Liquid chromatography tandem mass spectrometry assay to determine the pharmacokinetics of aildenafil in human plasma

Efficacy and safety of aildenafil citrate in Chinese men with erectile dysfunction: a multicenter, randomized, double-blind, placebo-controlled crossover trial

Background

To evaluate the efficacy and safety of aildenafil citrate in the treatment of erectile dysfunction (ED) in Chinese population.

Methods

A multicenter, randomized, double-blind, placebo-controlled, double-cycle crossover trial was conducted in three medical centers. Male patients with mild to moderate ED were randomized into two groups and received either aildenafil citrate or placebos, followed by a crossover administration after a 7-day washout. The primary outcome was the duration of penile rigidity over 60% measured by RigiScan^® Plus. Main secondary outcomes were the duration of penile rigidity over 80% and erectile hardness score (EHS).

Results

A total of 60 patients with mild to moderate ED were enrolled in the study and 57 of them completed the trial (30 in the aildenafil group and 27 in the placebo group). The median duration of penile tip rigidity over 60% was 4.25 (0.00, 19.00) min in the aildenafil group, as compared with 0.50 (0.00, 2.75) min in the placebo group (P<0.001). The median duration of penile base rigidity over 60% was 3.25 (0.00, 12.50) min in the aildenafil group, as compared with 0.00 (0.00, 2.50) min in the placebo group (P<0.001). The duration of penile base rigidity over 80% was significantly increased in the aildenafil group versus the placebo group (P=0.002). The EHS was significantly improved in the aildenafil group (P<0.001). No severe adverse events associated with aildenafil citrate occurred in both groups.

Conclusions

These results suggested that aildenafil citrate was efficient and well-tolerated in the treatment of Chinese men with mild to moderate ED.

Trial Registration

Chinese Clinical Trial Registry ChiCTR1900026025.

Use of high-pH (basic/alkaline) mobile phases for LC-MS or LC-MS/MS bioanalysis

High-pH or basic/alkaline mobile phases are not commonly used in LC-MS or LC-MS/MS bioanalysis because of the deeply rooted concern with column instability and reduced detection sensitivity for basic compounds in high-pH mobile phases owing to charge neutralization. With the advancement of LC column technology and the wide recognition of the "wrong-way-round" phenomena, high-pH mobile phases are more and more used in LC-MS or LC-MS/MS bioanalysis to improve chromatographic peak shape, retention, selectivity, resolution, and detection sensitivity, not only for basic compounds, but also for many other compounds. In this article, the benefits, practical considerations, application examples and cautions for using high-pH mobile phases in LC-MS or LC-MS/MS bioanalysis are reviewed, with a focus on quantification. Furthermore, the future trends in this field are also envisaged. A total of 84 references are cited in this review.

Metabolism of aildenafil in vivo in rats and in vitro in mouse, rat, dog, and human liver microsomes

Aildenafil, 1-{[3-(6, 7-dihydro-1-methyl-7-oxo-3-propyl-1H-pyrazolo [4, 3-d] primidin-5-yl)-4-ethoxyphenyl] sulfonyl}-cis-3, 5-dimethylpiperazine, a phosphodiesterase type V enzyme inhibitor (PDE5I), is under development for treatment of erectile dysfunction (ED). The purpose of this study was to elucidate metabolism of aildenafil in vivo in rats and in vitro in mouse, rat, dog, and human liver microsomes. Thirty-one phase I metabolites have been found by LTQ/Orbitrap hybrid mass spectrometry in rat urine, faeces, and bile after oral administration. Major biotransformation pathways of aildenafil included N-dealkylation of the piperazine ring, hydroxylation and dehydrogenation, aliphatic hydroxylation and loss of alkyl group of piperazine ring. Minor pathways involved hydroxylation on the phenyl ring, pyrazole N-demethylation, O-deethylation, loss of piperazine ring (cleavage of N-S bond) and dehydrogenation on the piperazine ring. Similar metabolic pathways of aildenafil were observed in the incubations of liver microsomes from mouse, rat, and dog as well as from human. The depletion rate of parent drug in mouse and rat liver microsomes was significantly different from that in human liver microsomes. The cytochrome P450 reaction phenotyping analysis was conducted using isozyme-specific inhibitors. The results indicated that CYP3A was the main isoenzyme involved in oxidative metabolism of aildenafil. Overall, these in vitro and in vivo findings should provide valuable information on possible metabolic behaviours of aildenafil in humans.

Sildenafil and analogous phosphodiesterase type 5 (PDE-5) inhibitors in herbal food supplements sampled on the Dutch market

Herbal food supplements, claiming to enhance sexual potency, may contain deliberately added active pharmacological ingredients (APIs) that can be used for the treatment of erectile dysfunction (ED). The aim of this study was to determine whether herbal food supplements on the Dutch market indeed contain APIs that inhibit phosphodiesterase type 5 (PDE-5) inhibitors, such as sildenafil and analogous PDE-5 inhibitors. Herbal food supplements intended to enhance sexual potency (n = 71), and two soft drinks, were sampled from 2003 up to and including 2012. In 23 herbal supplements, nine different PDE-5 inhibitors were identified; in a few cases (n = 3), more than one inhibitor was indentified. The presence of these APIs was however not stated on the label. The concentrations of PDE-5 inhibitors per dose unit were analysed. Furthermore, the potential pharmacologically active properties of the detected PDE-5 inhibitors were estimated by using data from the scientific and patent literature regarding (1) in vitro PDE-5 activity, (2) reported effective doses of registered drugs with PDE-5 inhibitor activity and (3) similarity to other structural analogues. It was concluded that 18 of the 23 herbal food supplements, when used as recommended, would have significant pharmacological effects due to added APIs. Adequate use of existing regulation and control measures seems necessary to protect consumers against the adverse effects of these products.

Fragmentation of toxicologically relevant drugs in positive-ion liquid chromatography-tandem mass spectrometry

The identification of drugs and related compounds by LC-MS-MS is an important analytical challenge in several application areas, including clinical and forensic toxicology, doping control analysis, and environmental analysis. Although target-compound based analytical strategies are most frequently applied, at some point the information content of the MS-MS spectra becomes relevant. In this article, the positive-ion MS-MS spectra of a wide variety of drugs and related substances are discussed. Starting point was an MS-MS mass spectral library of toxicologically relevant compounds, available on the internet. The positive-ion MS-MS spectra of ∼570 compounds were interpreted by chemical and therapeutic class, thus involving a wide variety of drug compound classes, such benzodiazepines, beta-blockers, angiotensin-converting enzyme inhibitors, phenothiazines, dihydropyridine calcium channel blockers, diuretics, local anesthetics, vasodilators, as well as various subclasses of anti-diabetic, antidepressant, analgesic, and antihistaminic drugs. In addition, the scientific literature was searched for available MS-MS data of these compound classes and the interpretation thereof. The results of this elaborate study are presented in this article. For each individual compound class, the emphasis is on class-specific fragmentation, as discussing fragmentation of all individual compounds would take far too much space. The recognition of class-specific fragmentation may be quite informative in determining the compound class of a specific unknown, which may further help in the identification. In addition, knowledge on (class-specific) fragmentation may further help in the optimization of the selectivity in targeted analytical approaches of compounds of one particular class.

Structural characterization of sulfoaildenafil, an analog of sildenafil

Phosphodiesterase type 5 (PDE-5) inhibitors represent a class of drugs used primarily in the treatment of erectile dysfunction. Currently, three PDE-5 inhibitors have been approved by the U.S. Food and Drug Administration (FDA) for use in the United States: sildenafil citrate, tadalafil, and vardenafil hydrochloride trihydrate. A bulk material, labeled as an ingredient for a dietary supplement, was analyzed for the presence of PDE-5 inhibitors. The compound that was detected displayed structural similarities to sildenafil, and was characterized further using LC-MS(n), FTICRMS, X-ray crystallography and NMR. The compound was given the name sulfoaildenafil. When compared to sildenafil, sulfoaildenafil contains a sulfur atom substitution for the oxygen atom in the pyrazolopyrimidine portion of the molecule, and a 3,5-dimethyl substitution on the piperazine ring, rather than the 4-methyl moiety. The X-ray crystallographic data indicate that the material in this sample is comprised of two polymorphs, which may affect the chemical and/or biological properties of any product formulated with this compound.