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Do expired drugs get more toxic?

Q - Many are drugs commonly hoarded by patients for future use. Do drugs become less effective with age? Do any become more toxic with age?

A - Medications frequently kept for future use include analgesics, antihistamines, indigestion remedies and antibiotics. Some do not have expiry dates, bearing only the date of dispensing.

Before marketing, stability tests are performed on drugs in the same containers in which they are to be sold. The expiry date identifies the period during which a preparation will maintain its labelled potency when stored as recommended. Some suspensions of antacids separate with a precipitate at the bottom and just require shaking. Once opened, fermentation in medicines containing sugars can occur.

Once a bottle of GTN is opened the active agent evaporates, the tablets become inactive and provide no relief of symptoms.

The bottle and its contents must be discarded after eight weeks and a new prescription dispensed. As an added safeguard, the tablets should be supplied in glass containers, closed with a foil-lined cap and contain no cotton wool wadding.

Tetracyclines, with the exception of doxycycline, worsen renal function in patients with renal impairment. Tetracycline undergoes oxidation in humid conditions to products which are more nephrotoxic. Citric acid, which was in tetracycline products to improve absorption, further enhanced degradation of tetracycline.

Tetracycline products have since been reformulated, and few reports of Fanconi syndrome have recently been reported.

Dr Richard Pearson, consultant physician in clinical pharmacology, Harold Wood and Oldchurch Hospitals, Essex

Symptoms subside after the drug is stopped.

Initial symptoms include frequent urination, lethargy and progressive weakness.

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