Laboratory and field evaluation of biodegradable polyesters for sustained release of isometamidium and ethidium - Minireview

An overview is presented of the results obtained with biodegradable sustain ed release devices (SRDs) containing a mixture of polymers and either isome tamidium (ISMM) or ethidium. Under controlled laboratory conditions (monthl y challenge with tsetse flies infected with Trypanosoma congolense) the pro tection period in SRD treated cattle could be extended by a factor 2.8 (for ethidium) up to 4.2 (for ISMM) as compared to animals treated intramuscula rly, with the same drugs. Using a competitive drug ELISA ISMM concentration s were detected up to 330 days after the implantation of the SRDs, whereas after i.m. injection the drug was no longer present three to four months po st treatment. Two field trials carried out in Mali under heavy tsetse chall enge showed that the cumulative infection rate was significantly lower in t he ISMM-SRD implanted cattle than in those which received ISMM intramuscula rly. Using ethidium SRD, however, contradictory, results were obtained infi eld trials in Zambia and in Mali. The potential advantages and inconvenient s of the use of SRDs are discussed and suggestions are made in order to fur ther improve the currently available devices.