The first thing you should do is discuss the issue with your doctor regarding your blood pressure dropping too low. This could be indicative that the dose of one or both may need adjusting.
However, if your blood pressure is well-controlled (and doesn't drop too low) when taking the HCTZ in the morning, and lisinopril at night, that is perfectly fine in most cases.
In fact, this may be the ideal way to take both medications.
HCTZ In The Morning
HCTZ (hydrochlorothiazide), a thiazide diuretic, can be taken anytime during the day but morning dosing is typically recommended.
Since HCTZ is a diuretic, and causes fluid loss through urination, taking it in the evening can cause interruptions with sleep since you may need to go to the bathroom more often.
Therefore, taking it in the morning may be wise to avoid disrupting your sleep.
Having said all of this, there have been some studies that suggest taking diuretics at nighttime lower blood pressure more effectively than taking them earlier in the day.
While this certainly may conflict with the negative effects of having to use the bathroom in the middle of the night, most studies point out the diuretic (i.e. water loss) effect of thiazide diuretics only lasts a few weeks after starting therapy. After this time, your bathroom habits may go back to normal.
The actual, long-term, blood pressure reducing mechanism of thiazide diuretics isn't well-understood and isn't necessarily only based on their diuretic effects. As one study puts it:
How thiazides reduce total peripheral resistance is unclear. One hypothesis involves thiazides exerting a direct action on blood vessels.
More studies are needed to determine the ideal dosing time for HCTZ, but as a general rule of thumb, morning is best for most people since it still effectively lowers blood pressure at this time and eliminates the risk of needing to go to the bathroom in the middle of the night.
Lisinopril At Night
The evidence for lisinopril being more effective with nighttime dosing than morning dosing is fairly strong.
We know that blood pressure follows our circadian rhythm and generally decreases slightly while we are asleep and spikes in the morning.
This morning blood pressure spike has been associated with an increased risk of cardiovascular events like stroke and heart attack.
It has been theorized that taking blood pressure medication (especially ACE-Inhibitors like lisinopril) at night would better control the early morning blood pressure spike since most medications may not be as effective at the end of their dosing interval (i.e. if you take a pill once every 24 hours, it may start to lose effect by the time you are scheduled to take your next dose).
Multiple studies have shown this to be accurate, that nighttime dosing of many different blood pressure medications do indeed lower blood pressure more effectively than when those same ones are taken in the morning.
Taking HCTZ in the morning and lisinopril in the evening is certainly an acceptable way to take these medications, and may, in fact, be ideal to lower the risk of side effects (like waking up to go to the bathroom) and increase effectiveness.
You always want to make sure that you discuss how you take your medication with your doctor first, however, before making any changes.
- ^ Hydrochlorothiazide Prescribing Information. AccessFDA
- ClinicalKey Elsevier ClinicalKey: Hydrochlorothiazide Monograph.
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