These
are controlled drug delivery systems .These type of drug delivery systems release
the active ingradient at an osmotically controlled rate over a prolonged period
of time ALZA Corporation
pioneered the development of osmotic drug delivery systems. They deliver the
drug by following zero order kinetics (Chein, 1989).
ALZET PUMP :
This is a implantable CrDDS
developed by Alza corporation.It comprises of –
1.Collapsible
,Impermeable polyester bag.
2.
Osmotically active salt
3.
Rigid housing walled with semipermeable memberane.
4.Active
Ingradient.
Design :
Drug
reservoir is enclosed in a collapsible,impermeable polyester bag .The external
surface of this bag is coated with osmotically active salt (Ex-NaCl).This total
system is sealed in a rigid housing which contains semipermeable memberane
around it.
Working :
1.At
the site of insertion ,Water present in surrounding tissues enters through the
semipermeable membrane of delivery system and dissolves osmotic salt
surrounding the collapsible bag.
2.This
creates osmotic pressure between
collapsible reservoir wall and rigid semi permeable housing.
3.Under
the osmotic pressure created ,The drug reservoir compartment is thus reduced in
volume.Hence forcing the release of drug from drug reservoir through flow
moderator at a controlled rate.
4.Drug
release is at a controlled rate and follows ZERO ORDER KINETICS.
In
this type of CrDDS drug can be enclosed either in solution form or solid form .
For
solution type Osmotic drug delivery systems rate of drug delivery is given by :
Where:
Pw =
water permeability.
Am =
effective surface area.
hm =
thickness of the semi permeable housing.
πs - πe = difference
of osmotic pressure between the drug delivery system with osmotic pressure (Ï€s) and environment with
osmotic pressure(Ï€e).
References :
References :
1.Encyclopedia of pharmaceutical technology,DOI:10
,1082
2. Rastogi, S.K. ,Vaya,N.,Mishra,B.,Eastern
pharmacist, 38,79-82.
3. Fix,J.,in; Encyclopedia of controlled drug
delivery,Edmathiowitz,vol-2, John Wiley and sons,Inc,700.
4. DRUG DELIVERY THROUGH OSMOTIC SYSTEMS – AN OVERVIEW by Tanmoy Ghosh, Amitava Ghosh,
Journal of Applied Pharmaceutical Science 01 (02); 2011: 38-49
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