Drugs & absorption ~ routes of administration

[Guest guest]

I always wondered about the reasons behind the different " routes " of

drugs.

I find things like this very interesting.

Elf

~~~~~~

This article explains the reasons behind these different ‘routes of

administration’, highlighting the advantages and disadvantages of each.

It also gives some tips on how to cope with having an injection, which

should be particularly useful for those taking drugs in the interferon

beta class.

How our bodies use medication

Clinicians have spent decades studying what happens to drugs once people

have taken them. This area of study - pharmacokinetics - analyses what

the body does to a drug: for instance, where the drug goes and how fast,

the way it is processed, and how it is cleared from the body.

Pharmacokinetic studies focus on four processes:

*absorption

*distribution

*bioavailability

*excretion

It is these four processes that Phase I clinical trials assess. The data

from these trials tell the physician how much of the drug to give and

how often.

Absorption

Every medication has its own special chemical properties that affect how

quickly and how completely it is absorbed into your body. Some drugs are

broken down in the stomach and are not absorbed at all, while others

cannot enter the bloodstream from the intestine and pass through the

digestive system.

Drugs are classified according to their properties, for example:

*fat soluble – they dissolve easily in fat tissue (e.g. vitamins A and

E, general anaesthetics, benzodiazepines)

*acidic – much like the stomach’s environment (e.g. aspirin)

*proteinaceous – a protein (e.g. insulin, the interferon beta class of

drugs)

*size

Distribution

Once absorbed by your body, the drug spreads throughout the body in

blood vessels. Blood vessels form a vast highway system that penetrates

every area of the body. They provide a route by which the drug travels

from one area (e.g. the point of entry) to another area (e.g. the target

tissue – where the drug exerts its desired effects).

Bioavailability

Not all the medication you take is available for the body to use. The

body processes or metabolizes drugs to varying degrees depending on the

point of entry of the drug. For example, 75-95% of some drugs taken

orally are broken down in the liver before they reach the general

circulation. This is known as the ‘first-pass effect’. Doses of oral

drugs have to be high to compensate for the amount lost in the liver.

Excretion

Once a drug has done its job (i.e. exerted its effects on the target

tissue), it is cleared from the body via several organs, including the

kidney (in urine), the gut (in faeces) and the lungs, and through sweat

and breast milk.

Now that we’ve seen what the body does to drugs, we can focus on the way

each formulation (the form of a drug) can affect absorption,

distribution, bioavailability and excretion.

Tablets

Most medications are available as tablets - taken by mouth and

swallowed. This is often the easiest way to administer a drug. This

formulation works well for acidic drugs (as the inside of the stomach is

acidic), or fat-soluble drugs (which are absorbed into your cells

quickly). Drugs that are proteins, such as insulin or the interferon

beta class of drugs, are broken down in the stomach in the same way as

the protein in food, meaning that oral administration is not very

effective.

Suppositories and pessaries

Each drug is designed both for a specific illness and a specific route

of administration. Suppositories, placed in the rectum, and pessaries,

placed in the vagina, can be unpleasant but are useful if a ‘local

effect’ is desired – in other words, if the drug is being used to treat

the colon, vagina or womb. Also, suppositories are useful if someone is

nauseous or vomiting, or cannot take medication by mouth.

Sublingual

Drugs given under the tongue (i.e. sublingually) are useful when both a

rapid response and self-administration are needed. The drug goes quickly

into the bloodstream via the delicate cells lining the mouth, therefore

avoiding the ‘first-pass effect’ of tablets that are swallowed. One

example is glyceryl trinitrate, which is given sublingually for angina.

Transdermal

Medication delivered transdermally enters the body via the skin. It is

given either as a cream or as a patch. Creams are most often used when a

local effect on the skin is desired (e.g. for an insect bite or rash).

Patches contain a reservoir of drug, which is released slowly and evenly

over a period of time. The drug passes through the skin and into the

bloodstream for onward transport through the body to its target tissue.

Transdermal delivery of nicotine in patches reduces the withdrawal

symptoms that accompany stopping smoking. Patches are also used to

deliver hormone replacement therapy for menopause, glyceryl trinitrate

for angina and hyoscine for seasickness.

Inhalants and nasal sprays

Inhalation is used for volatile and gaseous anaesthetics, and drugs that

affect the lungs (e.g. for asthma). Inhaled drugs pass quickly to the

bloodstream, avoiding the ‘first-pass effect’. The lungs contain a vast

network of tiny air sacs (alveoli) which provides a large surface area

through which the drug can travel from the inhaled air to the

bloodstream.

In addition to commonly used decongestants, nasal sprays are sometimes

used for very small protein drugs (called peptides) to avoid the need

for frequent injections. Examples include gonadotrophin-releasing

hormone (for infertility), and antidiuretic hormone (ADH - to promote

water retention). You may know ADH as desmopressin, which helps prevent

urination during the night in MS. Antihistamines are also sometimes

given through nasal sprays to treat colds, so that the drug can be

delivered directly to the source of congestion.

Eye drops

Eye drops are almost exclusively used to deliver a drug directly to the

eye (e.g. to treat glaucoma or an eye infection). To be effective,

however, the drugs in eyedrops need to be fat soluble. Some absorption

into the bloodstream does occur.

Injectables: intravenous (IV)

Intravenous administration involves injecting a liquid containing the

drug directly into veins. It is the quickest and most direct way of

delivering a drug, and avoids the ‘first-pass effect’. The bolus of drug

goes first to the heart and then to the general circulation. Some drugs

are given all at once; others are delivered over a certain period of

time (an infusion). You may have had intravenous injections of steroids

such as methylprednisolone.

Injectables: intrathecal

Intrathecal administration involves placing the needle into the area

around the spinal cord to deliver a drug directly to the central nervous

system. Spinal anaesthesics (e.g. when used in labour) are also

administered intrathecally.

Injectables: intramuscular (IM)

Some drugs are injected directly into muscle. Since muscle has a rich

blood supply, it provides a faster route to the rest of the body than

oral administration. Massaging the muscle after injection can increase

blood flow and therefore distribution to the rest of the body.

If slow administration is needed, drugs given intramuscularly can be

provided in a slow-release or depot form.

IM injections can be quite painful or uncomfortable because they

penetrate deep into the muscle layers, which are richly supplied with

nerves. Bruising may occur if a blood vessel is punctured during an

injection. IM drugs do not have to be given as often as IV or

subcutaneous (see below) injections, but they should be given by a

healthcare professional or under the supervision and guidance of a

healthcare professional because they have the skills needed to give such

a deep injection: they know how to avoid hitting a bone or nerve.

Injectables:subcutaneous (SC)

Subcutaneous injections deliver the drug to just below the fatty layer

underneath the skin. They are not very painful because there are very

few blood vessels or nerve endings in the subcutaneous area. The drug is

usually absorbed more slowly (and therefore steadily) than those given

intramuscularly. Depot drugs can be used to control the rate of

absorption. There is a limit to the amount of drug that can be delivered

by SC injections (large volumes are not feasible). Massaging the

injection site helps with absorption, as with IM injections. Localized

injection site reactions can occur but these can be managed by rotating

the injection sites.

Although people who need to inject themselves subcutaneously require

initial instruction from a healthcare professional, they can learn to

perform the injections on their own, providing flexibility and

independence. Many people regularly self-inject drugs subcutaneously.

http://www.ms-gateway.com/english/betafern/inject-b.html

[Guest guest]

Excellent information, Susie! Thank you.

[ ] Drugs & absorption ~ routes of administration

> I always wondered about the reasons behind the different " routes " of

> drugs.

> I find things like this very interesting.

> Elf

> ~~~~~~

> This article explains the reasons behind these different 'routes of

> administration', highlighting the advantages and disadvantages of

each.

> It also gives some tips on how to cope with having an injection, which

> should be particularly useful for those taking drugs in the interferon

> beta class.

>

> How our bodies use medication

> Clinicians have spent decades studying what happens to drugs once

people

> have taken them. This area of study - pharmacokinetics - analyses what

> the body does to a drug: for instance, where the drug goes and how

fast,

> the way it is processed, and how it is cleared from the body.

> Pharmacokinetic studies focus on four processes:

> *absorption

> *distribution

> *bioavailability

> *excretion

> It is these four processes that Phase I clinical trials assess. The

data

> from these trials tell the physician how much of the drug to give and

> how often.

>

> Absorption

> Every medication has its own special chemical properties that affect

how

> quickly and how completely it is absorbed into your body. Some drugs

are

> broken down in the stomach and are not absorbed at all, while others

> cannot enter the bloodstream from the intestine and pass through the

> digestive system.

>

> Drugs are classified according to their properties, for example:

> *fat soluble - they dissolve easily in fat tissue (e.g. vitamins A and

> E, general anaesthetics, benzodiazepines)

> *acidic - much like the stomach's environment (e.g. aspirin)

> *proteinaceous - a protein (e.g. insulin, the interferon beta class of

> drugs)

> *size

>

> Distribution

> Once absorbed by your body, the drug spreads throughout the body in

> blood vessels. Blood vessels form a vast highway system that

penetrates

> every area of the body. They provide a route by which the drug travels

> from one area (e.g. the point of entry) to another area (e.g. the

target

> tissue - where the drug exerts its desired effects).

>

> Bioavailability

> Not all the medication you take is available for the body to use. The

> body processes or metabolizes drugs to varying degrees depending on

the

> point of entry of the drug. For example, 75-95% of some drugs taken

> orally are broken down in the liver before they reach the general

> circulation. This is known as the 'first-pass effect'. Doses of oral

> drugs have to be high to compensate for the amount lost in the liver.

>

> Excretion

> Once a drug has done its job (i.e. exerted its effects on the target

> tissue), it is cleared from the body via several organs, including the

> kidney (in urine), the gut (in faeces) and the lungs, and through

sweat

> and breast milk.

>

> Now that we've seen what the body does to drugs, we can focus on the

way

> each formulation (the form of a drug) can affect absorption,

> distribution, bioavailability and excretion.

>

> Tablets

> Most medications are available as tablets - taken by mouth and

> swallowed. This is often the easiest way to administer a drug. This

> formulation works well for acidic drugs (as the inside of the stomach

is

> acidic), or fat-soluble drugs (which are absorbed into your cells

> quickly). Drugs that are proteins, such as insulin or the interferon

> beta class of drugs, are broken down in the stomach in the same way as

> the protein in food, meaning that oral administration is not very

> effective.

>

> Suppositories and pessaries

> Each drug is designed both for a specific illness and a specific route

> of administration. Suppositories, placed in the rectum, and pessaries,

> placed in the vagina, can be unpleasant but are useful if a 'local

> effect' is desired - in other words, if the drug is being used to

treat

> the colon, vagina or womb. Also, suppositories are useful if someone

is

> nauseous or vomiting, or cannot take medication by mouth.

>

> Sublingual

> Drugs given under the tongue (i.e. sublingually) are useful when both

a

> rapid response and self-administration are needed. The drug goes

quickly

> into the bloodstream via the delicate cells lining the mouth,

therefore

> avoiding the 'first-pass effect' of tablets that are swallowed. One

> example is glyceryl trinitrate, which is given sublingually for

angina.

>

> Transdermal

> Medication delivered transdermally enters the body via the skin. It is

> given either as a cream or as a patch. Creams are most often used when

a

> local effect on the skin is desired (e.g. for an insect bite or rash).

> Patches contain a reservoir of drug, which is released slowly and

evenly

> over a period of time. The drug passes through the skin and into the

> bloodstream for onward transport through the body to its target

tissue.

> Transdermal delivery of nicotine in patches reduces the withdrawal

> symptoms that accompany stopping smoking. Patches are also used to

> deliver hormone replacement therapy for menopause, glyceryl trinitrate

> for angina and hyoscine for seasickness.

>

> Inhalants and nasal sprays

> Inhalation is used for volatile and gaseous anaesthetics, and drugs

that

> affect the lungs (e.g. for asthma). Inhaled drugs pass quickly to the

> bloodstream, avoiding the 'first-pass effect'. The lungs contain a

vast

> network of tiny air sacs (alveoli) which provides a large surface area

> through which the drug can travel from the inhaled air to the

> bloodstream.

> In addition to commonly used decongestants, nasal sprays are sometimes

> used for very small protein drugs (called peptides) to avoid the need

> for frequent injections. Examples include gonadotrophin-releasing

> hormone (for infertility), and antidiuretic hormone (ADH - to promote

> water retention). You may know ADH as desmopressin, which helps

prevent

> urination during the night in MS. Antihistamines are also sometimes

> given through nasal sprays to treat colds, so that the drug can be

> delivered directly to the source of congestion.

>

> Eye drops

> Eye drops are almost exclusively used to deliver a drug directly to

the

> eye (e.g. to treat glaucoma or an eye infection). To be effective,

> however, the drugs in eyedrops need to be fat soluble. Some absorption

> into the bloodstream does occur.

>

> Injectables: intravenous (IV)

> Intravenous administration involves injecting a liquid containing the

> drug directly into veins. It is the quickest and most direct way of

> delivering a drug, and avoids the 'first-pass effect'. The bolus of

drug

> goes first to the heart and then to the general circulation. Some

drugs

> are given all at once; others are delivered over a certain period of

> time (an infusion). You may have had intravenous injections of

steroids

> such as methylprednisolone.

>

> Injectables: intrathecal

> Intrathecal administration involves placing the needle into the area

> around the spinal cord to deliver a drug directly to the central

nervous

> system. Spinal anaesthesics (e.g. when used in labour) are also

> administered intrathecally.

>

> Injectables: intramuscular (IM)

> Some drugs are injected directly into muscle. Since muscle has a rich

> blood supply, it provides a faster route to the rest of the body than

> oral administration. Massaging the muscle after injection can increase

> blood flow and therefore distribution to the rest of the body.

> If slow administration is needed, drugs given intramuscularly can be

> provided in a slow-release or depot form.

> IM injections can be quite painful or uncomfortable because they

> penetrate deep into the muscle layers, which are richly supplied with

> nerves. Bruising may occur if a blood vessel is punctured during an

> injection. IM drugs do not have to be given as often as IV or

> subcutaneous (see below) injections, but they should be given by a

> healthcare professional or under the supervision and guidance of a

> healthcare professional because they have the skills needed to give

such

> a deep injection: they know how to avoid hitting a bone or nerve.

>

> Injectables:subcutaneous (SC)

> Subcutaneous injections deliver the drug to just below the fatty layer

> underneath the skin. They are not very painful because there are very

> few blood vessels or nerve endings in the subcutaneous area. The drug

is

> usually absorbed more slowly (and therefore steadily) than those given

> intramuscularly. Depot drugs can be used to control the rate of

> absorption. There is a limit to the amount of drug that can be

delivered

> by SC injections (large volumes are not feasible). Massaging the

> injection site helps with absorption, as with IM injections. Localized

> injection site reactions can occur but these can be managed by

rotating

> the injection sites.

> Although people who need to inject themselves subcutaneously require

> initial instruction from a healthcare professional, they can learn to

> perform the injections on their own, providing flexibility and

> independence. Many people regularly self-inject drugs subcutaneously.

>

> http://www.ms-gateway.com/english/betafern/inject-b.html