Rash, fever, pruritus, erythema, urticaria, Stevens-Johnson syndrome, erythema multiforme, toxic epidermal necrolysis, serum sickness-like reactions, angioedema; mild to moderate hearing loss (children); nausea, vomiting, gagging, epigastric burning, GI bleeding and infection, abdominal pain, flatulence, ptyalism, indigestion, mouth ulcers, swollen tongue, anorexia, thirst, dyspepsia, stomach cramps, diarrhoea; decreased Hb and haematocrit, thrombocytosis, lymphocytosis, haemolytic anaemia, increased prothrombin time; transient increase in serum AST (SGOT), ALT (SGPT), alkaline phosphatase, LDH and bilirubin levels; transient increase in BUN and/or serum creatinine concentration, decreased CrCl, bilateral renal cortical necrosis; UTI, kidney pain, urethral pain or bleeding, dysuria, vaginitis, vaginal candidiasis, vulvovaginal pruritus, vaginal discharge or irritation; Jarisch-Herxheimer reaction; neck muscle spasm, muscle cramps or stiffness, chest pain or tightness, shortness of breath, tachycardia, chills, lockjaw-type reaction, viral illness, upper respiratory infection, sinusitis, cough, joint swelling, arthralgia; pain at injection site, thrombophlebitis (IV). Rarely, transient eosinophilia and neutropenia, pancytopenia, leucopenia, thrombocytopenia; headache, somnolence or sleepiness, dizziness, hyperactivity, irritable behaviour, myoclonic jerks, seizures, generalised hyperexcitability; jaundice; acute renal failure, interstitial nephritis.
Potentially Fatal: Anaphylaxis, pseudomembranous colitis.