Azithromycin 250mg tablets are a single dose antibiotic for the treatment of chlamydia, chlamydia is the most common STD in the UK & most people with it do not show any symptoms. Notes While taking Azithromycin: Avoid any sexual contact for 7 days after taking Azithromycin, untill no longer infectious. People with a positive chlamydia test & their sexual partners should be treated at the same time if possible Chlamydia tests take 6 weeks to go negative after chlamydia has been successfully treated. Warnings Serious side effects are unusual, the most common are stomach upset, nausea & diarrhoea. For details about azithromycin see the patient information leaflet supplied with the tablets. In the unlikely event that vomiting occurs within an hour of taking azithromycin the treatment should be repeated.