Is it permissible to urinate on the site of a marine animal's (jellyfish) sting to remove its thorns and harm?

Human urine is impure by scholarly consensus. The basic principle is that it is forbidden to seek medical treatment with something unlawful or impure, unless one is compelled to do so, and it is confirmed by a trustworthy physician that it contains medicine, and no permissible alternative is available. This is based on the Prophet's (peace be upon him) saying: "Indeed, Allah created both the ailment and the remedy, so seek treatment, but do not seek treatment with unlawful things." If a pure substance is available, then using an impure one is forbidden without dispute. The person who seeks treatment with an impure substance must wash the affected area before praying.