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Deconstructing a Full Prescribing Information: Part IV Thursday 1/13/11

Posted by smcgamer in Archive, Deconstucting The, Post-A-Day 2011.
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Tonight we enter the pharmacokinetics.

A Short Explanation of Pharmacokinetics

Pharmacokinetics can basically be defined as the study what the body does to the drug, as opposed to what the drug does to the body (pharmacodynamics).  Studies include its absorption, transmission, and duration of the action of the drug.

The study is separated into five categories:

  • Liberation: how the body releases the drug from its container
  • Absorption: the movement of a drug in the bloodstream
  • Distribution: how the drug gets to where it’s going
  • Metabolism: how the body transforms the parent compounds into daughter compounds
  • Excretion: how the body releases the used drug

The Pharmacokinetics of Lunesta

The pharmacokinetics of eszopiclone have been investigated in healthy subjects (adult and elderly) and in patients with hepatic disease or renal disease.  In healthy subjects, the pharmacokinetic profile was examined after single doses of up to 7.5 mg and after once-daily administration of 1, 3, and 6 mg for 7 days.  Eszopiclone is rapidly absorbed, with a time to peak concentration of approximately 1 hour and a terminal-phase elimination half-life of approximately 6 hours.

Absorption takes one hour, and the eliminaton half-life is 6 hours.  The elimination half-life is the time it takes for the drug to lose half its strength.  Six hours is probably good for Lunesta, seeing as its supposed to work for eight hours.  Much longer, and you’ll have a hard time waking up, shorter, and you’ll have a harder time staying asleep.

Note, though, that the drug will not be gone completely in 12 hours, half-lives are the time it takes to reduce by half; so in 12 hours, it will be 3/4 gone.

Absorption takes one hour, so you’ll probably have to take it one hour before bed.

In healthy adults, LUNESTA does not accumulate with once-daily administration, and its exposure is dose-proportional over the range of 1 to 6 mg.

Exposure is, well, exposure to tissue.

Absorption and Distribution

Eszopiclone is rapidly absorbed following oral administration.  Peak plasma concentrations are achieved within approximately 1 hour after oral administration.

Plasma is, I’m assuming, blood plasma.  Lunesta accumulates in blood plasma, which is also the carrier of blood cells.

Eszopiclone is weakly bound to plasma protein (52-59%).  The large free fraction suggests that eszopiclone disposition should not be affected by drug-drug interactions caused by protein binding.

Drug-drug interaction can be a bad thing, resulting of too many plasma bonds in the blood protein.

The blood-to-plasma ratio for eszopiclone is less than one, indicating no selective uptake by red blood cells.

The red blood cells won’t absorb the eszopiclone.  If they did, the effectiveness would be terrible, not to mention possibly damaging the cells.

Part Five comes tomorrow: We cover metabolism and elimination, and effect of food (and it’s good).

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    Comments»

    1. Deconstructing a Full Prescribing Information: Part V | Smc_Gamer's Blog - Sunday 1/16/11

    […] Note: For an explanation of pharmacokinetics, as well as a link to the Wikipedia page, please check Thursday’s post. […]


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