Abstract: Fifteen trials met the inclusion criteria (2284 participants, 69% males, 16% children). They were conducted in disparate malaria endemic areas, with the earlier studies conducted in Thailand (five) and India (two), and the more recent studies (eight) spread across three continents (South America, Africa, Asia). The 15 studies involved 41 treatment arms, 12 different drugs, and 28 different treatment regimens. Two studies examined P. vivax. Three-day azithromycin (AZ) monotherapy did not perform well for P. vivax or P. falciparum (Thailand: P. vivax failure rate 0.5 g daily, 56%, 95% CI 31 to 78. India: P. vivax failure rate 1 g daily,12%, 95% CI 7 to 21; P. falciparum failure rate 1 g daily, 64%, 95% CI 36 to 86.) A 1 g azithromycin and 0.6 g chloroquine combination daily for three days for uncomplicated P. falciparum infections was associated with increased treatment failure in India and Indonesia compared with the combination of sulphadoxine-pyrimethamine and chloroquine (pooled RR 2.66, 95% CI 1.25 to 5.67), and compared with the combination atovaquone-proguanil in a multicentre trial in Columbia and Surinam (RR 24.72, 95% CI 6.16 to 99.20). No increased risk of treatment failure was seen in two studies in Africa with mefloquine as the comparator drug (pooled RR 2.02, 95% CI 0.51 to 7.96, P = 0.3); the pooled RR for PCR-corrected data for the combination versus mefloquine was 1.01, 95% CI 0.18 to 5.84 (P = 1.0). An increased treatment failure risk was seen when comparing azithromycin in a dose of 1.2 to 1.5 mg in combination with artesunate (200 mg per day for three days) with artemether-lumefantrine (pooled RR 3.08, 95% CI 2.09 to 4.55; PCR-corrected pooled RR 3.63, 95% CI 2.02 to 6.52). Serious adverse events and treatment discontinuation were similar across treatment arms. More adverse events were reported when comparing the 1 g azithromycin/ 0.6 g chloroquine combination with mefloquine (pooled RR 1.20, 95% CI 1.06 to 1.36) or atovaquone-proguanil (RR 1.41, 95% CI 1.09 to1.83). Currently, there is no evidence for the superiority or equivalence of azithromycin monotherapy or combination therapy for the treatment of P. falciparum or P. vivax compared with other antimalarials or with the current first-line antimalarial combinations. The available evidence suggests that azithromycin is a weak antimalarial with some appealing safety characteristics. Unless the ongoing dose, formulation and product optimisation process results in a universally efficacious product, or a specific niche application is identified that is complementary to the current scala of more efficacious antimalarial combinations, azithromycin's future for the treatment of malaria does not look promising.

Plain-language summary: Our review of studies conducted over the past 14 years suggests that azithromycin is a relatively weak antimalarial whose efficacy depends on the drug dose and the partner drug in the combination therapy. The data suggest that, among adults, the higher doses needed to achieve an acceptable level of treatment success with malaria may be less well tolerated. Unless the ongoing product and dose optimisation process results in a universally efficacious product or identifies a specific niche application that is complementary to the current scala of more efficacious antimalarial combinations, azithromycin's future as an antimalarial does not look promising.