In vitro and in vivo evaluation of a primaquine prodrug without red blood cell membrane destabilization property

Abstract

Primaquine is an important therapeutic resource for malaria treatment and it has wide activity against several pathogens. The haematotoxicity of primaquine is the major problem for its therapeutic application. This effect is aggravated by repeated use at high doses and by the wide fluctuation of plasma levels after administration. The primaquine prodrug (Phe-Ala-PQ) was planned in order to modify the pharmacokinetics and toxicity of primaquine. The in vitro conversion of Phe-Ala-PQ to primaquine, and the primaquine pharmacokinetics were evaluated in four groups of rats: two groups that received a single dose of Phe-Ala-PQ, one by intravenous and the other by gavage route, and two other groups that received primaquine diphosphate, by intravenous and gavage routes. In addition, the erythrocyte osmotic fragility was compared in two groups of rats that received multiple doses of primaquine diphosphate or Phe-Ala-PQ, as a parameter of haematotoxicity. The in vitro conversion of Phe-Ala-PQ to primaquine by plasma enzyme action was observed. The pharmacokinetic profile of primaquine from Phe-Ala-PQ was more favourable due to the lower fluctuation of plasma concentrations. Haematotoxicity was not evidenced in the prodrug administration. The results reinforce the need for further studies with this prodrug, promising an alternative in the therapeutic use of primaquine.

Evaluation of Antimalarial Activity and Toxicity of a New Primaquine Prodrug

“…Phe-Ala-PQ, for example, is a prodrug containing the dipeptide phenylalanine-alanine as carrying group which shows in vitro and in vivo anti T. cruzi effects [17], [19]; however, the antimalarial effect has not yet been described. We have found that this compound causes less erythrocyte osmotic fragility and shows less fluctuation of plasma concentration [17]. The variation in PK parameters in Phe-Ala-PQ is due in part to increased water solubility caused by the introduction of the dipeptide.…”

“…The variation in PK parameters in Phe-Ala-PQ is due in part to increased water solubility caused by the introduction of the dipeptide. This modification allows sustained release of PQ by bioconversion of the prodrug, and it prolongs the mean residence time of PQ increasing its half life after oral administration [17]. All these effects are due to alterations in physico-chemical parameters such as partition coefficient (log P).…”

“…The rats were divided into three groups and treated as follows: control group: saline by gavage (four times a day for 4 days) (n = 10); PQ diphosphate group: PQ diphosphate by gavage (2.44 mg/kg free base; four times a day for 4 days) (n = 10); and Phe-Ala-PQ group: prodrug by gavage (9.00 mg/kg; four times a day for 4 days) (n = 10). This dose and frequency were derived on the basis of the dose regimen of malaria treatment in humans by allometric scaling, and considering oral bioavailability (approximately 50%) of prodrug determined in a previous study [17]. After treatment with the drugs, the animals were decapitated for collection of blood and samples of liver and kidneys (preserved in 10% formaldehyde).…”

“…6 h) [17], [18]. In addition, a hemolytic effect has been observed after the administration of multiple oral doses of PQ, whereas this hemolytic effect is not observed after Phe-Ala-PQ administration [17]. Therefore, in a continuing effort to develop new candidate drugs to treat malaria, we report here on the antimalarial activity, cytotoxicity, and biochemical, hematological and histopathological effects of the prodrug Phe-Ala-PQ, designed as an antimalarial agent.…”

“…The mean residence time (MRT) of PQ from prodrug is higher compared to PQ, showing that the prodrug approach could overcome the PK problems of PQ, such as short plasma half-life (ca. 6 h) [17], [18]. In addition, a hemolytic effect has been observed after the administration of multiple oral doses of PQ, whereas this hemolytic effect is not observed after Phe-Ala-PQ administration [17].…”