Pyrazolones

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Chapter: Essential pharmacology : Nonsteroidal Anti-inflammatory Drugs And Antipyreticanalgesics

Antipyrine (phenazone) and amidopyrine (aminopyrine) were introduced in 1884 as antipyretic and analgesic. Their use was associated with high incidence of agranulocytosis: are banned in many countries, including India. Phenylbutazone was introduced in 1949 and soon its active metabolite oxyphenbutazone was also marketed.


PYRAZOLONES

 

Antipyrine (phenazone) and amidopyrine (aminopyrine) were introduced in 1884 as antipyretic and analgesic. Their use was associated with high incidence of agranulocytosis: are banned in many countries, including India. Phenylbutazone was introduced in 1949 and soon its active metabolite oxyphenbutazone was also marketed. These two are potent anti-inflammatory drugs, inhibit COX, but have slow onset, weak analgesic and antipyretic action. Their gastric toxicity is high; edema due to Na+ and water retention is frequent and CNS side effects, hypersensitivity reactions, hypothyroidism are reported. They are banned in many countries and rarely used in others due to residual risk of bone marrow depression and other toxicity. Two other pyrazolones available in India—metamizol and propiphenazone are primarily used as analgesic and antipyretic.

 

Metamizol (Dipyrone)

 

In contrast to phenylbutazone, this derivative of amidopyrine is a potent and promptly acting analgesic and antipyretic but poor anti-inflammatory and not uricosuric. It can be given orally, i.m. as well as i.v, but gastric irritation, pain at injection site occurs. Occasionally, i.v. injection produces precipitous fall in BP.

 

Few cases of agranulocytosis were reported and metamizol is banned in the USA and some European countries. However, it has been extensively used in India and other European countries. Adverse reaction data collected over four decades shows that risk of serious toxicity with this drug is lower than with aspirin or many other NSAIDs. However, its fixed dose combination with antispasmodics is banned in India.

 

Dose: 0.5–1.5 g oral/i.m./i.v.; ANALGIN 0.5 g tab; NOVALGIN, BARALGAN 0.5 g tab, 0.5 g/ml in 2 ml and 5 ml amps; ULTRAGIN 0.5 g/ml inj in 2 ml amp and 30 ml vial.

 

Propiphenazone

 

Another pyrazolone, similar in properties to metamizol; claimed to be better tolerated. Agranulocytosis has not been reported.

 

Dose: 300–600 mg TDS; marketed only in combination in several ‘overthecounter’, preparations—in SARIDON, ANAFEBRIN: propiphenazone 150 mg + paracetamol 250 mg tab.

 

DART: propiphenazone 150 mg + paracetamol 300 mg + caffeine 50 mg tab.

 

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