# Phenytoin correction (Sheiner–Tozer)

Phenytoin correction

Status: LIVE
Price: $0.005 USDC
`GET /api/calc/phenytoin_correction`
HTML: https://magentlab.com/docs/phenytoin-correction
Markdown: https://magentlab.com/docs/phenytoin-correction.md

Not a medical device. Not a diagnosis, dose, or listing recommendation.

## What it computes

Estimate an albumin-adjusted total-equivalent phenytoin concentration from observed total phenytoin and albumin, with an optional renal binding-factor change.

## When to use

When an agent needs the published Winter–Tozer arithmetic and must not invent a free phenytoin immunoassay result.

## When not to use

- Not a free phenytoin level, immunoassay substitute, or dosing order. Liponi, Winter, and Tozer 1984 discuss altered binding in renal failure; magent applies factor 0.1 only when renal_impairment=true.
- Does not measure unbound phenytoin. Mauro 1989 (DICP) found poor agreement of these equations with measured free levels; treat the output as published arithmetic only.

## Formula

```
corrected_phenytoin_mcg_ml = phenytoin_mcg_ml / ((binding_factor * albumin_g_dl) + 0.1); binding_factor 0.2, or 0.1 if renal_impairment
```

## Citation

[Renal function and therapeutic concentrations of phenytoin](https://doi.org/10.1212/WNL.34.3.395)
Liponi DF, Winter ME, Tozer TN
Neurology. 1984;34(3):395-397
DOI: [10.1212/WNL.34.3.395](https://doi.org/10.1212/WNL.34.3.395)

## Worked example

### Observed 8 µg/mL, albumin 2.0 g/dL, no renal impairment

Given: `albumin_g_dl=2.0, phenytoin_mcg_ml=8.0, renal_impairment=false`

1. denominator = 0.2 × 2.0 + 0.1 = 0.5
2. corrected = 8.0 / 0.5 = 16.0 µg/mL


### Same labs with renal_impairment=true

Given: `albumin_g_dl=2.0, phenytoin_mcg_ml=8.0, renal_impairment=true`

1. denominator = 0.1 × 2.0 + 0.1 = 0.3
2. corrected = 8.0 / 0.3 = 26.7 µg/mL


## Also searched as

- Sheiner-Tozer phenytoin
- Winter-Tozer
- corrected phenytoin
- phenytoin albumin correction
- corrected total phenytoin

## Parameters

- `phenytoin_mcg_ml` (number, required): Observed total phenytoin in µg/mL (same as mg/L). Range 0.1-80.
- `albumin_g_dl` (number, optional): Serum albumin in g/dL (1-6). Provide this or albumin_g_l.
- `albumin_g_l` (number, optional): Serum albumin in g/L (10-60). Converted as g/dL = g/L / 10.
- `renal_impairment` (boolean, required): true uses binding factor 0.1 (Liponi/Winter–Tozer end-stage renal adjustment). false uses 0.2. true or false.

## Bulk (POST)

POST the same path with a JSON items array. The first item is the GET unit; each additional item is $0.002. Invalid items return HTTP 400 before settlement.

Method: `POST /api/calc/phenytoin_correction`
Max items: 25
Price: unit_amount + extra_item_amount * (n - 1) (unit 5000 atomic, extra 2000 atomic)
Status: PREVIEW

- 1 to 25 items. Each item uses the same keys as the GET query parameters.
- POST of 1 item costs the same as GET. Lists longer than 25: chunk into multiple POSTs. Extra items still execute; do not pad dummy rows.
- The first invalid item fails the whole request (index in the 400 JSON). You are not charged.
- HTTP 200 is {count, path, items}. Each items[i] is the GET 200 body for that row.
- Catalog misses (empty matches, found=false) stay paid 200s inside that slot.
- x402 resource URL is this path plus n and body_sha256. Browsers that prefer text/html get the same paywall as GET; Pay retries POST with the same items.

Example request:

```json
{
  "items": [
    {
      "albumin_g_dl": "2.0",
      "phenytoin_mcg_ml": "8.0",
      "renal_impairment": "false"
    },
    {
      "albumin_g_dl": "2.0",
      "phenytoin_mcg_ml": "8.0",
      "renal_impairment": "false"
    }
  ]
}
```

Human paywall (two-item fixture): https://api.magentlab.com/paywall/bulk/phenytoin-correction

Example 200:

```json
{
  "count": 2,
  "path": "/api/calc/phenytoin_correction",
  "items": [
    {
      "disclaimer": "Not a medical device. Deterministic published-formula or published-code output for autonomous agents. A licensed clinician remains responsible for patient care and billing submissions.",
      "citation": {
        "authors": "Liponi DF, Winter ME, Tozer TN",
        "doi": "10.1212/WNL.34.3.395",
        "id": "liponi-1984",
        "source": "Neurology. 1984;34(3):395-397",
        "title": "Renal function and therapeutic concentrations of phenytoin"
      },
      "formula": "sheiner_tozer",
      "formula_expression": "corrected_phenytoin_mcg_ml = phenytoin_mcg_ml / ((binding_factor * albumin_g_dl) + 0.1); binding_factor 0.2, or 0.1 if renal_impairment",
      "albumin_g_dl": 2.0,
      "binding_factor": 0.2,
      "corrected_phenytoin_mcg_ml": 16.0,
      "phenytoin_mcg_ml": 8.0,
      "renal_impairment": false
    },
    {
      "disclaimer": "Not a medical device. Deterministic published-formula or published-code output for autonomous agents. A licensed clinician remains responsible for patient care and billing submissions.",
      "citation": {
        "authors": "Liponi DF, Winter ME, Tozer TN",
        "doi": "10.1212/WNL.34.3.395",
        "id": "liponi-1984",
        "source": "Neurology. 1984;34(3):395-397",
        "title": "Renal function and therapeutic concentrations of phenytoin"
      },
      "formula": "sheiner_tozer",
      "formula_expression": "corrected_phenytoin_mcg_ml = phenytoin_mcg_ml / ((binding_factor * albumin_g_dl) + 0.1); binding_factor 0.2, or 0.1 if renal_impairment",
      "albumin_g_dl": 2.0,
      "binding_factor": 0.2,
      "corrected_phenytoin_mcg_ml": 16.0,
      "phenytoin_mcg_ml": 8.0,
      "renal_impairment": false
    }
  ]
}
```

## Response fields

- `formula` (string): sheiner_tozer
- `formula_expression` (string): Exact expression used
- `phenytoin_mcg_ml` (number): Observed total phenytoin used
- `albumin_g_dl` (number): Normalized albumin in g/dL
- `renal_impairment` (boolean): true when the renal binding factor 0.1 was used
- `binding_factor` (number): 0.2 normally, 0.1 when renal_impairment is true
- `corrected_phenytoin_mcg_ml` (number): Albumin-adjusted total-equivalent phenytoin in µg/mL, 1 decimal
- `citation` (object): Liponi, Winter, and Tozer 1984 citation
- `disclaimer` (string): Not-a-device notice

## Example JSON

Frozen fixture. Not a live lookup.

```json
{
  "disclaimer": "Not a medical device. Deterministic published-formula or published-code output for autonomous agents. A licensed clinician remains responsible for patient care and billing submissions.",
  "citation": {
    "authors": "Liponi DF, Winter ME, Tozer TN",
    "doi": "10.1212/WNL.34.3.395",
    "id": "liponi-1984",
    "source": "Neurology. 1984;34(3):395-397",
    "title": "Renal function and therapeutic concentrations of phenytoin"
  },
  "formula": "sheiner_tozer",
  "formula_expression": "corrected_phenytoin_mcg_ml = phenytoin_mcg_ml / ((binding_factor * albumin_g_dl) + 0.1); binding_factor 0.2, or 0.1 if renal_impairment",
  "albumin_g_dl": 2.0,
  "binding_factor": 0.2,
  "corrected_phenytoin_mcg_ml": 16.0,
  "phenytoin_mcg_ml": 8.0,
  "renal_impairment": false
}
```

## Errors

- HTTP 400 `invalid_phenytoin`: phenytoin_mcg_ml (same as mg/L) must be a number from 0.1 to 80. Returned before settlement; you are not charged.
- HTTP 400 `invalid_albumin`: albumin_g_dl (1-6) or albumin_g_l (10-60) is required Returned before settlement; you are not charged.
- HTTP 400 `invalid_flag`: boolean clinical flags must be true or false Returned before settlement; you are not charged.
- HTTP 400 `invalid_items`: POST body must be a JSON object with only an items array Returned before settlement; you are not charged.
- HTTP 400 `invalid_item_count`: items must be an array of 1 to 25 objects Returned before settlement; you are not charged.
- HTTP 400 `invalid_item`: each items entry must be a JSON object Returned before settlement; you are not charged.

Shared HTTP 402 and 503: https://magentlab.com/docs/payments

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## Payment

Unpaid requests return HTTP 402 even if query parameters or POST items are missing or invalid, so CDP and agents can index the path. After a PAYMENT-SIGNATURE, invalid params return HTTP 400 JSON before settlement. magent does not charge. Fix the params, then request a new 402 quote for that complete URL. Catalog misses (empty matches, found=false) are valid paid 200s.

- GET the tool with Accept: application/json (do not send Accept: text/html unless you want the human paywall).
- HTTP 402 means you have not paid. Decode the base64 PAYMENT-REQUIRED header. HTTP 503 is not a new quote.
- Sign accepts[0] (exact, EIP-3009) with validBefore = now + maxTimeoutSeconds (600 seconds), or accepts[1] (batch-settlement deposit/voucher) on product GET. Ping and POST {items} stay exact. Magent retries transient facilitator 429/5xx before answering.
- Retry the same URL with PAYMENT-SIGNATURE (base64 JSON echoing accepted, payload, and extensions when present).
- Success is HTTP 200 JSON plus PAYMENT-RESPONSE. exact settles before the tool. batch-settlement verifies (and deposit-settles) before the tool and commits the charge after HTTP 2xx. HTTP 503: retry the same PAYMENT-SIGNATURE. Mint a new exact nonce only after a new HTTP 402.

- offered `exact` on eip155:8453: Fixed-price USDC on Base. The buyer authorizes the advertised amount (EIP-3009). magent settles before the tool runs (paymentFlow upfront). extra.assetTransferMethod=eip3009 extra.paymentFlow=upfront.
- offered `batch-settlement` on eip155:8453: Payment-channel vouchers claimed later in batches. Exact stays accepts[0]. Same-path POST {items} is still exact. extra.assetTransferMethod=eip3009 extra.paymentFlow=authorization.

- not offered `upto`: Not offered. Usage-based: buyer authorizes a ceiling, seller settles the actual amount after work. Reserved for a future metered tool. Not for current calculators or code search.

Same-path POST {items} is still scheme exact: one EIP-3009 authorization for GET unit plus $0.002 per extra item. That is not x402 batch-settlement (payment channels / vouchers).

Shared HTTP 402 and 503 table: https://magentlab.com/docs/payments

Stdio MCP (one process per host): https://magentlab.com/docs/mcp

## Guarantees

- HTTP 402 is unpaid, including a missing query. After PAYMENT-SIGNATURE, invalid parameters return HTTP 400 before settlement. You are not charged.
- exact: settlement finishes before the tool (paymentFlow upfront). batch-settlement: verify/deposit before the tool; chargedCumulativeAmount commits after HTTP 2xx. Uncertain or failed settlement fails closed (HTTP 503). Retry the same PAYMENT-SIGNATURE.
- HTTP 402 is unpaid only. Do not sign a second authorization because of a 503.
- Execution is timeout-bounded and concurrency-capped.
- Calculator inputs are stored encrypted for allowlisted operators (Magent Console). They are not in public logs, SSH lookups, catalog, or rollups. Request logs store path without query.