Prepositions in the prescription

Basics of case governance

Latin prepositions (Praepositiones) are unchangeable function words. In medical and pharmaceutical terminology, they are never used arbitrarily or randomly. The strict grammatical rule states that each preposition requires the dependent word following it to be in a strictly defined case.

Unlike Russian, where there are many options for governance, Latin prepositions work exclusively with two cases:

• Accusativus (accusative case);
• Ablativus (ablative case, combining the functions of the Russian instrumental and prepositional cases).

A crucial nuance for study: you cannot rely on intuition. Case governance in our languages often diverges, so the combination of "preposition + required case" must be memorized immediately along with the dictionary meaning.

Prepositions with strict governance

Most prescription prepositions require the use of only one specific case. This is a static rule that does not depend on the context of the phrase.

The following prepositions are consistently used with the accusative case (Accusativus):

• ad (up to, for, at): ad 20,0 (up to 20 grams), ad usum internum (for internal use), ad decubitum (for pressure ulcers);
• contra (against): contra tussim (antitussive agent);
• inter (between): inter costas (between the ribs);
• per (through, by means of): per os (orally, by mouth), per inhalationem (by inhalation);
• post (after): post mortem (after death, post-mortem).

Another group of prepositions is used with the ablative (Ablativus):

• cum (with someone or something): cum extracto (with extract);
• ex (from): ex aqua (from water);
• pro (for): pro injectionibus (for injections).

Prepositions with double government

The prepositions in (in, on) and sub (under) present a special difficulty when writing prescriptions. They can govern two cases at once. The choice of grammatical construction depends entirely on the question asked of the noun according to the meaning of the action:

1. If the action indicates direction (we ask the question Where to? Into what?), Accusativus is used.
2. If the action indicates location (we ask the question Where? In what?), Ablativus is used.

Let's examine the difference with classic examples:

• To place in vitrum (translated as "into a vial", direction, where to?) — Accusativus is used.
• To store in vitro (translated as "in a vial", location, where?) — Ablativus is used.
• To place sub linguam (under the tongue, where to?) — Accusativus.
• Located sub lingua (under the tongue, where?) — Ablativus.

Professional prescription expressions

Fixed clichés with prepositions are constantly encountered in prescriptions and daily medical documentation. Students must know them by heart.

Expressions with prepositions EX and PER:

• ex tempore — as required (so-called extemporaneous prescription, when the medicine is prepared in the pharmacy before dispensing);
• per rectum — through the rectum (rectal administration);
• per se — in pure form (substance without added impurities).

Names of dosage forms (IN + Ablativus): Most often, the preposition in answers the question "in what?":

• in ampullis — in ampoules;
• in capsulis — in capsules (and in capsulis gelatinosis — in gelatin capsules);
• in tabulettis — in tablets (and in tabulettis obductis — in coated tablets).

Laboratory and clinical terms:

• in vitro nigro — in a dark vial (for protection from light);
• in vitro — in a test tube (in laboratory conditions, outside the organism);
• in vivo — in a living organism.

Prescriptions and dosages (PRO + Ablativus): The preposition pro is often used to indicate the recipient of the drug or its volume:

• pro infantibus — medicine for children;
• pro inhalatione — for inhalation;
• pro narcosi — for anesthesia;
• pro r(o)entgeno — for X-ray examination.

Terms for dosing are distinguished separately: pro dosi (single dose per administration) and pro die (total daily dose for the day). If a physician writes a prescription personally for themselves, they replace the patient's surname with the standard formula pro auctore (for the author) or pro me (for me).

Class and exam questions

What else to study on this topic

• Noun endings in Accusativus after the prepositions ad, per, and post
• Noun endings in Ablativus after the prepositions ex, cum, and pro
• Grammatical agreement of adjectives in the expressions in capsulis gelatinosis and in tabulettis obductis
• Differences in the clinical application of the terms in vitro and in vivo

Other topics in the section "Accusativus and Ablativus. Prepositions. Prescription. Prescription Line"

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.