# Extensions
Several extensions are needed to capture the metadata about formularies and the medications that they list.

_TODO: All of these extensions are using http://example.org/fhir as their baseurl, which is not real. Find an authoritative location to store these extensions._

For each formulary:
* {{link:USMedicationFormulary/Formulary-EffectiveFrom}}
* {{link:USMedicationFormulary/Formulary-EffectiveTo}}
* {{link:USMedicationFormulary/Formulary-PlanYear}}
  * _TODO: this is currently an `integer`. Should it be a string for the plans that span multiple years (e.g., 2007-2008)?_
* {{link:USMedicationFormulary/Formulary-HealthPlan}}
  * _TODO: this is currently a `string`. Should it be a reference instead?_
  * _TODO: should the reference be on the other side - plans reference the formularies that they include?_
* _TODO: Formulary ID, for handling associations between Health Plans and their respective formularies_
  * _Do plans ever have multiple formularies associated with them, or is it just a 1:1 relationship?_
* _TODO: Number of Drug Tiers as an `integer` (3, 4, 5, 6, others?)_
* _TODO: Co-payment/co-insurance amounts associated with each tier_

For each medication:
* _TODO: Drug Tier as an `integer`_
* _TODO: Drug Classification Code_
  * _This could be a WHO ATC code or a First Data Bank code?_
  * _This may also be a string, if no code system is widely used/available_
* {{link:USMedicationFormulary/Formulary-CoPayRequired}}
  * _TODO: Is this necessary if the drug tier dictates the copay amount?_
* {{link:USMedicationFormulary/Formulary-CoInsuranceRequired}}
  * _TODO: Is this necessary if the drug tier dictates the co-insurance amount?_
* {{link:USMedicationFormulary/Formulary-PriorAuthRequired}}
* {{link:USMedicationFormulary/Formulary-PriorAuthDescription}}
* {{link:USMedicationFormulary/Formulary-StepTherapyRequired}}
* {{link:USMedicationFormulary/Formulary-StepTherapyDescription}}
* {{link:USMedicationFormulary/Formulary-QuantityLimitImposed}}
* {{link:USMedicationFormulary/Formulary-QuantityLimitDescription}}
* {{link:USMedicationFormulary/Formulary-AgeLimitImposed}}
* {{link:USMedicationFormulary/Formulary-AgeLimitDescription}}
* {{link:USMedicationFormulary/Formulary-LimitedAccessImposed}}
* {{link:USMedicationFormulary/Formulary-LimitedAccessDescription}}
* {{link:USMedicationFormulary/Formulary-Injectable}}
* {{link:USMedicationFormulary/Formulary-MailOrder}}
* {{link:USMedicationFormulary/Formulary-PartBOrPartD}}