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The delivery of the drug through the respiratory tract is called pulmonary drug delivery.

In case of brochodialating drugs, this is advantageous as drug will deliver directly to region where its action is required so that the
drug effect will be faster and low dose of drug can be administered through this delivery system and so the side effects can be decreased.

Drugs like sodium carmoglicate are absorbed to less extent when given orally. And some other drugs like isoprenaline is metabolized in the liver. These types of drugs can be administered through pulmonary route.

Coming to the respiratory tract, it is divided into two regions namely

-conducting region

-respiratory region

Conducting region includes trachea, brochii, brochiloes,terminal and respiratory bronchioles.

The other region like respiratory and alveolar regions includes respiratory regions.

The physical and chemical parameters of the drug, formulation, the instrument used and how the patient use, will determine the deposition of the drug.

Particlesize: particle size is very important criteria in the aerosol formulation. Standardization is done by determining the particle aerodynamic diameter.

Aerodynamic diameter is the diameter which is equal to the diameter of a particle having a unit density and whose rate of settling is equal to that of the particle under test in the given air medium.

How does humidity influence particle size?

It is so simple. As the particle size moves into the body, automatically condensation will takes place. Now we have two criteria. Whether the particle
is soluble or insoluble in water. If it's soluble its size increases and the condensation will proceed till the equilibrium is achieved. If it is not soluble a film of water will be formed on the surface of the particle.

Particle size has a profound effect on the deposition phenomenon. The particle size should generally
range from 5 to 6 microns to deposit on alveoli. If the particle size remain larger, they will get deposited on the upper respiratory tract.

The deposition is because of 3 phenomenons.

gravitational sedimentation

Inertial impaction

Brownian diffusion

Particle size (microns)

Mechanism Mostly involved


to 5


Inertial impaction

Gravitational sedimentation

Brownian diffusion

Devices used:

Metered dose inhalers

Dry powder inhalers


Metered dose inhalers: These are most widely used inhalers. Here the drug may remain dispersed or dissolved in liquid propellants. And various excipients are added. These are packed in to
a canister which consists of the metering valve.

Dry powder inhalers: In these inhalers micronized drug is conveyed and since the drug is too small. Carrier is used to convey the drug to the body.

This has several advantages

-here propellants are not used

-more drug can be administered than MDI

Nebulizers: Sometimes the MDI and DPI cannot deliver the required dose of the drug. In those cases nebulizers are used which can release
more amount of the drug dispersion or solution. These are of following types

O Jet nebulizers

O Ultrasonic nebulizers

O Vibrating mesh nebulizers

Conclusion: Hence pulmonary drug delivery is one of the best routes and the patient should breath slowly, have to take a deep breath and has to hold the breath for a while gives the best deposition and so its effect. Hence I feel it's the duty of physician and pharmacist to guide the patient how to use to get optimum activity.


Pharmaceutics The science
of Dosage form Design edited by Aulton, second edition, Churchill livingstone publishers, page no 149 and 473 to 485.

"This blog does not contain plagiarized material"


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Vishnu Murthy Vummaneni's picture

Is there any dose limit to be given though Pulmonary route? If so, mention the limits.

Vishnu Murthy Vummaneni

Sravani kompella's picture

Into which region does the drug enter,the conducting or the respiratory?
Satyajeeth Pandey's picture

generally first respiratory and then conducting

Satyajit Panda Asst. professor Maharajah's College Of Pharmacy

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