Highlighting pharmacokinetics, pharmacodynamics and mechanism of action


« Topamax’s Pros and Cons | Topamax’s Everything Else »

US brand name: Topamax
Generic name: topiramate


Topamax’s Half-Life & How Long Until It Clears Your System

Half-life: 21 hours. Plasma Clearance: four to five days.

Steady State

Steady state is reached in four days

Half-life is the average time it takes for you to process half of the drug’s active ingredient. If a drug has a half-life of around 24 hours and you take a dose of 100mg, you’ll have roughly the equivalent a 50mg dose after one day, a 25mg dose after two days, and so on. The rule of thumb is: multiply the half-life by five and you get how long it is for the dose you took to be cleared from your bloodstream1.

Steady state is the flipside of half-life. This is when you can expect to get over side effects caused by fluctuating amounts of a medication in your bloodstream. Often, but not always the same amount of time as the plasma clearance above.

How topiramate Works

the current best guess at any rate
Topamax is a fairly broad-spectrum anticonvulsant. Topamax inhibits the voltage-gated (dependent) sodium and calcium channels, inhibits glutamate and carbonic anhydrase, and promotes the reception of GABA and/or increases the amount of GABA, depending on the location in your brain and the study you read. Topamax may also affect voltage-sensitive sodium channels, modulate voltage-gated potassium channels, and modulate voltage-gated calcium channels instead of merely inhibiting them.

In English: Topamax doesn’t just reduce the electrical activity being transmitted through sodium ion channels, but also calcium channels. Additionally it modulates potassium and calcium channels, so it smooths the peaks and valleys as well. Topamax doesn’t just help you use the GABA you have, it also increases the amount of GABA available. GABA = mellow and tipsy, less glutamate = less seizurey.

Topamax’s neuroprotective / antikindling effect is due to its positive GABAergic actions, particularly with GABAA1, and being an antagonist at specific glutamate receptors. Again, when it comes to epilepsy more GABA is good, less glutamate is better. For bipolar more GABA is tricky, and can result in mania.

Originally discounted as having any effect, being a CAI (mainly at CA2 & CA4) is an important part of topiramate’s MOA after all.

Topamax may have an effect on your 5-HT2C receptors. Working on serotonin explains lots of things, from being God’s gift to migraineurs to affecting mood in a positive or negative fashion.

And for the question that is asked at least once a week, how does Topamax make you lose weight? I may finally have an answer for that one. Topamax was initially developed as an oral hypoglycemic to control weight in diabetes 2. It is an inhibitor of gluconeogenesis. As such Topamax is similar to metformin. Being a CAI is also a contributory factor. Serotonin at 5-HT2C is also a factor in weight control, but it’s still not clear if Topamax does anything there at all, much less to what extent.

Zonegran is a CAI and, like Topamax, it’s also a supermodel drug. Diamox (acetazolamide) is used to treat altitude sickness and glaucoma, and is used off-label (in the US) as an AED. Diamox also causes weight loss, but the side effects suck so much more than Topamax and Zonegran combined that no one in their right mind would use Diamox, or any other CAI as a diet pill2. Being a CAI is also why Topamax makes carbonated beverages taste like ass and is responsible for kidney stones and other kidney problems, and metabolic acidosis being potentially serious problems for anyone who takes Topamax and Zonegran.

Active Ingredient

freebase topiramate USP

The active ingredient is usually the same as the generic name, but more often than not it’s a chemical salt of the substance identified as the generic. E.g. Fluoxetine is the generic for Prozac, but the active ingredient is fluoxetine hydrochloride (or HCl). It usually doesn’t make much of a difference outside of the more esoteric aspects of a drug’s pharmacology, but not always.

Shelf Life

Tablets: 3 years. Sprinkles: 2 years.

Keep Crazymeds on the air.
Donate some spare electronic currency
you have floating around The Cloud

« Topamax’s Pros and Cons | Topamax’s Everything Else »

Pages and Forum Topics Google Thinks are Relevant to Your Mental Health

1 After five times the half-life you'll have reached what's called "Plasma clearance," or "not enough left in your bloodstream to latch onto your brain and do anything." It's based on Julien's calculations from A Primer of Drug Action, and half-life multiplied by five is the generally accepted estimate of how long it takes a single dose of any given drug to be eliminated from the blood stream/plasma of someone with a normal metabolism. That's also the rough estimate for steady state if they can't get, or won't provide a number for that.
The next level is "Complete clearance", and is a complex equation based on a lot of factors which may or may not: be published in the PI sheet, include personal data like your weight, or even completely figured out by corporate and independent researchers. It usually winds up being within (as in usually, but not always, after) 2-5 days of plasma clearance no matter what, but sometimes can take weeks. Sometimes a drug will clear from your brain and other organs before it clears from your blood.
That's how it works for crazy meds. I have no idea what the average complete clearance is for other types of medications. For all I know there are drugs that utterly vanish from your system in under five passes, and others that won't let go of your squishy bits for years after you stop taking them.

2 Which is why the FDA has given tentative approval to Qnexa, a combination topiramate and phentermine, and Mayan for "you frelling idiot," to treat obesity. They also gave it a pregnancy category of X to prevent anyone who takes it from further polluting our already disgusting gene pool.

Last modified on Wed, 04 May, 2016 at 16:18:15 by JerodPoorePage Author Date created Tuesday, 11 January 2011 at 13:43:23
“Topamax (topiramate) Pharmacology” by Jerod Poore is copyright © 2011 Jerod Poore Published online 2011/01/11

Topamax, and all other drug names on this page and used throughout the site, are the trademarks of someone else. Topamax’s PI Sheet will probably have the name of the manufacturer and trademark owner (they’re not always the same company) at or near the very bottom. Or ask Google who the owner is. The way pharmaceutical companies buy each other and swap products like Monopoly™ real estate, the ownership of the trademark may have changed without my noticing. It may of changed hands by the time you finished reading this article.

Page design and explanatory material by Jerod Poore, copyright © 2003 - 2016. All rights reserved. See the full copyright notice for full copyright details.
Don’t automatically believe everything you read on teh Intergoogles. No warranty is expressed or implied in this information. Consult one or more doctors and/or pharmacists before taking, or changing how you take any neurological and/or psychiatric medication. Your mileage may vary. What happened to us won’t necessarily happen to you. For more details see the Crazymeds big-ass disclaimer.

Enable Crazymeds’ Financial Solvency!

Enable Crazymeds to keep spreading our knowledge. Donate some spare e-currency you have floating around The Cloud.

Improve Your Social Media Skills


Follow our Highly Irregular Updates and Paranoid Rants Other News


Square this Circle

For Site News and NeuroPsych Research


Show us teh like™

Crazymeds: The Blog

For Site News and Crap that Distracts me from my Fucked-up Life

Crazymeds’ Tumblr

Mentally Interesting Advocacy

OpEd News

Daily Kos

Sites That Probably Suck Less Than Crazymeds

Crazymeds Merchandise

Available at Straitjacket T-Shirts

Vaccines Cause Immunity bumpersticker at Straitjacket T-Shirts

Stuck Up
All stickers $5. Now Available in Packs of 10 & 50

Mentally Interesting button at Straitjacket T-Shirts

Button It!
2.25″ $4 & 3.5″ $4.50. Now Available in Packs of 10 & 100