Pharmacology Chapter 22: GI Drug Therapy

Gastrointestinal Disorders and Stool Consistency

• The large bowel significantly influences stool consistency based on water absorption; too much absorption results in constipation, while less leads to diarrhea.
• The alimentary canal encompasses the entire GI system; nutrient absorption occurs primarily in the small bowel.
• Stool is stored in the rectum before expulsion.

Assessing Bowel Movements

• Normal bowel habits vary greatly among individuals, with a range from multiple times daily to several times weekly.
• The consistency of stool is crucial for assessing bowel health; it should be soft yet not liquid.
• Further evaluation is necessary to identify causes of abnormal bowel movements, which may involve dietary adjustments or medication reviews.

Antiemetic for Chemotherapy-Induced Nausea

• Ondansetron (Zofran) is a preferred antiemetic for nausea/vomiting due to chemotherapy.
• Administered 30 minutes before chemotherapy, ondansetron specifically targets 5HT3 receptors to mitigate nausea.
• Alternatives like promethazine, metoclopramide, and cyclizine are less effective for chemotherapy-related symptoms.

Antihistamine for Motion Sickness

• Meclizine (Dramamine) is the recommended antihistamine for treating motion sickness and vertigo.
• It alleviates nausea, vomiting, and dizziness associated with motion or inner ear disorders.
• Other options like granisetron, prochlorperazine, and trimethobenzamide are not specifically suited for motion sickness.

Considerations for Antiemetic Use in Depression

• Metoclopramide (Reglan), a dopamine antagonist, should be avoided in patients with a history of depression due to its potential to exacerbate symptoms.
• Scopolamine, promethazine, and meclizine do not have known adverse effects on mood.

Adverse Effects of Promethazine

• Tardive dyskinesia is a serious potential side effect of promethazine, presenting as involuntary movements of the mouth, face, or limbs.
• Symptoms may include lip smacking, facial grimacing, and tongue movements and can occur after prolonged use.
• Immediate discontinuation of the medication is vital if tardive dyskinesia symptoms appear to prevent irreversible damage.

Serious Risks with Promethazine Administration

• Promethazine can cause tissue necrosis if administered undiluted via intravenous route.
• Clinicians should monitor for signs of adverse reactions to ensure prompt intervention.