RELENZA
Clinical safety rating: caution
Comprehensive clinical and safety monograph for RELENZA (RELENZA).
Neuraminidase inhibitor; prevents viral replication by inhibiting influenza virus neuraminidase, an enzyme that cleaves sialic acid residues from host cell receptors, thereby preventing release of progeny virions.
| Metabolism | Not significantly metabolized; primarily excreted unchanged in urine with a half-life of 2.5-5 hours. |
| Excretion | Renal: 60-70% unchanged via glomerular filtration and tubular secretion; fecal: 10-15% as unabsorbed drug; biliary: negligible. |
| Half-life | Terminal elimination half-life is 2.5-5.1 hours (mean ~2.5 h) after oral inhalation. Prolonged to up to 12-20 h in patients with renal impairment (CrCl <30 mL/min); no dosage adjustment needed but caution. |
| Protein binding | Less than 10% bound to plasma proteins (primarily albumin). |
| Volume of Distribution | Vd ~1.6 L/kg (range 0.4-2.6 L/kg), indicating distribution into total body water and high tissue penetration into respiratory tract. |
| Bioavailability | Oral inhalation: approximately 20% systemic bioavailability due to direct lung deposition; oral (swallowed) bioavailability is <2% due to poor absorption. |
| Onset of Action | Oral inhalation: clinical effect (virologic reduction) measurable within 24-48 hours; maximal effect within 72 hours. |
| Duration of Action | Duration of action lasts approximately 6-10 hours per dose; clinical use recommends twice-daily dosing for 5 days; no post-dose effect beyond dosing period. |
10 mg (two 5 mg blisters) inhaled orally twice daily for 5 days.
| Dosage form | POWDER |
| Renal impairment | No dose adjustment required for any degree of renal impairment. |
| Liver impairment | No dose adjustment required for hepatic impairment. |
| Pediatric use | Children ≥7 years: 10 mg inhaled orally twice daily for 5 days. Children 5-6 years: 10 mg inhaled orally twice daily for 5 days (based on limited data, appropriate dosing for this age group has not been established). |
| Geriatric use | No dose adjustment required; same dosing as adults. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for RELENZA (RELENZA).
| Breastfeeding | Unknown if excreted in human milk; M/P ratio not established; use caution in breastfeeding women. |
| Teratogenic Risk | No evidence of teratogenicity in animal studies; limited human data; zanamivir is not known to cause fetal harm across trimesters. |
| Fetal Monitoring | No specific fetal monitoring required; monitor maternal influenza symptoms and respiratory status. |
■ FDA Black Box Warning
Not applicable; Relenza does not have a black box warning.
| Serious Effects |
["Hypersensitivity to zanamivir or any component of the formulation","Patients with severe asthma or chronic obstructive pulmonary disease (COPD) due to risk of bronchospasm"]
| Precautions | ["Risk of bronchospasm and serious respiratory events in patients with underlying respiratory disease (e.g., asthma, COPD); use with caution and have rapid-acting bronchodilator available","Not recommended for treatment or prophylaxis in patients with severe asthma or uncontrolled chronic respiratory disease","May cause allergic reactions including anaphylaxis","Neuropsychiatric events (e.g., delirium, self-injury) reported primarily in pediatric patients with influenza; risk may be higher with this drug"] |
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| Fertility Effects | No adverse effects on fertility observed in animal studies. |