Is it permissible to purchase goods from the United States through a friend residing there who uses his own credit card, in exchange for sending him the price of the goods?

It is not permissible to use cards that obligate their holders to pay a financial penalty upon late payment. If your friend's card is free from this condition, there is no harm in authorizing him to make the purchase and then sending him the amount. However, if it includes this condition, you are not permitted to authorize him, because what a person is not allowed to do himself, he is not allowed to authorize another to do, "as the agent stands in the place of the principal." You should look for another method of purchase, especially since there are cards that can be loaded with specific amounts without usurious interest. If the card is free from the usurious condition, it is permissible to authorize the friend to make the purchase and then send the amount, and this is considered a loan, not an exchange.