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CHAPTER 2-20: ANTIVIRAL AND ANTIRETROVIRAL AGENTS

Conan MacDougall

INTRODUCTION

Antiviral drugs are used for a variety of infections, including herpesvirus, hepatitis B (HBV) and C (HCV), and influenza. Antiviral drugs that target human immunodeficiency virus (HIV) are referred to as antiretrovirals. A wide variety of antiretroviral agents from different mechanistic classes are now available (Table II–12). Antiretrovirals are typically given in combination to treat HIV infection. New multiple-drug combined formulations have been developed to decrease the number of pills to take per day and increase adherence to treatment regimens. Some antiretrovirals are also active against HBV. The management of HCV has been revolutionized by the development of new anti-HCV agents, usually given in combination.

TABLE II–12.ANTIVIRAL AND ANTIRETROVIRAL DRUGS
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TABLE II–12. ANTIVIRAL AND ANTIRETROVIRAL DRUGS
Drug Half-life Toxic Dose or Serum Level Toxicity
Antiherpesvirus drugs

 Acyclovir

 Valacyclovir (acyclovir prodrug)

 2.5–3.3 h Chronic High-dose chronic therapy has caused crystalluria and renal failure, leukopenia. Coma, seizures, renal failure after large acute overdoses. Hallucinations and confusion after IV administration, especially in renal impairment.
 Cidofovir 2.5 h 16.3 and 17.4 mg/kg (case reports) No renal dysfunction after treatment with probenecid and IV hydration.
 Foscarnet 3.3–4 h 1.14–8 times recommended dose (average, 4 times) Seizures, renal impairment. One patient had seizures and died after receiving 12.5 g daily for 3 days.

 Ganciclovir

 Valganciclovir (ganciclovir prodrug)

3.5 h (IV)

4 h (oral val-ganciclovir)

 Adults: 5–7 g or 25 mg/kg IV Neutropenia, thrombocytopenia, pancytopenia, increased serum creatinine; 9 mg/kg IV caused a seizure; 10 mg/kg IV daily caused hepatitis. Children: 1 g instead of 31 mg in a 21-month-old had no toxic effect; an 18-month-old received 60 mg/kg IV, was treated with exchange transfusion, and had no effect; a 4-month-old received 500 mg, was treated with peritoneal dialysis, and had no effect; 40 mg in a 2-kg infant caused hepatitis. One adult developed fatal bone marrow suppression after several days of dosing with valganciclovir at a level 10-fold greater than recommended for the patient's renal function.

 Penciclovir

Famciclovir (penciclovir produg)

 2–2.3 h   Extensive intracellular metabolism.
 Trifluridine 12–18 minutes (ophthalmic) 15–30 mg/kg IV Reversible bone marrow toxicity reported after 3–5 courses of IV treatment. Systemic absorption is negligible after ophthalmic instillation. Ingestion of contents of one bottle (7.5 mL, 75 mg) unlikely to cause any adverse effects.
 Vidarabine Rapid deamination to ara-hypoxanthine metabolite, whose half-life is 2.4–3.3 h Chronic 1–20 mg/kg/d IV for 10–15 d Nausea, vomiting, diarrhea, dizziness, ataxia, tremor, confusion, hallucinations, psychosis; decreased Hct, Hgb, WBC, platelets; increased AST, ALT, LDH. Poorly absorbed orally; no toxicity expected if one tube (3.5 g, 105 mg) ingested.
Anti-influenza drugs
 Oseltamivir carboxylate 6–10 h Chronic Doses up to 1,000 mg resulted only in nausea and vomiting in clinical trials. Delirium, hallucinations, psychosis, seizures reported with therapeutic use; may relate to underlying influenza infection.
 Peramivir 20 h Chronic No reported overdoses
 Zanamivir 2.5–5.1 h Chronic Bronchospasm with therapeutic use
Nucleoside (NRTIs) or nucleotide (NtRTIs) ...

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