[In vitro effect against Giardia of 14 plant extracts]

To investigate antigiardiasic activity in plants used in Mexico as antidiarrheics and/or antiparasitics.

Fourteen species were evaluated. The antigiardiasic activity was measured in vitro in a blinded fashion using trophozoites of Giardia duodenalis incubated with plant extracts. The viability of trophozoites was ascertained using MTT (3-[4,5-dimethylthiazol-2-il]-2, 5-diphenyl tetrazolium bromide) which is reduced to MTT-formazan by the activity of live trophozoites. The reduced MTT was extracted with an acidified alcohol (2-propanol with HCI 0.04 M) and measured in a spectrophotometer at 570 nm. Negative (trophozoites without extract) and positive controls (incubated with tinadazol) were included.

The scientific and trivial names of the plants are given (trivials in Spanish marked by an asterisk). They had the following trophozoite mortality (mean +/- SD in percent): Justicia spicigera (muicle*) = 91 +/- 0.5; Lipia beriandieri (oregano) = 90 +/- 0.6; Psidium guajava (guava) = 87 +/- 1.0; positive control of tinidazol = 79 +/- 1.9; Punica granutus (granado*) = 78 +/- 1.3; Magnifera indica (mango) = 77 +/- 1.0; Plantago major (lante*) = 76 +/- 1.2; Cupressus semperbirens (cipres) = 73 +/- 1.2; Castella tormentosa (chaparro amargoso*) = 70 +/- 0.7; Hematoxilon campechanum (palo de Campeche*) = 67 +/- 1.2. Without or with a low mean activity were Prosopis juliflora (mesquite*) and Rizophora mangle (mangle*) with 0%, Oriza sativa (rice) with 5%, Capsicum annum (pimiento*) with 21% and Persea americana (avocado) with 23%. There were no associations of the antigiardiasic effect with concentration or osmolality of the extracts.

A clear in vitro antigiardiasic effects was seen in nine species. Three of them were superior to tinidazol which is a drug of common use in the treatment of giardiasis.