Class: Medication

Description of: Medication

Class steward is Orders/Observation
Medication is an indirect care-intervention using a material substance as a therapeutic agent. The effect of the therapeutic substance is typically established on a biochemical basis, however, that is not a requirement. For example, radiotherapy can largely be described in the same way, especially if it is a systemic therapy such as radio-iodine. Whether or not radiotherapy will be covered by a separate class is open.

Medication as a service indicates the administration of a generic class of medication to a patient. The administration of a particular preparation (in the U.S. typically represented by NDC code) requires the association of the material class with the Medication service. The material information is usually added to the order by the pharmacist when the prescription is filled as a revision or substitution to the original order.

Because medication deploys material substances, a number of attributes arguably pertain to the material rather than the medication action. Therefore, some information may be representable in two ways: as attributes of the medication service or as attributes of the material. This is especially obvious with the kind of substance applied. For example, an Amoxicillin treatment is usually described as Medication.type_cd = Amoxicillin; however, it could also be described as Medication.type_cd = administer with an associated Material target of type Amoxicillin. At this point naming the Service Action after the generic administered substance is the preferred strategy.

This design allow simple medications to be described without having to use the Material class. Only if such actions as dispensing, or such information as the manufacturer are relevant, or if a recipe prescription is written, should one have to deploy the Material class.

Attribute definitions for: Medication

dose_check_qty :: PQ

This attribute should not generally be used, it is only provided for a special purpose. In some countries, especially Japan, there is a regulatory requirement to note the total daily dose on the prescription and associated documentation. The purpose of this requirement obviously is to encourage and facilitate reviewing the total dose prescribed to avoid over- (or under-) dosage. Rather than to define a "total daily dose" attribute as HL7 v2.3 did, we define this general purpose dose_check_qty attribute that can be used in various ways as required by local business rules or regulations. For example, in Japan one would use this field as a total daily dose by calculating the "real" dose as noted above and then adjusting the denominator to 1 d. For example, with Erythromycin 250 mg 1 tablet 3 times a day one can calculate the total daily dose as

dosis_check_qty = dosis_qty (1) * strength_qty (250 mg) * frequency (3 /d) = 750 mg/d.

For the i.v. example above this term would be

dosis_check_qty = dosis_qty (100 ml) * strength_qty (1) / rate_qty (1 h) = 100 mL/h

which can be calculated on a daily basis as

dosis_check_qty = 100 mL/h * 24 h/d = 2400 mL/d = 2.4 L/d.

So, in Japan, the denominator of the dosis_check_qty unit must always be 1 /d. In other countries the constraints on the dosis_check_qty may be different or, most likely, the attribute would not be used at all. In any case this dosis_check_qty attribute must not be used to carry any functional information.

dose_qty :: PQ

The dose is the amount of the therapeutic agent given at one administration event. This attribute can be used all by itself, or in combination with a strength. In theory, a physician’s prescription could suffice with just the dose specification. For example, if Azythromycin is to be given at 80 mg once a day for three days, there is no need to specify a strength. The pharmacist can figure out the right preparation given what is available in stock or on the marketplace. When the pharmacist dispenses a particular preparation with a particular strength and packet size from a particular manufacturer, etc., this detail should be communicated using the Material class.

form_cd :: CD

The dose form of the therapeutic substance. Examples are tablet, capsule, suppository, etc.

OpenIssue: This field must have a mandatory HL7 table for interoperability purpose. Such a table could cover at least 90% of all cases.

rate_qty :: PQ

With continuously divisible dose forms (e.g., liquids, gases) a dose rate can be specified. The Medication.rate_qty is specified as a physical quantity in time (a duration.) Hence, the rate_qty is really the denominator of the dose rate. For example, if an Ringer solution is to be given at 100 mL/h i.v., the dosis_qty would be 100 mL and the rate_qty would be 1 h. Note that there is no difference in the actual values of dosis_qty and rate_qty as long as the quotient of both has the same value. In this example, we could just as well specify dosis_qty as 50 mL and rate_qty as 30 min, or 200 mL and 2 h or any other combination where the quotient equals 100 mL/h.

Note that in principle one could again suffice with just the dosis_qty attribute specifying the rate right in that one attribute (e.g., dosis_qty = 100 mL/h.) However this practice is not allowed. Systems that implement the semantics of units according to the Unified Code for Units of Measure would have no problem noting the fact that a dose_qty is really a rate. Other system however will have difficulties to tell an at-once dose from a dose rate from just looking at the units. If a system wishes to deal only with a single quantity describing the dosage, it can always calculate such a quantity as

real_dosis_qty = dosis_qty x strength_qty / rate_qty.

route_cd :: CD

The route of the medication. Medication route is similar to an anatomic body site through which the therapeutic agent is incorporated or otherwise applied to the body. It is an open issue whether a specialized route_cd could be replaced by a general anatomic site code. The typical routes are per os (PO), sublingual (SL), rectal (PR), per inhalationem (IH), ophtalmic (OP), nasal (NS), otic (OT), vaginal (VG) , intra-dermal (ID), subcutaneous (SC), intra-venous (IV), and intra-cardial (IC).

However, as the table below suggests there are other routes and there are many variations as to how to access a specific route. For instance, an oral administration with the patient swallowing will usually have the same effect as if the same substance is given through a gastric tube. A more systematic approach to analyze the route into components such as site of primary entry (e.g. oral, nasal), site/system of substance uptake (e.g. gastrointestinal, bronchial, nasal mucosa), method (e.g., swallow, inhale), and device (e.g., gastric tube, tracheal tube) should be considered. At this point the version 2.x code table is used.

strength_qty :: PQ

The strength of a medication is the amount of therapeutic agent per each unit of administration (entitic mass, amount of substance, etc.) If the dose form is continuously divisible (e.g., liquid, gas), the strength is a concentration (volumic mass, amount of substance, etc.)

We generally discourage using this attribute, because in theory, a physician’s prescription could suffice with just the dose specification. For example, if Azythromycin is to be given at 80 mg once a day for three days, there is no need to specify a strength. The pharmacist can figure out the right preparation given what is available in stock or on the marketplace. When the pharmacist dispenses a particular preparation with a particular strength and packet size from a particular manufacturer, etc., this detail should be communicated using the Material class.

When the strength attribute is used, the actual administered amount is the product of dose_qty and strength_qty.