A sedative (subhypnotic) dose of a barbiturate should be expected to produce which of the following?

Correct answer: A. A decrease in basal metabolic rate

• A. CORRECT. At a SEDATIVE dose, barbiturates depress the reticular activating system and reduce overall metabolic activity, lowering the BASAL METABOLIC RATE along with a mild reduction in body temperature. This is a predictable, dose-related CNS-depressant effect that occurs well below anesthetic doses.
• B. Barbiturates have NO analgesic property. Worse, at low doses they are ANTANALGESIC (hyperalgesic) — they can lower the pain threshold and make an unmedicated patient more responsive to painful stimuli. This is a classic board point and the reason barbiturates are never used alone for a painful procedure.
• C. Skeletal muscle relaxation occurs only at anesthetic concentrations; true paralysis requires a neuromuscular blocking agent.
• D. Clinically significant respiratory depression is a feature of HYPNOTIC and ANESTHETIC doses, not sedative doses. Barbiturates are dangerous precisely because that margin is narrow and the dose-response curve is steep, but a sedative dose alone should not depress respiration markedly.

Note: ⚑ Flag for the group — this item is written ambiguously and different recall keys answer it differently. The reliably testable facts are: barbiturates are ANTANALGESIC at low dose, they induce hepatic CYP450 (drug interactions), they are contraindicated in PORPHYRIA, and they have a low therapeutic index with no reversal agent — which is why benzodiazepines replaced them for dental sedation.