On penicillin levels in young and geriatric subjects

Drug Problems in the Geriatric Patient

Older persons have altered responses to drugs because of physiologic and anatomic changes which influence drug absorption, tissue localization, metabolism, receptor sites, homeostatic adjustments, and excretion. Deteriorating mental and physical faculties produce other untoward, bizarre, or exaggerated effect.

This paper reviews problems in the use of endocrines, antihypertensives, cardiac glycosides, analgesics, psychoactive drugs, antibiotics, antiparkinsonians, iron, anticoagulants, gastrointestinal agents, and ophthalmics and some factors involved in allergenics and drug-induced jaundice.

The elderly also often have problems involving the proper use of drugs, obtaining drugs, or in the improper use of non-prescription drugs. Suggestions are made for the physician and pharmacist to keep these problems to a minimum.

Penicillin dosing for pneumococcal pneumonia

Most textbook authors still endorse penicillin G as the specific antibiotic of choice for pneumococcal pneumonia. However, problems with early precise etiologic diagnosis of pneumonia and the emergence of drug-resistant pneumococci cause penicillin to be seldom used for this purpose today. A third explanation for the infrequent use of penicillin is lack of clear consensus dosing guidelines. Emergence of pneumococci resistant to the newer cephalosporins and concerns about overuse of vancomycin, however, have prompted renewed interest in the development of precise, rapid methods for diagnosis of pneumococcal pneumonia with the implication that penicillin might be used more frequently. We review several issues concerning penicillin dosing: intermittent vs continuous therapy, high dose vs low dose, relationship of dose to resistance, and cost-effective pharmacology. An optimum "high-dose" regimen for life-threatening pneumococcal pneumonia in a 70-kg adult consists of a 3 million unit (mu) loading dose followed by continuous infusion of 10 to 12 mu of freshly prepared drug every 12 h. The maintenance dose should be reduced in elderly patients and in patients with renal failure according to the following formula: dose (mu/24 h = 4+[creatinine clearance divided by 7]). This regimen provides a penicillin serum level of 16 to 20 microg/mL, which should suffice for all but the most highly resistant strains (minimum inhibitory concentration > or = 4 microg/mL). Newer cephalosporins and vancomycin can be reserved for patients with suspected meningitis or endocarditis or for localities in which highly resistant pneumococci are known to be prevalent.

Serum levels of cloxacillin and benzylpenicillin in adults undergoing open-heart surgery

Serum levels of cloxacillin and benzylpenicillin were monitored in 35 consecutive adult patients undergoing elective open-heart surgery. Serial serum samples were analyzed during a 24-hour period. After oral intake of cloxacillin and phenoxymethylpenicillin on the preceding evening, very low concentrations remained in serum at the start of operation. Such preoperative medication is inappropriate. Intravenously administered cloxacillin (2 g) and benzylpenicillin (3 g) appeared to be adequate during the first 4 hours of surgery, as the serum half-life of the drugs was twice as long in the patients as in healthy adults, but repetition of the doses is recommended for further antibiotic protection during surgery.

Pharmacokinetic properties of mezlocillin in ambulatory elderly subjects

Twelve healthy ambulatory elderly subjects (mean age, 73-78 years) randomly received either a 4-g or 5-g dose of mezlocillin intravenously. One week later the regimen was repeated and patients crossed over to the other dose. Peak serum concentrations were 165 mg/L and 281 mg/L for the 4-g and 5-g doses, respectively. For both doses, differences in t1/2 beta (1.32 hr vs 1.13 hr), AUC (275 mg.hr/L vs 403 mg.hr/L), CL (207 mL/min vs 174 mL/min), CLR (59 mL/min vs 45 mL/min), CLNR (152 mL/min vs 130 mL/min) were not statistically significant. The differences in Varea (22.4L vs 168.8L, P less than or equal to .01) and Cmax (216.6 mg/L vs 317 mg/L, P less than or equal to .05) were statistically significant. Comparison with pharmacokinetic parameters obtained in younger subjects following the 5-g dose reveals that in the elderly the AUC, Varea, and CLNR are higher whereas the CL and CLR are lower. The elderly demonstrated an increase in nonrenal clearance compared with young subjects that is not fully compensatory. The increased AUC in the elderly group suggests that clinical studies examining mezlocillin doses and dose intervals in the treatment of serious infections are warranted in infected elderly patients.

Single-dose pharmacokinetics of dicloxacillin in healthy subjects of young and old age

Dicloxacillin was administered as 2 g single intravenous doses to healthy young and old subjects of both sexes aged 19-32 years and 65-76 years, respectively, and the pharmacokinetics were studied. Peak serum concentrations were higher in young than in elderly subjects and in each age group in females than in males. The elimination rate was similar in all groups and the only striking pharmacokinetic differences observed were that the urinary recovery of active dicloxacillin was higher in young subjects and that the non-renal clearance was higher in elderly volunteers. The findings were interpreted to be due to a systemic metabolism of dicloxacillin, compensating for a reduced renal elimination in the elderly subjects. In all subjects dicloxacillin was well tolerated. No increases of serum creatinine were observed.

Drug distribution and renal excretion in the elderly

Drug responsiveness in the elderly often differs from that in younger individuals. A causative factor is often thought to be age-related changes in the quantitative fashion in which the body handles the drug. It is speculated that changes in body size, composition, and tissue perfusion lead to differences in drug distribution. The limited supportive evidence for this is reviewed, along with the practical consequences in drug therapy. More definitive data is presented on the age-related impairment of renal function and its effects on the urinary elimination of drugs and metabolites. Methods are presented to permit rationale dosage regimen modifications for elderly patients with reduced renal function.

Zimelidine to geriatric patients: a pharmacokinetic and clinical study

To evaluate the clinical efficacy, tolerance and pharmacokinetic properties of zimelidine in elderly people, twelve hospitalized depressed patients with a mean age of 80 years were included in a clinical trial. Zimelidine was administered twice daily at a dose of 50 mg during the first week, 75 mg during the second week and 100 mg during the third to sixty week. The patients also received a single oral test dose of 75 mg of zimelidine during an initial placebo week. All patients that completed the study improved according to the rating scales used. The drug was well tolerated, and adverse reactions were few and of mild or moderate severity. No influence of clinical importance was noted on hematology, liver and kidney functions, ECG, blood pressure or pulse rate. The mean elimination half-lives of zimelidine and norzimelidine were found to be 15 h and 35 h, respectively, which were longer than the half-lives earlier obtained in younger patients. The blood levels (AUC) in the geriatric patients were about twice those obtained earlier in healthy volunteers. The AUC values for both zimelidine and norzimelidine increased in close proportion to the increase in dose and, thus, the pharmacokinetics of zimelidine was apparently not dose-dependent in the dose interval used. The results obtained may indicate a reduction in the rate of metabolism for zimelidine in the elderly, possibly combined with increased total bioavailability of the drug. A reduction of the regular zimelidine dose may be recommended in the treatment of elderly patients.

Kinetic study of serum penicillin concentrations after single doses of benzathine and benethamine penicillins in young and old people

In a comparative kinetic study of the serum concentrations of two penicillin complexes--medium-long-acting (benethamine penicillin) and long-acting (benzathine bipenicillin)--after a single injection in young adults and elderly people, the following results were confirmed statistically: (a) age was a major factor in the variations in serum penicillin concentrations and in their persistence in the serum; (b) the penicillin was absorbed faster in young than in elderly subjects even when a long-acting complex was used; (c) serum concentrations below the level regarded as lethal for treponemes appeared much earlier and more frequently in young than in old people; and (d) the bioequivalence between penicillin preparations could not be estimated solely for the number of units of the agent used but from the bioavailability of the chosen formulation. Thus a uniform and standard penicillin dosage allowing no safety margin may help in the superficial healing of a syphilitic chancre or the resolution of a roseola but it will certainly be insufficient to kill Treponema pallidum. It seems essential therefore to provide an antibiotic cover at high dosage over a long period of time.

Pharmacokinetics in the elderly

The elderly are generally considered to be different from young people in terms of drug response and this applies particularly to quantitative differences. While altered drug handling is a major potential source of difference in responsiveness to drugs, the relative contribution of pharmacokinetics and pharmacodynamics to this difference is not clear. In the present review we have examined the available data on pharmacokinetics in the elderly. In the past, data pertaining to animal models have been extrapolated to man and in the absence of human experimentation these assumptions have tended to hold sway. This is best exemplified by studies on drug absorption. The absorption of actively transported substance may in fact be diminished in the elderly. However, most drugs are absorbed by passive diffusion and the recently available evidence in man indicates that there is no age-dependent change. While definitive data on the effect of old age on drug metabolising ability in animals is available, no direct assessments have been made in man. Many of the studies carried out using drug plasma half-life and clearance assessments are complicated by changes in distribution. This is best illustrated by a definitive study with diazepam, in which marked prolongation of plasma half-life was accompained by an increase in apparent volume of distribution in the elderly. This latter change influences plasma drug clearance and, possibly, drug concentration at its site of action. Thus, the implications for drug effect of such changes in volume of distribution remain to be clarified. In theory, the rate of elimination of antipyrine should provide a good index of drug metabolising ability. Both plasma half-life and clearance values suggest a decreased in metabolism in the elderly. No other drug has been studied as intensively and the evidence for a diminished metabolism of other drug in the elderly is less definite. Thus, while it is likely that the metabolism of some drugs is imparied in old age, it is not possible at this time to generalise with regard to the effect of age on drug metabolising ability in man. It is also difficult to generalise about age-related changes in plasma protein binding of drugs. With some drugs, binding to plasma protein does not appear to be altered and for two drugs-warfarin and phenytoin, the findings of different investigators conflict. Diminution of glomerular filtration rate, renal plasma flow and associated tubular function with age have been well documented. Drug clearance comparisons between old and young have been carried out for only three renally excreted drugs-digoxin, propicillin and sulphamethizole. With digoxine and sulphamethizole, the evidence is that renal excretion is diminished in the elderly. With propicillin, changes in volume of distribution predominate, resulting in higher plasma levels in the elderly but similar percent recovery in urine...