What type of nausea and vomiting are phenothiazines typically ineffective against?

Phenothiazines, such as prochlorperazine and promethazine, are primarily effective against nausea and vomiting caused by a variety of conditions, including chemotherapy-induced nausea and vomiting, radiation-induced nausea, and post-operative nausea. However, they are typically ineffective against motion sickness.

Motion sickness is primarily related to the vestibular system and involves the brain's interpretation of sensory signals. The nausea and vomiting in cases of motion sickness arise from a mismatch between the visual and vestibular inputs, which is not effectively countered by phenothiazines. These drugs work by blocking dopamine receptors in the central nervous system, which can alleviate nausea related to certain triggers but do not target the specific mechanisms involved in motion sickness. Instead, antihistamines, particularly those with anticholinergic properties, are more effective for preventing and treating nausea associated with motion sickness.

Thus, phenothiazines are less suitable as a treatment for motion sickness compared to other antiemetic options.