Omeprazole absorption and timing of administration
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Omeprazole Absorption: Oral, Transdermal, and Rectal Routes
Omeprazole is most commonly administered orally in enteric-coated formulations to protect the drug from stomach acid, as it is acid-labile. Studies show that oral absorption can be unpredictable, but repeated dosing increases the area under the plasma concentration-time curve (AUC), indicating higher systemic availability. This is likely due to omeprazole’s own inhibition of gastric acid, which reduces its degradation in the stomach and decreases first-pass metabolism over time Prichard1985Andersson1990Howden1984.
Alternative routes, such as transdermal and rectal administration, have been explored. Transdermal absorption of omeprazole is extremely poor, with plasma concentrations about 1,000 times lower than oral dosing, making this route ineffective for clinical use . Rectal administration via suppository achieves similar rates and extents of absorption compared to oral capsules, but does not offer significant improvement in overall absorption .
Timing of Omeprazole Administration and Its Impact
The timing of omeprazole administration can influence its pharmacodynamic and pharmacokinetic effects. When given in the morning or evening, both dosing times significantly increase gastric pH, but morning dosing has a slightly greater effect on daytime pH levels . The relative bioavailability of omeprazole increases with repeated dosing, more so with evening administration, likely due to cumulative acid suppression and reduced drug degradation Prichard1985Andersson1990Howden1984.
Influence of Gastric Acidity and Co-Administration with Acid-Reducing Agents
Omeprazole is formulated as enteric-coated granules to bypass the acidic stomach environment. Studies show that the overall extent of absorption (AUC) is not significantly affected by gastric acidity when using these granules, but the maximum plasma concentration (Cmax) is higher and reached faster if gastric acid is suppressed (e.g., by prior administration of ranitidine) . This suggests that while acid suppression does not change the total amount absorbed, it can speed up absorption and increase peak levels.
Formulation Differences and Absorption Kinetics
Comparisons between delayed-release capsules and simplified omeprazole suspensions (SOS) reveal that the suspension is absorbed faster (shorter time to Cmax), but the total amount absorbed (AUC) is lower than with capsules. After repeated dosing, absorption from both formulations becomes faster, but the capsule maintains higher overall bioavailability .
Omeprazole’s Effect on Absorption of Other Drugs
Omeprazole’s acid-suppressing action can affect the absorption of other drugs that require an acidic environment for optimal absorption. For example, omeprazole significantly reduces the bioavailability of pH-sensitive drugs like dasatinib, with reductions in Cmax and AUC of up to 96% and 89%, respectively, when the two drugs are administered close together . Similarly, omeprazole can reduce the peak concentration of drugs like furazolidone, likely by altering absorption kinetics or first-pass metabolism .
Long-Term Omeprazole Use and Intestinal Absorption
Prolonged omeprazole administration can impair the absorption of certain minerals, such as magnesium, throughout the intestinal tract. This effect is most pronounced in the small intestine and is associated with compensatory increases in transporter expression, indicating a physiological response to malabsorption .
Conclusion
Omeprazole absorption is most effective with oral enteric-coated formulations, and repeated dosing increases its bioavailability due to reduced gastric acidity and first-pass metabolism. Timing of administration can influence the degree of acid suppression and absorption kinetics, with morning dosing providing slightly greater daytime acid control. Co-administration with other acid-reducing agents or pH-sensitive drugs can significantly alter omeprazole’s absorption profile and the absorption of other medications. Alternative routes like transdermal and rectal administration do not offer significant advantages over oral dosing. Understanding these factors is important for optimizing omeprazole therapy and managing potential drug interactions.
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Most relevant research papers on this topic
Severe Impact of Omeprazole Timing on pH‐Sensitive Dasatinib Absorption: Unveiling Substantial Drug–Drug Interaction
Omeprazole timing significantly reduces the absorption of pH-sensitive dasatinib by 96% and 89%, highlighting the need for optimal clinical management.
Omeprazole: a study of its inhibition of gastric pH and oral pharmacokinetics after morning or evening dosage.
Omeprazole is a highly potent antisecretory agent in humans, with morning dosage having a greater effect than evening dosage, and its optimal effect may not be observed for several days.
Influence of acid secretory status on absorption of omeprazole from enteric coated granules.
Gastric acidity has minimal influence on the absorption of omeprazole from enteric coated granules, but its maximum plasma concentration is higher and time to reach Cmax is shorter after a ranitidine dose.
Pharmacokinetic comparison of omeprazole capsules and a simplified omeprazole suspension.
After one week of therapy, omeprazole absorption was faster and time to Cmax was 70% shorter for SOS than for the capsule formulation, but AUC0-infinity was 49% lower for SOS.
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