What is the onset of action for Zantac (ranitidine)?

Onset of Action for Zantac (Ranitidine)

Ranitidine has a rapid onset of action with peak plasma concentrations occurring 2 to 3 hours after oral administration of a 150 mg dose. 1

Pharmacokinetics

• Ranitidine is a competitive, reversible inhibitor of histamine at H2-receptors on gastric cells 1
• After oral administration, ranitidine is approximately 50% absorbed 1
• Mean peak plasma levels of 440 to 545 ng/mL occur 2-3 hours after a 150 mg oral dose 1, 2
• The bioavailability of oral ranitidine is approximately 50% due to presystemic hepatic metabolism 2
• Absorption is not significantly impaired by food or most antacids 1
• The elimination half-life is 2.5 to 3 hours in adults with normal renal function 1, 2

Onset of Action Considerations

• While peak plasma concentrations occur at 2-3 hours, the clinical onset of acid suppression begins more rapidly 2, 3
• Ranitidine effervescent tablets have been shown to have an almost immediate onset of action compared to standard tablets 3
• The relationship between plasma concentration and suppression of gastric acid production shows wide interindividual variability 2

Special Populations

• In elderly patients:

  • The elimination half-life is prolonged to 3-4 hours 1
  • Peak levels occur at about 3 hours following a 150 mg dose 1
  • Plasma clearance is reduced due to decreased renal function 1

• In pediatric patients:

  • The pharmacokinetics are similar to adults when corrected for body weight 1
  • The bioavailability in pediatric patients is comparable to adults at approximately 48% 1

• In patients with renal impairment:

  • The plasma half-life is prolonged (average 4.8 hours in patients with creatinine clearance 25-35 mL/min) 1
  • Dosage adjustment is recommended based on creatinine clearance 1

Safety Profile

• Ranitidine is generally well-tolerated with an adverse event profile similar to placebo in clinical trials 4
• Most common side effects include headaches, tiredness, dizziness, and mild gastrointestinal disturbances 5
• Serious side effects are rare, with cardiovascular side effects occurring in approximately 1 in 1 million patients 5

Clinical Implications

• For treatment of acid-related disorders, the onset of therapeutic effect begins shortly after administration, though peak plasma levels occur at 2-3 hours 1, 2
• The standard dosing of ranitidine is 150 mg twice daily for most acid-related conditions 6
• Single nighttime dosing of 150 mg has been shown to be effective in preventing ulcer recurrence 6