Inhibition of the active principle of the weak opioid tilidine by the triazole antifungal voriconazole.

AIMS: To investigate in vivo the influence of the potent CYP2C19 and CYP3A4 inhibitor voriconazole on the pharmacokinetics and analgesic effects of tilidine. METHODS: Sixteen healthy volunteers received voriconazole (400 mg) or placebo together with a single oral dose of tilidine (100 mg). Blood samples and urine were collected for 24 h and experimental pain was determined by using the cold pressor test. Noncompartimental analysis was performed to determine pharmacokinetic parameters of tilidine, nortilidine and voriconazole, whereas pharmacodynamic parameters were analysed by nonparametric repeated measures ANOVA (Friedman). RESULTS: Voriconazole caused a 20-fold increase in exposition of tilidine in serum [AUC 1250.8 h*ng ml(-1), 95% confidence interval (CI) 1076.8, 1424.9 vs. 61 h*ng ml(-1), 95% CI 42.6, 80.9; P < 0.0001], whereas the AUC of nortilidine also increased 2.5-fold. After voriconazole much lower serum concentrations of bisnortilidine were observed. The onset of analgesic activity occurred later with voriconazole, which is in agreement with the prolonged t(max) of nortilidine (0.78 h, 95% CI 0.63, 0.93 vs. 2.5 h, 95% CI 1.85, 3.18; P < 0.0001) due to the additional inhibition of nortilidine metabolism to bisnortilidine. After voriconazole the AUC under the pain withdrawal-time curve was reduced compared with placebo (149 s h(-1), 95% CI 112, 185 vs. 175 s h(-1), 95% CI 138, 213; P < 0.016), mainly due to the shorter withdrawal time 0.75 h after tilidine administration. CONCLUSIONS: Voriconazole significantly inhibited the sequential metabolism of tilidine with increased exposure of the active nortilidine. Furthermore, the incidence of adverse events was almost doubled after voriconazole and tilidine.

In vitro metabolism of the opioid tilidine and interaction of tilidine and nortilidine with CYP3A4, CYP2C19, and CYP2D6.

Tilidine is one of the most widely used narcotics in Germany and Belgium. The compound's active metabolite nortilidine easily penetrates the blood-brain barrier and activates the mu-opioid receptor. Thus far, the enzymes involved in tilidine metabolism are unknown. Therefore, the aim of our study was to identify the cytochrome P450 isozymes (CYPs) involved in N-demethylation of tilidine in vitro. We used human liver microsomes as well as recombinant CYPs to investigate the demethylation of tilidine to nortilidine and quantified nortilidine by liquid chromatography-tandem mass spectrometry. Inhibition of CYPs was quantified with commercial kits. Moreover, inhibition of ABCB1 and ABCG2 was investigated. Our results demonstrated that N-demethylation of tilidine to nortilidine followed a Michaelis-Menten kinetic with a K(m) value of 36 +/- 13 microM and a v(max) value of 85 +/- 18 nmol/mg/h. This metabolic step was inhibited by CYP3A4 and CYP2C19 inhibitors. Investigations with recombinant CYP3A4 and CYP2C19 confirmed that the demethylation of tilidine occurs via these two CYPs. Inhibition assays demonstrated that tilidine and nortilidine can also inhibit CYP3A4, CYP2C19, CYP2D6, ABCB1, but not ABCG2, whereas inhibition of CYP2D6 and possibly also of CYP3A4 might be clinically relevant. By calculating the metabolic clearance based on the in vitro and published in vivo data, CYP3A4 and CYP2C19 were identified as the main elimination routes of tilidine. In vivo, drug-drug interactions of tilidine with CYP3A4 or CYP2C19 inhibitors are to be anticipated, whereas substrates of CYP2C19, ABCB1, or ABCG2 will presumably not be influenced by tilidine or nortilidine.

Sequential first-pass metabolism of nortilidine: the active metabolite of the synthetic opioid drug tilidine.

The disposition of nortildine, the active metabolite of the synthetic opioid drug tilidine, was investigated in healthy volunteers in a randomized, single-dose, three-way crossover design. Three different treatments were administered: tilidine 50 mg intravenously, tilidine 50 mg orally, and nortilidine 10 mg intravenously. The plasma concentrations of tilidine, nortilidine, and bisnortilidine were determined and subjected to pharmacokinetic analysis using noncompartmental methods. The systemic bioavailability of tilidine was low (7.6% +/- 5.3%) due to a pronounced first-pass metabolism. The areas under the plasma concentration versus time curves (A UC) of nortilidine were similar following either oral or intravenous administration of tilidine 50 mg (375 +/- 184 vs. 364 +/- 124 ng.h.ml(-1)). AUC of nortilidine was 229 +/- 42 ng.h.ml(-1) after IV infusion of nortilidine 10 mg and thus much greater than after IV tilidine corrected for differences in dose. Nortilidine had a much lower volume of distribution (275 +/- 79 vs. 1326 +/- 477 L) and a somewhat lower clearance (749 +/- 119 vs. 1198 +/- 228 ml/min) than tilidine. About two-thirds of the dose of tilidine was metabolized to nortilidine, although only half of the latter fraction was available in the peripheral circulation. Nortilidine was subsequently metabolized to bisnortilidine. The mean ratio of the AUC of bisnortilidine to nortilidine was 0.65 +/- 0.14 following IV administration of nortilidine but 1.69 +/- 0.38 and 1.40 +/- 0.27 following oral and intravenous administration of tilidine, respectively. The shapes of the plasma concentration-time curves of the metabolites and parent drug declined in parallel, indicating that the disposition of the metabolites is formation rate limited. Thus, although two-thirds of the dose of tilidine is metabolized to nortilidine, only one-third of the dose is available systemically as nortilidine for interaction with the opiate receptors after both intravenous and oral dosing of tilidine. The remaining part of nortilidine is retained in the liver and is subsequently metabolized to bisnortilidine and yet unknown compounds.

Pharmacokinetics of tilidine and metabolites in man.

Tilidine is a prodrug from which the active metabolite nortilidine is formed by demethylation. The pharmacokinetics of tilidine (T), nortilidine (NT) and bisnortilidine (BNT) were studied in nine healthy subjects following single intravenous (10 min infusion) and oral 50 mg T-HCl dose as well as following multiple 50 mg T-HCl oral doses. Systemic availability of the parent substance was 6% and of the active metabolite NT 99%. The terminal half-life of NT was 3.3 h following single oral administration, 4.9 h following intravenous administration and 3.6 h following multiple dosing. Following intravenous infusion, concentrations of unchanged substance were found which were 30 times higher than following oral administration. BNT was eliminated with half-lives of 5 h after oral administration and 6.9 h after intravenous administration. Renal elimination of unchanged substance was 1.6% of the dose following intravenous administration and less than 0.1% of the dose following oral administration. Approximately 3% were recovered in urine as NT and 5% as BNT following both routes of administration.

Comparison of a GLC-NPD method with a GLC-MS-SIM procedure for the determination of tilidine and its metabolites in plasma.

A gas liquid chromatographic method with nitrogen-phosphorus detection (GLC-NPD) is compared to a GLC-mass spectrometric determination employing selected ion monitoring (GLC-MS-SIM). These two methods of gas chromatographic separation were shown to be suitable for therapeutic monitoring of tilidine, nortilidine, and bisnortilidine in patients. The pharmacokinetic profile of tilidine was also studied in three normal humans after a single oral dose. Pharmacokinetic parameters such as Cmax, tmax, (t1/2) beta, AUC, AUMC, Vd beta, Cltot, beta, and MRT are derived from model independent pharmacokinetic techniques.

Disposition of tilidine in a fatal poisoning in man.

A fatal intoxication due to the ingestion of tilidine, a narcotic analgesic, in conjunction with ethanol, is described. Tilidine and its two active metabolites, nortilidine and bisnortilidine, were identified and quantitated in the biological fluids and tissues by thin-layer chromatography (TLC), gas-liquid chromatography with sensitive nitrogen-phosphorus detection (GLC/NPD) and gas-liquid chromatography with mass spectrometric detection (GC/MS). The toxicological results are compared with previously reported 14C-tilidine tissue distributions in rats following oral administration and limited tissue data in a previously reported human fatality. In the present case, the death was attributed to the combined central nervous system-depressing effects of ethanol and tilidine.

The opiate-like action of tilidine is mediated by metabolites.

The analgesic effect of tilidine in rats is completely antagonized by the narcotic antagonist naloxone. Radioreceptor assays revealed, however, that the main metabolites of tilidine, nortilidine and bisnortilidine, rather than tilidine exhibit affinity to opiate receptors. These findings were confirmed in studies using the electrically stimulated guinea pig ileum and the mouse vas deferens. Chronic tilidine administration to rats caused a considerable degree of physical dependence, which was expected from the ability of the intact animal to metabolize tilidine. In the isolated ileum from chronically morphinized guinea pigs, both nortilidine and bisnortilidine fully substituted for morphine in preventing induction of withdrawal, indicating dependence liability of these metabolites.

[ On the metabolism of ethyl-DL-trans-2-dimethylamino-1-phenyl-cyclohex-3-ene-trans-1-carboxylate-hydrochloride (Tilidine-HCl). 2nd Communication: Studies with 14C-labelled substance on rats and dogs]. / Zum Metabolismus von DL-trans-2-Dimethylamino-1-phenyl-cyclohex-3-en-trans-1-carbonsäureäthylester-hydrochlorid (Tilidin-HCl). 2. Mitteilung: Untersuchungen mit der radioaktiv markierten Substanz an Ratten und Hunden

Absorption, distribution, metabolism and excretion of the potent analgesic ethyl-DL-trans-2-timethylamino-1-phenyl-chclohex-3-ene-trans-1-carboxylate-hydrochloride (tilidine-HCl, Gö 1261 C, active ingredient of Vloron) were investigated in rats and dogs, using the radioactively labelled substance. Following oral administration, tilidine-HCl is rapidly and completely absorbed from the duodenum. During absorption, tilidine undergoes a marked first-pass effect. In plasma several metabolites are found, part of them occurring in higher concentrations than the unchanged substance. The metabolites are also formed rapidly after parenteral administration, unchanged tilidine being found in higher concentrations than any of the metabolites at all times measured. Following both routes of administration, the Met. I (nortilidine), also possessing a strong analgesic activity, reaches similar plasma levels. 14C distribution studies in rats showed a relatively high concentration of the radioactivity in the excretory organs, liver and kidneys. In brain, muscle tissue and blood much lower 14C concentrations are found. The concentrations measured in the foetal organs correspond to those in the muscle tissue of the mother animals and are, therefore, much lower than in most maternal organs. The radioactivity is eliminated from the foetal organs at the same rate as from the maternal organs. Tilidine is rapidly and completely eliminated with the excrements, nearly exclusively in the form of metabolic products. Rats eliminate 50% of the given radioactivity via the kidneys. The relatively high fecal elimination is based on the biliary metabolites. Following intraduodenal and intravenous administration to rats with an interrupted enterohepatic circulation, about 80% of the dose is eliminated with bile. The biliary metabolites are partly reabsorbed. In dogs, approx. 80% of the applied radioactivity is eliminated with urine.

[Analog computer analysis of radioactivity kinetics in man following oral administration of tilidine HCl-14C]. / Analogrechneranalyse der Radioaktivitätskinetik beim Menschen nach oraler Gabe von Tilidin HCl-14-C

Models for studying the absorption and elimination kinetics of 14-C labelled DL-Ethyl-trans-2-dimethylamino-1-phenyl-cyclohex-3-ene-trans-1-carboxylate-hydrochloride (Tilidine - HCl, Valoron) are developed, based on the concentration vs. time of radioactivity in the plasma following a single oral administration in man. For this purpose, the average concentration values in the plasma of 3 healthy adults, as given by Vollmer and Poisson [12] were employed. 1. Two three-compartment-models were developed which simulate with sufficient accuracy the 14-C-Valoron concentration curve in the plasma. 2. Computer analysis enables one to determine the distribution of 14-C-Valoron among the intra- and extravasal compartments and the half life for absorption t1/2 equals 0.57 h, for transport from plasma into the extravasal compartment t1/2 equals 3.31 h, for resorption t1/2 equals 4.11 h, for elimination with feces t1/2 equals 29.5 h and for elimination in urine t1/2 equals 8.75 h. 3. The use of two different models allows one to draw conclusions concerning the participation of parenchymatous organs in storage and elimination. 4. The probable radioactivity curve is calculated for repeated oral application of 14-C-Valoron in 8 hours intervals.