Interactions between various anti-malarial drugs have been reported to improve efficacy and mitigate toxicity of PQ. In particular, there have been a number of clinical evidences presented over the years showing that quinine (QN) and chloroquine (CQ) can favourably affect the efficacy of 8-AQs; further, there are intriguing suggestions that the haemolytic toxicity of the 8-AQ class can be reduced. For instance, the addition of CQ increased the effectiveness of PQ and pamaquine while reducing the associated toxicity in Korean patients . In a study to assess the toxicity of pentaquine, using doses two- to three-fold higher than therapeutic doses, ten patients were experimentally infected with malaria. Each patient received 120 mg pentaquine with or without QN . Five subjects receiving pentaquine only experienced marked drops in haemoglobin (average 2.6 g/dl), but the five concomitantly receiving QN showed no change in haemoglobin. Moreover, no patient in the pentaquine/QN group had a relapse in 12 months compared to two in the pentaquine-only group, who had relapses in 12 and 26 days, respectively. Associated side effects of syncope and postural hypotension were not reported in the pentaquine/QN group compared to pentaquine-only group . Thus, this study not only demonstrated the attenuation of the toxic effects of pentaquine by QN, it showed that QN improved the therapeutic efficacy of pentaquine. A similar observation, including an increase in plasma pentaquine concentration in the presence of QN, was reported by Alving and co-workers . Being an 8-AQ like PQ, whose mechanism of toxicity might be similar, this observation suggests similar beneficial drug interactions with PQ. Since the pharmacological activity of the 8-AQs are dependent on their metabolites, the knowledge of the roles of each metabolites may be deductible from observed pharmacodynamic changes due to inhibition or facilitation of the formation of known metabolites by other agents.