Rheological Properties Effect on IM Injectable Dosage Forms
The rheological properties effect on the formulation, design & use of IM injectable dosage forms.
These formulations may be:
- aqueous.
- lipophilic (oily).
As a form of:
- solutions
- suspensions
Aqueous or lipophilic?
Aqueous
Because after the dosage form injected, the active ingredient is absorbed MORE QUICKLY from an aqueous formulation than its lipophilic counterpart.
Suspension or solution (for depot)?
Suspension
Because incorporation of the active ingredient as a suspension in either type of base of ethers a further opportunity of slowing the rate of release. (benefit property of depot inj.)
The solvent effects on the rate of drug release is in part due to its compatibility with the tissue through its:
- Nature (compatible with tissue targeted)
- Viscosity
Increasing the viscosity of the oil extends the dosing interval, but it has to be borne in mind that the product needs to be able to be drawn into a syringe via a needle, (syringabillity, a prefomulation property): the diameter of which must not be so large as to alarm or discomfort the patient.
Others,
- polymers to the formulation,
- altering the particle size of the suspended particles.
These can induce marked alterations in the rheological properties such that the injection may become more plastic, pseudoplastic or even dilatent.
If it does become plastic, then provided that the yield value is not too high it may be possible to pass through a syringe needle by application of a force which it is reasonable to achieve with a syringe. (more syringabile).
This will not be applicable in the case if the SUSPENSION BECOMES DILATANT since as the applied force is increased, the product will become more solid.
Often the ideal formulation is one which is PSEUDOPLASTIC, because as the force is increased so the apparent viscosity will all making it easier to be injected higher flowability through needle
Ideally the product should also be truly thixotropic since once it has been injected into the muscle then the reduction in shear rate will mean that the bolus will gel and thus form a depot from which release of the drug may be expected to be delayed.
Characteristics on storage can be also predicted by development of rheological properties.
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Resource Person: Amr Ali
