ate treatment is essential in the management of paracetamol overdose. Despite a lack of significant early symptoms, patients should be referred to hospital urgently for immediate medical attention. Symptoms may be limited to nausea or vomiting and may not reflect the severity of overdose or the risk of organ damage. Management should be in accordance with established treatment guidelines, see British National Formulary (BNF) overdose section.
Treatment with activated charcoal should be considered if the overdose has been taken within one hour. Plasma paracetamol concentration should be measured at four hours or later after ingestion (earlier concentrations are unreliable). Treatment with N-acetylcysteine, may be used up to 24 hours after ingestion of paracetamol, however, the maximum protective effect is obtained up to eight hours post-ingestion.
The effectiveness of the antidote declines sharply after this time. If required the patient should be given intravenous N-acetylcysteine, in line with the established dosage schedule. If vomiting is not a problem, oral methionine may be a suitable alternative for remote areas, outside hospital. Management of patients who present with serious hepatic dysfunction beyond 24 hours from ingestion should be discussed with the National Poisons Information Service (NPIS) or a liver unit.
GUAIFENESIN
Symptoms and signs
Very large doses of guaifenesin cause nausea and vomiting.
Treatment
Vomiting would be treated by fluid replacement and monitoring of electrolytes if indicated.
PHENYLEPHRINE HYDROCHLORIDE
Symptoms and signs
Phenylephrine overdosage is likely to result in effects similar to those listed under adverse reactions. Additional symptoms may include hypertension and possibly reflux bradycardia. In severe cases confusion, hallucinations, seizures and arrhythmias may occur. However the amount required to produce serious phenylephrine toxicity would be greater than required to cause paracetamol-related toxicity.There have been rare reports of allergic reactions.
Treatment
Treatment should be as clinically appropriate. Severe hypertension may need to be treated with an alpha blocking drug such as phentolamine.
5. Pharmacological properties
5.1 Pharmacodynamic properties
Pharmacotherapeutic Group:
ATC code:
Other analgesics and antipyretics &
Other cold combination preparations
N02B E51
Paracetamol is an analgesic and antipyretic.
Guaifenesin is an expectorant.
Phenylephrine Hydrochloride is a sympathomimetic decongestant.
The active ingredients are not known to cause sedation.
5.2 Pharmacokinetic properties
Paracetamol is rapidly absorbed from the gastrointestinal tract. It is metabolised in the liver and excreted in the urine, mainly as the glucuronide and sulphate conjugates.
Guaifenesin is rapidly absorbed after oral administration. It is rapidly metabolised by oxidation to β-(2 methyoxy-phenoxy) lactic acid, which is excreted in the urine.
Phenylephrine hydrochloride is irregularly absorbed from the gastrointestinal tract and undergoes first-pass metabolism by monoamine oxidase in the gut and liver; orally administered phenylephrine thus has reduced bioavailability. It is excreted in the urine almost entirely as the sulphate conjugate.
5.3 Preclinical safety data
Precl
