Factors Affecting Primaquine Combination Treatment in Malaria Patients in Selangor, Malaysia

Malaria Cases in a Tertiary Hospital in Kuala Lumpur, Malaysia: A 16-Year (2005-2020) Retrospective Review

While there has been a tremendous decline in malaria disease burden in the remote parts of Malaysia, little is known about malaria incidence in its urban localities. This study aimed to analyze trends of malaria cases in urban Kuala Lumpur, Malaysia. All suspected cases presented to a university hospital in Kuala Lumpur from January 2005 to December 2020 were examined by microscopy. Infection status was analyzed using descriptive statistics and curve estimation analysis. Of 3105 blood films examined, 92 (3%) were microscopically confirmed malaria cases. Plasmodium vivax infections accounted for the majority (36.9%) of all malaria cases. Nearly half (47.8%) of cases were found among foreign cases (p < 0.001). The majority of foreign cases were male (86.4%) and came from Southeast Asian countries (65.9%). The curve estimation analysis showed significant decreases in malaria cases due to P. vivax (R² = 0.598; p < 0.001) and Plasmodium falciparum (R² = 0.298, p = 0.029), but increases for Plasmodium knowlesi (R² = 0.325, p = 0.021) during the 16 years. This study showed that malaria incidence in urban Kuala Lumpur is low and has remained stable since 2005. However, P. knowlesi has played a significant role in the increase in overall malaria in the area, highlighting the importance of continued vigilance and improved surveillance.

The gender-related variability in the pharmacokinetics and antiplasmodial activity of naphthoquine in rodents

BACKGROUND

Naphthoquine (NQ) is a suitable partner anti-malarial for the artemisinin-based combination therapy (ACT), which is recommended to be taken orally as a single-dose regimen. The metabolism of NQ was mainly mediated by CYP2D6, which is well-known to show gender-specific differences in its expression. In spite of its clinical use, there is limited information on the pharmacokinetics of NQ, and no data are available for females. In this study, the effect of gender on the pharmacokinetics and antiplasmodial efficacy of NQ in rodents was evaluated. The underlying factors leading to the potential gender difference, i.e., plasma protein binding and metabolic clearance, were also evaluated.

METHODS

The pharmacokinetic profiles of NQ were investigated in healthy male or female rats after a single oral administration of NQ. The antiplasmodial efficacy of NQ was studied in male or female mice infected with Plasmodium yoelii. The recrudescence and survival time of infected mice were also recorded after drug treatment. Plasma protein binding of NQ was determined in pooled plasma collected from male or female mice, rat or human. In vitro metabolism experiments were performed in the liver microsomes of male or female mice, rat or human.

RESULTS

The results showed that the gender of rats did not affect NQ exposure (AUC_0-t and C_max) significantly (P > 0.05). However, a significant (P < 0.05) longer t_1/2 was found for NQ in male rats (192.1 ± 47.7), compared with female rats (143.9 ± 27.1). Slightly higher but not significant (P > 0.05) antiplasmodial activity was found for NQ in male mice (ED₉₀, 1.10 mg/kg) infected with P. yoelii, compared with female mice (ED₉₀, 1.67 mg/kg). The binding rates of NQ to plasma protein were similar in males and females. There was no metabolic difference for NQ in male and female mice, rat or human liver microsomes.

CONCLUSIONS

These results indicated that the pharmacokinetic profiles of NQ were similar between male and female rats, except for a longer t_1/2 in male rats. The difference was not associated with plasma protein binding or hepatic metabolic clearance. Equivalent antiplasmodial activity was found for NQ in male and female mice infected with P. yoelii. This study will be helpful for the rational design of clinical trials for NQ.