VSR-Phenothiazine Preanesthetics

Summary

The video introduces phenothiazine derivatives used as veterinary pre-anesthetic drugs, following an earlier lesson on anticholinergic pre-anesthetics. It focuses mainly on acepromazine, chlorpromazine, triflupromazine, and promazine.

Phenothiazines: Structure and General Effects

Phenothiazines have a three-ring structure: two benzene rings linked by sulfur and nitrogen atoms. The presenter describes them as central nervous system depressants that act on the brain stem and connections of the cerebral cortex.

Their effects include blocking dopamine receptors and catecholamine action at alpha-1 receptors. They also have relatively weak anticholinergic effects. Commonly mentioned phenothiazines include acepromazine, triflupromazine, chlorpromazine, promazine, promethazine, and methotrimeprazine. Promethazine is also described as an antihistamine.

Their principal pre-anesthetic effects are sedation, calming, and reduced motor activity. They can suppress vomiting by antagonizing dopamine-related pathways. At high doses, they may cause extrapyramidal signs such as rigidity, tremors, and catalepsy.

Pulmonary function is generally maintained, although respiratory rate may decrease slightly. Urine production may increase because of blockade of antidiuretic hormone.

Phenothiazines provide no analgesia, though the lecture says they can provide good muscle relaxation and reduce the amount of general anesthetic needed. The presenter cautions against using them for tranquilization in animals undergoing epidural, spinal, or segmental anesthesia.

Acepromazine

Acepromazine maleate is described as a phenothiazine neuroleptic supplied as a yellow, odorless, bitter powder. Its onset is relatively slow: the lecture gives up to about 15 minutes after intravenous administration, with peak effects in 30–60 minutes.

The presenter says phenothiazines should not be used in epileptic animals or animals susceptible to seizures.

Breed caution: The lecture specifically warns that Boxer dogs may be sensitive to acepromazine and says not to use it as a tranquilizer, sedative, or pre-anesthetic in that breed.

Other effects mentioned include bradycardia and changes in blood pressure and heart rate. The presenter also says acepromazine may help counter temperature-related problems but does not explain this point further.

The video refers to a clinical-dose table but does not provide dose values in the spoken subtitles. The presenter advises consulting dose information rather than memorizing it.

Drug Interactions and Precautions

The lecture highlights these potential interactions:

• Organophosphate deworming agents: Do not give acepromazine within one month of worming with an organophosphate agent.
• Quinidine: May add to cardiac depression.
• Antidiarrheal mixtures containing kaolin, pectin, or bismuth subsalicylate, and antacids: May reduce gastrointestinal absorption of oral phenothiazines.
• Propranolol: The presenter warns that blood levels of both drugs may increase when they are given together.
• Procaine: Its activity may be enhanced by phenothiazines.
• Phenytoin: Phenothiazines may reduce its metabolism, according to the lecture.

Other Drugs Discussed

• Chlorpromazine: Described as broadly similar to acepromazine. As an antiemetic, it is said to inhibit apomorphine-induced vomiting in dogs, but not cats. The lecture notes that it is well absorbed after intramuscular injection.
• Triflupromazine: Named as a veterinary pre-anesthetic and shown in a product presentation, but the subtitles provide few specific details.
• Promazine: Described as structurally related to other phenothiazines and functionally similar to chlorpromazine and acepromazine. The lecture says it is absorbed orally in non-ruminants and is approved for use in dogs, cats, and horses.

The presenter mentions tablets and injectable preparations but does not provide a detailed comparison of products or doses.

Speakers and Sources Featured

• Speaker: One unnamed presenter associated with Edu with Channel / EDU VET.
• Sources cited: No external speakers or named references are identified in the subtitles. The video refers to a clinical-dose table and shows medication presentations, but the table’s dose values are not spoken.