Kan Jang capsules appear to be more effective than isolated andrographis (despite andrographis being the primary active ingredient) so it would probably be prudent to try to find a combination supplement or Kan Jang capsules themselves for acute treatment of colds.
Three divided doses of 400 mg total of 1200 mg daily, of the basic plant extract itself, appears to be effective in reducing the length and severity of colds. Doses of up to 6 g has been taken with efficacy (as the duration of supplement usage is only 3-5 days as it is ceased after the cold is gone).
900 mg tends to refer to the overall root weight. Dosing is thrice daily, usually taken before meals. Pelargonium sidoides is highly effective for bronchitis specifically, and while it also has promise in treating the common cold with similar potency it is not as well studied, general upper respiratory tract infections are only slightly benefited from this herb.
Specifically, garlic consumption as a daily preventative seems to greatly reduce the chance of getting sick (by around 60%) but only minorly reduces symptom severity (20% or less) and when you are sick it does not help with the frequency of symptoms.
Higher than normal doses of garlic have been used to ward off colds (either 180mg allicin which is equivalent to 9 g of raw cloves, or 2,650mg of Aged Garlic Extract).
For the creation of this content, I have used Examine.com as a main source of data-driven information.