Pharmacological effects

Posaconazole (posaconazole) is derived from itraconazole. It is currently subject to III phase clinical trials. Its pharmacological effects are similar with azoles, but compared with itraconazole, it has a stronger inhibitory effect on the C14 demethylation of steroid, especially for Aspergillus.

Pharmacokinetics

Studies on dosage and dosage protocol have shown that the rate of absorption and elimination rate is in line with the single-compartment model. There are significant differences on the relative bioavailability of different doses of oral suspension. It can be taken separately (every 12 hours or every 6 hours) which can significantly improve the bioavailability with the protein binding rate of 98% to 99%. With respect to tablets, the bioavailability of suspensions increase and food can significantly improve the speed and extent of absorption of drug absorption. An investigation of renal dysfunction on the pharmacokinetics of the drug study results has showed that the drug can’t be removed by hemodialysis without being affected by hemodialysis. Single-dose study has showed that patients with varying degrees of chronic kidney disease have no necessity for dosage adjustment. The Half-life of this is about 25 hours which can be primarily metabolized by the liver.

Clinical indications and usage

It can be clinically used for the treatment of aspergillosis, zygnmycosis, and fusariumsis and can also be used for infection caused by part of fluconazole-resistant Candida genus. Studies have shown that posaconazole can widely and effectively applied to the treatment of phaeohyphomycosis and improve the infection survival rate of dermatitidis infection in a dose-dependent manner. The drug, as second-line drugs, has an effective rate of 44% to 78% against the invasive aspergillosis which is resistant to amphotericin B and itraconazole. It also has an effective rate of 71% against the zygomycete fungi. The drug is an oral suspension with the recommended dose of 200mg and 4 times per day with meals and taken orally for 7 to 10 days. This dose can also be maintained or changed to 400mg with oral administration of 2 times per day. The steady-state plasma concentration can reach within 7 to 10 days.
The above information is edited by the Chemicalbook of Dai Xiongfeng.

Description

Posaconazole, launched in the UK, is the newest member of the azole class of antifungal agents to reach the market. It is indicated for the treatment and prophylaxis of a range of invasive fungal infections, including aspergillosis,fusariosis, chromoblastomycosis, mycetoma, and coccidiomycosis in patients who are refractory to, or intolerant of, standard therapy with amphotericin B and/or itraconazole. In the US, it is approved for the prophylaxis of invasive Aspergillus and Candida infections in patients 13 years of age who are at high risk of developing these infections due to being severely immunocompromised. Additionally, it is approved for the treatment of oropharyngeal candidiasis. Posaconazole has an expanded spectrum of activity over other members of the azole antifungals. In addition to potent activity against refractory cases of aspergillosis and fluconazole-resistant Candida, it demonstrates activity against Zygomycetes.

Chemical Properties

White Solid

Originator

Schering-Plough (US)

Uses

Orally active triazole antifungal.

Uses

Posaconazole has been used:

• in antifungal susceptibility testing of Aspergillus terreus
• as a lanosterol?14α-demethylase (CYP51)-specific inhibitor to study its effects on membrane permeability in Candida albicans cells
• to study its effects on promastigotes

Uses

Posaconazole is a sterol C14ɑ demethylase inhibitor with an IC50 of 0.25 nM

Definition

ChEBI: An N-arylpiperazine that consists of piperazine carrying two 4-substituted phenyl groups at positions 1 and 4. A triazole antifungal drug.

brand name

Noxafil

Antimicrobial activity

The spectrum includes dimorphic fungi (Blast. dermatitidis, Coccidioides spp., Hist. capsulatum, Pen. marneffei, and Spor. schenckii), molds (Aspergillus spp., Mucor spp., Rhizomucor spp. and Rhizopus spp.), some dematiaceous fungi and yeasts (Candida spp. and Cryptococcus spp.).

General Description

Technetium (^99mTc) exametazime is a mixture of unstablelipophilic enantiomers that rapidly cross the blood-brain barrierand is trapped in the tissues. The proposed trapping mechanismfor localization includes reduction by glutathione. Asimilar diffusion and trapping process occurs with autologouslymphocytes in vitro.
Exametazime is also known as hexamethylpropyleneamineoxime or HMPAO. The radiolabeled complex is indicated for cerebral perfusion in stroke, but is most commonlyused for the radiolabeling of autologous leukocytesas an adjunct in the localization of intra-abdominal infectionand inflammatory bowel disease.
Each kit includes several components: (a) reaction vialscontaining a mixture of exametazime, stannous chloride,and sodium chloride; (b) vials of 1% methylene blue; (c)vials of phosphate buffer in 0.9% NaCl; and (d) 0.45-μm syringefilters. Product preparation depends on the intendeduse.

Pharmaceutical Applications

A synthetic triazole available for oral administration.

Biochem/physiol Actions

Posaconazole is a highly potent broadspectrum antifungal agent against the yeast infection caused especially by Candida sp. It blocks the growth of fungi by inhibiting the enzyme?lanosterol?14α-demethylase (CYP51). In contrast to other antifungal azoles, posaconazole has been reported not to induce the efflux pump mechanism. Posaconazole exhibits antichagasic effects against different strains of Trypanosoma cruzi causing Chagas disease.

Pharmacokinetics

C_max 200 mg oral: 0.5 mg/L after 4 h
Plasma half-life: 35 h
Volume of distribution: 1774 L
Plasma protein binding: >98%
Absorption
Oral absorption is slow. Absorption from the gastrointestinal tract is improved if the drug is given with a high-fat meal. Blood concentrations increase in proportion to dosage up to 800 mg.
Distribution
It is extensively distributed into body tissues.
Metabolism and excretion
It is not as extensively metabolized by the hepatic cytochrome P₄₅₀ system as other triazole antifungals. More than 70% of an administered dose is eliminated in the feces, predominantly as unchanged drug. The remainder is excreted as glucuronidated derivatives in the urine. Posaconazole is a substrate for intestinal P-glycoprotein,an adenosine triphosphate-dependent plasma membrane transporter responsible for drug efflux from cells. Multiple peaks in blood concentrations have been observed, suggesting that effluxed drug is reabsorbed into the systemic circulation.

Clinical Use

Invasive aspergillosis
Fusarium infection
Chromoblastomycosis and mycetoma
Coccidioidomycosis
Oropharyngeal candidosis
Prophylaxis of invasive fungal infections in patients at serious risk
With the exception of oropharyngeal candidosis and prophylaxis, use is presently restricted to patients with disease that is refractory to other antifungal drugs, or who are intolerant to them.

Side effects

It is generally well tolerated even for long periods. Unwanted effects include gastrointestinal discomfort and mild to moderate, transient abnormalities of liver enzymes. Rare side effects include cholestasis and hepatic failure.

Synthesis

Several routes to the synthesis of posaconazole have been published in the literature. The most likely route to large scale synthesis uses convergent synthesis of a key chiral THF subunit 101 and aryl piperazine amine 102 followed by introduction of the triazole subunit at the end.The readily accessible allyl alcohol 94 was brominated (PBr3) to give bromide 95 which was alkylated with sodium diethylmalonate and the resulting diester was reduced with NaBH4/LiCl, to give the key diol 97 in very good yields. After scanning many hydrolases to desymmetrize the diol via selective acylation, hydrolase SP 435 was found to be suitable. Thus reaction of the diol 97 in the presence of SP 435 with vinyl acetate in acetonitrile gave monoacetate 98 in greater than 90% yield. Iodine mediated cyclization of the monoacetate 98 with iodine in dichloromethane gave chiral iodide 99 in 86% yield. The iodide was converted to triazole (sodiumtriazole, DMF: DMPU) and immediately followed by hydrolysis of the acetate with sodium hydroxide to provide alcohol 100. Activation of the alcohol to the pchlorobenzene sulfonate 101 proceeded in 76% yield which was then coupled with commercially available amino alcohol piperazine 102 with aqueous sodium hydroxide in DMSO to give amine intermediate 103 in 96% yield. The amine was reacted with benzoyl chloride to give benzoate 104 (97%), which was subsequently converted to triazine of posaconazole.
For the preparation of chiral hydrazine 107, intermediate needed to make the triazolone, lactam 105 was reduced with Red-Al to give (S)-2-benzyloxy propanal 106 (94%) which was then reacted with formyl hydrazine to give hydrazone 107 in 81% yield. Addition of EtMgBr directly to formyl hydrozones 107 gave mixture of (S,S)stereoisomer 109 and (S,R)-diastereomer 110 in relative good diastereoselectivity (94:6) in 55% yield. However, protection of the formyl group as TBDMS ether 108 followed by treatment of the EtMgCl gave 95% yield of the (S,S)-diastereomer 109 and (S,R)-diastereomer 110 in 99:1 ratio.
For finishing off the synthesis, the formyl hydrazine 109 was coupled with the phenyl carbamate 104 in toluene at 75 - 85??C for 12 ¨C 24 hrs. After the completion of coupling, the intermediate was heated at 100 ¨C 110??C for 24 ¨C 48 hrs to completely cyclize to the benzyloxy triazolone 108, which was deprotected with 5% Pd/C and formic acid at room temperature overnight and 40??C for 24 h to give posaconazole (XV) in 80% overall yield.

target

C14ɑ demethylase

Drug interactions

Potentially hazardous interactions with other drugs
Analgesics: concentration of fentanyl possibly increased.
Anti-arrhythmics: avoid concomitant use with dronedarone.
Antibacterials: rifamycins may reduce posaconazole concentration; avoid unless benefit outweighs risk; rifabutin concentration increased.
Anticoagulants: avoid with apixiban and rivaroxaban.
Antidepressants: avoid concomitant use with reboxetine.
Antidiabetics: posaconazole can decrease glucose concentrations, monitor glucose levels in diabetic patients; possibly enhances hypoglycaemic effect of glipizide.
Antiepileptics: phenytoin, fosphenytoin, carbamazepine, phenobarbital and primidone may reduce posaconazole concentration - avoid unless benefit outweighs risk.
Antimalarials: avoid with artemether/lumefantrine and piperaquine with artenimol.
Antipsychotics: increased risk of ventricular arrhythmias with pimozide - avoid; possibly increase quetiapine levels - reduce dose of quetiapine; possibly increases lurasidone concentration - avoid.
Antivirals: concentration of atazanavir increased and possibly daclatasvir and simeprevir (reduce dose of daclatasvir, avoid with simeprevir); concentration reduced by efavirenz and possibly fosamprenavir; possibly increases saquinavir levels; increased risk of ventricular arrhythmias with telaprevir; concentration of both drugs increased with dasabuvir and paritaprevir - avoid.
Anxiolytics and hypnotics: increases midazolam levels.
Ciclosporin: increases posaconazole concentration; posaconazole can increase ciclosporin concentration - dose reduction may be required.
Cytotoxics: concentration of bosutinib increased - avoid or reduce dose of bosutinib; possibly increased everolimus concentration - avoid; avoid with lapatinib; reduce dose of panobinostat and ruxolitinib; possibly inhibits metabolism of vinblastine and vincristine, increased risk of neurotoxicity.
Ergot alkaloids: may increase ergot alkaloid concentration leading to ergotism - avoid.
Guanfacine: possibly increases guanfacine concentration - halve guanfacine dose.
Ivacaftor: possibly increased concentration of ivacaftor.
Lipid-lowering drugs: avoid with lomitapide; possibly increased risk of myopathy with atorvastatin or simvastatin - avoid.1
Lumacaftor: posaconazole concentration possibly reduced - reduce dose of lumacaftor with ivacaftor.
Ranolazine: possibly increased ranolazine concentration - avoid.
Sirolimus: may increase concentration of sirolimus - adjust sirolimus dose as required according to levels.
Sulphonylureas: posaconazole can decrease glucose concentrations, monitor glucose levels in diabetic patients.
Tacrolimus: increases Cmax and AUC of tacrolimus by 121% and 358% respectively - reduce tacrolimus dose to about a third of current dose and adjust as required.
Ulcer-healing drugs: cimetidine may reduce posaconazole concentration by 39% - avoid unless benefit outweighs risk; avoid with histamine H2- antagonists and proton pump inhibitors.

Metabolism

Limited metabolism, most circulating metabolites are glucuronide conjugates with only small amounts of oxidative metabolites. The main elimination route of posaconazole is via the faeces (77%) where 66% of a dose is excreted unchanged. About 14% of a dose is excreted in the urine with only trace amounts excreted unchanged.

References

[1] hanan k. munayyer, paul a. mann, andrew s. chau, taisa yarosh-tomaine, jonathan r. greene, roberta s. hare, larry heimark, robert e. palermo, david loebenberg and paul m. mcnicholas. posaconazole is a potent inhibitor of sterol 14α-demethylation in yeasts and molds. antimicrobial agents and chemotherapy. 2004; 48(10): 3690-3696
[2] daryl s. schiller and horatio b. fung. posaconazole: an extended-spectrum triazole antifungal agent. clinical therapeutics. 2007; 29(9): 1862-1886