Misonidazole and benznidazole inhibit hydroxylation of CCNU by mouse liver microsomal cytochrome P-450 in vitro

Drug-drug interactions between antiretrovirals and drugs used in the management of neglected tropical diseases: important considerations in the WHO 2020 Roadmap and London Declaration on Neglected Tropical Diseases

The group of infections known as the neglected tropical diseases (NTDs) collectively affect one billion people worldwide, equivalent to one-sixth of the world's population. The NTDs cause severe physical and emotional morbidity, and have a profound effect on cycles of poverty; it is estimated that NTDs account for 534 000 deaths per year. NTDs such as soil-transmitted helminth infections and the vector-borne protozoal infections leishmaniasis and trypanosomiasis occur predominantly in the most economically disadvantaged and marginalized communities. It is estimated that all low-income countries harbour at least five of the NTDs simultaneously. NTDs are neglected because they do not individually rank highly in terms of mortality data, and because they affect populations with little political voice. There is considerable geographic overlap between areas with high prevalence of NTDs and HIV, raising the possibility of complex polypharmacy and drug-drug interactions. Antiretrovirals pose a particularly high risk for potential drug-drug interactions, which may be pharmacokinetic or pharmacodynamic in nature and can result in raising or lowering plasma or tissue concentrations of co-prescribed drugs. Elevated drug concentrations may be associated with drug toxicity and lower drug concentrations may be associated with therapeutic failure. The aim of this paper is to review the currently available data on interactions between antiretrovirals and drugs used in the management of NTDs. It is intended to serve as a resource for policy makers and clinicians caring for these patients, and to support the recent WHO 2020 Roadmap and the 2012 London Declaration on NTDs.

Pediatric clinical pharmacology studies in Chagas disease: focus on Argentina

Chagas disease is a neglected parasitic disease endemic in the Americas. It mainly affects impoverished populations and the acute phase of the infection mostly affects children. Many cases have also been detected in nonendemic countries as a result of recent migratory trends. The chronic phase is relatively asymptomatic, but 30% of patients with chronic infection eventually develop cardiac and digestive complications that commonly lead to death or disability. Only two drugs are available for the treatment of Chagas disease, benznidazole and nifurtimox. These drugs have been shown to be effective in the treatment of both acute and early chronic phases in children, but the pharmacokinetics of these drugs have never been studied in this population. We have set out to conduct a pharmacokinetics study of benznidazole in a pediatric population with Chagas disease. The results of this study are expected to allow better estimation of the optimal doses and schedule of pharmacotherapy for Chagas disease in children.

Identification of imidazole as L-arginine-competitive inhibitor of porcine brain nitric oxide synthase

Imidazole acts as a heme-site inhibitor of nitric oxide synthase (NOS). We used this compound to investigate whether the substrate L-arginine binds directly to the heme or to a separate domain of brain NOS. Enzyme kinetic experiments showed that imidazole enhanced the apparent Km for L-arginine without affecting maximal enzyme activity, and binding studies revealed that the inhibitor displaced the radioligand NG-nitro-L-[3H]arginine in a concentration-dependent fashion. These results demonstrate that imidazole exerts its effects on NOS in an L-arginine-competitive manner and that the substrate site of the enzyme may be identical with the prosthetic heme group.

Biodistribution of misonidazole and 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) in rats bearing unclamped and clamped 9L subcutaneous tumors

The biodistribution of misonidazole (MISO) and 1,3bis(2-chloroethyl)-1-nitrosourea (BCNU) was studied using the subcutaneous (s.c.) 9L tumor model in male Fisher 344 rats. A transient hypoxia in these tumors was created by clamping the blood supply to the tumor. Reoxygenation occurred upon release of the clamp. The plasma and tumor concentrations of MISO and BCNU were quantitated by high pressure liquid chromatography. When 12 mg/kg of BCNU was given i.p. without MISO, the peak plasma concentration was about 6 micrograms/ml, and the elimination half-time was about 16 min. When 2.5 mmole/kg of MISO was given i.p. 150 min before the BCNU, the peak plasma concentration of BCNU increased by approximately 33%, and the plasma elimination half-time increased by approximately 57%. Clamping the tumor for 120 min did not significantly change the BCNU concentration in plasma, but in tumors the time to reach the peak level was delayed slightly, and the peak concentration was reduced when compared to that in the unclamped tumors. MISO pretreatment decreased the BCNU peak concentration in both unclamped and clamped tumors, but the decrease was more pronounced in the unclamped tumors. In both unclamped and clamped tumors, the BCNU concentration and its rate of disappearance were identical about 30 min after BCNU administration, with or without MISO pretreatment. The elimination half-time of MISO from the plasma (approximately 142 min) was identical for rats with unclamped or clamped tumors. The half-time for the disappearance of MISO from unclamped tumors was about 98 min. BCNU had no effect on the MISO concentration in plasma and unclamped tumors. MISO disappeared in the clamped tumors with a half-time of about 40 min. When the clamp was released, the MISO concentration returned to the level in the unclamped tumors after about 45 min. BCNU delayed the return of the MISO concentration to the unclamped tumor level by about 60 min. Two conclusions can be drawn from this study. First, the pharmacokinetics of each drug changed when the two drugs were combined. Second, the data indicate that alterations in the tumor BCNU pharmacokinetics are not the major mechanism responsible for the chemopotentiation previously measured in s.c. 9L tumors.

Micropharmacokinetics of chemical modifiers

Classical pharmacokinetic analysis of plasma, urine and tissue specimens continues to be of major value to the rational development of chemical modifiers of cancer treatment. However, in addition, increasingly sophisticated analytical techniques are becoming available which allow the pathways of microdistribution and micrometabolism of drugs to be traced down to the cellular and molecular level. New developments described here include flow cytometry, magnetic resonance spectroscopy, and molecular enzymology. These are predicted to have a major impact on the optimization of chemical modification.