For how long is an active ingredient active?

[navigator9]

I have a question, and no amount of Googling has brought me any closer to an answer, so I'm hoping some of the brilliant minds here might have an answer. For how long are active ingredients in a product that gets applied to the skin active, after being applied? I'm guessing it depends on the individual ingredient, but for some reason, right or wrong, I've always felt that whatever it may be, is most active immediately after being applied, and that once the cream or lotion has dried or been absorbed into the skin, the active ingredient is pretty much kaput. I'm asking because I've been using some cream for rosacea, and while it seems to be helping, I'm not wild about the way it feels on my face, kind of sticky. So I was wondering if I would get the same benefit if I applied it, left it on for a while, and then washed it off. Anyone know anything about this?

 

[NsMar42111]

I would think the same as you that it would oxidize or whatnot. Could you try one area for yourself? Just wash half your face?

 

[earlene]

If you are talking about actual drugs, they all have half lives which exponentially reduces over time. This is true of topical drugs as well as those taken orally or otherwise.

So, it would depend on each individual drug contained in the topical application. If you know the active ingredients, perhaps you can find out what their half-lives are and use a calculator to determine how long they continue to deliver the desired effect. https://www.mdapp.co/medicine-half-life-calculator-81/

 

[navigator9]

Thank you both for your info. Earlene, I was thinking about all and any active ingredients actually, but the half life idea gives me a new direction to explore. Thanks!

 

[Lin19687]

What about applying it a short bit before you go to bed ? Then it won't matter what it feels like as you will be sleeping

 

[OldHippie]

This is true of topical drugs as well as those taken orally or otherwise.

I don't see why this would be. Do you have a source for this information?

 

[DeeAnna]

Another aspect of this question is how the chemical interacts with your body. That can take time too. Maybe fast, maybe slow.

One thing I sometimes do with a gooey/sticky lotion or salve is wet my hands or fingers with water (or even dampen my face with water) and spread the product in an extra thin layer over my skin with the help of the water. Not sure if that would help the skin feel in your case, Navigator, but it might be worth a try?

 

[lenarenee]

I don't see why this would be. Do you have a source for this information?

Earlene is correct. The pharmacological term is biological half life and a key aspect in determining dosage rate and timing. The U.S. Pharmacopeia states the half life of each drug listed. (I'm a former licensed pharmacy technician)

 

[earlene]

Of course I do, and

I don't see why this would be. Do you have a source for this information?

My professional training.

To become a Registered Nurse I had to learn about half lives of drugs in nursing school for obvious reasons. There is a lot of information about about drugs and their half-lives if you want to learn more. Lenarenee's response suffices, IMO, so I will leave it at that.

 

[navigator9]

What about applying it a short bit before you go to bed ? Then it won't matter what it feels like as you will be sleeping

I do apply it before bed, but it's supposed to be used both morning and evening. And it just got me to wondering about active ingredients in general, all the different things we apply to our skin. I like to use olive squalane on my face, so I thought maybe I could leave the rosacea cream on for a while, wash it off and then apply the squalane. Not a big deal really, but it just got me thinking.....

 

[OldHippie]

Earlene is correct. The pharmacological term is biological half life and a key aspect in determining dosage rate and timing. The U.S. Pharmacopeia states the half life of each drug listed. (I'm a former licensed pharmacy technician)

If you were actually paying attention to my post, you would have seen that I'm not talking about the biological half life of ingested or intravenous drugs, which is what is published in the referenced source, but the claimed half-life of a drug applied topically.

To become a Registered Nurse I had to learn about half lives of drugs in nursing school for obvious reasons. There is a lot of information about about drugs and their half-lives if you want to learn more. Lenarenee's response suffices, IMO, so I will leave it at that.

I won't leave it at that, because the answer was not responsive to the question. Did your "professional training" teach you anything about the half life of topically applied drugs?

 

[lenarenee]

Yes I was paying attention. It does apply to topical drugs including cream, nasal, salve, ointment and transdermal drugs. Some topical drugs can be very systemic (enter the body system as though it were ingested).

 

[OldHippie]

Yes I was paying attention. It does apply to topical drugs including cream, nasal, salve, ointment and transdermal drugs. Some topical drugs can be very systemic (enter the body system as though it were ingested).

So, what does this have to do with the original question? "For how long are active ingredients in a product that gets applied to the skin active, after being applied?" I suspect that the answer has more to do with mechanical factors, such as how thick it was put on and how fast it rubs off, rather than chemical factors (think sunscreen).

 

[earlene]

I won't leave it at that, because the answer was not responsive to the question. Did your "professional training" teach you anything about the half life of topically applied drugs?

Yes.

An example of a topical drug that is absorbed transdermally is nitropaste, used in cardiac patients to help prevent angina. It is absorbed through the skin, but then systemically in the blood stream, which is how it gets to the heart. The reason why the nurse removes the old application before applying the new one is that the old one may still be imparting drug transdermally (because the drug continues to impart more nitro until it has used up all of it's potency (reduced potency due to decreasing half-life, but it continues just the same) and to have both on the skin at the same time can cause serious complications. And yes, I have seen it happen with nitropaste dosages not removed when the new ones were placed and the issue was so severe, I had to report the medication nurse to the director of nursing.

As an aside, but pertinent to the issue of the half-life of drugs, certain factors can and will affect or alter the 'average' half-life. Because the liver plays a part in the clearing of the drugs from the system, any liver malfunction or liver disease can lengthen or even halt the process.

So, the bottom line is that with topical drugs that are absorbed into the blood stream they will still have a half-life. Whether or not the half-life exists is not based on the method of delivery. Some methods deliver the drug faster, and some slower, but the half-life is inherent in the drug.

Having seen your last post pop up while I was writing, to clarify this is about your question, not the OP's question, BTW, but it also pertains to the OP's original question.

 

[OldHippie]

Yes.

An example of a topical drug that is absorbed transdermally is nitropaste, used in cardiac patients to help prevent angina. It is absorbed through the skin, but then systemically in the blood stream, which is how it gets to the heart. The reason why the nurse removes the old application before applying the new one is that the old one may still be imparting drug transdermally (because the drug continues to impart more nitro until it has used up all of it's potency (reduced potency due to decreasing half-life, but it continues just the same) and to have both on the skin at the same time can cause serious complications. And yes, I have seen it happen with nitropaste dosages not removed when the new ones were placed and the issue was so severe, I had to report the medication nurse to the director of nursing.

As an aside, but pertinent to the issue of the half-life of drugs, certain factors can and will affect or alter the 'average' half-life. Because the liver plays a part in the clearing of the drugs from the system, any liver malfunction or liver disease can lengthen or even halt the process.

So, the bottom line is that with topical drugs that are absorbed into the blood stream they will still have a half-life. Whether or not the half-life exists is not based on the method of delivery. Some methods deliver the drug faster, and some slower, but the half-life is inherent in the drug.

Having seen your last post pop up while I was writing, to clarify this is about your question, not the OP's question, BTW, but it also pertains to the OP's original question.

Clearly we're talking about two difference things. Your answers about how long a substance lasts INSIDE the body are not relevant to a question about how long a substance OUTSIDE the body will remain effective.

 

[lenarenee]

So, what does this have to do with the original question? "For how long are active ingredients in a product that gets applied to the skin active, after being applied?" I suspect that the answer has more to do with mechanical factors, such as how thick it was put on and how fast it rubs off, rather than chemical factors (think sunscreen).

The op didn't mention the name of the product, as is her right. The book I mentioned above, the U.S. Pharmacopeia lists the half life of each drug. Many libraries have them, every pharmacy has at least one on hand, there are also online sources.

Oddly enough, mechanical factors do not necessarily apply. Thickness application for instance....you can only coat your skin once, more or thicker doesn't always mean more active ingredient is absorbed. Each product's half life is evaluated based on correct application directions.

ETA: regarding OldHippie's last comment: A product that is outside the body has absolutely no effect. There must have some level of absorption.

If a substance isn't in the Pharmacopeia, (ex: essential oils) chances are very good that no one has a scientifically verifiable answer.

 

[earlene]

Sigh. How long a drug lasts inside the body is the whole point of measuring the half-life of the drug and directly pertains to how long the drug is effective. My answer to the OP was 'it depends on the active ingredient' and if the active ingredient is a drug, it has a half-life which contributes to the answer of how long it will remain effective.

In my example of the nitropaste, the delivery is from a topical application. As long as the drug stays on the skin, it delivers the drug until it is removed or runs out of drug in the paste. As long as it continues to deliver the drug via the skin, the half-life does continue to be important in topical applications of drugs. Many OTC topically applied items include some drug or another, and although the OP did not specify a drug, I pointed this out because it may apply. Maybe it does not. Maybe the product in question does not contain a drug at all.

In my perception of the OP's question, what I said pertains, given the information I had at the time. Apparently in your perception it does not. Since we cannot agree, I would like to suggest that we let it go, if you don't mind.

 

[Susie]

Clearly we're talking about two difference things. Your answers about how long a substance lasts INSIDE the body are not relevant to a question about how long a substance OUTSIDE the body will remain effective.

So that you understand why you are asking the wrong questions, here is the rosacea website: https://www.rosacea.org/patients/allaboutrosacea.php.

The reason I think you are misunderstanding is that the medication applied TO the skin is actually aimed at working UNDER all the dead layers of cells and IN the skin. Therefore, it is actually INSIDE the body. The half-life of medication applied thusly is exactly what is in question, as it is not just what is ON the skin, it is what gets INTO the skin, and how long that lasts. navigator9 wants to know if she can leave it on a short period of time, yet get an equal effect of leaving it on. Therefore, the answer to the half-life of the drug is where the answer starts, the other part, though, is how the cream is formulated, as some are formulated for slower release of medication than others. With this being a twice a day treatment, it sounds like an anti-inflammatory of some sort, which again could be either a fast release or a slow one.

My best suggestion is to take that question up with BOTH your doctor and whichever pharmacist dispenses it to you. If no answer is forthcoming from them, I would find a compounding pharmacist in your area, and ask them. Especially if that compounding pharmacist compounds topical medications.

 

[DeeAnna]

Hey, Earlene, Lenarenee, and Susie -- Thank you for sharing information about half life from a health care perspective. My earlier post was based on my understanding of half-life as it relates to the decomposition of chemicals in the general environment, not about decay of chemicals in a healthcare sense because that's far outside my fields of study. What I was thinking of are things like the half life of radioactive chemicals, fertilizers, or pesticides. I wanted to take a moment to thank you -- I have learned a lot from your thoughtful posts in this thread and want you to know I appreciate and have benefited from the time and thought that you all have put into your explanations. They have been really interesting and helpful!