Primidone

Buy now to access the full article, existing subscribers login

Sections available in full article Name, Class of drug, Description, Uses, Administration, Routes of administration, Dosage, Pharmocokinetics, Normal, Precautions, Contra-indications, Use with care, Interactions, Adverse reactions, Sources, Publications,
Contributors Dr Kyle Braund BVSc MVSc PhD FRCVS DipACVIM
Synonyms 2-deoxybarbiturate

Name

  • Primidone.

Class of drug

  • Barbiturate derivative.

Uses

Action

  • Raises electrically induced seizure thresholds and alters seizure patterns.
  • The exact mechanism of seizure prevention is unknown.
  • Rapidly metabolized to the active metabolites phenobarbitone Phenobarbital and phenylethamalonamide (PEMA).
  • In dogs the major anti-seizure activity is thought to be due to the phenobarbitone, with some potentiation by PEMA.

Indications

  • Management of seizures Epilepsy: idiopathic.

Adverse reactions

Other reported reactions

  • Acute toxicity includes:
    • Sedation.
    • Ataxia.
    • PU/PD.
    • Nystagmus.
    • Profound tachycardia.
    • Episodic hyperventilation.
    • Anorexia.
  • Hepatotoxicity: associated with the duration rather than daily dose.
  • Histopathological changes after 6 months of therapy include hepatocellular hypertrophy and necrosis, lipidosis, and extramedullary hematopoiesis.
  • If medication is discontinued after this time, these changes will result in hepatic fibrosis with some permanent loss of function.
  • Primidone intoxication associated with concurrent use of chloramphenicol.
  • Dermatitis associated with the use of primidone in a dog:
    • Excessive licking of paws.
    • Alopecia.
    • Pruritus.
    • Scaling.
    • Pigmentation.
    • Ulceration over back, elbows, hocks, face and ears.
  • Biopsy - severe diffuse parakeratotic hyperkeratosis of epidermis and hair follicles, frequently associated with epidermal hyperplasia, dyskeratosis, and intra-cellular vacuolation. Hint of anti-IgG staining.
  • Polyphagia.
  • Personality changes.
  • Sedation and ataxia (often seen early in therapy and may subside with time) may indicate development of toxic serum levels.
  • Chronic therapy may cause hepatic abnormalities:
    • Increase in liver enzymes (ALT, ALP, glutamate dehydrogenase).
    • Decreased serum albumin.
  • Neutropenia, thrombocytopenia, anemia and splenomegaly reported in dogs receiving phenobarbitone therefore potential for these to develop on primidone.

Investigation of adverse reaction

  • Dose reduction or monitoring of serum levels is indicated if any adverse effects are present.
  • Therapeutic serum levels vary with different laboratories but are in the region of 20-40 ug/ml.
  • Chronic therapy; liver enzymes should be monitored at least yearly.

Sample content only, to unlock the full article login or buy now

Loading...