Drug Interaction & Formulary Checker#

Overview#

This skill checks drug-drug interactions, allergy contraindications, formulary coverage, and dosing guidelines using free public APIs — no credentials required out of the box.

What it can do:

• Check interactions between 2 or more drugs
• Look up a full medication list for interactions
• Check formulary tier and coverage for a payer
• Flag allergy contraindications
• Provide standard adult dosing ranges
• Suggest therapeutic alternatives when a drug is not covered

APIs used (all free, no key needed):

• OpenFDA — drug interactions, adverse events, labeling
• RxNorm API (NLM) — drug name normalization and RxCUI lookup
• NLM DailyMed — official drug labeling and prescribing info

⚠️ Clinical Disclaimer: All output is informational only and must be reviewed by a licensed clinician or pharmacist before any prescribing or dispensing decision.

🔒 Privacy / PHI Warning: This skill sends drug names and allergy information to public APIs (RxNorm, OpenFDA, DailyMed). Do not include patient-identifiable information (names, MRNs, DOBs, addresses, or other PHI) in any query. Use drug names and clinical terms only. For production use with real patient data, ensure your deployment satisfies HIPAA requirements and that a BAA is in place with any third-party service.

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Trigger Phrases#

• "Check interactions for [drug list]"
• "Is it safe to take [drug A] with [drug B]?"
• "Check this patient's med list for interactions"
• "What tier is [drug] on [payer] formulary?"
• "Is [drug] covered by BlueCross?"
• "What's the standard dose for [drug]?"
• "Are there any contraindications with [drug] for a patient allergic to [allergen]?"
• "Suggest an alternative to [drug] that's on formulary"

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Drug Interaction Checks#

Single pair check#

text

"Check interactions between Warfarin and Aspirin"
"Is it safe to combine Metformin and Lisinopril?"

Full medication list check#

text

"Check this med list for interactions:
- Metformin 1000mg BID
- Lisinopril 10mg daily
- Atorvastatin 40mg daily
- Aspirin 81mg daily
- Omeprazole 20mg daily"

What the agent does:

1. Normalizes all drug names via RxNorm API
2. Queries OpenFDA drug interactions for each pair
3. Ranks interactions by severity (Major / Moderate / Minor)
4. Returns a structured interaction report

Example output:

text

DRUG INTERACTION REPORT
Patient Med List: 5 medications checked
Pairs checked: 10

⛔ MAJOR (1):
• Warfarin + Aspirin
  Risk: Increased bleeding risk. Combined antiplatelet
  and anticoagulant effect.
  Action: Monitor INR closely. Consider GI protection.

⚠️ MODERATE (2):
• Lisinopril + Potassium supplements
  Risk: Hyperkalemia risk.
  Action: Monitor serum potassium.

• Atorvastatin + Clarithromycin
  Risk: Increased statin exposure, myopathy risk.
  Action: Temporarily hold statin if antibiotic needed.

✅ MINOR / NO INTERACTION (7):
  Remaining pairs — no clinically significant interactions found.

Source: OpenFDA + RxNorm | For clinician review only

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Allergy Contraindication Check#

text

"Check if any of these meds are contraindicated
 for a patient with penicillin allergy"

"Patient is allergic to sulfa drugs —
 is Bactrim safe?"

What the agent does:

1. Looks up drug class and cross-reactivity data from OpenFDA labeling
2. Flags any drugs in the same class as the allergen
3. Suggests safe alternatives where available

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Formulary & Coverage Lookup#

text

"What tier is Ozempic on BlueCross formulary?"
"Is Humira covered by Aetna?"
"Find a formulary-covered alternative to Jardiance"

What the agent does:

1. Looks up the drug's generic name and drug class via RxNorm
2. If FORMULARY_API_KEY is set: queries the real-time payer formulary API for tier and coverage data
3. If no key is set: instructs the agent to tell the user to verify tier directly with the payer's online formulary tool — no estimated or cached data is used
4. Suggests covered alternatives in the same drug class based on RxNorm drug class data

Note: Without FORMULARY_API_KEY, this skill does not provide formulary tier estimates. Always confirm coverage with the payer's online formulary tool or pharmacy benefit line before clinical use.

Example output:

text

FORMULARY CHECK — Ozempic (semaglutide)
Payer: BlueCross BlueShield PPO

Tier: 4 (Non-Preferred Brand)
Est. Copay: $80-120/month (with standard benefit)
Prior Auth Required: Yes
Step Therapy Required: Yes (must try Metformin first)

Covered Alternatives (Tier 2):
• Trulicity (dulaglutide) — Tier 2, $45/month
• Victoza (liraglutide) — Tier 2, $50/month

Recommendation: Consider Trulicity as first-line
if cost is a barrier. PA may be approved if
patient has failed oral agents.

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Dosing Reference#

text

"What's the standard dose for Metformin?"
"Dosing for Lisinopril in CKD?"
"Max dose of Acetaminophen per day?"

Example output:

text

DOSING REFERENCE — Metformin (metformin HCl)

Standard Adult Dose:
• Starting: 500mg BID or 850mg once daily with meals
• Titration: Increase by 500mg/week as tolerated
• Maximum: 2550mg/day (divided doses)

Renal Dosing:
• eGFR 30-45: Use with caution, max 1000mg/day
• eGFR <30: CONTRAINDICATED

Common Side Effects: GI upset, nausea (take with food)
Black Box Warning: Lactic acidosis (rare)

Source: FDA prescribing information via OpenFDA

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API Reference#

RxNorm — Drug Name Normalization#

text

GET https://rxnav.nlm.nih.gov/REST/rxcui.json?name={drug_name}
→ Returns RxCUI (standard drug identifier)

GET https://rxnav.nlm.nih.gov/REST/interaction/interaction.json?rxcui={id}
→ Returns interaction data for a drug

OpenFDA — Interactions & Labeling#

text

GET https://api.fda.gov/drug/label.json?search=openfda.brand_name:{name}
→ Returns full drug labeling including interactions section

GET https://api.fda.gov/drug/event.json?search=patient.drug.medicinalproduct:{name}
→ Returns adverse event reports

NLM DailyMed#

text

GET https://dailymed.nlm.nih.gov/dailymed/services/v2/spls.json?drug_name={name}
→ Returns structured product labeling

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Example Workflows#

Quick interaction check before prescribing#

text

Clinician: "Adding Clarithromycin for a patient
            already on Atorvastatin — any issues?"

Agent: "⚠️ MODERATE INTERACTION DETECTED
        Clarithromycin inhibits CYP3A4, significantly
        increasing Atorvastatin exposure. Risk of myopathy
        and rhabdomyolysis.

        Recommendation: Temporarily hold Atorvastatin
        during antibiotic course, or switch to Azithromycin
        which has no significant statin interaction."

Full med reconciliation on admission#

text

Clinician: "Patient admitted with these home meds,
            check for interactions:
            Warfarin, Amiodarone, Metoprolol,
            Furosemide, Potassium Chloride, Digoxin"

Agent: [Checks all 15 pairs]
       "⛔ 2 MAJOR interactions found:
        • Amiodarone + Warfarin: Markedly increases
          INR. Reduce Warfarin dose by 30-50%.
        • Amiodarone + Digoxin: Increases Digoxin
          levels. Monitor levels and reduce dose."

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Version History#

VersionDateChanges1.0.02026-03-29Initial release. Interaction checks, formulary lookup, dosing reference, allergy contraindication check.