Which of the following medications can induce diarrhea: ceftriaxone (Ceftriaxone) 1gm in 30ml Normal Saline (NS) over 1 hour twice daily (BD), Doxycycline (Doxycycline) 50mg orally (PO) half strength, Medomol (not a standard medication, possibly a brand name, assuming it's a medication) 6ml, or Junior Lanzole (possibly a brand name, assuming it's a medication, generic name not specified) 15mg orally once daily?

Medications That Can Induce Diarrhea in This Regimen

Both ceftriaxone and doxycycline can cause diarrhea, with ceftriaxone being the most likely culprit in this regimen, while lansoprazole (Junior Lanzole) can also contribute through Clostridium difficile-associated diarrhea.

Primary Offenders

Ceftriaxone (1gm IV BD)

• Ceftriaxone causes diarrhea in approximately 34% of pediatric patients, with onset typically after 2-14 doses and persistence for 2-8 days 1
• The mechanism involves disruption of normal gut flora, osmotic effects, and potential for C. difficile overgrowth 2
• Diarrhea is listed as a common adverse effect occurring in 3.8% of adult patients in controlled trials, though this likely underestimates real-world incidence 3
• Antimicrobials are responsible for 25% of all drug-induced diarrhea cases 2
• The diarrhea is usually mild to moderate and does not require discontinuation of therapy 1

Doxycycline (50mg PO BD)

• Doxycycline is well-documented to cause gastrointestinal side effects, particularly diarrhea 3
• Tetracyclines like doxycycline can cause gastrointestinal side effects, which is why doxycycline is preferred over tetracycline due to better compliance 3
• The mechanism involves direct mucosal irritation and alteration of intestinal flora 2

Lansoprazole/Junior Lanzole (15mg PO daily)

• Lansoprazole causes diarrhea in 3.8% of patients in clinical trials, with higher rates (7.4%) at 60mg doses 4
• More concerning is the risk of Clostridium difficile-associated diarrhea, which is a serious adverse reaction listed in the FDA label 4
• Proton pump inhibitors alter gastric pH, which can predispose to bacterial overgrowth and infectious diarrhea 4

Medomol (Paracetamol/Acetaminophen Syrup)

• Paracetamol/acetaminophen is not typically associated with diarrhea and is generally well-tolerated gastrointestinally
• This medication is the least likely cause in this regimen

Clinical Algorithm for Identifying the Culprit

Timing Assessment

• If diarrhea began within 2-14 doses of starting ceftriaxone: ceftriaxone is the most likely cause 1
• If diarrhea began within the first few days of any antibiotic: consider both ceftriaxone and doxycycline 2
• If diarrhea is delayed (weeks after starting therapy): consider lansoprazole-associated C. difficile infection 4

Severity and Character Assessment

• Mild, watery diarrhea (4+ bowel movements/day): most consistent with ceftriaxone-induced osmotic diarrhea 1
• Diarrhea with fever, blood, or mucus: evaluate for C. difficile colitis, particularly if on lansoprazole 4
• Cramping with diarrhea: can occur with any of these agents but consider doxycycline if associated with nausea 2

Management Approach

• Do not discontinue ceftriaxone unless diarrhea is severe or C. difficile is confirmed, as the infection being treated takes priority 1
• Test for C. difficile toxin if diarrhea is severe, persistent beyond expected antibiotic-associated diarrhea, or associated with fever/leukocytosis 3
• Supportive care with hydration is usually sufficient for antibiotic-associated diarrhea 1
• Consider probiotics, though evidence is mixed for prevention

Important Caveats

• Multiple mechanisms can coexist: a patient on this regimen has three potential diarrhea-inducing agents simultaneously 2
• The combination of antibiotics increases risk: dual antibiotic therapy (ceftriaxone + doxycycline) compounds the disruption of normal gut flora 2
• Lansoprazole increases C. difficile risk: the acid suppression from lansoprazole can facilitate C. difficile colonization when combined with antibiotics 4
• Diaper rash is a marker of severity: in the pediatric study, 88% of patients with ceftriaxone-induced diarrhea developed diaper rash requiring additional care 1