, renal insufficiency, and in healthy volunteers who received concomitant cimetidine and probenecid, respectively.
Elimination: The pharmacokinetic disposition of acyclovir delivered by valacyclovir is consistent with previous experience from intravenous and oral acyclovir. Following the oral administration of a single 1 gram dose of radiolabeled valacyclovir to 4 healthy subjects, 46% and 47% of administered radioactivity was recovered in urine and feces, respectively, over 96 hours. Acyclovir accounted for 89% of the radioactivity excreted in the urine. Renal clearance of acyclovir following the administration of a single 1 gram dose of valacyclovir hydrochloride to 12 healthy volunteers was approximately 255 ± 86 mL/min which represents 42% of total acyclovir apparent plasma clearance.
The plasma elimination half-life of acyclovir typically averaged 2.5 to 3.3 hours in all studies of valacyclovir hydrochloride in volunteers with normal renal function.
Specific Populations: Renal Impairment: Reduction in dosage is recommended in patients with renal impairment
[see
Dosage and Administration (2.4),
Use in Specific Populations (8.5),
(8.6)].
Following administration of valacyclovir hydrochloride to volunteers with ESRD, the average acyclovir half-life is approximately 14 hours. During hemodialysis, the acyclovir half-life is approximately 4 hours. Approximately one third of acyclovir in the body is removed by dialysis during a 4-hour hemodialysis session. Apparent plasma clearance of acyclovir in dialysis patients was 86.3 ± 21.3 mL/min/1.73 m
2 compared with 679.16 ± 162.76 mL/min/1.73 m
2 in healthy volunteers.
Hepatic Impairment: Administration of valacyclovir hydrochloride to patients with moderate (biopsy-proven cirrhosis) or severe (with and without ascites and biopsy-proven cirrhosis) liver disease indicated that the rate but not the extent of conversion of valacyclovir to acyclovir is reduced, and the acyclovir half-life is not affected. Dosage modification is not recommended for patients with cirrhosis.
HIV Disease: In 9 patients with HIV disease and CD4+ cell counts <150 cells/mm
3 who received valacyclovir hydrochloride at a dosage of 1 gram 4 times daily for 30 days, the pharmacokinetics of valacyclovir and acyclovir were not different from that observed in healthy volunteers.
Geriatrics: After single-dose administration of 1 gram of valacyclovir hydrochloride in healthy geriatric volunteers, the half-life of acyclovir was 3.11 ± 0.51 hours, compared with 2.91 ± 0.63 hours in healthy younger adult volunteers. The pharmacokinetics of acyclovir following single- and multiple-dose oral administration of valacyclovir hydrochloride in geriatric volunteers varied with renal function. Dose reduction may be required in geriatric patients, depending on the underlying renal status of the patient
[see
Dosage and Administration (2.4),
Use in Specific Populations (8.5),
(8.6)]
.
Pediatrics: Acyclovir pharmacokinetics have been evaluated in a total of 98 pediatric patients (1 month to <12 years of age) following administration of the first dose of an extemporaneous oral suspension of valacyclovir
[see
Adverse Reactions (6.2),
Use in Specific Populations (8.4)]
. Acyclovir pharmacokinetic parameter estimates following a 20 mg/kg dose are provided in Table 4.
Table 4. Mean (±SD) Plasma Acyclovir Pharmacokinetic Parameter Estimates Following First-Dose Administration of 20 mg/kg Valacyclovir Oral Suspension to Pediatric Patients vs. 1 Gram Single Dose of Valacyclovir Hydrochloride to Adults |
Parameter
|
| Pediatric Patients
(20 mg/kg Oral Suspension)
|
| Adults
1 gram Solid Dose
of Valacyclovir
hydrochloride
a(N = 15)
|
| 1 - <2 yr
(N = 6)
| 2 - <6 yr
(N = 12)
| 6 - <12 yr
(N = 8)
|
|
AUC (mcg•hr/mL) C
max (mcg/mL)
| 14.4 (±6.26)
4.03 (±1.37)
| 10.1 (±3.35)
3.75 (±1.14)
| 13.1 (±3.43)
4.71 (±1.20)
| 17.2 (±3.10)
4.72 (±1.37)
|
Drug Interactions: When valacyclovir hydrochloride is coadministered with antacids, cimetidine and/or probenicid, digoxin, or thiazide diuretics in patients with normal renal function, the effects are not considered to be of clinical significance (see below). Therefore, when valacyclovir hydrochloride is coadministered with these drugs in patients with normal renal function, no dosage adjustment is recommended.
Antacids: The pharmacokinetics of acyclovir after a single dose of valacyclovir hydrochloride (1 gram) were unchanged by coadministration of a single dose of antacids (Al
3+ or Mg
++).
Cimetidine: Acyclovir C
max and AUC following a single dose of valacyclovir hydrochloride (1 gram) increased by 8% and 32%, respectively, after a single dose of cimetidine (800 mg).
Cimetidine Plus Probenecid: Acyclovir C
max and AUC following a single dose of valacyclovir hydrochloride (1 gram) increased by 30% and 78%, respectively, after a combination of cimetidine and probenecid, primarily due to a reduction in renal clearance of acyclovir.
Digoxin: The pharmacokinetics of digoxin were not affected by coadministration of valacyclovir hydrochloride 1 gram 3 times daily, and the pharmacokinetics of acyclovir after a single dose of valacyclovir hydrochloride (1 gram) was unchanged by coadministration of digoxin (2 doses of 0.75 mg).
Probenecid: Acyclovir C
max and AUC following a single dose of valacyclovir hydrochloride (1 gram) increased by 22% and 49%, respectively, after probenecid (1 gram).
Thiazide Diuretics: The pharmacokinetics of acyclovir after a single dose of valacyclovir hydrochloride (1 gram) were unchanged by coadministration of multiple doses of thiazide diuretics.
Subjects with 9 or fewer recurrences per year showed comparable results with valacyclovir hydrochloride 500 mg once daily.
In a second study, 293 HIV-infected adults on stable antiretroviral therapy with a history of 4 or more recurrences of ano-genital herpes per year were randomized to receive either valacyclovir hydrochloride 500 mg twice daily (n = 194) or matching placebo (n = 99) for 6 months. The median duration of recurrent genital herpes in enrolled subjects was 8 years, and the median number of recurrences in the year prior to enrollment was 5. Overall, the median prestudy HIV-1 RNA was 2.6 log
10 copies/mL. Among patients who received valacyclovir hydrochloride, the prestudy median CD4+ cell count was 336 cells/mm
3; 11% had <100 cells/mm
3, 16% had 100 to 199 cells/mm
3, 42% had 200 to 499 cells/mm
3, and 31% had ≥500 cells/mm
3. Outcomes for the overall study population are shown in Table 6.
Table 6. Recurrence Rates in HIV-Infected Adults at 6 Months |
Outcome
| Valacyclovir hydrochloride
500 mg twice daily
(n = 194)
| Placebo
(n = 99)
|
Recurrence free
| 65%
| 26%
|
Recurrences
| 17%
| 57%
|
Unknown
a
| 18%
| 17%
|
Reduction of Transmission of Genital Herpes: A double-blind, placebo-controlled study to assess transmission of genital herpes was conducted in 1,484 monogamous, heterosexual, immunocompetent adult couples. The couples were discordant for HSV-2 infection. The source partner had a history of 9 or fewer genital herpes episodes per year. Both partners were counseled on safer sex practices and were advised to use condoms throughout the study period. Source partners were randomized to treatment with either valacyclovir hydrochloride 500 mg once daily or placebo once daily for 8 months. The primary efficacy endpoint was symptomatic acquisition of HSV-2 in susceptible partners. Overall HSV-2 acquisition was defined as symptomatic HSV-2 acquisition and/or HSV-2 seroconversion in susceptible partners. The efficacy results are summarized in Table 7.
Table 7. Percentage of Susceptible Partners Who Acquired HSV-2 Defined by the Primary and Selected Secondary Endpoints |
Endpoint
| Valacyclovir hydrochloride
a (n = 743)
| Placebo
(n = 741)
|
Symptomatic HSV-2 acquisition
| 4 (0.5%)
| 16 (2.2%)
|
HSV-2 seroconversion
| 12 (1.6%)
| 24 (3.2%)
|
Overall HSV-2 acquisition
| 14 (1.9%)
| 27 (3.6%)
|