Development of resistance by malaria parasites to conventional antimalarial drugs has rejuvenated the exploration of herbal medicine as alternatives. Also, the increasing rate of the use of herbal antimalarial remedies in combination with conventional antimalarial drugs (both synthetic and semi-synthetic) has inspired researchers to validate their herb-drug interaction effects. This review evaluated the interaction outcomes between herbal antimalarial drugs in combination with conventional antimalarial drugs. With the aid of electronic databases, Pubmed and Google scholar, articles related to this subject were sourced from English peer reviewed scientific journals published from 2003 to 2020. Search terms used include “antimalarial-herbal drugs interaction”, “antimalarial medicinal plant interactions with conventional antimalarial drugs”, “drug-herbal interactions, “antimalarial drugs and medicinal plants”. Synergistic, antagonistic and none effects were reported among 30 studies reviewed. Among 18 in vivo studies on P. berghei and P. yoelii nigerense infected mice model, 14 showed synergism, 3 showed antagonism and 1 involving three plants showed both effects. Among 9 in-vivo studies involving normal animal (non-infected), 2 showed antagonism, 2 showed synergism and 5 showed none-effects. Two (2) studies on human volunteers and one (1) in vitro quantitative study showed that Garcinia kola reduced plasma concentrations of quinine and halofantrine. Generally, majority of herbal antimalarial drugs showed synergistic effects with CAMDs. Vernonia amygdalina was the most studied plant compared to others. Consequently, herbal remedies that produced synergistic effects with conventional antimalarial drugs may be prospects for standardization and development of antimalarial-medicinal plant combination therapy that could curtail malaria resistance to conventional antimalarial therapies.

The genus Psydrax is one of the ethno-medicinally important genera of the Rubiaceae family which has only received a limited scientific attention, despite coming from a pharmacologically and phytochemically important plant family. The genus has found applications in ethnomedical management of diabetes, stomach disorders, inflammations, cardiovascular diseases, epilepsy, wounds, malaria and fever. To unveil knowledge gaps, stimulate research interest and unravel opportunities for drug discovery from the genus Psydrax , we have carried out an extensive review on its traditional applications, phytochemistry and pharmacology for the first time. Literature on these topics was obtained from Google Scholar, Pubmed and ScienceDirect journal articles published from 1788 to September, 2021. Only articles written in English were reviewed. While several species of Pysdrax used in traditional medicine have not been chemically explored for drug discovery, over a hundred secondary metabolites have so far been identified in few species of the genus, and majority of these chemotaxonomic markers are iridoids. Bioactive extracts and some isolated constituents of Psydrax species have shown various in vitro and in vivo pharmacological properties including anti-hyperglycemia, anti-inflammatory, anticonvulsant and antimicrobial, and thus, support some of the ethnomedical uses of the plants. For an evidence-informed application of the genus, Psydrax , in traditional medicine, more ethnobotanical surveys, elaborate in vivo pharmacological assays, in-depth toxicity and holistic phytochemical studies are required to fully exploit more species of the genus prior to future clinical studies. Following documented traditional uses of Psydrax species, the deliberate cultivation of medicinal plants under this genus is recommended for sustainability in medicinal plant utilization.

The proper documentation of ethnopharmacological application of widely used indigenous plants and their phytochemical analysis has positively impacted the drug discovery pipeline. Medicinal plants with potential commercial value and prospects for clinical application need to be properly identified and authenticated to avoid confusion, adulteration and substitution. Oldenlandia affinis (OA) has continued to attract scientific attention following the discovery of extremely stable cyclotides (circular peptides) that are not expressed in many investigated members of the contentious genus, Oldenlandia (synonym – Hedyotis); yet there is a lack of an elaborate review covering some broader aspects of its traditional uses, ethnopharmacology and phytochemistry of the species. More importantly, the age long but lingering confusion and taxonomic inconsistencies common to the Oldenlandia–Hedyotis debate could foster species mismatching, increase cases of misidentification, promote adulteration of OA and thereby limit its proper clinical application. Here, we aim to reveal the extent of indigenous use of and research on OA from 1960 till date, unveil knowledge gaps, document hitherto unknown traditional applications, ethnopharmacological uses, pharmacological properties, and reported phytochemical profile. In addition, to encourage proper selection and utilization of genuine crude drug, the chemotaxonomically important phytoconstituents of OA have been presented and the modern approach of chemophenetic study of OA proposed to resolve the lack of consensus in the taxonomy of OA as well as the morphologically and anatomically close members of the taxon. The abundant cyclotide expression in OA represents a new chemotaxonomic marker for its unambiguous identification, utilization and reproducibility of research findings on the species.

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