Are there any interactions or side effects with Pepsid (famotidine), Complete, and Valtrex (valacyclovir)?

Interactions and Side Effects Between Famotidine (Pepcid), Complete, and Valacyclovir (Valtrex)

There is a potential interaction between famotidine and valacyclovir that may increase valacyclovir levels, but this interaction is generally not clinically significant enough to warrant dose adjustments or contraindicate their concurrent use.

Famotidine (Pepcid) and Valacyclovir (Valtrex) Interaction

• Famotidine (an H2-receptor antagonist) can increase the plasma concentration of valacyclovir and its metabolite acyclovir by approximately 27% (AUC) and 8% (Cmax) 1
• This interaction occurs through competitive inhibition of membrane transport of valacyclovir and acyclovir in the liver and kidney 1
• Despite this pharmacokinetic interaction, studies have shown that these modifications do not significantly affect the tolerability of valacyclovir 1

Famotidine Dosing Considerations

• Famotidine can be safely administered with valacyclovir at doses not exceeding 40 mg 2
• No specific dose adjustment of either medication is required when co-administered 1

Complete (Antacid) Considerations

• "Complete" typically refers to an antacid product that may contain calcium carbonate, magnesium hydroxide, and/or other antacid components
• Antacids can potentially affect the absorption of some medications by altering gastric pH 3
• However, there are no documented clinically significant interactions between standard antacids and valacyclovir or famotidine that would require intervention 3

Common Side Effects to Be Aware Of

Valacyclovir (Valtrex)

• Most common side effects include headache, nausea, and abdominal pain 4
• Rare but serious: Thrombotic thrombocytopenic purpura/hemolytic uremic syndrome (in immunocompromised patients) 4
• Very rare: Clostridium difficile colitis has been reported with valacyclovir use 5

Famotidine (Pepcid)

• Common side effects include headache, dizziness, and constipation 2
• Generally well-tolerated with minimal drug interactions 2

Complete (Antacid)

• Common side effects may include constipation, diarrhea, or changes in bowel habits 3
• Antacids may reduce absorption of some medications, but this effect is not documented with valacyclovir 3

Special Considerations

• If taking other medications that affect renal function, more careful monitoring may be warranted as both valacyclovir and famotidine are eliminated through the kidneys 1
• Unlike some drug combinations that involve P-glycoprotein (P-gp) transport mechanisms, the interaction between famotidine and valacyclovir is considered mild and generally does not require intervention 1
• Avoid high-dose proton pump inhibitors with valacyclovir if possible, as they may have more significant effects on drug absorption than H2-receptor antagonists like famotidine 2

Conclusion Points

• The combination of famotidine, Complete (antacid), and valacyclovir can generally be used together safely 1, 3
• Monitor for increased side effects of valacyclovir such as headache or nausea, although these are unlikely to be significantly exacerbated 1, 4
• No specific timing separation between these medications is required 2