Voltaren gel contains diclofenac, an NSAID (non-steroidal anti-inflammatory drug), and is used (primarily) to treat osteoarthritis. A common question we get from our readers who are prescribed Voltaren gel is whether or not it is absorbed systemically (i.e. into the bloodstream) after it is applied.
Systemic absorption of diclofenac is of significant concern when it comes to several areas including potential side effects and drug interactions.
Regarding side effects specifically, many studies report that diclofenac has a higher risk of gastrointestinal and liver toxicity when compared to other oral NSAIDs.
Therefore, knowing just how much of the drug is absorbed when you apply it is important to consider. In this article, I take a look at published information regarding Voltaren absorption.
Diclofenac is a nonsteroidal anti-inflammatory drug (NSAID), belonging specifically to the acetic acid chemical class of NSAIDs. NSAIDs, in general, are used for their anti-inflammatory, analgesic (i.e. pain-relieving) and antipyretic (i.e. fever reducing) properties.
Diclofenac is one of the most versatile NSAIDs when it comes to how it is utilized in prescription drugs. It is available in a multitude of products and dosage forms, including:
Of the oral products, you may notice that is available as both diclofenac sodium and diclofenac potassium, different salt forms of the same drug.
Potassium salts of diclofenac (e.g. Cataflam) are absorbed more quickly and produce higher plasma concentrations, which is generally why they have a faster onset of action than other oral forms of diclofenac. The sodium salt of diclofenac (e.g. Voltaren tablets) has a slower onset of action compared to diclofenac potassium.
As a general point, oral diclofenac products aren't prescribed as often as other NSAIDs, since studies show that it is likely to cause higher rates of liver and GI toxicity than most other NSAIDs.
It is extremely important to point out, and remember, that Voltaren gel is supplied in a strength of 1% (meaning 1000 mg of diclofenac per 100 grams of gel).
Even though the total amount of Voltaren gel applied seems quite large (generally between 16 and 48 grams per day), the amount of actual diclofenac you are applying is relatively low.
This article deals specifically with Voltaren Gel absorption.
All of the other topical dosage forms (e.g. Flector patches, Pennsaid solution) have different absorption characteristics so be sure not to extrapolate data on Voltaren Gel to those other products.
If you have questions about any other product that contains diclofenac, be sure to ask one of our pharmacists.
At the outset, the good news is that multiple studies report that topical NSAIDs, like Voltaren Gel, work as well as oral forms for the treatment of a variety of conditions, including:
Additionally, most studies find no difference in topical NSAIDs from placebo in reported systemic side effects like stomach upset and gastrointestinal bleeding.
One of the largest review studies on topical NSAIDs states the following:
Topical NSAIDs penetrate the skin, enter tissues or joints, and reduce processes causing pain in the tissue. Drug levels in the blood with topical NSAIDs are very much lower than with the same drug taken by mouth. This minimises the risk of harmful effects.
In terms of how much Voltaren gel is absorbed systemically, the prescribing information says the following:
Systemic exposure (area under the concentration-time curve) and maximum plasma concentrations of diclofenac are significantly lower with Voltaren® Gel than with comparable oral treatment of diclofenac sodium.
While 'significantly lower' is somewhat vague, fortunately, the prescribing information gives more detailed information on total systemic absorption to the drug after applying topically.
The following is reported based on pharmacokinetic studies of the drug:
The following is a data chart straight from the prescribing information for Voltaren gel quantifying these characteristics.
This comparison information for topical Voltaren gel and oral diclofenac from the figure above is summarized in the below chart:
|Drug||Maximum Systemic Concentration (ng/mL)||Avg % Concentration Compared To Oral Diclofenac (150 mg per day)||% AUC (i.e. Total systemic exposure) Compared To Oral Diclofenac (150 mg per day)|
|Voltaren Gel (16 grams gel per day = 160mg diclofenac)||15 ± 7.3||0.6%||5.8%|
|Voltaren Gel (48 grams gel per day = 480 mg diclofenac)||53.8 ± 32||2.2%||19.7%|
|Diclofenac Sodium Oral Tablets (150 mg)||2270 ± 778||100%||100%|
To clarify why 16 grams of Voltaren gel contains 160 mg of diclofenac, remember that in one of the sections above (How Much Diclofenac Is In Voltaren Gel?), we pointed out that Voltaren gel is available in a 1% strength, meaning that it contains 1 gram of diclofenac (1,000 mg) per 100 grams of gel.
This is why 16 grams of Voltaren gel contains only 160mg of diclofenac (16 grams * 1% = 0.16 grams, or 160 mg).
So, overall, you can see that both maximum concentrations in the plasma and total systemic absorption of Voltaren gel are extremely low when compared to oral diclofenac.
Even if you are applying a very high dose of Voltaren gel (48 grams per day), maximum concentrations and total systemic exposure are, respectively, only 2.2% and 19.7% when compared to taking 150 mg of oral diclofenac.
However, and this is important to note, there aren’t any studies that have charted the correlation between plasma concentrations and the risk of side effects or drug interactions. While it certainly makes sense that the risk of side effects and interactions would be significantly lower with topical Voltaren gel, you can’t rule out them occurring.
In most cases, it is not recommended to use both a topical and oral NSAID together. Studies show that combining them doesn't seem to work better than either alone and may increase the risk of side effects.
Additionally, the clinical trials of Voltaren Gel (as referenced in the prescribing information for the drug) prohibited concomitant use of oral NSAIDs, so we don't know how patients would have responded to both.
As discussed in this article, there at least is some is systemic exposure to diclofenac following normal use of Voltaren Gel, and therefore, there may be an increased risk of side effects if used with oral NSAIDs.
So overall, due to the lack of safety data (and the fact that preliminary studies suggest that the combo isn't effective), you shouldn't combine an oral and topical NSAID unless otherwise directed by your doctor.