Pharmacokinetics of posaconazole in koalas (Phascolarctos cinereus) after intravenous and oral administration

Development of an HPLC-UV method for quantification of posaconazole in low-volume plasma samples: design of experiments and machine learning models

Posaconazole (PCZ) is a triazole antifungal agent with a broad-spectrum activity. Our research aims to present a novel approach by combining a 2-level fractional factorial design and machine learning to optimize both chromatography and extraction experiments, allowing for the development of a rapid method with a low limit of quantification (LOQ) in low-volume plasma samples. The PCZ retention time at the optimized condition (organic phase 58%, methanol 6%, mobile pH = 7, column temperature: 39 °C, and flow rate of 1.2 mL/min) was found to be 8.2 ± 0.2 min, and the recovery of the PCZ at the optimized extraction condition (500 µL extraction solvent, NaCl 10% w/v, plasma pH = 11, extraction time = 10 min, and centrifuge time = 1 min) was calculated above 98%. The results of machine learning models were in line with the results of experimental design. Method validation was performed according to ICH guideline. The method was linear in the range of 50-2000 ng/mL and LOQ was found to be 50 ng/mL. Additionally, the validated method was applied to analyze PCZ nanomicelles and conduct pharmacokinetic studies on rats. Half-life (t1/2), mean residence time (MRT), and the area under the drug concentration-time curve (AUC) were found to be 7.1 ± 0.6 h, 10.5 ± 0.9 h, and 1725.7 ± 44.1 ng × h/mL, respectively.

Pharmacokinetic profile of oral and subcutaneous administration of paracetamol in the koala (Phascolarctos cinereus) and prediction of its analgesic efficacy

The pharmacokinetic profile of paracetamol in koalas is described when administered orally at 15 mg/kg; followed by the same dose, administered every 12 hours (hrs), repeated five times. After the initial oral administration, the median (range) maximal plasma concentration (Cmax), the time Cmax was reached (Tmax) and elimination half-life (t1/2) were 16.93 μg/mL (13.66 to 20.25 μg/mL); 4 hrs (4 to 8 hrs) and 5.54 hrs (4.66 to 7.67 hrs), respectively. When paracetamol was administered orally at 15 mg/mL every 12 hrs, the trough total plasma concentration range remained comparable to the therapeutic range in humans i.e. 4 to 20 μg/mL that is known to provide some analgesia. However, there is a smaller proportion of free drug (i.e. not bound to plasma proteins; and the active form) available in koala plasma (approximately 40% unbound) compared to human plasma (approximately 80% unbound). Consequently, even when there are similar total drug plasma concentrations in both koala and human plasma, the therapeutic efficacy may be reduced in koalas compared to humans. The initial oral dose and subsequent twice daily doses resulted in no obvious adverse effects in any koala. Haematology, plasma electrolyte and biochemical analyte values remained within their reference ranges eight hrs after the last dose but there was a significant change in alanine transaminase (ALT) levels (an increase), and in total protein (a decrease) (both p = 0.03). A dose of 15 mg/kg was also administered as a subcutaneous injection, diluted 50:50 with saline, to two koalas. As the oral formulation and the subcutaneous administration resulted in comparable absorption, the study focused on the oral profile. Based on these results there is an argument to recommend a slight increase in the oral paracetamol dose for the koala, however further investigation is required to confirm whether repeated administration of a slightly higher dose may be associated with more severe or additional significant changes in haematology, electrolytes or biochemical analytes. However, a preferable recommendation would be to administer this dosage of paracetamol in combination with another analgesic such as tramadol, as a subcutaneous injection, to improve efficacy.

Advancing posaconazole quantification analysis with a new reverse-phase HPLC method in its bulk and marketed dosage form

Introduction: Posaconazole is a widely used antifungal drug, and its accurate quantification is essential for quality control and assessment of its pharmaceutical products. This study aimed to develop and validate a reverse-phase high-performance liquid chromatography (HPLC) analytical method for quantifying Posaconazole in bulk and dosage form. Methods: The HPLC method was developed and validated based on International Conference on Harmonisation (ICH) guidelines. The developed method was then applied to quantify Posaconazole in a marketed tablet formulation. The method's specificity, linearity, precision, accuracy, robustness, and stability were evaluated. Results: The developed HPLC method showed good linearity over a 2-20 μg/mL concentration range. The percentage recovery of Posaconazole from the bulk and marketed formulations was found to be 99.01% and 99.05%, respectively. The intra-day and inter-day precisions were less than 1%, and the method was stable under different conditions. The HPLC method was successfully applied to quantify Posaconazole in the marketed formulation. Conclusion: The developed and validated HPLC method is reliable and efficient for analyzing Posaconazole in bulk and dosage forms. The method's accuracy, precision, specificity, linearity, robustness, and stability demonstrate its effectiveness. The method can be used for the quality control and assessment of Posaconazole-containing pharmaceutical products.

Disposition of posaconazole after single oral administration in large falcons (Falco spp): Effect of meal and dosage and a non-compartmental model to predict effective dosage

Posaconazole has been used anecdotally to treat aspergillosis in falcons resistant to voriconazole. In human medicine, it is used prophylactically in immunosuppressed human subjects with invasive pulmonary aspergillosis. So far, no studies have been performed in birds. The aim of this study was to evaluate the in-vivo pharmacokinetic behavior of oral posaconazole after a single administration in six large falcons (i.e gyrfalcons, saker falcons). Posaconazole oral suspension (Noxafil, 40 mg/ml, Schering-Plough) was administered per os without meal in a single dosage of 12.5 mg/kg in 3 falcons. A comparison was done in two more falcons, one with a natural fatty meal at the same single dose, and one with a natural fatty meal and a higher dosage (20 mg/kg). Finally, six falcons received posaconazole pre-dissolved in corn oil with a natural low-fat meal in the higher single dose (20 mg/kg). No side effects were observed in the falcons in any of the experiments. In starved state posaconazole was poorly absorbed, more so than in other species. As expected, absorption of posaconazole was higher with the administration of meal or in the presence of plant (corn) oil, with a fourfold increase in apparent bioavailability. Despite the preferential absorption in the presence of fat, for both dosing schemes the AUC24 : MIC ratio was lower than described in human medicine to achieve a therapeutic effect. The AUCinf : MIC which is an indicator of efficacy after steady-state, while variable, did indicate that the drug is worth trying when susceptibility testing shows to be the only effective drug.

LAY ABSTRACT

The focus of this work is to determine the pharmacokinetic parameters of oral posaconazole in large falcons for the first time after a single dose. Posaconazole has higher bioavailability when administered with meal and fatty components. No adverse reactions have been observed. The ratio of the area under the curve (AUC24) to minimum inhibitory concentration was lower compared to the therapeutic level in human.

Pharmacokinetic profile of injectable tramadol in the koala (Phascolarctos cinereus) and prediction of its analgesic efficacy

Tramadol is used as an analgesic in humans and some animal species. When tramadol is administered to most species it undergoes metabolism to its main metabolites M1 or O-desmethyltramadol, and M2 or N-desmethyltramadol, and many other metabolites. This study describes the pharmacokinetic profile of tramadol when a single subcutaneous bolus of 2 mg/kg was initially administered to two koalas. Based on the results of these two koalas, subsequently 4 mg/kg as a single subcutaneous injection, was administered to an additional four koalas. M1 is recognised as an active metabolite and has greater analgesic activity than tramadol, while M2 is considered inactive. A liquid chromatography assay to quantify tramadol, M1 and M2 in koala plasma was developed and validated. Liquid chromatography-mass spectrometry confirmed that M1 had been identified. Additionally, the metabolite didesmethyltramadol was identified in chromatograms of two of the male koalas. When 4 mg/kg tramadol was administered, the median half-life of tramadol and M1 were 2.89 h and 24.69 h, respectively. The M1 plasma concentration remained well above the minimally effective M1 plasma concentration in humans (approximately 36 ng/mL) over 12 hours. The M1 plasma concentration, when tramadol was administered at 2 mg/kg, did not exceed 36 ng/mL at any time-point. When tramadol was administered at 2 mg/kg and 4 mg/kg the area under the curve M1: tramadol ratios were 0.33 and 0.50, respectively. Tramadol and M1 binding to plasma protein were determined using thawed, frozen koala plasma and the mean binding was 20% and 75%, respectively. It is concluded that when tramadol is administered at 4 mg/kg as a subcutaneous injection to the koala, it is predicted to have some analgesic activity.

Posaconazole aggravates vincristine-related hypertension in children with acute lymphoblastic leukemia: a case report

Vincristine-related secondary hypertension is rare. This study reports two children who were treated with vincristine for acute lymphoblastic leukemia (ALL) and posaconazole for fungal infections who experienced vincristine-related secondary hypertension. Blood pressure normalized in both children after halting the drugs and providing antihypertensive treatment. Thus, posaconazole can interact with vincristine and induce secondary hypertension in children with ALL. As an adverse event, this interaction is a rare occurrence.

Pharmacokinetic profile of amoxicillin and its glucuronide-like metabolite when administered subcutaneously to koalas (Phascolarctos cinereus)

Amoxicillin was administered as a single subcutaneous injection at 12.5 mg/kg to four koalas and changes in amoxicillin plasma concentrations over 24 hr were quantified. Amoxicillin had a relatively low average ± SD maximum plasma concentration (C_max ) of 1.72 ± 0.47 µg/ml; at an average ± SD time to reach C_max (T_max ) of 2.25 ± 1.26 hr, and an elimination half-life of 4.38 ± 2.40 hr. The pharmacokinetic profile indicated relatively poor subcutaneous absorption. A metabolite was also identified, likely associated with glucuronic acid conjugation. Bacterial growth inhibition assays demonstrated that all plasma samples other than t = 0 hr, inhibited the growth of Escherichia coli ATCC 25922 and Staphylococcus aureus ATCC 29213 to some extent. Calculated pharmacokinetic indices were used to predict whether this dose could attain a plasma concentration to inhibit some susceptible Gram-negative and Gram-positive pathogens. It was predicted that a twice daily dose of 12.5 mg/kg would be efficacious to inhibit susceptible bacteria with an amoxicillin minimum inhibitory concentration (MIC) ≤ 0.75 µg/ml such as susceptible Bordetella bronchiseptica, E. coli, Staphylococcus spp. and Streptococcus spp. pathogens.

Cryptococcosis in the koala (Phascolarctos cinereus): pathogenesis and treatment in the context of two atypical cases

Disseminated cryptococcosis caused by Cryptococcus gattii (molecular type VGI) was diagnosed in an adult free-ranging female koala (Phascolarctos cinereus). Subclinical cryptococcosis was later diagnosed in this koala's joey. In the adult koala, a pathological fracture of the tibia was associated with the bone lysis of marked focal cryptococcal osteomyelitis. Limb-sparing orthopedic intervention, in the setting of disseminated cryptococcosis, was judged to have a poor prognosis, and the adult koala was euthanized. The joey was removed and hand-reared. Serological testing revealed persistent and increasing cryptococcal capsular antigenemia in the absence of clinical signs of disease and it was subsequently treated with oral fluconazole for approximately 16 months, rehabilitated and released into the wild. It was sighted 3 months post-release in a good state of health and again at 18 months post-release but was not recaptured on either occasion. This is the first published report of cryptococcal appendicular osteomyelitis in a koala. It is also the first report of concurrent disease in a dependent juvenile and the successful treatment of subclinical cryptococcosis to full resolution of the cryptococcal antigenemia in a free-ranging koala. This paper provides a discussion of cryptococcal osteomyelitis in animals, host-pathogen-environment interactions and treatment and monitoring protocols for cryptococcosis in koalas. Published reports describing the treatment of cryptococcosis in koalas are also collated and summarised.

Review of some pharmacokinetic and pharmacodynamic properties of anti-infective medicines administered to the koala (Phascolarctos cinereus)

Although koalas are iconic Australian animals, no pharmacokinetic studies of any first-line medicines used to treat diseased or injured koalas had been published prior to 2010. Traditionally, medicine dosages suggested for this species underwent linear extrapolation from those recommended for domesticated species. The koala, a specialist folivore whose natural diet consists of almost exclusively Eucalyptus spp. foliage has anatomical and physiological adaptations for detoxifying their diet which also affect medicine pharmacokinetic profiles. This review addresses aspects of medicine absorption, clearance, and other indices (such as medicine binding to plasma proteins) of enrofloxacin/marbofloxacin and chloramphenicol used for the systemic treatment of chlamydiosis, and fluconazole ± amphotericin, and posaconazole for the treatment of cryptococcosis. Based on observations from published studies, this review includes suggestions to improve therapeutic outcomes when administering medicines to diseased koalas.