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. |
| Molecular Weight | 332.31 |
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 | Limited human data; animal studies show no teratogenicity at clinically relevant doses. |
| 2nd trimester | No adverse fetal effects reported in limited human studies. |
| 3rd trimester | No adverse fetal effects reported; consider maternal benefit vs risk. |
Clinical note
Comprehensive clinical and safety monograph for RELENZA (RELENZA).
| Placental transfer | Zanamivir crosses the placenta in small amounts; fetal exposure is low relative to maternal plasma concentrations. |
| Breastfeeding | Zanamivir is excreted into breast milk in very low concentrations (0.14% of maternal dose). No adverse effects in infants reported. Considered compatible with breastfeeding. |
| Lactation Rating |
■ FDA Black Box Warning
Not applicable; Relenza does not have a black box warning.
| Serious Effects |
Hypersensitivity to zanamivir or any excipientHistory of anaphylaxis to lactose or milk protein
| 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 |
| Food/Dietary | No significant food interactions. No dietary restrictions. |
Loading safety data…
| L2 (Limited data - probably compatible) |
| 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. |
| Fertility Effects | No adverse effects on fertility observed in animal studies. |
| Clinical Pearls | Administer via inhalation only using the provided Diskhaler device. Not for treatment of severe influenza requiring hospitalization. Initiate within 48 hours of symptom onset for best efficacy. Contraindicated in patients with asthma or COPD due to risk of bronchospasm; ensure rescue bronchodilator is available. Not recommended for patients with end-stage renal disease on dialysis. Zanamivir is not a substitute for annual influenza vaccination. |
| Patient Advice | Use only the inhaler device provided; do not open capsules or inhale contents differently. · Start treatment as soon as possible after symptoms appear, ideally within 48 hours. · Complete the full course even if you feel better; usually 5 days, twice daily. · Do not use this medication for prevention of flu unless directed by a healthcare provider. · If you have asthma or COPD, have a fast-acting bronchodilator available and stop zanamivir and seek medical help if breathing worsens. · Report any signs of allergic reaction (rash, difficulty breathing, swelling) immediately. |