Tetroquinol PK

Code: R18M01OM

The study was conducted based on the WADA's interest in conducting an excretion study with trimetoquinol in order to determine the possibility of establishing a reporting threshold for this substance in the anti-doping context.

Trimetoquinol (tretoquinol, 1-(3', 4', 5'-trimetoxybenzyl)-6,7-dihydroxy-1,2,3-tetrahydroisoquinoline), non-selective β-agonist, [1] is explicitly listed as a banned substance on the WADA Prohibited List 2019.[2] The corresponding substance is therapeutically used for treating asthma, and the pharmaceutical product Inolin® is available in Japan, Indonesia and Chinese Taipei.[3] The over-the-counter pharmaceuticals are also available (max. dosage 6 mg/day) on Japanese market, and the fact means that it is easy to purchase for Japanese athletes.

In the previous metabolism studies,[4,5] free form, glucoronide conjugate, and sulphate conjugate of trimetoquinol and the O-methylated trimetoquinol were reported (Scheme 1).Trimetoquinol is metabolized by Catechol-O-methyl transferase (COMT), and the β-stimulating effect of the methoxymetabolites is lower than that of trimetoquinol.[6] Moreover, the β-blocking action of 6-methoxytrimetoquinol is a tenth that of propranolo. Similarly, these findings have been reported in other β-stimulants, popssessing a catechol moiety, e.g. 3-methoxyisoproterenol (isoproterenol metabolite) and coclaurine (higenamine metabolite).[6,7] Therefore, the concentration of the O-methylated metabolites and their conjugated metabolites was not considered in this study, such as our previous study in higenamine.[8]

This minimum required performance level (MRPL) of β2-agonist is set to 20 ng/mL.[9] The reporting threshold for higenamine and salmeterol is defined as 10 ng/mL (50% MRPL of each parent compound).[9] Moreover, the WADA threshold concentration is based on the sum of free form and the glucuronide conjugate of parent β2-agonists (i.e., salbutamol and formoterol).[10] However, little information is available concerning the urinary concentration in which trimetoquinol can be identified in human urine after administration.

Based on these backgrounds, in this study, a liquid chromatography-tandem mass spectrometry (LC-MS/MS) for the quantification of trimetoquinol (free pluc glucuronid conjugate) in human urine was developed. Moreover, trimetoquinol hydrochloride hydrate was orally administered to six Japanese volunteers (3 males and 3 females). Urine samples were analysed using the developed method and the excretion profile was examined.

Main findings

Trimetoquinol (tretoquinol) is a non-selective beta-2 agonist, which has been explicitly listed as an example of prohibited beta-2 agonists under class S3 of the 2019 Prohibited List. Trimetoquinol is used therapeutically for the treatment of asthma (sold as Inolin® in several Asian countries) and is also used as an ingredient of over-the-counter (OTC) cold and flu medications.

Studies on trimetoquinol metabolism have shown that it is excreted in urine either as free form (minor) of phase-II conjugates (glucuronide and sulfate). However, there is no information available about the urinary concentrations after oral administration.

In this study, volunteers were administered 6 mg of oral trimetoquinol hydrochloride hydrate (as per manufacturer's recommendations) to determine the excretion kinetics of trimetoquinol. The results indicate that a conservative reporting limit of 20 ng/m of trimetoquinol (free plus glucuronde conjugate) should avoid the reporting of an Adverse Finding which may have resulted from the inadvertent use of the trimetoquinol-containing OTC medications before the 2019 Prohibited List comes into effect on 1 January 2019.