The most common adverse effects reported in patients using clarithromycin capsules included diarrhea (3%), nausea (3%), alterations in the sense of taste (3%), indigestion (2%), abdominal pain and disorders (2%) and headache (2%).
The following terminologies have been used in order to classify the occurrence of undesirable effects: Very common (>1/10), common (>1/100, <1/10), uncommon (>1/1,000, <1/100), rare (>1/10,000, <1/1,000) and very rare (<1/10,000).
Infections and infestations:
Common: Oral candidosis. As with other antibiotics, the long term use of clarithromycin may result in the excessive growth of resistant organisms.
Blood and the lymphatic system disorders:
Uncommon: Leucopenia. Very rare: Thrombocytopenia.
Immune system disorders:
Uncommon: Allergic reactions, the severity of which varies from urticaria and mild skin symptoms to anaphylaxis.
Very rare: Anxiety, insomnia, hallucinations, psychosis, disorientation, depersonalisation, nightmares and confusion.
Nervous system disorders:
Common: headache, alteration in the sense of smell. Very rare: dizziness, vertigo, tactile hallucinations, convulsions.
Ear and labyrinth disorders:
Rare: tinnitus. Very rare: Reversible hearing loss.
Very rare: QT prolongation, ventricular tachycardia and torsades de pointes.
Common: Nausea, diarrhea, vomiting, abdominal pain, dyspepsia, stomatitis, glossitis, reversible tooth and tongue discolouration and taste perversion, e.g. bitter or metallic taste. Very rare: Pancreatitis.
Clarithromycin treatment has been very rarely associated with reports of pseudomembraneous colitis, which has ranged in severity from mild to life threatening.
Uncommon: Hepatic dysfunction, usually transient and reversible, as well as hepatitis and cholestasis, which may be associated with jaundice.
Very rare: Fatal hepatic impairment has been reported especially in patients with previous hepatic conditions or patients using other hepatotoxic drugs.
Skin and subcutaneous tissue disorders:
Very rare: Stevens-Johnson syndrome and toxic epidermal necrolysis.
Musculoskeletal and connective tissue:
Uncommon: Arthralgia, myalgia.
Renal and urinary disorders:
Very rare: intestinal nephritis, renal failure.
Common: Elevated BUN.
Uncommon: Prolongation of prothrombin time, elevated serum creatinine, altered liver function tests (increased transaminase levels).
Very rare: Hypoglycaemia has been observed especially after concomitant administration with antidiabetic medicinal products and insulin.