WHAT ARE THE BEERS CRITERIA?
The Beers criteria are a list of potentially dangerous medications that should be avoided, or used with caution, in geriatric patients. The list is also used to assess and evaluate inappropriate prescribing patterns. The Beers criteria were updated in 2003, and a severity rating (low or high) was assigned to each medication or drug class.
The updated Beers Criteria are comprised of two lists: medications that should generally be avoided in older adults (65 years or older) and medications that should be avoided in older adults known to have a specific medical condition. For example, long-acting or high doses of benzodiazepines should rarely be prescribed to a geriatric patient. The severity rating is high due to the concern for oversedation, extended medication half-life, and the potential increased risk of falls. The authors also advise against prescribing certain selective serotonin reuptake inhibitors (SSRIs) to geriatric patients with hyponatremia, as these drugs may exacerbate or cause a syndrome of inappropriate antidiuretic hormone (SIADH). This recommendation is given a low severity rating.
The complete Beers Criteria with updated recommendations are available online at the Archives of Internal Medicine.1
CAN YOU EXPLAIN TIME-
DEPENDENT VERSUS CONCENTRATION-DEPENDENT KILLING OF BACTERIA?
Antibiotics may be classified as having either concentration-dependent or time-dependent effects. The dose, frequency of administration, and efficacy of antibiotics rely on these characteristics. Two commonly studied concentration-dependent antibiotic classes are the aminoglycosides and fluoroquinolones. The beta-lactam antibiotics (for example penicillins) and vancomycin (Vancocin, generics) are time-dependent killers.
Time-dependent killing of bacteria means that a certain amount of time above the minimum inhibitory concentration (MIC) is required for an antibiotic to be effective. The MIC is the lowest concentration of a drug that inhibits bacterial growth. Once the MIC is reached, increasing the dose of the antibiotic does not result in enhanced antimicrobial effect. Time-dependent drugs should be dosed in such a frequency that concentrations remain above the MIC for most of the dosing interval. Continuous infusion of antibiotics [such as piperacillin/tazobactam (Zosyn, generics)] is based on the principle that maximizing time above the MIC will increase efficacy.
In contrast, antibiotics that exhibit concentration-dependent killing of bacteria rely on high concentrations and a postantibiotic effect (PAE). Antimicrobial activity increases with progressively higher antibiotic doses, and concentrations will reach well above
the MIC. A PAE effect occurs when stunting of bacterial growth persists after the antibiotic has been cleared from the system. This is the rationale behind once daily dosing of aminoglycosides. A high peak concentration and a PAE allow for infrequent dosing.
To summarize, the goal for time-dependent antibiotics is to maximize the time above the MIC. This may be obtained with frequent dosing intervals or continuous infusions. The goal for concentration-dependent antibiotics is to achieve high peak concentrations, while avoiding toxicity. With a once-daily aminoglycoside dosing schedule, the trough concentrations are often undetectable. Dosing nomograms may prove helpful.
HOW SHOULD METOPROLOL BE DOSED WHEN CHANGING FROM THE IMMEDIATE-RELEASETO THE EXTENDED-RELEASE FORM?
When changing dosage forms from immediate-release metoprolol (metoprolol tartrate, Lopressor, generics) to extended-release metoprolol (metoprolol succinate, Toprol XL, generics), use the same total daily dosage. For example, if a patient is taking metoprolol immediate-release 50 mg orally twice a day, then the corresponding metoprolol extended-release dosage would be 100 mg orally once a day.
A common error is to change a person from metoprolol tartrate (immediate-release) 50 mg orally twice a day to metoprolol succinate (extended-release) 50 mg once daily. If you are unsure about equivalent dosing of drugs, your hospital pharmacy or a local retail pharmacy should be able to help. Note that the Institute for Safe Medication Practices recommends against using the abbreviations IR and ER (for immediate-release and extended-release) because they could be overlooked or misread. JAAPA
Larissa DeDea, PharmD, BCPS, PA-C, completed a pharmacy practice residency at Gallup Indian Medical Center, Gallup, New Mexico, and has worked on the Navajo Reservation as a pharmacist for the Public Health Service. In addition to being board certified in pharmacotherapy, she is a recent graduate of the Yale University PA Program.
REFERENCE
1. Fick DM, Cooper JW, Wade WE, et al. Updating the Beers criteria for potentially inappropriate medication use in older adults: results of a US consensus panel of experts. Arch Intern Med. 2003;163(22):2716-2724.