Table 3.

Common dosage forms for sustained systemic delivery at a fixed site for longer than 1 day.

Extended Delivery System	Key Attributes
Transdermal Patches	Pros Self-administered, needle-free Cons Visible (may not be discreet), limited drug load, low transmission rate, poor skin permeation of most drugs, skin irritation with extended application, potential to fall off, frequent administration, inconsistent adhesion
Injectable Depots	Pros Exceptionally consistent drug delivery rate for current generation of formulations, good to excellent PK, continuous medication once administered, duration of a single administration can approach three or more months, compatible with direct observed therapy by clinician Cons Injection, often requires caregiver administration, patients commonly discontinue therapy, large injection volumes and/or lower doses or limitation to very potent agents, potential for burst release especially for hydrophilic drugs, dosing tails after therapeutic period, poor reversibility
Implantable Systems	Pros Excellent control of delivery rate, potential for extended delivery periods out to six months or longer Cons Surgery, cost, potential limited patient access, dose limitation, poor reversibility, implant site erosion and side effects, retrieval often requires a second surgery
Vaginal Systems	Pros Prolonged release, self-administration possible, discreet Cons Gender specificity, lifestyle interference, low compliance, variable systemic delivery in some applications