Cetirizine is an antihistamine used to relieve allergy symptoms such as watery eyes, runny nose, itching eyes/nose, sneezing, hives, and itching. It works by blocking a certain natural substance histamine that your body makes during an allergic reaction.
Phenylephrine is an active ingredient that has different uses in over-the-counter medicines. When used as a nasal decongestant, phenylephrine relieves a stuffy nose due to the common cold or other ailments. It  also shrinks the swelling caused by hemorrhoids. Paracetamol  also known as acetaminophen is a pain reliever and a fever reducer. The exact mechanism of action of is not known. Paracetamol is used to treat many conditions such as headache, muscle aches, arthritis, backache, toothaches, colds, and fevers

The combination of this medication , Cetirizine+Paracetamol/Acetaminophen+Phenylephrine is used in the treatment of common cold symptoms.

Mechanism of action
This is a combination of three medicines: Cetirizine, Paracetamol/Acetaminophen and Phenylephrine, which relieves common cold symptoms. Cetirizine is an antiallergic which blocks histamine (a chemical messenger) to relieve allergy symptoms like runny nose, watery eyes and sneezing. Paracetamol/Acetaminophen is an analgesic (pain reliever) and antipyretic (fever reducer). It blocks the release of certain chemical messengers in the brain that are responsible for pain and fever. Phenylephrine is a decongestant which narrows the small blood vessels providing relief from congestion or stuffiness in the nose.

Cetirizine, the active metabolite of the piperazine H1-receptor antagonist hydroxyzine, minimizes or eliminates the symptoms of chronic idiopathic urticaria, perennial allergic rhinitis, seasonal allergic rhinitis, allergic asthma, physical urticaria, and atopic dermatitis. The clinical efficacy of cetirizine for allergic respiratory diseases has been well established in numerous trials.
Phenylephrine is an alpha-1 adrenergic agonist that raises blood pressure,dilates the pupils, and causes local vasoconstriction. Ophthalmic formulations of phenylephrine act for 3-8 hours7 while intravenous solutions have an effective half life of 5 minutes and an elimination half life of 2.5 hours. Patients taking ophthalmic formulations of phenylephrine should be counselled about the risk of arrhythmia, hypertension, and rebound miosis.
Paracetamol Unlike NSAIDs such as aspirin, paracetamol does not appear to inhibit the function of any cyclooxygenase (COX) enzyme outside the central nervous system, and this appears to be the reason why it is not useful as an anti-inflammatory. It does appear to selectively inhibit COX activities in the brain, which may contribute to its ability to treat fever and pain. This activity does not appear to be direct inhibition by blocking an active site, but rather by reducing COX, which must be oxidized in order to function. Paracetamol apparently might modulate the endogenous cannabinoid system in the brain through its metabolite, AM404, which appears to inhibit the reuptake of the endogenous


Absorption: Cetirizine was rapidly absorbed with a time to maximum concentration (Tmax) of about 1 hour after oral administration of tablets or syrup formulation in adult volunteers . Bioavailability was found to be similar between the tablet and syrup dosage forms.
Metabolism: A mass balance clinical trial comprised of 6 healthy male study volunteers showed that 70% of the administered radioactivity was measured in the urine and 10% in the feces after cetirizine administration. About 50% of the radioactivity was measured in the urine as unchanged cetirizine. Most of the rapid increase in peak plasma
radioactivity was related to the parent drug, implying a low level of first pass metabolism.
Cetirizine is metabolized partially by oxidative O-dealkylation to a metabolite with insignificant antihistaminic activity.
Elimination:Mainly eliminated in the urine. Between 70 – 85% of an orally administered dose can be found in the urine and 10 – 13% in the feces 1.

Absorption: Phenylephrine is 38% orally bioavailable. Clinically significant systemic absorption of ophthalmic formulations is possible, especially at higher strengths and when the cornea is damaged
Metabolism:Phenylephrine is mainly metabolized by monoamine oxidase A, monoamine oxidase B, and SULT1A3. The major metabolite is the inactive meta-hydroxymandelic acid, followed by sulfate conjugates. Phenylephrine can also be metabolized to phenylephrine glucuronide.
Elimination: 86% of a dose of phenylephrine is recovered in the urine with 16% as the unmetabolized drug, 57% as the inactive meta-hydroxymendelic acid, and 8% as inactive sulfate conjugates

Acetaminophen/ Paracetamol
Absorption: Acetaminophen has 88% oral bioavailability and reaches its highest plasma concentration 90 minutes after ingestion. Peak blood levels of free acetaminophen are not reached until 3 hours after rectal administration of the suppository form of acetaminophen and the peak blood concentration is approximately 50% of the observed concentration after the ingestion of an equivalent oral dose.
Distribution: Volume of distribution is about 0.9L/kg. 10 to 20% of the drug is bound to red blood cells. Acetaminophen appears to be widely distributed throughout most body tissues except in fat.
Metabolism: Acetaminophen is the major metabolite of phenacetin and acetanilid. It is mainly metabolized in the liver and its metabolism of comprised of 3 pathways: conjugation with glucuronide, conjugation with sulfate, and oxidation through the cytochrome P450 enzyme pathway, mainly CYP2E1, to produce a reactive metabolite . At normal therapeutic doses, NAPQI undergoes fast conjugation with glutathione and is Elimination: Acetaminophen metabolites are mainly excreted in the urine. Less than 5% is excreted in the urine as free acetaminophen and at least 90% of the administered dose is excreted within 24 hours

Side Effects:
Common side effects include:
● Nausea
●Fatigue, Dizziness
●Dryness in mouth
●Allergic reaction