Codeine Phosphate: What is it? Formula, Presentation, Indications, Mechanism of Action, Dosage, Side Effects and Interactions

It is an alkaloid obtained from opium or prepared from morphine by methylation and occurs as white crystals.

Codeine is a pain reliever that is sometimes called a narcotic. Its active ingredient is found in many different medications that treat pain and cough.

Codeine phosphate is an analgesic that although it is related to morphine, its analgesic properties are less powerful and its sedative effects are milder.

Chemical formula

  • C18H24NO7P.


Codeine phosphate is available in the form of tablets and syrup.

Each tablet contains 30 mg or 60 mg of codeine phosphate, lactose, and sucrose.

Indications of codeine phosphate

Codeine phosphate is a natural phenanthrene alkaloid and opioid agonist with analgesic, antidiarrheal, and antitussive activities.

Codeine phosphate is an analgesic indicated for the relief of mild to moderate pain.

Mechanism of action

The drug works by blocking responses to pain, suppressing the cough reflex, and causing drowsiness.

Codeine mimics the actions of endogenous opiates by binding to opioid receptors at many sites within the central nervous system.

Stimulation of opioid receptors results in decreased release of nociceptive neurotransmitters such as substance P, GABA, dopamine, acetylcholine, and norepinephrine.

In addition, morphine, the metabolite of codeine, induces the opening of rectifying potassium channels internally coupled to G protein and blocks the opening of N-type voltage-gated calcium channels, resulting in hyperpolarization and reduced neuronal excitability.

Stimulation of opioid receptors of the intestinal mu subtype produces a reduction in intestinal motility and delays intestinal transit times.

Antitussive activity is mediated by the action of codeine in the cough center in the medulla.


The dose of codeine phosphate should be adjusted according to the intensity of pain and the response shown by the patient.

In adults: 15 to 60 mg every 4 to 6 hours (usual adult dose, 30 mg).

In children: 1 year of age and older a dose of 0.5 mg / kg of body weight every 4 to 6 hours.

Side effects of codeine phosphate

The most common side effects of codeine include:

  • Daze.
  • Dizziness.
  • Nausea.
  • Threw up.
  • Short of breath.
  • Sedation.
  • Allergic reactions.
  • Constipation .
  • Abdominal pain.
  • Eruption.
  • Itch.

Serious side effects of codeine include:

  • Life-threatening respiratory depression.
  • Severe low blood pressure .
  • Suprarrenal insufficiency.

Accidental ingestion of codeine can lead to fatal overdose

Warnings and Contraindications

Codeine should not be given if you are allergic to it or to some of the ingredients of the drug or if you have trouble breathing.

If you experience any of the following symptoms after starting treatment, you may be allergic to the medicine and should see a doctor immediately:

Before taking the medicine, you should tell your doctor if you have:

  • He is a patient at special risk: Codeine should be administered with caution to certain patients, such as the elderly or the debilitated and those with hypothyroidism, Addison’s disease, and prostatic hypertrophy or urethral stricture.
  • Renal or liver dysfunction: Codeine phosphate may have a prolonged cumulative effect in patients with kidney or liver dysfunction.
  • Problems with the stomach or intestines, including a blockage in the intestinal tract and an inflammatory bowel disease: Administration of codeine or other narcotics may obscure the diagnosis or clinical course in patients with acute abdominal conditions.
  • A recent head injury and increased intracranial pressure: The respiratory depressant effects of narcotic drugs and their ability to raise cerebrospinal fluid pressure may be markedly exaggerated in the presence of head injuries, other intracranial injuries, or a pre-existing increase in intracranial pressure.

In addition, narcotics produce adverse reactions that can obscure the clinical course in patients with head injuries.

Codeine phosphate can disturb the mental and physical capacities of the patient and that are required for the performance of tasks, such as driving a vehicle or operating machinery that could be potentially dangerous.

Animal reproduction studies have not been performed with codeine phosphate. It is also not known whether codeine phosphate can cause fetal harm when administered to a pregnant woman or whether it can affect the ability to reproduce.

Based on the historical use of codeine phosphate during all stages of pregnancy, there is no known risk of fetal abnormality. Codeine phosphate should be given to a pregnant woman only if clearly necessary.

The use of codeine phosphate in obstetrics can prolong labor.

It is also known that it crosses the placental barrier, being able to produce respiratory depression in the newborn, it may even be necessary to administer naloxone for resuscitation in cases of severe depression.

Codeine passes into the milk of nursing mothers, caution should be exercised when administered to a nursing woman.

Codeine phosphate interactions

Codeine in combination with other narcotic pain relievers, general anesthetics, phenothiazines, tranquilizers, sedative-hypnotics, or other central nervous system depressants (including alcohol) have additive depressant effects.

The doses of combination therapy with these drugs should be reviewed and reduced.