Administer a medication or infusion to a parent through the use of a needle syringe:[1]

Some Poskim[2] however prohibit this only if the medication will be administered through a vein, however if it will be administered through a muscle, then they are lenient to permit it on the basis that is not for certain that blood will be drawn. Other Poskim[3] however are stringent in all cases to prohibit one from being done. [Regarding the administration of a daily dose of insulin to a parent, ideally it would be forbidden under the above clause, unless it is an emergency, and another doctor is not available. However, in the event that going to a doctor or other person every single day in order to have this done would involve much difficulty, then it is permitted for the son to administer it to his parent, as explained above.[4] The same rules would apply to doing a daily prick to the parents skin in order to get a blood sugar level reading.]

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[1] Gesher Hachaim 2:1; Minchas Yitzchak 1:27; Mishneh Halachos 9:404; Minchas Shlomo 1:32; Beir Moshe 4:84; Shevet Halevi 2:112-4; 8:79-2; Kneses Yechezkal 1:58

[2] Gesher Hachaim 2:1; Minchas Shlomo 1:32

[3] Rav Pesach Tzevi Frank in Gesher Hachaim ibid; Implication of Poskim ibid

[4] Pesakim Uteshuvos 241:4