Low Central Nervous System Posaconazole Concentrations during Cerebral Phaeohyphomycosis

TEXT

Posaconazole is a broad-spectrum triazole antifungal agent used for prophylaxis of invasive fungal infections (IFIs) among high-risk hematology patients and as salvage therapy of IFIs such as invasive aspergillosis (1, 2). However, available data regarding central nervous system (CNS) diffusion of posaconazole are scarce. There is no published report of in vivo CNS measurements of posaconazole in humans, except in cerebrospinal fluid (CSF).

In 2018, a woman in her 50s with a history of Crohn’s disease treated with corticosteroids, azathioprine, and mesalazine was seen in the emergency room because of progressive headaches associated with vertigo, anterograde amnesia, dysphasia, and pain of the left upper limb. She was afebrile, alert, and experiencing expressive aphasia. The patient had an otherwise unremarkable clinical evaluation. Her blood count showed 5,100 leukocytes/mm³, and her C-reactive protein level was 12.9 mg/dl. Noncontrasted cerebral computed tomography (CT) showed left parietotemporal cystic lesions associated with vasogenic edema and left uncal herniation.

The patient was admitted for further investigation. CSF analysis was unremarkable. Serum and CSF Aspergillus galactomannan antigen tests were negative. Serum and CSF β-d-glucan levels were 313 and >500 pg/ml, respectively. A keyhole aspiration of the main lesion was carried out, with the evacuation of a small amount of creamy greenish pus. Direct microscopic examination of the aspiration fluid stained with Gram and hematoxylin-eosin revealed several moniliform hyphal structures. Pus was seeded onto blood agar, chocolate agar (PolyViteX), Coletsos agar, Sabouraud agar, Schaedler agar, and Schaedler broth supplemented with 0.02% vitamin K. Voriconazole (6 mg/kg twice-daily loading dose followed by 4 mg/kg intravenous [i.v.] twice daily) was started because of suspected invasive Aspergillus infection. After 13 days of incubation at 35°C, black fungi appeared, and cultures were sent to the French National Reference Center for Mycoses and Antifungals (Institut Pasteur, Paris, France).

Postcontrast axial T1-weighted brain magnetic resonance imaging (MRI) showed one large left parietotemporal rim-enhancing polycyclic lesion with partial lateral sinus thrombosis (Fig. 1A). Axial diffusion-weighted MRI showed increased signal intensity with low apparent diffusion coefficient, suggesting abscesses. On the basis of morphological features, the fungus was identified as Rhinocladiella mackenziei, which was confirmed by nucleotide sequence analysis of the internal transcribed spacer and the 28S ribosomal subunit (3). After the identification, the patient was switched to posaconazole (300 mg i.v. once daily, which was then secondarily increased to 400 mg i.v. once daily because of insufficient trough concentration). Posaconazole plasma concentrations were monitored once a week, aiming at trough concentrations between 2,000 and 5,000 ng/ml.

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FIG 1

Postcontrast axial T1-weighted MRI images. (A) Rim-enhancing left temporal lesion with central hypointensity (baseline). (B) Postsurgical cavity with decreased perilesional edema (3 months after surgery).

One month after the initial keyhole aspiration, the patient underwent neurosurgery. The abscess shell was particularly rigid. About 97% of the brain abscess was surgically removed, with a small residual lesion remaining in the left transversal sinus. There was no intraoperative complication. During surgery, several samples were taken for posaconazole concentration measurement in plasma, superficial brain parenchyma, abscess pus, surgical piece, meninges, and CSF (lumbar puncture was contraindicated because of the risk of temporal herniation).

Plasma and CSF posaconazole concentrations were measured using routine liquid chromatography-mass spectrometry (LC-MS). Purification sample preparation of both plasma and CSF (50 μl) was conducted using acetonitrile for protein precipitation. After centrifugation, 5 μl of the supernatant was injected into the LC-MS/MS system (Waters Acquity UPLC-TQD system, Milford, MA). The chromatographic separation was performed on a C₁₈ BEH column. The calibration range was from 200 to 5,000 ng/ml (Chromsystems). Other CNS samples were stored at –80°C before analysis. Brain samples were accurately weighed, homogenized in phosphate-buffered saline 1X using Precellys 24 (Bertin Technologies, Montigny-le-Bretonneux, France), and then quantified by LC-MS. Posaconazole concentration measurements are reported in Table 1.

A couple of days after surgery, the patient was conscious and had stable neurological status. The patient was discharged 4 weeks after neurosurgery, and treatment by posaconazole (400 mg oral once daily) was continued. Three months after surgery, the patient showed almost complete neurological recovery except for a slight word-finding difficulty. MRI showed a postsurgical cavity with decreased perilesional edema and persistent partial lateral sinus thrombosis (Fig. 1B). Posaconazole was well tolerated, with transient paresthesia appearing as the sole potential related adverse event.

To our knowledge, this is the first case summary that reports on simultaneous posaconazole measurement performed in various CNS tissues in vivo in humans, including cerebral parenchyma. Posaconazole concentrations obtained in CSF and all CNS specimens were low compared with plasma concentrations, with a sample-to-plasma ratio of 8% for CSF and between 5% and 22% for cerebral tissues.

A huge variability in the CNS diffusion of posaconazole was previously reported, with an average CSF-to-plasma ratio of 0.57% in a patient with hematopoietic stem cell transplantation with pulmonary aspergillosis (4), 40% to 50% in a patient with cerebral abscesses, and 230% in a patient with bacterial meningitis and cerebral aspergillosis (5). Based on these reports, alteration of the blood-brain barrier (BBB) appears to be a major determinant of the diffusion of posaconazole into CSF. However, this diffusion was only 8% in our patient, despite the local fungal infection likely increasing the permeability of the BBB.

Regarding diffusion into brain tissues, the tissue-to-plasma ratios presently observed were lower than the values of ∼100% that were retrieved in biopsy specimens taken at autopsy from seven patients under posaconazole prophylaxis after allogeneic stem cell transplantation (6). Nevertheless, a postmortem change in the diffusion of posaconazole across the BBB cannot be excluded.

Compared to animal studies, our findings suggest lower CNS penetration of posaconazole in humans than in murine models of invasive fungal infection. For example, Calvo et al. (7) showed a dose-dependent efficacy of posaconazole in reducing the fungal load in cerebral phaeohyphomycosis due to Fonsecaea monophora and a posaconazole brain tissue-to-serum concentration ratio of between 39% and 69%.

The diffusion and concentration of triazoles in the CNS depend on several factors, such as molecular weight and structure, lipophilicity, local inflammation, mechanisms of active efflux, and protein binding (8, 9). Posaconazole has a high degree of structural similarity to itraconazole and a rather high molecular weight (∼700 Da) combined with extensive binding to plasma proteins (>98%), which would predict poor CNS penetration. However, posaconazole lipophilicity is close to that of voriconazole, another triazole that can achieve concentrations in CNS tissue much higher than in CSF and higher than would be anticipated from the unbound fraction (9). It remains unclear whether P-glycoprotein, which mediates active efflux of itraconazole at the level of the BBB, can also induce posaconazole active efflux from the brain (10).

Our patient was treated by combining surgery and posaconazole treatment, which was previously shown to be an effective antimicrobial agent in the treatment of CNS fungal infection (11, 12), especially in this kind of phaeohyphomycosis infection (3, 13). Despite evidence of low posaconazole concentrations in her CNS samples, the patient showed rapid and steady clinical improvement after surgery. This suggests that, whereas posaconazole might remain the best triazole agent to use in patients with CNS invasive phaeohyphomycosis, prompt and extensive neurosurgical treatment is critical in the management of such patients.