McKenna's Pharmacology for Nursing, 2e

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C H A P T E R 1 0  Antiviral agents

Clinically important drug–drug interactions There is an increased risk of renal toxicity if these drugs are taken with other nephrotoxic drugs. If such a combi- nation is used, monitor the person closely. An evaluation of risks versus benefits may be necessary if renal function begins to deteriorate. Prototype summary: Adefovir Indications: Treatment of chronic hepatitis B in adults with evidence of active viral replication and either evidence of persistent elevations in alanine aminotransferase (ALT) and aspartate aminotransferase (AST) or histologically active disease. Actions: Inhibits hepatitis B virus reverse transcriptase, causes DNA chain termination and blocks viral replication. Pharmacokinetics: Route Onset Peak Duration Oral Rapid 0.6–4 hours Unknown T 1/2 : 7.5 hours; excreted in the urine.

any of these drugs crosses the placenta or enters breast milk. Peak effects of boceprevir occur in 2 hours and for telaprevir in 4 to 5 hours. Telaprevir has a half-life of 4.0 to 4.7 hours and boceprevir has a half-life of 3.4 hours. Contraindications and cautions These drugs are contraindicated with any known allergy to the drugs and with breastfeeding because of potential toxicity to the infant. Use caution when administering these drugs to individuals with renal impairment and severe liver disease and women who are pregnant. Adverse effects The adverse effects most frequently seen with these drugs are headache, dizziness, nausea, diarrhoea and elevated liver enzymes. Severe hepatomegaly with steatosis, sometimes fatal, has been reported with adefovir and telbivudine use. Lactic acidosis and renal impairment have been reported with entecavir and adefovir. A potential risk for hepatitis B exacerbation could occur when the drugs are stopped. Therefore, teach people the importance of not running out of their drugs and use extreme caution when discontinuing these drugs. Common adverse effects for both boceprevir and telaprevir include anaemia, pruritus and nervous system disorders.

Adverse effects: Headache, asthenia, nausea, severe-to-fatal hepatomegaly with steatosis, nephrotoxicity, lactic acidosis, exacerbation of hepatitis B when discontinued.

TABLE 10.4

DRUGS IN FOCUS Anti-hepatitis B and C agents

Drug name

Dosage/route

Usual indications

Hepatitis B

Adult: 10 mg/day PO Renal impairment:

Treatment of hepatitis B with evidence of active viral replication and persistent elevations in liver enzymes Treatment of chronic hepatitis B in adults with evidence of active viral replication and persistent liver enzyme elevations Treatment of chronic hepatitis B in people >16 years with evidence of viral replication and persistent liver enzyme elevations

adefovir (Hepsera)

CrCl 30–49 mL/min: 10 mg PO q 48 hours CrCl 10–29 mL/min: 10 mg PO q 72 hours Adults and children (≥16 years): 0.5 mg/day; also receiving lamivudine: 1 mg/day Reduce dose with renal impairment Adults and children >16 years: 600 mg/day PO; reduce dose with renal impairment

entecavir (Baraclude)

telbivudine (Sebivo)

Hepatitis C boceprevir (Victrelis)

Adult: 800 mg PO t.d.s.

Treatment of adults with chronic hepatitis C in combination with peginterferon alfa and ribavirin

telaprevir (Incivo)

Adult: 750 mg PO q 8 hours

Treatment of chronic hepatitis C in adults with compensated liver disease

CrCl, creatinine clearance.