From the Guidelines
For patients who have undergone Roux-en-Y gastric bypass surgery, immediate-release (IR) venlafaxine is the preferred formulation over extended-release (ER) venlafaxine due to the altered gastrointestinal anatomy affecting drug absorption. The shortened intestinal transit time and reduced surface area for absorption after Roux-en-Y gastric bypass surgery may prevent ER formulations from being properly absorbed and released as designed 1.
Key Considerations
- The altered gastrointestinal anatomy after Roux-en-Y gastric bypass surgery can significantly impact the absorption of medications, particularly extended-release formulations.
- Immediate-release venlafaxine is more likely to be adequately absorbed in the modified GI tract compared to extended-release venlafaxine.
- When switching from ER to IR formulation after surgery, the same total daily dose can typically be used but should be divided into multiple doses (usually twice or three times daily) due to the shorter half-life of the IR formulation.
Monitoring and Side Effects
- Patients should be monitored closely for efficacy and side effects after surgery, as dose adjustments may be necessary.
- Common side effects to watch for include nausea, headache, dizziness, and increased blood pressure.
- If the IR formulation causes significant nausea, taking it with food may help reduce this side effect.
- Dumping syndrome, which can occur after bariatric surgery, may also impact the absorption and efficacy of venlafaxine, and its management should be considered in the context of venlafaxine therapy 1.
From the Research
Venlafaxine IR vs ER after Roux-en-Y Gastric Bypass Surgery
- The study 2 compared the bioavailability of single-dose extended-release venlafaxine capsules in obese patients before and after gastric bypass surgery, and found that the areas under the serum concentration-time curves for venlafaxine and its primary metabolite, O-desmethylvenlafaxine (ODV), were similar before and after Roux-en-Y gastric bypass (RYGB).
- The results of this study suggest that RYGB does not significantly alter the amount of venlafaxine or its active metabolite, ODV, absorbed from a venlafaxine ER capsule or the time over which it is absorbed.
- However, other studies have shown that malabsorption can occur after RYGB, including malabsorption of fat 3, calcium 4, and oxalate 5.
- A study on pharmacokinetic considerations in RYGB patients 6 suggests that the decrease in gastric and intestinal absorptive surface area may affect the oral bioavailability of some drugs, particularly those that require a more acidic environment for absorption or rely on intestinal transporters located in the duodenum for proper absorption.
- The study 6 recommends considering the pK(a), log P, and intestinal transport mechanisms when determining which drugs may have altered pharmacokinetics in patients who have undergone RYGB.
- In the case of venlafaxine, the study 2 found no significant difference in bioavailability between pre- and post-RYGB, suggesting that the ER form may be a suitable option for patients after RYGB surgery.