Identification and quantitation of 1-arylpiperazines, metabolites resulting from side-chain cleavage of (4-substituted aryl-1-piperazinyl)alkyl heterocyclic derivatives in rat plasma and brain

Studies on the Human Metabolism and the Toxicologic Detection of the Cough Suppressant Dropropizine in Urine Using Gas Chromatography-Mass Spectrometry

Studies are described on the metabolism and the toxicologic analysis of the nonopioid cough suppressant dropropizine [R,S-3-(4-phenyl-1-piperazinyl)1,2-propandiol, DRO] in human urine using gas chromatography-mass spectrometry (GC-MS). The metabolism studies showed that DRO was metabolized in humans mainly by hydroxylation of the aromatic ring, by N-dealkylation of the parent drug and of the hydroxyl-metabolite to the corresponding N-phenylpiperazines, and by degradation of the piperazine moiety. The authors' systematic toxicologic analysis (STA) procedure using full-scan GC-MS after acid hydrolysis, liquid-liquid extraction, and microwave-assisted acetylation allowed the unambiguous detection of DRO and its above-mentioned metabolites in human urine up to about 32 hours after intake of a single common therapeutic dose. The target analytes were found to be the parent compound DRO (earlier phase of excretion) and the hydroxylated metabolite para-hydroxy-DRO (later phase of excretion). Both allowed unambiguous detection of an intake of DRO and also differentiation from other phenylpiperazine derivatives.

Toxicological detection of the new designer drug 1-(4-methoxyphenyl)piperazine and its metabolites in urine and differentiation from an intake of structurally related medicaments using gas chromatography–mass spectrometry

Studies are described on the toxicological analysis of the piperazine-derived designer drug 1-(4-methoxyphenyl)piperazine (MeOPP) in rat urine using gas chromatography-mass spectrometry (GC-MS). The authors' systematic toxicological analysis (STA) procedure using full-scan GC-MS after acid hydrolysis, liquid-liquid extraction and microwave-assisted acetylation allowed the detection of MeOPP and its metabolites 1-(4-hydroxy phenyl)piperazine and 4-hydroxyaniline in rat urine after administration of a single dose corresponding to doses commonly taken by drug users. Therefore, this procedure should also be suitable for detection of a MeOPP intake in human urine. However, the metabolites of MeOPP are not unique and can be produced from other drugs. Therefore, differentiation of use of this designer drug from use of the medicaments dropropizine, oxypertine or others, which are metabolized to the MeOPP isomer 1-(2-methoxyphenyl)piperazine, is discussed.

Determination of piribedil and its basic metabolites in plasma by high-performance liquid chromatography

A high-performance liquid chromatographic method for the determination of piribedil and its p-hydroxylated, catechol and N-oxide metabolites in plasma is described. After addition of an internal standard (buspirone), the plasma samples were subjected to a three-step extraction procedure. The final extracts were evaporated to dryness under nitrogen, and the residues were reconstituted in 100 microliters of mobile phase (0.01 M phosphate buffer-acetonitrile, 50:50, v/v) and chromatographed by acetonitrile gradient elution on a C18 reversed-phase column coupled to an ultraviolet detector set at 240 nm. The method was selective for piribedil and its metabolites, and sufficiently sensitive and precise for studies aimed at elucidating the role of the metabolites in the parent drug's pharmacological effects.

Kinetics and brain uptake of S 9795, a new xanthine derivate, in rats

The relationships between plasma and brain concentrations of S 9795 and its main metabolites after single intravenous doses of S 9795 were examined in rats by high-performance liquid chromatography with UV detection. S 9795 disappeared from plasma and brain almost in parallel, with comparable elimination t1/2 of about 0.8 h, regardless of the dose administered. The volume of distribution was high (about 3 1/kg) but total clearance was also high (about 40 ml/min/kg) and this explains the relatively short plasma and brain t1/2 of the drug in the rat. Among the possible metabolites examined, the N-dearylated metabolite S 10238 rapidly appeared in both plasma and brain. Thereafter, S 10238 was likewise eliminated in parallel from both compartments, although at a slower rate (t1/2 of about 1.4 h) than its parent compound. Norcyclizine, a metabolite resulting from cleavage of the parent drug side-chain, was detected only in the brain and only at the highest dose tested. The brain AUC to plasma AUC ratio was slightly less than 1 for S 9795, about 0.1 for S 10238 and possibly more than 2 for norcyclizine, this latter being present in rat plasma at concentrations below the limits of sensitivity of the method (0.08 nmol/ml). The results indicate that S 9795 and some of its metabolites enter the central nervous system, although to different extents, and support the hypothesis that the lack of central effects of S 9795 is probably the consequence of the poor adenosine brain receptor antagonism by this compound.

Lipophilicity and disposition of 1-aryl-piperazines in the rat

The disposition of eight 1-aryl-piperazines was investigated in rats after i.v. administration. The concentration of 1-aryl-piperazine in body fluids and tissues was determined by h.p.l.c. or electron-capture g.l.c. Correlations of kinetics and physiological parameters with the lipophilicity of each 1-aryl-piperazine, determined by h.p.l.c. retention on a reverse-phase C18 column at neutral pH, were investigated. Binding to rat plasma proteins varied within the series, increasing with lipophilicity. For the majority of the derivatives the blood-to-plasma ratio was close to unity, implying an almost equal distribution between erythrocytes and plasma. The most lipophilic 1-aryl-piperazine of the series partitioned more into erythrocytes. The eight compounds differed widely in Vss and total Cl values and as a general trend both values increased with lipophilicity. The percentage of the dose excreted unchanged in the urine decreased progressively with increasing lipophilicity. 1-Aryl-piperazines were distributed extensively in all the tissues examined, concentrating particularly in the eliminating organs and lung. They easily entered the rat brain, Cmax values generally being reached within five minutes of parenteral injection. 1-Aryl-piperazine brain uptake increased with lipophilicity.

1-(o-Methoxyphenyl)piperazine is a metabolite of drugs bearing a methoxyphenylpiperazine side-chain

Drugs bearing an o-methoxyphenylpiperazine (oOCH3PP) moiety in the side-chain of their molecule may form oOCH3PP during biotransformation in-vivo in the rat. This has been verified by combined gas chromatography-mass spectrometry of urine from rats given orally a series of relatively new o-methoxyphenylpiperazine-substituted derivatives. The metabolite is reported to be biochemically and pharmacologically active and therefore its formation may have pharmacological significance, at least for derivatives undergoing extensive cleavage of the arylpiperazine side-chain.

Quantitative analysis of 1-(2-pyrimidinyl)piperazine in plasma by capillary gas chromatography-mass spectrometry

A sensitive method for detecting and quantifying 1-(2-pyrimidinyl)piperazine, an important metabolite of buspirone, in human plasma was developed and validated. The range of the method is 0.2-15 ng/ml. The analyte was removed from buffered, sodium chloride-saturated plasma with benzene, extracted into aqueous acid, washed with diethyl ether and reextracted into benzene. The processed extract was derivatized with pentafluorobenzoyl chloride. Instrumental analysis involved on-column injection into a fused-silica capillary gas chromatography column and detection by selected-ion monitoring mass spectrometry.

Disposition of the psychotropic drugs buspirone, MJ-13805 and piribedil, and of their common active metabolite 1-(2-pyrimidinyl)-piperazine in the rat

1-(2-Pyrimidinyl)-piperazine (PmP) is a common metabolite of the structurally related drugs buspirone, MJ-13805 and piribedil. After i.v. injection (25 mumol/kg) to rats, all three parent drugs are rapidly cleared with a t 1/2 (beta) of about 30 min. The metabolite t 1/2 is about four times that of its parent drugs. About 25, 23 and 2% of buspirone, MJ-13805 and piribedil, respectively, reaches the systemic circulation as PmP. The metabolite concentrates in the brain where its A.U.C. is about twice those of buspirone and MJ-13805. Results indicate that PmP formation is a pharmacologically significant process for both buspirone and MJ-13805 but it is probably less important for piribedil.

Ionization constants and partition coefficients of 1-arylpiperazine derivatives

The ionization constant (pKa) and liposolubilities (log P) of fourteen 1-arylpiperazines were determined by n-octanol/buffer partition. pKa varied little across the entire series. Log P values ranged from less than 1 to about 2 for the highly lipophilic derivatives of the preset series. The results are discussed in relation to the extent to which these derivatives, known to be centrally active, may enter the brain.

In-vivo metabolism in the rat and mouse of antrafenine to 1-m-trifluoromethylphenylpiperazine

The analgesic antrafenine forms 1-m-trifluoromethylphenylpiperazine (mCF3PP) during its biotransformation in the rat and mouse. At least 14 and 3% of an antrafenine dose (25 mg kg-1 p.o.) reaches the systemic circulation as mCF3PP in the mouse and rat respectively. The metabolite easily enters the brain, reaching concentrations several times those in body fluids. This, together with the fact that mCF3PP is known to produce several pharmacological effects compatible with a stimulatory action on 5-hydroxytryptamine postsynaptic receptors, suggests that this metabolite may contribute to the parent drug's pharmacological effects.