The two types of antiviral drugs known to be effective against the swine flu virus are oseltamivir (Tamiflu Ò ) and zanamir (Relenza Ò ). They are neuraminidase inhibitors and act by preventing the virus from budding and escaping from the host cells. Oseltamivir is given in the form of oral capsules and zanamivir is given as an inhaler (Diskhaler). The safety of these antiviral drugs in pregnancy has been looked at from experience with their usage in seasonal flu in some countries and from recent data from Canada. Although oseltamivir has been shown to cross the placenta and breast milk in small amounts, no adverse effects on the fetus or pregnancy have been recorded. As zanamivir acts in the respiratory tract with no absorption into the blood stream, it is recommended as first line treatment of swine flu in pregnancy in the United Kingdom. However, if the woman is unable to tolerate the inhaler e.g. if she has severe asthma or is admitted to hospital with complications such as pneumonia, oseltamivir is the recommended drug for treatment. The benefits of antiviral treatment are most noticeable if it is commenced within 48 h of symptom onset but recent experience with hospitalised patients reveals that antivirals given more than 48 h after symptom onset also confer benefit.