Highlighting pharmacokinetics, pharmacodynamics and mechanism of action


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

US brand name: Lamictal
Generic name: lamotrigine


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

Half-life: 25–32 hours , depending on all sorts of factors. And that’s the median average. Plasma Clearance: 6–8 days.

Steady State

Steady state reached in 14–28 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 lamotrigine Works

the current best guess at any rate
Originally designed as a folate antagonist (like antimalarial drugs), it was thought to have one of the simplest mechanism of action of any AED, doing nothing else except inhibiting voltage-sensitive sodium channels and maybe having a little affect on sigma opioid receptors (which are now being studied for all sorts of things). Now it looks like it also inhibits gated sodium and calcium channels, maybe even potassium. It’s still one of the least GABAergic AEDs around.

Active Ingredient

freebase lamotrigine 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

2mg chewable & ODTs: 2 years. Tablets and other chewable & ODTs: 3 years.

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

« Lamictal’s Pros and Cons | Lamictal’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.

Last modified on Wed, 04 May, 2016 at 17:22:00 by JerodPoorePage Author Date created January 18, 2011, at 15:16:23
“Lamictal (lamotrigine) Pharmacology” by Jerod Poore is copyright © 2011 Jerod Poore Published online 2011/01/18

Lamictal, and all other drug names on this page and used throughout the site, are the trademarks of someone else. Lamictal’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