From the FDA Drug Label
Sildenafil metabolism is principally mediated by the CYP3A (major route) and CYP2C9 (minor route) cytochrome P450 isoforms. Therefore, inhibitors of these isoenzymes may reduce sildenafil clearance and inducers of these isoenzymes may increase sildenafil clearance CYP3A Inhibitors and Beta Blockers Population pharmacokinetic analysis of data from patients in clinical trials indicated an approximately 30% reduction in sildenafil clearance when it was co-administered with mild/moderate CYP3A inhibitors and an approximately 34% reductions in sildenafil clearance when co-administered with beta-blockers Sildenafil exposure without concomitant medication is shown to be 5-fold higher at a dose of 80 mg TID compared to its exposure at a dose of 20 mg TID. This concentration range covers the same increased sildenafil exposure observed in specifically-designed drug interaction studies with CYP3A inhibitors (except for potent inhibitors such as ketoconazole, itraconazole, and ritonavir) Especially tell your doctor if you take ... Itraconazole (Sporanox)
Sildenafil Interaction with Itraconazole:
- Sildenafil is metabolized by the CYP3A cytochrome P450 isoform.
- Itraconazole is a potent CYP3A inhibitor.
- The co-administration of itraconazole with sildenafil may reduce sildenafil clearance, leading to increased sildenafil exposure.
- The FDA drug label warns about the potential interaction between sildenafil and itraconazole, advising patients to inform their doctor if they are taking itraconazole 1.
From the Research
Yes, sildenafil (Viagra) does interact significantly with itraconazole, and when taking itraconazole, the recommended maximum dose of sildenafil should be reduced to 25 mg within a 48-hour period. This is because itraconazole is a strong inhibitor of the CYP3A4 enzyme, which is responsible for metabolizing sildenafil in the liver, as mentioned in the study 2. When these medications are taken together, itraconazole can increase sildenafil blood levels, substantially increasing the risk of side effects such as severe hypotension, visual disturbances, priapism, and headaches.
The mechanism of this interaction is that itraconazole blocks the breakdown of sildenafil, allowing it to accumulate in the body. This is similar to the effect of other CYP3A4 inhibitors, such as ketoconazole, which is also mentioned in the study 2. Patients should inform their healthcare provider about all medications they are taking before starting either of these drugs, and any unusual side effects should be reported immediately.
Some key points to consider when taking sildenafil with itraconazole include:
- The increased risk of side effects due to the elevated blood levels of sildenafil
- The importance of informing healthcare providers about all medications being taken
- The potential need for alternative medications with fewer interactions, as discussed in the example answer
- The dose-related nature of side effects, as reported in the study 3
It is essential to prioritize the patient's safety and well-being when considering the use of sildenafil with itraconazole, and to carefully weigh the potential benefits against the potential risks, as discussed in the study 4. If you're currently taking itraconazole and need erectile dysfunction treatment, your doctor might recommend alternative medications with fewer interactions.