A friend has interest money in his bank account. He has a friend who is suffering from debts, so can my friend clear his friend's debt with this interest money?

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

Taking Riba (usury and/or interest) is a major sin. Riba is a declaration of war with Allah.

Allah Says (what means): {O you who have believed, fear Allah and give up what remains [due to you] of interest, if you should be believers. And if you do not, then be informed of a war [against you] from Allah and His Messenger. But if you repent, you may have your principal - [thus] you do no wrong, nor are you wronged.} [Quran 2: 278-279]

Besides, the Prophet said on the seriousness and danger of Riba: “To consume one Dirham of Riba is worse than committing Zina (adultery and fornication) thirty-six times.” [Ahmad and others]

The Prophet also said: “Riba consists of seventy-three kinds of evil; the least of them is like having sex with one's own mother.” [Ibn Majah, al-Hakim and others]

The dealer in Riba is cursed; the Prophet said: “Allah has cursed the one who consumes Riba …” [Muslim]

So, it is a duty for one who deals in Riba to repent sincerely and to seek forgiveness from Allah as much as possible.

In addition, one has to get rid of Riba money by spending it on the general welfare of the Muslims. So, there is no harm in giving it (or some of it) to a friend according to his need, but one is not allowed to use it in order to settle a personal debt that he owes to his creditor, or to give it to those whom he is responsible to spend on.

Allah knows best.