Comparison of Pharmacological and Pharmacokinetic Properties of Metamizol andTramadol

Summary

In the present paper pharmacological properties and pharmacokinetic parameters of twoeffective analgesics, metamizol and tramadol, from two completely pharmacologically differentgroups were compared. Due to the absolutely different doses (metamizol was administered ina dose of 1000 mg and tramadol in a dose of 100 mg), mutual comparison of the dose dependentpharmacokinetic parameters is impossible. However, elimination half-lives and renal clearan-ces of both investigated drugs can be compared. It was shown that elimination half-life ofmetamizol, notably its most important metabolite 4-methylaminoantipyrine, is about one halfof that of tramadol after oral administration of both drugs. Tramadol clearance is, however,two orders faster than that of metamizol. Plasma protein binding of two active metabolites ofmetamizol equals about 50%. On the other hand, about 65% tramadol is bound to plasmaproteins. It is therefore obvious that plasma protein binding cannot contribute to the explana-tion of the obvious difference when comparing these two drugs.Contrary to pharmacokinetics there are, however, significant differences in the efficacy of thesetwo drugs. Tramadol proved to be a similarly effective analgesic as metamizol after recommen-ced doses of 100 mg and 2.5 g, respectively. Alike tramadol, metamizol exerts a significantintrinsic antispasmodic activity. It is therefore obvious that in colicky pain the reliable analgesicactivity of metamizol is effectively combined with its pronounced antispasmodic effect. Incontrast, adverse central depressive effects of tramadol, especially after parenteral administra-tion, may clearly limit the usefulness of this drug in the general practitioner’s office, becauseof practical immobilisation of the patient for a certain time. Metamizol, on the other hand, showsno depressive central actions and in addition, metamizol cannot enhance depressive effects ofother centrally depressant drugs including alcohol. After parenteral administration of metami-zol the patient is fully competent to drive motor vehicles, and even after high doses there is nodanger of respiratory depression. Similarly as tramadol, metamizol did not prove to exert anyclinical significant anti-inflammatory effect; however, alike tramadol, metamizol has a powerfulantipyretic effect, which can be effectively used if necessary. Last but not least, very slightside-effects of metamizol during short-term acute administration can be omitted.

Key words:
metamizol - tramadol - pharmacology - pharmacokinetics - therapy.