(T1330-07-41) From Pill to Patch: Transforming Plasmodium vivax Malaria Therapy with Hydrogel Microarray Patches

Purpose: Malaria continues to pose a significant threat to global health, with over 608,000 deaths recorded in 2022, predominantly affecting low- and middle-income countries [1]. Among the Plasmodium species, Plasmodium vivax poses a particular challenge, accounting for 6.9 million cases in 2022 alone [1]. Standard therapy for P. vivax malaria involves the combination of chloroquine (CQ), which targets blood-stage parasites, and primaquine (PQ), which eliminates dormant liver-stage hypnozoites to prevent relapses [2]. PQ requires daily dosing for two weeks [3], with 620 mg administered initially, followed by 310 mg at 6–8 hours on the first day and on the subsequent two days [4]. These prolonged and complicated regimens contribute to poor patient adherence, increasing the risk of treatment failure and relapse [5]. Additionally, hepatoxicity and the need for sustained administration highlight the limitations of current oral therapies, underscoring the urgent need for alternative delivery systems [6,7]. To address these challenges and improve treatment for P. vivax malaria, we present, for the first time, the development of lyophilised drug reservoirs containing CQ or PQ designed for use with hydrogel-forming microarray patches (MAPs). This study aims to support the development of a novel, patient-friendly transdermal delivery platform capable of enhancing adherence, reducing side effects, and improving therapeutic outcomes in malaria-endemic settings.

Methods: The reservoirs were separately prepared and optimised with individual drugs CQ and PQ, using a lyophilisation technique. Hydrogel-forming MAPs were fabricated by casting an aqueous blend containing 15% w/w poly(vinyl alcohol) (MW 85-124 kDa), 10% w/w poly(vinyl pyrrolidone) (MW 58 kDa), and 1.5% w/w citric acid into silicone moulds (11 × 11 conical needle array over a 0.5 cm² area, each needle measuring 600 µm in height). All MAP formulations were visualised using a digital microscope and scanning electron microscopy (SEM). Their mechanical strength was evaluated using a Texture Analyser under a compressive force of 32 N, simulating manual thumb pressure [8]. Insertion capability was assessed using both Parafilm^® M, as a skin simulant, and ex vivo full-thickness neonatal porcine skin, with optical coherence tomography (OCT) used to evaluate penetration depth. In vitro permeation studies were conducted using modified Franz diffusion cells to measure drug permeation across dermatomed porcine skin (350 µm thickness). Pharmacokinetic studies were conducted over four days in male Sprague-Dawley rats, comparing MAP application to oral gavage. To evaluate potential hepatotoxicity, livers were collected post-mortem and examined histologically using haematoxylin and eosin (H&E) staining. Lastly, the therapeutic efficacy of the formulations was assessed in a murine model infected with Plasmodium berghei, determining the antimalarial potential of the CQ- and PQ-loaded reservoirs incorporating with hydrogel-forming MAPs.

Results: The lyophilised drug reservoirs were successfully prepared, optimised, and characterised, as shown in Figure 1. Hydrogel-forming MAPs formed uniform and well-defined arrays, as illustrated in Figure 2. When a force of 32 N/array was applied, needle height was reduced by less than 10%, demonstrating acceptable mechanical strength. Insertion studies confirmed effective penetration into ex vivo neonatal porcine skin, reaching depths of approximately 490 µm. In vitro studies revealed that approximately 2.81 mg of CQ and 3.15 mg of PQ were deposited into the skin over 24 hours. Transdermal delivery results showed that both drugs achieved comparable delivery levels of around 41 mg, corresponding to 78% of the drug released from the lyophilised reservoirs. Pharmacokinetic analysis showed that MAP administration significantly increased C_max values for both drugs, CQ from 0.23 ng/mL to 2.23 ng/mL, and PQ from 13.84 ng/mL to 59.22 ng/mL. Moreover, the area under the curve (AUC) for the MAP group was 35-fold and 2-fold higher than the oral treatment group for CQ and PQ, respectively. For CQ, MAP delivery also extended the drug’s half-life to 31 hours, nearly twice that of the oral route. Efficacy studies in a murine Plasmodium berghei model demonstrated that MAP-delivered PQ and CQ reduced parasitaemia by 99.8%. Histological analysis of liver tissues revealed that oral administration caused significant hepatic injury, including vacuolisation and hepatocyte death, whereas MAP-treated animals exhibited minimal liver damage, suggesting that MAP delivery may reduce hepatotoxicity compared to oral administration.

Conclusion: These findings highlight the potential of hydrogel-forming MAPs as a non-invasive, sustained drug delivery system for malaria treatment. Considering the well-documented hepatotoxicity associated with prolonged oral antimalarial therapy, the painless and user-friendly application of MAPs offers a promising strategy to improve treatment adherence, minimise systemic toxicity, and enhance therapeutic outcomes in the management of malaria.

References: [1] World malaria report 2023, (n.d.). https://www.who.int/teams/global-malaria-programme/reports/world-malaria-report-2023 (accessed January 7, 2025).
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Figure 1. (A) Schematic illustration of the preparation of drug reservoirs via lyophilisation. Characterisation of lyophilised reservoirs: Response surface plots showing the effects of drug and sorbitol concentrations on the dissolution time of reservoirs containing (B) chloroquine (CQ) and (C) primaquine (PQ), along with (D) predicted versus observed responses for the optimised formulations. (E) Physical appearance of CQ and PQ lyophilised reservoir formulations. (F) Drug content recovered from CQ and PQ lyophilised reservoirs (mean ± SD, n = 4). (G–H) FTIR spectra, DSC thermograms, and TGA curves of lyophilised (Lyo) reservoirs containing PQ (G) and CQ (H), compared with pure drugs, pure sorbitol, pure gelatin, and their physical mixtures (PM).


Figure 2. (A) Light microscopy and SEM images of hydrogel-forming MAPs. (B) Comparison of needle height reduction (%) following the application of a 32 N force for 30 seconds using a texture analyser (TA) (means ± SD, n = 20). (C) Percentage of holes formed in each Parafilm® layer and estimated insertion depths after insertion of hydrogel-forming MAPs (means ± SD, n = 3). (D) Insertion depths of hydrogel-forming MAPs into Parafilm® and excised neonatal porcine skin, measured from optical coherence tomography (OCT) images using ImageJ® software (means ± SD, n = 20). (E) OCT images showing hydrogel-forming MAPs inserted into Parafilm® layers and excised full-thickness neonatal porcine skin following application of a 32 N force for 30 seconds using a TA (false colour images). (F) Cumulative permeation profiles of chloroquine (CQ) and primaquine (PQ) from lyophilised reservoirs delivered via hydrogel-forming MAPs (mean ± SD, n = 3). (G) Total amounts of drug delivered to the receiver compartment and deposited in dermatomed skin after 24 hours (means ± SD, n = 3).


Figure 3. (A) Schematic illustration of in vivo delivery of CQ and PQ via hydrogel-forming MAPs incorporating lyophilised reservoirs. (B) Plasma concentrations of CQ and (C) PQ over time in rats treated with hydrogel-forming MAPs or oral gavage (means ± SEM, n = 6). Pharmacokinetic parameters including area under the curve (AUC), maximum plasma concentration (Cmax), time to reach Cmax (Tmax), elimination half-life (T₁/₂), and mean residence time (MRT) following administration (means ± SEM, n = 6). (E) Parasitaemia progression over seven days post-infection in mice infected with Plasmodium berghei. Groups were treated with CQ and PQ either orally or via hydrogel-forming MAPs (means ± SD, n = 7). (F) Representative histological images of rat liver sections from different treatment groups: oral CQ, oral PQ, MAP-delivered CQ, MAP-delivered PQ, and untreated control. Yellow arrows indicate regions of liver necrosis.