Published: 3 September 2020


Gathering knowledge from adverse reaction reports: September 2020

Published: 3 September 2020
Prescriber Update 41(3): 58–59
September 2020

Adverse reaction reporting is an important component of medicine safety monitoring. Case reports can highlight significant safety issues concerning therapeutic products and their use.

The table below presents a selection of recent informative cases from the Centre for Adverse Reactions Monitoring (CARM) database.

Case detailsa,b Reaction description and data sheet informationb,c

CARM ID: 135306

Age: 87

Gender: Female

Medicine(s): Carbamazepine, rivaroxaban

Reaction(s): Drug ineffective, drug interaction

An 87-year-old patient already taking carbamazepine was prescribed rivaroxaban. While taking rivaroxaban, the patient developed pulmonary emboli.

The interaction between carbamazepine and rivaroxaban is described in both the Tegretol and Xarelto data sheets. Carbamazepine is a potent CYP3A4 inducer and CYP3A4 is one of the main pathways by which rivaroxaban is cleared. Therefore, co-administration may lead to reduced levels of rivaroxaban.

CARM ID: 135633

Age: 42

Gender: Female

Medicine(s): Amphotericin B, gabapentin, methadone

Reaction(s): Cardiac arrest, hyperkalaemia

Following treatment with amphotericin B, the patient experienced hyperkalaemia with subsequent fatal cardiac arrest.

The AmBisome data sheet states that hyperkalaemia has been reported with an incidence of less than 1 percent, and there have been post-marketing reports of cardiac arrest.

CARM ID: 136715

Age: 8

Gender: Female

Medicine(s): Oxybutynin

Reaction(s): Anxiety, fear, hallucination, psychotic disorder, sleep disorder

Shortly after starting oxybutynin, the patient developed anxiety and fear, which then progressed to hallucinations. She was unable to sleep due to the severity of the hallucinations. The symptoms resolved once the medicine was stopped.

The Warnings and precautions section of the Apo-oxybutynin data sheet states that anticholinergic CNS effects (eg, hallucinations, agitation, confusion and somnolence) have been reported. Monitoring is recommended, especially in first few months after initiating therapy or increasing the dose. Anxiety and hallucinations are listed as Undesirable effects.

CARM ID: 136785

Age: Unknown

Gender: Male

Medicine(s): Cetirizine

Reaction(s): Rebound effect

The patient experienced severe itch and hives upon discontinuation of cetirizine.

Rebound pruritus is described in the Warnings and precautions section of the Zista data sheet. Pruritus and/or urticaria may occur when cetirizine is stopped, even if those symptoms were not present before treatment initiation. In some cases, the symptoms may be intense and may require treatment to be restarted. The symptoms should resolve when the treatment is restarted.

CARM ID: 136860

Age: 5

Gender: Male

Medicine(s): Topiramate

Reaction(s): Dyspnoea, metabolic acidosis

While gradually increasing the topiramate dose, the patient experienced heavy breathing. Although clinically well, the patient’s venous blood gas results showed compensated metabolic acidosis.

Metabolic acidosis is described in the Topamax and Topiramate Actavis data sheets. Topiramate inhibits renal carbonic anhydrase resulting in decreased serum bicarbonate levels. If metabolic acidosis develops and persists, consideration should be given to reducing the dose or discontinuing topiramate (using dose tapering).


  1. Only the medicines suspected to have caused the reaction are listed in the table.
  2. The reactions listed in the ‘Case details’ column are coded according to the Medical Dictionary for Regulatory Activities (MedDRA), an internationally used set of standardised terms relating to medical conditions, medicines and medical devices. The reactions listed in the ‘Reaction description’ column are based on what was reported to CARM, and do not always match the MedDRA term.
  3. If the suspect medicine’s brand name is not described in the report to CARM, only the data sheet for the funded medicine is included in the table.

Information about suspected adverse reactions reported to CARM is available on the Medsafe website using the Suspected Medicines Adverse Reaction Search (SMARS).

By selecting the ingredient of a medicine, you can find out:

  • the number of reports and suspected adverse reactions for that ingredient. The suspected reactions are grouped by body system or organs (Summary report)
  • single case reports, listing the medicines involved that contain the ingredient and the suspected adverse reactions (Detail report).
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