Clinical pharmacology and bioanalysis of antileishmanial drugs: Towards improved treatment strategies for leishmaniasis

Abstract

The tropical infectious disease leishmaniasis almost exclusively affects low-income populations in developing countries, generally receiving limited treatment and research funding. Treatment options for leishmaniasis are therefore limited, making it crucial to optimize treatment with the currently available drugs. This thesis focuses on the optimization of antileishmanial therapy by investigating the bioanalysis and clinical pharmacokinetics and pharmacodynamics of antileishmanial drugs. For decades, determining drug concentrations in blood plasma have been considered the gold standard as an approximation for a drug’s target site exposure. This thesis describes the validation of novel bioanalytical methods to quantify miltefosine, currently the only oral drug in treatment of leishmaniasis, in other human matrices, for two reasons. First, to simplify blood sampling in the remote areas where leishmaniasis is endemic, two analytical methods were developed to quantify miltefosine in dried blood: the dried blood spot (DBS) and volumetric absorptive microsampling (VAMS) method. Both methods are more patient-friendly due to blood collection with a finger-prick instead of venous sampling and the subsequent storage at room temperature is much cheaper. Second, to more accurately approximate target site exposure, we developed a method to quantify miltefosine in peripheral blood mononuclear cells (PBMCs), as the Leishmania parasite resides and replicates within macrophages, a subset of PBMCs. We investigated the plasma and intracellular miltefosine pharmacokinetics in Colombian adults and children with cutaneous leishmaniasis, a parasitic infection of the skin. We identified a significant miltefosine underexposure in children compared to adults after receiving the conventional 2.5 mg/kg/day dose proportional to weight, as found earlier in paediatric patients with visceral leishmaniasis, a parasitic infection of the internal organs. Both intracellular and plasma exposure were significantly related to probability of cure. To increase paediatric miltefosine exposure to adult levels, a novel miltefosine dosing regimen for children was evaluated, where patients with a smaller body size received a relatively higher mg/kg dose. In Eastern African paediatric visceral leishmaniasis patients treated with this novel dosing regimen, variability in exposure declined compared to results after conventional dosing. In addition, miltefosine concentrations accumulated faster at start of treatment, contributing to an overall increase in exposure. These observations could have contributed to the observed increase in efficacy. In Bangladeshi children with post-kala-azar dermal leishmaniasis infection, a skin infection developing within three years after visceral leishmaniasis in 10-20% of cases in Southeast Asia, exposure increased to adult levels with this new dosing regimen. Female patients, however, reached a significantly lower exposure than males. Furthermore, in a vulnerable adult visceral leishmaniasis population, co-infected with HIV, we identified a decreased exposure to the antileishmanial drugs miltefosine and liposomal amphotericin B. Finally, we provided the first longitudinal evaluation of a biomarker, the macrophage activation marker neopterin, in the monitoring of visceral leishmaniasis treatment response. Pharmacodynamic markers are urgently needed in visceral leishmaniasis to predict recurrence of clinical symptoms. In East African patients, a significantly higher neopterin concentration increase was observed within one month after end of treatment in patients experiencing recurrence of symptoms within half a year after treatment, compared to cured patients.