Metamisole

Metamisole, also known as dipyrone or novalgin, is a non-steroidal anti-inflammatory drug (NSAID) that is used for its analgesic, antipyretic, and antispasmodic properties. It is primarily used to treat moderate to severe pain and fever.

Developed in Germany in 1920, metamisole was once widely prescribed. However, concerns about a rare but potentially fatal side effect, agranulocytosis, led to its withdrawal or restriction in many countries, including the United States, Canada, and Australia. Despite these concerns, metamisole remains available and commonly used in many other countries, particularly in Europe, Latin America, and parts of Asia and Africa.

The exact mechanism of action of metamisole is not fully understood, but it is believed to involve inhibition of cyclooxygenase (COX) enzymes and possibly other pathways involved in pain and inflammation. Its antispasmodic effects are thought to be related to its action on smooth muscle.

Metamisole is typically administered orally, intravenously, or intramuscularly. Common side effects, apart from the rare agranulocytosis, can include skin reactions, gastrointestinal upset, and a drop in blood pressure. Due to the risk of agranulocytosis, regular blood monitoring is sometimes recommended for patients on long-term metamisole therapy in countries where it is still prescribed. The decision to use metamisole often involves weighing its perceived benefits against potential risks, with regulatory bodies in different nations having reached varying conclusions.