[Metamizol--a new effective analgesic with a long history. Overview of its pharmacology and clinical use]

Metamizol is an effective, non-opioid analgesics which was originally introduced to the therapy in the year 1922. However, with the reference to the side effects of other related pyrazolone derivatives its administration, similarly as the usage of other pyrazolones, was significantly limited. Later, metamizol has been used, usually mixed, with spasmolytic agents and quite recently it has been introduced as a mono-component medicament. Metamizol proved to be a very effective analgesic. When administered in equipotent doses, it had its effects comparable to various opioid analgesics, such as tramadol, pentazocine and pethidine. Beside the strong analgesic effect, it produces also significant antipyretic and splasmolytic effects without the adverse, unpleasant anticholinergic impact. Its spasmolytic effect on the smooth muscle of the sphincter Oddi, urinary tract, and the gal bladder is comparable to the effects of buthylscopolamine. Unlike aspirin and other nonsteroidal antiinflammatory drugs it has, however, no antiinflammatory activity when administered in clinical doses. Similarly, metamizol has no effect on the CNS, cardiovascular system, renal and metabolic functions. On the other hand, metamizol, like aspirin, has got a significant effect on the aggregation of platelets. Metamizol is basically a prodrug. The parent substance is not effective before its conversion into two active metabolites (4-methylaninoantipyrine and 4-aminoantipyrine) in the body. Metamizol is well absorbed from the small intestine but only two above mentioned active metabolites and no parent drug can be detected in the blood. The active metabolites are consequently metabolised to ineffective metabolites including the relevant acetylderivatives, in which the acetylation phenotypes can be distinguished. In the therapy, metamizol can be used, as an analgesic, at post-surgical pain, patient's controlled analgesia (PCA), at the cancer's pain and in the pains of different origin (post-traumatic pain, the pain at myocardial infarction, craniocerebral trauma, and the invasive diagnostic interventions), as well as at he pain of neuromuscular origin, headache and migraine. Its spasmolytic effect in connection with a strong analgesic activity is very useful at various colic attacks. Further, metamizol is a useful antipyretic both in the adults and children. Its adverse effects are not pronounced and drug interactions are minimal. Only when metamizol is administered together with cyclosporine, the blood levels of the last substance should be regularly checked.