First: What is an API?
All tablets of all the drugs you buy through a chemist or pharmacy are made up of the Active Pharmaceutical Ingredient (API) and a filler. In the case of tablets or capsules this filler might be chalk or lactose or some form of cellulose or any other inert powder that can be squeezed into a tablet or mixed with the concentrated powder to fill a capsule. In some cases the API is mixed with a sugary syrup or water and ethanol to make a liquid dose.
So the API is the concentrate, the active ingredient in any medicine: tablet, capsule, syrup.
Before Bangladesh started making Twinvir, before Sofosbuvir was licensed in India the only option for a generic Hepatitis C treatment with the new Direct Acting Antiviral (DAA) drugs was to buy APIs from China and make them into doses ones self or, where possible, to get a chemist/pharmacist to do that job for you. In the “old days” all chemists could do this. Indeed many or most prescriptions were filled by the chemist directly by making the medicines from APIs however now days 99.9% of medicine is mass produced and chemists/pharmacists simply sell pre-packed tablets and capsules.
However in most countries there are still specialist Compounding Chemists who will make up APIs into medicines. Most will require a prescription to do this.
So up until December 2015 a lot of people did take the Hep C API treatment option and imported APIs from China, mostly from Mesochem, a large company that specialises in making the APIs for all kinds of drugs, including Hep C medicines. Mesochem made the pure active ingredients; 99.9% pure Sofosbuvir and Ledipasvir and Daclatasvir.
Buying your Hep C treatment in API form offers several advantages. Of course back in 2015 it was the only way of getting Ledipasvir or Daclatasvir to add to Sofosbuvir to treat the various genotypes of Hep C.
But even today with licensed Indian generic Hep C drugs readily available there are still advantages in considering treating your Hep C with APIs.