Implants are small, sterile cylinders of drug, inserted beneath the skin or into muscle tissue to provide slow absorption and prolonged action therapy.
Implants are small,
sterile cylinders of drug, inserted beneath the skin or into muscle tissue to provide slow absorption and prolonged action
therapy. This is
principally based on the fact
that such drugs,
invariably hormones, are almost insoluble in water and
yet the implant provides
a rate of dissolution sufficient for a therapeutic
effect. Implants are manufactured from
the pure drug made into tablet form by compression or fusion. No other ingredient can be included
because this may be insoluble or toxic, or, most importantly,
may influence the rate of drug release. Copolymers such as polylactic acid/polyglycolic acid may be used as the implant matrix to provide a controlled rate of
drug delivery.
Compression of sterile drugs must be conducted
under aseptic
conditions using sterile
machine parts and materials. After manufacture, the outer surface
of the implant is sterilized by immersion in 0.002% w/v phenylmercuric
nitrate at 75 °C for 12 hours.
After the surface has been dried, each implant
is placed aseptically into a sterile glass
vial with a cotton wool plug at both ends. This prevents damage
and reduces the risk of glass
specules, formed
when the vial is opened,
adhering to the implant. This compression process
is not ideal and fusion processes may be used provided
that the drug is heatstable. The pure drug is melted at 5–10 °C above its melting temperature and
poured into moulds.
The interior of the implant
will be automatically sterilized by this process if the melting
temperature is high enough. It is
also possible to dry heat
sterilize the implant
after packaging provided that
the melting temperature is above 160 °C. Clearly, it is easier
to manufacture sterile
implants by fusion
as the process does not require presterilized ingredients or aseptic processing. The implant
hardness is also
very convenient.
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