Acyclovir

MEDICATION SAFETY ISSUES
Sound-alike/look-alike issues:
Acyclovir may be confused with ganciclovir, Retrovir®, valACYclovir
Zovirax® may be confused with Valtrex®, Zithromax®, Zostrix®, Zyloprim®, Zyvox®

International issues:
Opthavir® [Mexico] may be confused with Optivar® which is a brand name for azelastine in the U.S.

U.S. BRAND NAMES — Zovirax®

PHARMACOLOGIC CATEGORY
Antiviral Agent
Antiviral Agent, Topical

DOSING: ADULTS — Note: Obese patients should be dosed using ideal body weight

Genital HSV:
I.V.: Immunocompetent: Initial episode, severe: 5 mg/kg/dose every 8 hours for 5-7 days
Oral:
Initial episode: 200 mg every 4 hours while awake (5 times/day) for 10 days (per manufacturer's labeling); 400 mg 3 times/day for 5-10 days has also been reported
Recurrence: 200 mg every 4 hours while awake (5 times/day) for 5 days (per manufacturer's labeling; begin at earliest signs of disease); 400 mg 3 times/day for 5 days has also been reported
Chronic suppression: 400 mg twice daily or 200 mg 3-5 times/day, for up to 12 months followed by re-evaluation (per manufacturer's labeling); 400-1200 mg/day in 2-3 divided doses has also been reported
Topical: Immunocompromised: Ointment: Initial episode: 1/2" ribbon of ointment for a 4" square surface area every 3 hours (6 times/day) for 7 days

Herpes labialis (cold sores): Topical: Apply 5 times/day for 4 days

Herpes zoster (shingles):
Oral: Immunocompetent: 800 mg every 4 hours (5 times/day) for 7-10 days
I.V.: Immunocompromised: 10 mg/kg/dose or 500 mg/m2/dose every 8 hours for 7 days

HSV encephalitis: I.V.: 10 mg/kg/dose every 8 hours for 10 days (per manufacturer's labeling); 10-15 mg/kg/dose every 8 hours for 14-21 days also reported

Mucocutaneous HSV:
I.V.: Immunocompromised: 5 mg/kg/dose every 8 hours for 7 days (per manufacturer's labeling); dosing for up to 14 days also reported
Oral: Immunocompromised (unlabeled use): 400 mg 5 times a day for 7-14 days
Topical: Ointment: Nonlife-threatening, immunocompromised: 1/2" ribbon of ointment for a 4" square surface area every 3 hours (6 times/day) for 7 days

Varicella-zoster (chickenpox): Begin treatment within the first 24 hours of rash onset:
Oral: >40 kg (immunocompetent): 800 mg/dose 4 times a day for 5 days
I.V.:
Manufacturer's labeling (immunocompromised): 10 mg/kg/dose every 8 hours for 7 days
AIDSinfo guidelines (immunocompromised): 10-15 mg/kg/dose every 8 hours for 7-10 days

Prevention of HSV reactivation in HIV-positive patients, for use only when recurrences are frequent or severe (unlabeled use): Oral: 200 mg 3 times/day or 400 mg 2 times/day

Prevention of HSV reactivation in HSCT (unlabeled use):CDC recommendation:Note: Start at the beginning of conditioning therapy and continue until engraftment or until mucositis resolves (~30 days)
Oral: 200 mg 3 times/day
I.V.: 250 mg/m2/dose every 12 hours

Prevention of VZV reactivation in allogeneic HSCT (unlabeled use):NCCN guidelines: Oral: 800 mg twice a day

Prevention of CMV reactivation in low-risk allogeneic HSCT (unlabeled use):NCCN guidelines:Note: Requires close monitoring (due to weak activity); not for use in patients at high risk for CMV disease: Oral: 800 mg 4 times/day

Treatment of disseminated HSV or VZV or empiric treatment of suspected encephalitis in immunocompromised patients with cancer: (unlabeled use):NCCN guidelines: I.V.: 10-12 mg/kg/dose every 8 hours

DOSING: PEDIATRIC — Note: Obese patients should be dosed using ideal body weight

(For additional information see "Acyclovir: Pediatric drug information")

Genital HSV:
I.V.: Children ≥ 12 years: Refer to adult dosing.
Oral:
Initial episode (unlabeled use): 40-80 mg/kg/day divided into 3-4 doses for 5-10 days (maximum: 1 g/day)
Chronic suppression (unlabeled use; limited data): 80 mg/kg/day in 3 divided doses (maximum: 1 g/day), re-evaluate after 12 months of treatment

Herpes labialis (cold sores): Topical: Children ≥ 12 years: Refer to adult dosing.

Herpes zoster (shingles): I.V.:
Children <12 years (immunocompromised): 20 mg/kg/dose every 8 hours for 7 days
Children ≥ 12 years: Refer to adult dosing.

HSV encephalitis: I.V.:
Children 3 months to 12 years: 20 mg/kg/dose every 8 hours for 10 days (per manufacturer's labeling); dosing for 14-21 days also reported
Children ≥ 12 years: Refer to adult dosing.

Mucocutaneous HSV: I.V.:
Children <12 years (immunocompromised): 10 mg/kg/dose every 8 hours for 7 days
Children ≥ 12 years: Refer to adult dosing.

Neonatal HSV: I.V.: Neonate: Birth to 3 months: 10 mg/kg/dose every 8 hours for 10 days (manufacturer's labeling); 15 mg/kg/dose or 20 mg/kg/dose every 8 hours for 14-21 days has also been reported

Varicella-zoster (chickenpox): Begin treatment within the first 24 hours of rash onset:
Oral:Note: The AIDSinfo guidelines recommended duration of therapy is 7-10 days or until no new lesions for 48 hours (for patients with mild varicella and no or moderate immune suppression).
Children ≥ 2 years and ≤ 40 kg (immunocompetent): 20 mg/kg/dose (up to 800 mg/dose) 4 times/day for 5 days
Children >40 kg: Refer to adult dosing.
I.V.:
Manufacturer's labeling (immunocompromised):
Children <12 years: 20 mg/kg/dose every 8 hours for 7 days
Children ≥ 12 years: 10 mg/kg/dose every 8 hours for 7 days
AIDSinfo guidelines (immunocompromised):
Children <1 year: 10 mg/kg/dose every 8 hours for 7-10 days or until no new lesions for 48 hours
Children ≥ 1 year: 10 mg/kg/dose or 500 mg/m2/dose every 8 hours for 7-10 days or until no new lesions for 48 hours
Adolescents: Refer to adult dosing.

Prevention of HSV reactivation in HIV-positive patients, for use only when recurrences are frequent or severe (unlabeled use): Oral: 80 mg/kg/day in 3-4 divided doses

Prevention of HSV reactivation in HSCT (unlabeled use):CDC recommendation:Note: Start at the beginning of conditioning therapy and continue until engraftment or until mucositis resolves (~30 days): I.V.: 250 mg/m2/dose every 8 hours or 125 mg/m2/dose every 6 hours

DOSING: ELDERLY — Refer to adult dosing.

DOSING: RENAL IMPAIRMENT
Oral:
Clcr 10-25 mL/minute/1.73 m2: Normal dosing regimen 800 mg every 4 hours: Administer 800 mg every 8 hours
Clcr <10 mL/minute/1.73 m2:
Normal dosing regimen 200 mg every 4 hours or 400 mg every 12 hours: Administer 200 mg every 12 hours
Normal dosing regimen 800 mg every 4 hours: Administer 800 mg every 12 hours

I.V.:
Clcr 25-50 mL/minute/1.73 m2: Administer recommended dose every 12 hours
Clcr 10-25 mL/minute/1.73 m2: Administer recommended dose every 24 hours
Clcr <10 mL/minute/1.73 m2: Administer 50% of recommended dose every 24 hours

Hemodialysis: Administer dose after dialysis

Continuous ambulatory peritoneal dialysis (CAPD): Administer 50% of normal dose once daily; no supplemental dose needed

Continuous renal replacement therapy (CRRT): Drug clearance is highly dependent on the method of renal replacement, filter type, and flow rate. Appropriate dosing requires close monitoring of pharmacologic response, signs of adverse reactions due to drug accumulation, as well as drug levels in relation to target trough (if appropriate). The following are general recommendations only (based on dialysate flow/ultrafiltration rates of 1 L/hour) and should not supersede clinical judgment:
CVVH or CVVHD/CVVHDF: 5-7.5 mg/kg every 24 hours
Note: The higher dose of 7.5 mg/kg is recommended for infections with CNS involvement (Trotman, 2005).

DOSAGE FORMS — Excipient information presented when available (limited, particularly for generics); consult specific product labeling.

Capsule: 200 mg
Zovirax®: 200 mg

Cream, topical:
Zovirax®: 5% (2 g, 5 g)

Injection, powder for reconstitution, as sodium: 500 mg [base strength], 1000 mg [base strength]

Injection, solution, as sodium [preservative free]: 50 mg/mL (10 mL, 20 mL) [base strength]

Ointment, topical:
Zovirax®: 5% (15 g)

Suspension, oral: 200 mg/5 mL (480 mL)
Zovirax®: 200 mg/5 mL (480 mL) [banana flavor]

Tablet: 400 mg, 800 mg
Zovirax®: 400 mg, 800 mg

DOSAGE FORMS: CONCISE
Capsule: 200 mg
Zovirax®: 200 mg

Cream, topical:
Zovirax®: 5% (2 g, 5 g)

Injection, powder for reconstitution: 500 mg, 1000 mg

Injection, solution [preservative free]: 50 mg/mL (10 mL, 20 mL)

Ointment, topical:
Zovirax®: 5% (15 g)

Suspension, oral: 200 mg/5 mL
Zovirax®: 200 mg/5 mL

Tablet: 400 mg, 800 mg
Zovirax®: 400 mg, 800 mg

GENERIC EQUIVALENT AVAILABLE — Yes: Excludes cream, ointment

ADMINISTRATION
Oral: May be administered with or without food.

I.V.: Avoid rapid infusion; infuse over 1 hour to prevent renal damage; maintain adequate hydration of patient; check for phlebitis and rotate infusion sites. Avoid I.M. or SubQ administration.

Topical: Not for use in the eye. Apply using a finger cot or rubber glove to avoid transmission to other parts of the body or to other persons.

COMPATIBILITY — Stable in D5W, D5NS, D51/4NS, D51/2NS, LR, NS.

Incompatible with blood products and protein-containing solutions.

Y-site administration: Compatible: Allopurinol, amikacin, amphotericin B cholesteryl sulfate complex, ampicillin, anidulafungin, cefazolin, cefotaxime, cefoxitin, ceftazidime, ceftizoxime, ceftriaxone, cefuroxime, chloramphenicol, cimetidine, clindamycin, co-trimoxazole, dexamethasone sodium phosphate, dimenhydrinate, diphenhydramine, docetaxel, doxorubicin liposome, doxycycline, erythromycin lactobionate, etoposide phosphate, famotidine, filgrastim, fluconazole, gallium nitrate, gentamicin, granisetron, heparin, hydrocortisone sodium succinate, hydromorphone, imipenem/cilastatin, linezolid, lorazepam, magnesium sulfate, melphalan, methylprednisolone sodium succinate, metoclopramide, metronidazole, milrinone, multivitamins, nafcillin, oxacillin, paclitaxel, pemetrexed, penicillin G potassium, pentobarbital, piperacillin, potassium chloride, propofol, ranitidine, remifentanil, sodium bicarbonate, teniposide, theophylline, thiotepa, tobramycin, vancomycin, zidovudine. Incompatible: Amifostine, amsacrine, aztreonam, cefepime, dobutamine, dopamine, fludarabine, foscarnet, gemcitabine, idarubicin, levofloxacin, ondansetron, piperacillin/tazobactam, sargramostim, tacrolimus, vinorelbine. Variable (consult detailed reference): Cisatracurium, diltiazem, meperidine, meropenem, morphine, TPN.

Compatibility in syringe: Incompatible: Caffeine citrate, pantoprazole.

Compatibility when admixed: Compatible: Fluconazole. Incompatible: Dobutamine, dopamine. Variable (consult detailed reference): Meropenem.

USE — Treatment of genital herpes simplex virus (HSV), herpes labialis (cold sores), herpes zoster (shingles), HSV encephalitis, neonatal HSV, mucocutaneous HSV in immunocompromised patients, varicella-zoster (chickenpox)

USE - UNLABELED / INVESTIGATIONAL — Prevention of HSV reactivation in HIV-positive patients; prevention of HSV reactivation in hematopoietic stem cell transplant (HSCT); prevention of HSV reactivation during periods of neutropenia in patients with cancer; prevention of varicella zoster virus (VZV) reactivation in allogenic HSCT; prevention of CMV reactivation in low-risk allogeneic HSCT; treatment of disseminated HSV or VZV in immunocompromised patients with cancer; empiric treatment of suspected encephalitis in immunocompromised patients with cancer

ADVERSE REACTIONS SIGNIFICANT
Systemic: Oral:

>10%: Central nervous system: Malaise (≤ 12%)

1% to 10%:
Central nervous system: Headache (≤ 2%)
Gastrointestinal: Nausea (2% to 5%), vomiting (≤ 3%), diarrhea (2% to 3%)

Systemic: Parenteral:

1% to 10%:
Dermatologic: Hives (2%), itching (2%), rash (2%)
Gastrointestinal: Nausea/vomiting (7%)
Hepatic: Liver function tests increased (1% to 2%)
Local: Inflammation at injection site or phlebitis (9%)
Renal: BUN increased (5% to 10%), creatinine increased (5% to 10%), acute renal failure

Topical:

>10%: Dermatologic: Mild pain, burning, or stinging (ointment 30%)

1% to 10%: Dermatologic: Pruritus (ointment 4%), itching

All forms: <1% (Limited to important or life-threatening): Abdominal pain, aggression, agitation, alopecia, anaphylaxis, anemia, angioedema, anorexia, ataxia, coma, confusion, consciousness decreased, delirium, desquamation, disseminated intravascular coagulopathy (DIC), dizziness, dry lips, dysarthria, encephalopathy, erythema multiforme, fatigue, fever, gastrointestinal distress, hallucinations, hematuria, hemolysis, hepatitis, hyperbilirubinemia, hypotension, insomnia, jaundice, leukocytoclastic vasculitis, leukocytosis, leukopenia, local tissue necrosis (following extravasation), lymphadenopathy, mental depression, myalgia, neutrophilia, pain, paresthesia, peripheral edema, photosensitization, pruritus, psychosis, renal failure, renal pain, seizure, somnolence, sore throat, Stevens-Johnson syndrome, thrombocytopenia, thrombocytopenic purpura/hemolytic uremic syndrome (TTP/HUS), thrombocytosis, toxic epidermal necrolysis, tremor, urticaria, visual disturbances

CONTRAINDICATIONS — Hypersensitivity to acyclovir, valacyclovir, or any component of the formulation

WARNINGS / PRECAUTIONS
Concerns related to adverse effects: Renal effects: Renal failure (sometimes fatal) has been reported. Dehydration, pre-existing renal disease and nephrotoxic drugs increase risk; infuse over at least 1 hour to reduce risk of renal tubular damage. Thrombocytopenic purpura/hemolytic uremic syndrome (TTP/HUS): Has been reported in immunocompromised patients receiving acyclovir.

Disease-related concerns: Genital herpes: Appropriate use: Physical contact should be avoided when lesions are present; transmission may also occur in the absence of symptoms. Treatment should begin with the first signs or symptoms. Herpes labialis: Appropriate use: For external use only to the lips and face; do not apply to eye or inside the mouth or nose. Treatment should begin with the first signs or symptoms. Herpes zoster: Appropriate use: Therapy should be started within 72 hours of appearance of rash to be effective. Renal impairment: Use with caution in patients with pre-existing renal impairment; dosage adjustments recommended. Varicella-zoster: Appropriate use: Treatment should begin within 24 hours of appearance of rash; oral route not recommended for routine use in otherwise healthy children with varicella, but may be effective in patients at increased risk of moderate-to-severe infection (>12 years of age, chronic cutaneous or pulmonary disorders, long-term salicylate therapy, corticosteroid therapy).

Concurrent drug therapy issues: Nephrotoxic drugs: Use with caution in patients receiving other nephrotoxic drugs.

Special populations: Elderly: Use with caution in the elderly; higher risk for CNS, renal, and gastrointestinal adverse events. Immunocompromised patients: Use with caution in immunocompromised patients. Pediatrics: Safety and efficacy of oral formulations have not been established in children <2 years of age.

Dosage form specific issues: Injection: Use I.V. preparation with caution in patients with underlying neurologic abnormalities, serious hepatic or electrolyte abnormalities, or substantial hypoxia.

Other warnings/precautions: Adequate hydration: Maintain adequate hydration during oral or intravenous therapy.

DRUG INTERACTIONS
Mycophenolate: Acyclovir-Valacyclovir may increase the serum concentration of Mycophenolate. Mycophenolate may increase the serum concentration of Acyclovir-Valacyclovir. Risk C: Monitor therapy

Tenofovir: Acyclovir-Valacyclovir may decrease the excretion of Tenofovir. Risk C: Monitor therapy

Zidovudine: Acyclovir-Valacyclovir may enhance the CNS depressant effect of Zidovudine. Risk C: Monitor therapy

Zoster Vaccine: Acyclovir-Valacyclovir may diminish the therapeutic effect of Zoster Vaccine. Management: When possible, discontinue antiviral agents with anti-zoster activity (i.e., acyclovir, valacyclovir, famciclovir) for at least 24 hours prior to and 14 days after receiving a live attenuated zoster vaccine. Risk X: Avoid combination

ETHANOL / NUTRITION / HERB INTERACTIONS — Food: Does not affect absorption of oral acyclovir.

PREGNANCY RISK FACTOR — B (show table)

PREGNANCY IMPLICATIONS — Teratogenic effects were not observed in animal studies. Acyclovir has been shown to cross the human placenta. There are no adequate and well-controlled studies in pregnant women. Results from a pregnancy registry, established in 1984 and closed in 1999, did not find an increase in the number of birth defects with exposure to acyclovir when compared to those expected in the general population. However, due to the small size of the registry and lack of long-term data, the manufacturer recommends using during pregnancy with caution and only when clearly needed. Data from the pregnancy registry may be obtained from GlaxoSmithKline.

LACTATION — Enters breast milk/use with caution (AAP rates "compatible")

BREAST-FEEDING CONSIDERATIONS — Nursing mothers with herpetic lesions near or on the breast should avoid breast-feeding. Limited data suggest exposure to the nursing infant of ~0.3 mg/kg/day following oral administration of acyclovir to the mother.

DIETARY CONSIDERATIONS — May be taken with or without food. Acyclovir 500 mg injection contains sodium ~50 mg (~2 mEq).

PRICING — (data from drugstore.com)
Capsules (Acyclovir)
200 mg (30): $12.99

Capsules (Zovirax)
200 mg (30): $92.39

Cream (Zovirax)
5% (2): $66.96
5% (5): $147.47

Ointment (Zovirax)
5% (15): $165.27

Suspension (Acyclovir)
200 mg/5 mL (473): $123.97

Suspension (Zovirax)
200 mg/5 mL (473): $252.77

Tablets (Acyclovir)
400 mg (60): $28.99
800 mg (30): $24.99

Tablets (Zovirax)
400 mg (60): $344.72
800 mg (30): $324.98

MONITORING PARAMETERS — Urinalysis, BUN, serum creatinine, liver enzymes, CBC

CANADIAN BRAND NAMES — Apo-Acyclovir®; Gen-Acyclovir; Novo-Acyclovir; Nu-Acyclovir; ratio-Acyclovir; Zovirax®

INTERNATIONAL BRAND NAMES — Abbovir (PL); ACERPES (DE); Acic Creme (DE); Aciclobeta (AU); Acicloftal (IT); Aciclor (VE); Aciclosina (PE); Aciclovir (PL); aciclovir von ct (LU); Aciclovir-BC IV (AU); Acicvir (NZ); Acifur (MX); Acihexal (AU); Acivir Cream (IL, IN); Acivir Eye (IN); Acix (PL); Aclova (KP); Aclovir (HR, TH, TW); Aclovirax (HK); ACS (KP); Activir (FR); Acyclo-V (AU, BH, NZ); Acyclostad (PL); Acyclovir (PL); Acyclovir Stada (PL); Acyhex (PH); Acyklowir (PL); Acylene (MY); Acyrova (KP); Acyvir (EC, HK, IT); Aias (KP); Antivir (PL); Apo-Acyclovir (PL); Avorax (HK, MY, SG); Avorax Cream (MY); Awirol (PL); Cicloferon (MX); Cicloviral (CO); Ciklovir (HU); Clinovir (ID, TH); Clirbest (MX); Clorixan (MX); Clovir (BR, KP); Cloviran (CN); Clyvorax (MX); Colsor (TH); Cusiviral (HK, MY, PL, SG); Cyclivex (ZA); Cyclomed (IL); Cyclorax (HK); Cyclostad (PH); Cyclovir (BF, BJ, CI, ET, GH, GM, GN, KE, LR, MA, ML, MR, MU, MW, NE, NG, SC, SD, SL, SN, TN, TZ, UG, ZA, ZM, ZW); Cyllanvir (PH); Danovir (SG); Declovir (HK); Deherp (TH, TW); Dravyr (SG); Duvimex (AE, BH, CY, EG, IL, IQ, IR, JO, KW, LB, LY, OM, QA, SA, SY, YE); Ecuvir (EC); Entir (SG, TH); Erlvirax (SG); Euroclovir (HK); Eurovir (PY); Exavir (BR); Expit (UY); Geavir (DK, SE); Genovix (MX); Hascovir (PL); Helvevir (CH); Herax (ID); Hercivir (MX); Herpefug (DE); Herpesin (HU, PL); Herpetad (CR, DO, GT, HN, NI, PA, SV); Herpevir (FR); Herpex (BH, IN, PL); Herpizyg (TH); Herpoviric (DE); Herpoviric Rp Creme (DE); Heviran (PL); Ignis (MX); Inmerax (CN); Jersin (MX); Juviral (DE); Laciken (MX); Lermex (TH); Licovir (ID); Lisovyr (AR, CN); Lovir (AU, HK); Lovir Cold Sore Cream (AU); Lovire (ZA); Mapox (LU); Marvir (TH); Maynor (ES); Medovir (AE, BF, BG, BH, BJ, CI, CY, EG, ET, GH, GM, GN, IL, IQ, IR, JO, KE, KW, LB, LR, LY, MA, ML, MR, MU, MW, MY, NE, NG, OM, QA, SA, SC, SD, SG, SL, SN, SY, TN, TW, TZ, UG, YE, ZA, ZM, ZW); Molavir (ID); Norum (TH); Oppvir (TH, TW); Opthavir (MX); Ozvir (AU); Poviral (EC); Proviral (AR); Qualiclovir (HK); Quavir (ID); Ranvir (TH); Ranviran (PL); Reclovax (TH); Remex (FR); Skirax (TW); Sophivir Ungena (MX); Supra-Vir (IL); Supraviran (DE, LU, PL); Supraviran Creme (AE, BH, CY, DE, EG, IL, IQ, IR, JO, KW, LB, LY, OM, QA, SA, SY, YE); Syntovir (HK); Telviran (HU); Vacrax (MY); Vacrovir (KP); Vermis (TH); Vicorax (TH, TW); Victoclir (MX); Viracir (PL); Viralex-DS (PH); Viralis (ID); Virax (KP); Virest (MY, SG); Virestat (MX); Virex (CO); Virherpes (ES); Virless (CL, SG, TW); Viroclear (HK); Virogon (TH); Virokill (HU); Virolan (TW); Virolex (HR, HU, PL); Viromed (TH); Virucid (HK); Virules (HK); Vivir (KP); Warviron (HK); Zeven Cream (MY); Zevin (TH); Zirconia (MX); Ziverone (MX); Zodiac (KP); Zoral (HK, SG); Zoral Cream (MY); Zorax (SG); Zoter (ID); Zoteran (PH); Zovir (DK); Zovirax (AE, AR, AT, AU, BB, BD, BE, BF, BG, BH, BJ, BM, BO, BR, BS, BZ, CH, CI, CL, CN, CO, CR, CY, CZ, DE, DK, DO, EC, EG, ES, ET, FI, FR, GB, GH, GM, GN, GR, GT, GY, HK, HN, HR, HU, ID, IE, IL, IN, IQ, IR, IT, JM, JO, JP, KE, KP, KW, LB, LR, LU, LY, MA, ML, MR, MU, MW, MX, MY, NE, NG, NI, NL, NO, OM, PA, PE, PH, PK, PR, PT, PY, QA, RU, SA, SC, SD, SE, SG, SL, SN, SR, SV, SY, TH, TN, TR, TT, TW, TZ, UG, UY, VE, YE, ZA, ZM, ZW); Zovirax [tabs./susp./ungt.] (PL); Zyclorax (ID); Zyvir (KE)

MECHANISM OF ACTION — Acyclovir is converted to acyclovir monophosphate by virus-specific thymidine kinase then further converted to acyclovir triphosphate by other cellular enzymes. Acyclovir triphosphate inhibits DNA synthesis and viral replication by competing with deoxyguanosine triphosphate for viral DNA polymerase and being incorporated into viral DNA.

PHARMACODYNAMICS / KINETICS
Absorption: Oral: 15% to 30%

Distribution: Vd: 0.8 L/kg (63.6 L): Widely (eg, brain, kidney, lungs, liver, spleen, muscle, uterus, vagina, CSF)

Protein binding: 9% to 33%

Metabolism: Converted by viral enzymes to acyclovir monophosphate, and further converted to diphosphate then triphosphate (active form) by cellular enzymes

Bioavailability: Oral: 10% to 20% with normal renal function (bioavailability decreases with increased dose)

Half-life elimination: Terminal: Neonates: 4 hours; Children 1-12 years: 2-3 hours; Adults: 3 hours

Time to peak, serum: Oral: Within 1.5-2 hours

Excretion: Urine (62% to 90% as unchanged drug and metabolite)

PATIENT INFORMATION — This is not a cure for herpes (recurrences tend to continually reappear every 3-6 months after original infection), nor will this medication reduce the risk of transmission to others when lesions are present; avoid sexual intercourse when visible lesions are present. Take as directed for full course of therapy; do not discontinue even if feeling better. Oral doses may be taken with food.