When is methylnaltrexone typically administered?

Methylnaltrexone is specifically indicated for the treatment of opioid-induced constipation in patients who are taking opioids for chronic pain. This medication works as a peripherally acting mu-opioid receptor antagonist, which means it effectively blocks the constipating effects of opioids in the gastrointestinal tract without affecting the analgesic effects Central nervous system (CNS) related to opioid usage. Methylnaltrexone is particularly valuable for patients who continue to experience constipation despite the use of laxatives.

The other conditions mentioned, such as severe headaches, hypertension, and anxiety, do not align with the pharmacological action or intended use of methylnaltrexone. Therefore, its primary use is indeed in the management of opioid-induced constipation, confirming the appropriateness of the selected response.