Phenazone

Products

Phenazone is currently marketed in many countries exclusively in the form of ear drops. Tablets have not been available since the “group analgesics review” conducted by the Medicines Agency. This is in contrast to other countries. This article refers to oral therapy. Phenazone is one of the first synthetically produced analgesics and antipyretics. It was synthesized in the 1880s in Erlangen, Germany, by Ludwig Knorr and launched as antipyrine in 1884.

Structure and properties

Phenazone (C11H12N2O, Mr = 188.2 g/mol) exists as a white crystalline powder or as colorless crystals and is very soluble in water. It belongs to the pyrazolones.

Effects

Phenazone (ATC N02BB01) has analgesic, antipyretic, and to a lesser extent anti-inflammatory and spasmolytic properties. It has both peripheral effects (prostaglandin synthesis inhibition) and central effects. The half-life is in the range of 11 to 12 hours.

Indications

For the treatment of pain, headache, and migraine.

Dosage

According to the prescribing information. Adults may take 1 to 2 500 mg tablets up to four times daily. The dosing interval is 4 to 8 hours. Intake is independent of meals.

Contraindications

  • Hypersensitivity
  • Pyrazolone and pyrazolidine allergy
  • Genetic glucose-6-phosphate dehydrogenase deficiency.
  • Acute hepatic porphyria
  • Pregnancy and lactation
  • Children <12 years

Full precautions can be found in the drug label.

Interactions

Drug-drug interactions have been described with vitamin K antagonists (warfarin), enzyme inducers, cimetidine, disulfiram, beta blockers, calcium channel blockers, antiarrhythmic agents, oral contraceptives, and ketoconazole.

Adverse effects

Possible adverse effects include skin reactions such as redness, itching, inflammation, and hives. Rarely, severe skin disorders such as toxic epidermal necrolysis may occur. Also rare is a severe allergic reaction (anaphylaxis). In isolated cases, blood count changes have been reported (agranulocytosis). An overdose is life-threatening. When iron chloride is taken, the urine may turn red.