Dexamathasone is a steroid medication.  It has been around since 1958 and is quite inexpensive.  Because of its strong anti-inflammatory function, it is used for everything from rheumatoid arthritis to dental extractions, from speeding fetal development in utero to combatting severe altitude sickness for mountaineers.  Sometimes long-term usage, sometimes for a very brief period around a specific medical event.

For cancer, it used mainly for its anti-emetic effect.  From Wikipedia: 

People with cancer undergoing chemotherapy are often given dexamethasone to counteract certain side effects of their antitumor treatments. Dexamethasone can increase the antiemetic effect of 5-HT₃ receptor antagonists, such as ondansetron.^[16] The exact mechanism of this interaction is not well-defined, but it has been theorized that this effect may be due to, among many other causes, inhibition of prostaglandin synthesis, anti-inflammatory effects, immunosuppressive effects, decreased release of endogenous opioids, or a combination of the aforementioned.^[17]

Dex is one of the meds that I am given prior to chemo.  I take 20 mg at 12 hours and 6 hours pre-chemo.  Then, as a pre-chemo med, I am given another 10 mg as a slow push injection into my IV line.  That’s 50 mg of Dex in about 13 hours.  Then, post-chemo, I am supposed to take 4 mg Dex with Ondansetron/Zofran (as mentioned above) for an anti-emetic response.  This medication combo is taken for 5 doses, one on the evening of Day 1 (chemo day), then again am and evening on Day 2 and Day 3. 

It’s known side effects are vast and varied.  When taken long term, these include type 2 diabetes because of the glucose-elevating effect of the drug.  But short-term use, such as my use of it, still has significant side effects. 

The most obvious is its effect on blood sugars.  Much has been written about this, as elevating the blood sugar appears to have the effect of feeding the cancer.  But the effect, while pronounced, is very short term and the keto diet, with its consistent blood sugar lowering effect and insulin-lowering effects, makes the sugar levels return to normal almost immediately after cessation of the drug. In my own case, I have seen my blood sugars skyrocket into a fully diabetic blood sugar range on chemo morning, thanks to the high dose Dex.  My fasting blood sugar yesterday, the last day of cycle 4, was 4.1 and ketones were 0.3, mild nutritional ketosis.  This morning, after 36 hours fasting, and 40 mg Dex, they were FBS 6.5 and Ketones 3.3, well up into ketosis.  By 2 hours later, when I was having my blood work done at the cancer clinic, my BS value (still a fasting, except for some black coffee) was 8.5!  Normal is less than 3.5-6.0 for fasting blood sugar and less than 7 for random blood sugars (meaning that blood was taken at any time after the first meal of the day). 

It’s usually physiologically unlikely that blood sugar and ketones would be up together.  It happens in type 1 diabetes with the life-threatening condition of diabetic ketoacidosis, but in that situation, blood sugars are in the 20’s or higher, can be into the 30’s or 40’s, and ketones are over 10, with zero insulin present to allow for the situation to correct itself.  This is NOT my situation.  I am in no danger…

The Dex also wires one up, making your energy higher and more restless, but without the normal shutoff valves of non-drug induced restlessness. So sleep is affected.  I hate this side-effect. 

The anti-nausea effect is important, but I am not apparently having this chemo drug side effect (thanks to the fasting, I believe), so I have been having problems justifying the ongoing doses of the Dex and Ondansetron(Zofran).  After the 2^nd chemo, I switched the Day 2 evening Dex and Zofran to 6 pm instead of at bedtime, then skipped the last dose on evening Day 3 (one less dose overall).  No negative impacts.  After the 3^rd chemo, I skipped both the Day 3 doses (two doses reduced overall).  After the 4^th cycle, I mistakenly took a double dose on the evening of Day 1 (I was distracted and grumbly about my need to take them at all, so made a mistake).  That resulted in me not taking my Day 2 am dose and I decided to skip my Day 2 evening dose as well.  So, no side effect meds at all except for the day of chemo itself.  This resulted in better sleep, though still not great – I still have the chemo drug effects, the interperitoneal fluid infusion effects and the fasting effects.  And better bowel regularity (that’s a Zofran side effect. 

Now that it’s cycle 5, I plan to take one dose of Zofran and Dex this evening, and will likely be up for part of tonight.  But that’s it, I hope.  No additional meds after today, unless I feel some creeping nausea on Day 3-4.  Then I will take my as-needed Stemetil.  I needed it once in Cycle 3, a minimal intervention.  (Down 4 doses overall from original prescription)

The following study looked at fasting effects on blood sugars, the effect of Dex on blood sugars, and the cardioprotective impact of fasting when Carboplatin is used.  

Fasting regulates EGR1 and protects from glucose- and dexamethasone-dependent sensitization to chemotherapy.

Di Biase S¹, Shim HS¹, Kim KH¹, Vinciguerra M^2,3,4, Rappa F⁵, Wei M¹, Brandhorst S¹, Cappello F^5,6, Mirzaei H¹, Lee C¹, Longo VD^1,7.

The chart below, one of many in the article, shows that the overall survival of the mice treated with short term starvation (fasting) was vastly better than ad lib eating or STS with glucose added. 

I’m sure that Dex is an important part of my pre-chemo routine, and I won’t be messing with that part of it, despite the obvious blood sugar consequences.  In terms of “feeding the tumour,” I’m sure that one day or so of elevated values are not putting me at any increased risk.  But as far as the post chemo side effect management goes, I appear to be managing the aftereffects well with my fasting and keto protocols and I have no qualms about minimizing the negative effects of the Dex and Zofran on those days. 

Everyone’s mileage will vary, and this is not medical recommendation or advice in any way, but it is my experience and I have informed my oncology clinic team that I am doing this.  Not asked for permission but informed them.  Be aware of your own body, be your own advocate for best care, and make your decisions based on your own experience and your intuition.  Each of us is an N=1 experiment, and we need to customize our treatments to our own experience.