dosage

[Shaani]

to all pharmacists and people who have the relevent knowledge lol :

is there any difference in the dosage given to a patient if they are using an inhaler or tablets? (i.e do tablets contain more "drug" in them or can they be set to have the same amount?)

[richtagg]

Re: dosage

Hi there,

It depends on the drug. As a rule of thumb it is safe to say that there is a difference between the amount of drug needed to obtain therapeutic concentrations depending on the route you administer the drug.

A drug administered orally will need to enter the system via absorption through the Gastro-intestinal system whereas a drug administered via an inhaler will need to be absorbed through the lungs. These are very different environments so there are differences in the amount of drug absorbed.

If you consider the example of Salbutamol, a drug used in asthma to relax the muscles in the lungs, you need to give more of the drug if you give tablets rather than inhalers.

Does this answer your question?

[Linnear]

Re: dosage

This depends on the actual drug being introduced.

If the drug is for asthma then the dosage doesn't have to be as high as the drug is almost a topical prep. Salbutamol tabs 4 or 8 mg usual dose salbutamol inhaler 100-200 mcg.

For other things then you can get a bioequivalent dose but all comes down to pharmacodynamics of the situation.

Exubera (inhaled insulin) website states that 100units of insulin need to be deposited in the nose to get 10 units into the system.


So a dose can usually be found to equal another dosage form but will usually be a different amount depending on the target site.

[Shaani]

Re: dosage

Hi there,

It depends on the drug. As a rule of thumb it is safe to say that there is a difference between the amount of drug needed to obtain therapeutic concentrations depending on the route you administer the drug.

A drug administered orally will need to enter the system via absorption through the Gastro-intestinal system whereas a drug administered via an inhaler will need to be absorbed through the lungs. These are very different environments so there are differences in the amount of drug absorbed.

If you consider the example of Salbutamol, a drug used in asthma to relax the muscles in the lungs, you need to give more of the drug if you give tablets rather than inhalers.

Does this answer your question?

yeah it does - cheers!

so am i right in thinking that because the drug e.g. Salbutamol goes through the Gastro-intestinal system, there's more chance that some of it will not be absorbed (and therefore excreted) hence why a larger dose is required than if inhaling Salbutamol cos its going more or less directly into the blood stream via the lungs (no digestion and more drug absorbtion taking place)?

[Shaani]

Re: dosage

This depends on the actual drug being introduced.

Exubera (inhaled insulin) website states that 100units of insulin need to be deposited in the nose to get 10 units into the system.

So a dose can usually be found to equal another dosage form but will usually be a different amount depending on the target site.

so in this case its likely that 90% of Exubera will be "lost", im guessing nasal hairs would accumulate a fair amount of it.

btw - wouldnt all target sites for medicines/drugs be the blood stream? (sorry for being difficult!! lol)

[johnep]

Re: dosage

Often suggest to pts who have been vomiting that place 'kwells', stemetil etc under tongue for quicker effect. would have thought that even insulin might have some effect s/l.
johnep

[Linnear]

Re: dosage

so in this case its likely that 90% of Exubera will be "lost", im guessing nasal hairs would accumulate a fair amount of it.

btw - wouldnt all target sites for medicines/drugs be the blood stream? (sorry for being difficult!! lol)

The blood stream is usually just the route to get the drug to the target site.
e.g.
Asthma drugs: Target: lungs
Beta blockers: Target: heart muscle
Diuretics: Target: kidneys

[_Rob_]

Re: dosage

so am i right in thinking that because the drug e.g. Salbutamol goes through the Gastro-intestinal system, there's more chance that some of it will not be absorbed (and therefore excreted) hence why a larger dose is required than if inhaling Salbutamol cos its going more or less directly into the blood stream via the lungs (no digestion and more drug absorbtion taking place)?

Hi,

The majority of the ingested salbutamol is absorbed. Salbutamol is mainly hepatically metabolised (basically; the salbutamol is broken down in the liver). The anatomy of the gastro-intestinal tract means the the blood flow from the stomach and intestines goes to the liver, then on into the inferior vena cava, into the heart, round the lungs and then back to the heart, then off to the rest of the body. This is important because lots of the absorbed salbutamol is metabolised when it first passes through the liver. Giving the salbutamol via an inhaled process means it misses this first pass metabolism and hence the dosage required is smaller (although not entirely true because salbutamol has a topical effect in the lungs).

Some medicines have major first pass metabolism. Propanolol is nearly 90% first pass metabolised. Given orally, we use doses of 80-360mg/day but when given intravenously (where 100% gets into the blood) we use doses of 5-10mg.

Hope this ain't too confusing?!

[Shaani]

Re: dosage

Hi,

The majority of the ingested salbutamol is absorbed. Salbutamol is mainly hepatically metabolised (basically; the salbutamol is broken down in the liver). The anatomy of the gastro-intestinal tract means the the blood flow from the stomach and intestines goes to the liver, then on into the inferior vena cava, into the heart, round the lungs and then back to the heart, then off to the rest of the body. This is important because lots of the absorbed salbutamol is metabolised when it first passes through the liver. Giving the salbutamol via an inhaled process means it misses this first pass metabolism and hence the dosage required is smaller (although not entirely true because salbutamol has a topical effect in the lungs).

Some medicines have major first pass metabolism. Propanolol is nearly 90% first pass metabolised. Given orally, we use doses of 80-360mg/day but when given intravenously (where 100% gets into the blood) we use doses of 5-10mg.

Hope this ain't too confusing?!

nope, its a gud explanation!! when a drug like salbutamol is being inhaled, wouldnt its chemical coating (if any) be different to when its being swallowed as a tablet (as its being digested)? if there is a difference could that affect the functioning of the drug in the body?

[Pharmanaut]

Re: dosage

nope, its a gud explanation!! when a drug like salbutamol is being inhaled, wouldnt its chemical coating (if any) be different to when its being swallowed as a tablet (as its being digested)? if there is a difference could that affect the functioning of the drug in the body?

For inhaled dosages, other criteria such as particle size come into play. Also if the drug forms 'clumps' it will drop out of the inhaled aerosol hit the back of the throat and make the person cough, or end up being swallowed.
Generally if you can put the drug where you want it to act you minimise side effects.

Drug metabolism can involve portions of active drug, active metabolites, less active metabolites and inactivated drug. Some drugs are even inactive when taken deliberately so that the liver metabolism produces the active drug so that some of the first pass metabolism is 'used up' without inactivating too much of the drug.

Its fun all this science isn't it.

[johnep]

Re: dosage

Alfacalcidol relies on the liver to activate it.
johnep