Generic Name

Prilosec (lansoprazole)

Mechanism

• Selective irreversible inhibition of the H⁺/K⁺‑ATPase (gastric proton pump) in parietal cells.
• Blocks the last step in acid secretion, reducing intragastric acidity to pH > 3.
• Onset of maximal inhibition ~ 1‑2 h after oral dosing; effect persists for 24 h due to covalent binding.

Pharmacokinetics

• Absorption: ~ 50% oral bioavailability; peak plasma ~2 h post‑dose.
• Distribution: ~ 10 % protein binding (mostly albumin).
• Metabolism: Primarily CYP2C19 & CYP3A4 → active metabolites (e.g., 2‑hydroxy‑lansoprazole).
• Elimination: ~ 30 % renal excretion; 70 % fecal.
• Half‑life: 1‑1.5 h (terminal), but clinical effect lasts ~24 h.
• Drug interactions: potent CYP2C19 inhibitor; caution with clopidogrel, warfarin, itraconazole.

Indications

• Gastroesophageal reflux disease (GERD): erosive esophagitis, symptomatic reflux, Barrett’s esophagus.
• Peptic ulcer disease (PUD): H. pylori eradication regimens and ulcer healing.
• Non‑steroidal anti‑inflammatory drug (NSAID)-induced gastropathy.
• Zollinger‑Ellison syndrome (gastrin‑secreting tumor).
• Gastric protection when co‑prescribed with chronic NSAIDs or corticosteroids.

Contraindications

• Allergy to lansoprazole or any excipient.
• CYP2C19 poor metabolizers requiring dose adjustment because of increased exposure.
• Severe hepatic impairment: monitor for toxicity; lower dose or switch to alternative.
• Pregnancy category B: use only if benefits outweigh risks.
• Long‑term therapy (>8 weeks): assess for vitamin B12, magnesium, or iron deficiency; monitor renal function.

Dosing

• Form: oral capsule or tablet; in hospital, IV 30 mg/240 mL over 30 min.
• Take: 30 min before a meal, preferably 30–60 min before breakfast.
• Rescue dose: not recommended; adjust therapy instead.

Adverse Effects

• Common
• Headache, nausea, abdominal pain, diarrhea, flatulence.
• Mild dysgeusia (taste disturbance).
• Serious
• Hypomagnesemia → muscle cramps, arrhythmias.
• Vitamin B12 deficiency → pernicious anemia.
• Clostridioides difficile infection (altered gut flora).
• Pneumonia in immunocompromised patients.
• Long‑term risk: osteoporosis‑related fractures.

Monitoring

• Baseline labs: CBC, serum magnesium, electrolytes, liver enzymes.
• Follow‑up:
• Magnesium, calcium, vitamin B12 after 6–12 mo of therapy.
• Bone density annually in high‑risk patients.
• Renal function if concomitant nephrotoxic drugs.
• Symptom assessment: daily diary for GERD and ulcer pain; 24‑hr pH monitoring if refractory.

Clinical Pearls

• Therapeutic window: Because of covalent enzyme inhibition, *once‑daily dosing* maximizes efficacy while minimizing side‑effects.
• Perioperative use: Lansoprazole reduces the risk of stress ulcers in high‑risk surgical patients; consider 40 mg twice daily for 3–5 days pre‑op.
• Drug–drug synergy: Combine with doxycycline or amoxicillin for H. pylori eradication; avoid clopidogrel concurrently if possible due to CYP2C19 inhibition.
• Rebound acid hypersecretion: Taper dose rather than abrupt cessation to avoid post‑discontinuation heartburn.
• Bioavailability tweak: Take capsules with a full glass of water – gastric pH affects dissolution; avoid taking with antacids.
• Patient adherence tip: Pre‑meal dosing is critical; remind patients to take it before breakfast, not after, to achieve optimal acid suppression.

Prilosec remains the cornerstone for acid‑related disorders, but mindful dosing, monitoring, and patient education are key to maximizing therapeutic benefit and minimizing adverse events.