Clinical bottom line:

Based on the current evidence, oral doxycycline (10mg/kg PO q24h or 5mg/kg PO q12h) for at least 21 days represents the most efficacious treatment, both in terms of clinical improvement and permanent clearance of Chlamydophila felis infection in cats. In chronic infections, or where the duration of disease is unknown, a longer treatment course of 28 days is indicated. There is limited evidence that co-amoxiclav (12.5-22.5mg/kg q12h PO) may be used as an alternative, though a treatment period of at least 30 days is required.