Of 5,125 mostly elderly out-patients, average age 78.2 years, 1,594 (31%) had at least one interacting drug combination according to the Swedish National Formulary. On average, each patient with drug-drug interactions (DDIs) had 1.6 DDIs. There was no difference in the sex or age between those having DDIs and those without. However, patients with one or more DDIs used a significantly larger number of drugs than those without DDIs, on average 8.1 versus 5.2. This significant difference was independent of age and sex. When classified for clinical significance according to the handbook "Drug Interactions and Updates" by Hansten and Horn, 155 (3%) patients had interactions of 'major clinical significance'. The most common were interactions between beta-adrenergic blockers and antidiabetics, followed by potassium-sparing diuretics and potassium, and carbamazepine and dextropropoxyphene. The methodology allows us to screen routinely for DDIs and to plan further studies with emphasis on clinical outcome.

1 Eight healthy subjects received 50, 100, 300, 600 and 900 mg allopurinol daily for 1 week each, in random order with 1 week separating each treatment period. The pre-dose plasma concentration of oxypurinol, the extent of inhibition of xanthine oxidase, plasma urate concentration and urine urate excretion rate were assessed on the last 2 days of each treatment week. 2 The ratio of 1-methyluric acid ( 1MU) over 1-methylxanthine (1MX) in the urine, following a dose of 50 mg 1MX infused intravenously over 20 min, was used to measure the inhibition of xanthine oxidase. 3 The steady-state plasma concentration of oxypurinol increased linearly with increasing dose of allopurinol between 50 mg to 600 mg day−1, with a weak indication of saturation at the higher 900 mg day−1 dose rate. 4 The relationships between plasma oxypurinol concentration and xanthine oxidase inhibition ( 1MU/1MX ratio), plasma urate concentration and urine urate excretion rate were fitted to an inhibition sigmoid E max model and the C 50 values for oxypurinol were 26.38±4.87, (mean±s.d.) 36.58±8.36 and 24.61±9.08 m, respectively. 5 1MU/1MX ratio appeared to be a reliable index of xanthine oxidase activity in vivo as the C 50 for oxypurinol observed for 1MU/1MX ratio, plasma urate concentration and urine urate excretion rate were similar. 6 The concentration of oxypurinol required for inhibition of xanthine oxidase, as indicated by C 50 , was lower than those often observed in clinical practice.

In hospitalised patients a significant overuse of AST was observed, particularly among pulmonary patients. More adequate use of AST can contribute to substantial savings for the health-care system.

A descriptive study of national sales data from Sweden to find out the effect of over-the-counter (OTC) switches on total sales of a number of drugs. During the period 1980-94, 16 drugs were changed from prescription only (Rx) status to the Swedish OTC market. Total sales increased for 14 out of these 16 drugs. The increase was seen soon after the change to OTC status. Two years after the change an average increase of 36% was seen. In the following 2 years, the increase was typically very modest (average 1%). Large differences in the changes were seen for the individual drugs. The prescription of OTC packs decreased on average by 26% during the first 2 years after the switch. Converting this decrease in sales in terms of number of packs no longer prescribed led to an estimated yearly saving of SEK 200 million ($US 30 million) for the national drug budget. Taking account of the total increase in defined daily doses (DDDs) 2 years after the change for those 16 drugs led to an estimated yearly saving of SEK 2.5 billion ($US 400 million).

This study has shown that the combination of CBZ and dextropropoxyphene is hazardous in elderly patients and should be used with caution.