The frequency categories associated with the adverse events as follows are estimates. For most events, suitable data for estimating incidence were not available. In addition, adverse events may vary in their incidence depending on the indication.
The following convention has been used for the classification of adverse effects in terms of frequency: Very common ≥1/10, common ≥1/100 and <1/10, uncommon ≥1/1000 and <1/100, rare ≥1/10,000 and <1/1000, very rare <1/10,000.
Blood and Lymphatic System Disorders:
Uncommon: Decreases in haematological indices (anaemia, thrombocytopenia, leukopenia).
Immune System Disorders:
Very Rare: Anaphylaxis.
Psychiatric and Nervous System Disorders:
Very Rare: Headache, dizziness, agitation, confusion, tremor, ataxia, dysarthria, hallucinations, psychotic symptoms, convulsions, somnolence, encephalopathy, coma.
The previously mentioned events are generally reversible and usually reported in patients with renal impairment or with other predisposing factors (see Precautions).
Respiratory, Thoracic and Mediastinal Disorders:
Very Rare: Dyspnoea.
Common: Nausea, vomiting. Very Rare: Diarrhoea, abdominal pain.
Common: Reversible increases in liver-related enzymes. Very Rare: Reversible increases in bilirubin, jaundice, hepatitis.
Skin and Subcutaneous Tissue Disorders:
Common: Pruritus, urticaria, rashes (including photosensitivity). Very Rare: Angioedema.
Renal and Urinary Disorders:
Common: Increases in blood urea and creatinine. Rapid increases in blood urea and creatinine levels are believed to be related to the peak plasma levels and the state of hydration of the patient. To avoid this effect the drug should not be given as an IV bolus injection but by slow infusion over a 1-hr period. Very Rare: Renal impairment, acute renal failure, renal pain.
Adequate hydration should be maintained. Renal impairment usually responds rapidly to rehydration of the patient and/or dosage reduction or withdrawal of the drug. Progression to acute renal failure, however, can occur in exceptional cases. Renal pain may be associated with renal failure.
General Disorders and Administration Site Conditions:
Very Rare: Fatigue, fever, local inflammatory reactions.
Severe local inflammatory reactions sometimes leading to breakdown of the skin have occurred when Zovirax IV for infusion has been inadvertantly infused into extracellular tissues.