GoodRx CDS Price Comparison

Overview
The complete source code for this example is available at example/goodrx-cds-price-comparison. CDS Clients can connect to the service for test purposes only at sero-goodrx-cds.fly.dev/cds-services.
A full demo of this example.
Transparency on drug pricing changes the decisions doctors make. Good data on what drugs cost while they are prescribing them is both something (1) doctors say they want and (2) doctors who have the data have been shown to have reduced per-patient drug costs than those who do not. Meanwhile, open standards have emerged (CDS Hooks) as a way of getting decision support to doctors directly inside of the EHR (i.e. patient specific recommendations on drug pricing).
In this example, we introduce the use of third party consumer pricing data (GoodRx) over a decision support API provided by the Sero toolkit to deliver drug price to doctors while they are writing the prescription. Sero can be used to make decision support APIs and SMART on FHIR apps.
Walkthrough
Sero implements an open decision support API called CDS Hooks. As part of HL7, and closely related to FHIR, CDS Hooks is the only open standard for 3rd party developers to deliver decision support to doctors directly inside of the EHRs they are already working with. You can learn more about decision support API's in our How to build in health the easy way ebook.
This code walkthrough will focus primarily on good-rx-compare-price.ts, the actual decision support service. We'll make use of helper functions we've written to work with the GoodRx API, but the vast majority of the example is contained in good-rx-compare-price.ts.
Imports
We start by importing the Service and Card classes. We'll use these to create our decision support service and to describe our responses to inbound requests. We also import an helper class, NoDecisionResponse, used to reply with a standard "no comment" response. We're also importing HookRequest and Hooks - which are TypeScript declarations. Lastly, we import our helper method for the GoodRx API.
TypeScript
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import {
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    Service,
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    Card,
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    HookRequest,
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    NoDecisionResponse
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} from "@sero.run/sero";
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import { Hooks } from "@sero.run/sero/cds-hooks/util"
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import { comparePrice } from "./api.js";
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Options
Every decision support service provided by a server in the CDS Hooks model identifies itself as part of a response to /cds-services. We define an options object that we will use in the construction of Service. Importantly, we declare that the Service expects to respond to the order-select hook request.
TypeScript
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const options = {
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  id: "good-rx-comparison",
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  title: "GoodRx Compare Price Service for MedicationRequest",
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  hook: "order-select" as Hooks,
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  description: "GoodRx's Compare Price API is used to provide drug cost estimates during the prescription order workflow",
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};
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Handler
The most critical part of our decision support API is the function that we run when we get a request for decision support from our consumers like EHRs. We define an async function called handler:
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const handler = async (request) => {
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  ...
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}
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Every decision support request includes a context attribute that we validate the presence of in Sero. When the handler function executes, a developer can have confidence that a draftOrders key will exist on request.context and that it will be shaped like a FHIR Bundle (we're using the @types/fhir to annotate that here).
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const { draftOrders }: { draftOrders: fhir4.Bundle } = request.context;
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The order-select hook requires that a Bundle of FHIR Resources be provided at draftOrders, but those resources could be NutritionOrder, ServiceRequest, or VisionPrescription in addition to the one we care about: MedicationRequest. We filter the draftOrders for MedicationRequest resources.
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const medicationRequest = draftOrders.entry
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  ?.find((e) => e.resource?.resourceType == "MedicationRequest")
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  ?.resource as fhir4.MedicationRequest
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If no MedicationRequest was found, we throw a NoDecisionResponse because we can only provide decision support when one is present. This thrown error is handled by Sero automatically, sending back response the CDS Hooks specification expects:
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if (!medicationRequest) throw new NoDecisionResponse();
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Otherwise, we do have a MedicationRequest, so let's use the text associated with the request (i.e. the "name" of the drug) to make a price comparison request to the GoodRx Compare Price API (here we have abstracted the API requirements into a small utility library). The utility uses async/await but we can also make use of Promise:
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const response = await comparePrice(medicationRequest);
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With the response from GoodRx, our handler function can now return relavent pricing data related to the MedicationRequest. We create an return a Card containing a summary of the low/high price, the brand name, generic names, the cheapest pharmacy, and an associated coupon.
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return {
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    cards: [
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      new Card({
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        source: {
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          label: "GoodRx"
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        },
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        summary: `${response.display} ($${Math.min(...response.prices)} - $${Math.max(...response.prices)})`,
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        indicator: "info",
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        detail: `
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          * Brand: ${response.brand.join(", ")}
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          * Generic: ${response.generic.join(", ")}
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          * Cheapest pharmacy: ${response.price_detail.pharmacy[0]} (${response.price_detail.savings[0]} savings)
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          * Coupon: ${response.price_detail.url[0]}
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        `,
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      })
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    ]
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}
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Creating the service
Finally, we construct the Service:
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export default new Service(options, handler);
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The boilerplate in index.ts takes this module and boots a fully functional, end-to-end conformant CDS Hooks 1.1 API using the Service we defined in this example.
Running it locally
We've provided a Dockerfile to build and run the project in isolation. Note that in order to actually successfully make requests to the Good RX Compare Price API you must set two environment variables GOOD_RX_API_KEY and GOOD_RX_SECRET_KEY which only GoodRx can issue.
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docker build -t goodrx-cds:latest .
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docker run -p 8080:8080 -ti --rm goodrx-cds:latest
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Confirm the service is running and responding:
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curl http://localhost:8080/cds-services
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