What medications can be prescribed to a 22-year-old patient with frequent watery stools and vomiting?

Management of Frequent Watery Stools and Vomiting in a 22-Year-Old

For a 22-year-old with frequent watery stools and vomiting, initiate ondansetron 8 mg orally (or IV if unable to tolerate oral) every 8 hours for vomiting control, combined with loperamide 2 mg after each loose stool (maximum 16 mg/day) for diarrhea once adequately hydrated, while simultaneously starting oral rehydration solution (ORS) at 100 mL/kg over 2-4 hours if moderate dehydration is present. 1, 2

Immediate Assessment and Hydration Status

• Assess dehydration severity through clinical signs: skin turgor, mental status, mucous membrane moisture, capillary refill, and vital signs to categorize as mild (3-5%), moderate (6-9%), or severe (≥10%) 2
• For moderate dehydration (6-9% deficit), administer ORS at 100 mL/kg over 2-4 hours, replacing ongoing losses with 10 mL/kg ORS for each watery stool and 2 mL/kg for each vomiting episode 2
• For severe dehydration (≥10% deficit), initiate IV isotonic fluids (lactated Ringer's or normal saline) until pulse, perfusion, and mental status normalize, then transition to ORS 2

Antiemetic Therapy

Ondansetron is the first-line antiemetic due to superior safety profile without sedation or akathisia risk 3:

• Administer ondansetron 8 mg orally every 8 hours (or 16-24 mg once daily as alternative) starting 30 minutes before expected vomiting 4, 5, 6
• If oral route not feasible due to ongoing vomiting, use IV ondansetron 8 mg every 8 hours or rectal administration 4
• Ondansetron reduces vomiting incidence significantly (RR: 0.33 for first 8 hours, RR: 0.15 for next 24 hours) 7

Alternative antiemetics if ondansetron fails or is unavailable 4, 1:

• Metoclopramide 10-40 mg orally or IV every 4-6 hours (monitor for extrapyramidal symptoms, particularly in young males) 4, 1
• Prochlorperazine 10 mg orally or IV every 4-6 hours (monitor for akathisia) 4, 1

Antidiarrheal Therapy

Loperamide is appropriate for immunocompetent adults with acute watery diarrhea once adequately hydrated 2:

• Administer loperamide 2 mg after each loose stool (maximum 16 mg/day or 8 doses) 4
• Do NOT use loperamide if bloody diarrhea develops, as this may indicate bacterial dysentery requiring different management 2

Critical Diagnostic Workup

Obtain baseline laboratory studies to exclude metabolic causes and assess dehydration 1:

• Complete blood count, serum electrolytes (particularly potassium and magnesium), glucose, liver function tests, lipase, and urinalysis 1
• Correct hypokalemia and hypomagnesemia aggressively, as prolonged vomiting causes hypochloremic metabolic alkalosis 1

Screen for cannabis use given the patient's age, as Cannabis Hyperemesis Syndrome (CHS) is common in this demographic and requires different management approach 1:

• If heavy cannabis use preceded symptom onset, CHS should be suspected 1
• Definitive CHS diagnosis requires 6 months cannabis cessation or at least 3 typical cycle lengths without vomiting 1

Nutritional Management

• Resume age-appropriate diet immediately during or after rehydration rather than fasting 2
• Avoid foods high in simple sugars (soft drinks, undiluted apple juice), high-fat foods, and caffeinated beverages, as these exacerbate diarrhea through osmotic effects and increased intestinal motility 2
• Continue oral intake with small, frequent meals once vomiting controlled 1

Red Flags Requiring Hospitalization

Admit immediately if any of the following are present 2:

• Severe dehydration (≥10% fluid deficit) with altered mental status, prolonged skin tenting >2 seconds, or signs of shock 2
• Failure of oral rehydration therapy despite appropriate ondansetron administration 2
• Persistent tachycardia or hypotension despite initial fluid resuscitation 2
• Bloody diarrhea with fever and systemic toxicity (may indicate Salmonella, Shigella, or enterohemorrhagic E. coli) 2
• Intractable vomiting despite IV antiemetics 2

Common Pitfalls to Avoid

• Do not delay rehydration while awaiting diagnostic testing—initiate ORS or IV fluids immediately based on clinical assessment 2
• Do not use inappropriate fluids like sports drinks or apple juice as primary rehydration solutions for moderate to severe dehydration 2
• Monitor for QTc prolongation when using ondansetron, especially if combining with other QT-prolonging medications 1
• Recognize that ondansetron may increase stool volume/diarrhea in some patients, though antiemetic benefit typically outweighs this effect 1
• Avoid antimotility agents if bloody diarrhea develops, as this can worsen outcomes in bacterial dysentery 2

Follow-Up and Reassessment

• Reassess hydration status after 2-4 hours of ORS administration; if still dehydrated, reestimate deficit and restart rehydration 2
• If symptoms persist beyond 48 hours despite appropriate therapy, consider one-time esophagogastroduodenoscopy (EGD) or upper GI imaging to exclude obstructive lesions 1
• Before discharge, ensure patient is tolerating oral intake, producing adequate urine output, and clinically rehydrated 2