Norplant subcutaneous implantation

Nondegradable subcutaneous implants as diffusion-controlled drug delivery systems, including Norplant, have been reviewed.89 99 Unlike biodegradable implants with long-term toxicological concern for metabolism of the polymer, nondegradable implants cannot avoid removal of the... 

Fig. 7 Diagrammatic illustration of the subcutaneous implantation of Norplant implants. The subcutaneous release profile of levonorgestrel in female volunteers for up to 6 years and the resultant plasma profile as compared to those obtained by oral administration. (Adapted from Refs. l)...

Implantable drug delivery systems are defined as longterm (>30 days) implantable products that are resorbable or removable. The resorbable implants are injectables incorporating lyophilized microspheres. The removable version is typically a subcutaneous implant, requiring minor outpatient procedures for insertion and removal. The main commercialized product in this category is Norplant , a contraceptive implant. Medtronic Corporation has two products in the implantable area that allow drug delivery into the intrathecal space (where the spinal fluid circulates). One of these products delivers baclofen for spasticity, and the other delivers anaesthetics for pain control. Both products utilize Medtronic s SynchroMed infusion pump, which can be electronically programmed to deliver any type of preset dose. 

Some limitations are that the amount of drug that can be injected in this fashion is fairly small and that the injected drug must not irritate or inflame the subcutaneous tissues. The subcutaneous route can also be used when certain types of drug preparations are implanted surgically beneath the skin, so that the drug is slowly dispersed from the implanted preparation and then absorbed into the bloodstream for prolonged periods of time.62,86 A common example of this form of subcutaneous administration is the use of implanted hormonal contraceptive products (e.g., Norplant).9,53 The use of these implantable contraceptives is discussed in more detail in Chapter 30. 

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