Drug therapy: drug disposition in old age

Disposition of clotiazepam: influence of age, sex, oral contraceptives, cimetidine, isoniazid and ethanol

Factors influencing the disposition of clotiazepam in man were evaluated in a series of pharmacokinetic studies in healthy volunteers given a single 5 mg dose. Old age caused an increased volume of distribution of clotiazepam in women, and its clearance tended to be reduced in elderly men. Use of oral contraceptives, cimetidine, isoniazid or a single dose of ethanol had no significant effect on the kinetics of clotiazepam. Although clotiazepam is biotransformed by microsomal oxidation, its clearance appears to be relatively uninfluenced by factors known to alter the clearance of other oxidized benzodiazepines.

Differential effect of isoniazid on triazolam oxidation and oxazepam conjugation

Healthy volunteers received a single dose of triazolam (0.5 mg) or oxazepam (30 mg) on two occasions, once in the control state and again during coadministration of isoniazid (INH) base, 180 mg day. INH coadministration prolonged triazolam half-life (3.3 vs 2.5 h, P less than 0.05) and increased total area under the curve (38.6 vs 26.5 ng ml-1 h, P less than 0.01) consistent with a reduction of apparent oral clearance (3.9 vs 6.8 ml min-1 kg-1, 0.05 less than P less than 0.1). INH coadministration had no influence on the kinetics of oxazepam. INH impairs hepatic microsomal oxidation of triazolam, leading to reduced first-pass hepatic extraction as well as prolonged half-life. However INH had no influence on oxazepam conjugation.

Antipyretic analgesic drugs as models for studies of drug disposition in old age

Alterations in drug metabolizing capacity associated with the aging process can be elucidated using analgesic-antipyretic agents as model compounds. Antipyrine serves to profile drug oxidizing capacity. Drug oxidation is significantly impaired in old age, but age-related changes are far greater in men than in women. Acetaminophen analogously serves to profile conjugating capacity, which is minimally influenced by age both in men and in women. Changes in the capacity to biotransform these model compounds are reasonably well predictive of parallel changes in the same person's ability to metabolize other drugs transformed by the same pathway.

Pharmacokinetics of oxprenolol in the elderly

This paper is a brief review of the problems associated with drug therapy in the elderly. Although the elderly are more prone to suffer adverse reactions to drugs and to respond abnormally, impaired drug handling should not be blamed for these problems until other factors have been evaluated. Renal function deteriorates as people grow older, but the absorption, metabolism and distribution of most drugs may not be adversely affected by advancing age. Evidence to the contrary is sometimes based on studies of convalescent patients in whom an effect of disease or drug therapy cannot be excluded. For an assessment of the effects of aging on the pharmacokinetics of oxprenolol, 2 groups of 8 healthy females, mean age 21 and 68 years, respectively, were studied. Oxprenolol, 80 mg, was given orally in a single dose on day 1 and day 8 of a course of treatment; on the intervening days, oxprenolol, 80 mg, was given twice daily. The mean plasma concentration:time curves for both day 1 and day 8 for the 2 age groups were comparable. Thus, age alone does not affect the pharmacokinetics of oxprenolol.

Distribution and excretion of 2,3,6,2',3',6'- and 2,4,5,2',4',5'-hexachlorobiphenyl in senescent rats

The disposition of two symmetrical [14C]hexachlorobiphenyls (HCBs), 2,3,6,2',3',6'-HCB (236) and 2,4,5,2',4',5'-HCB (245), was studied in 24-month-old male Sprague-Dawley rats after iv treatment. Because body composition changes with age, complete dissections were performed on all rats to determine the size of the skin and adipose tissue depots. More than 50% of 236 was metabolized and excreted via the bile into the feces within 2 days. In contrast, 245 redistributed from the liver, muscle, and skin to adipose tissue where it accumulated without being metabolized. Only 2% of the total dose of 245 was excreted primarily in the feces within 21 days. The data obtained in this study were compared to results previously obtained from 2- to 3-month-old rats in this laboratory (Matthews and Tuey, 1980, Toxicol. Appl. Pharmacol. 53, 377-388). Although the general pattern of HCB disposition did not change with age, i.e., metabolism and excretion of 236 versus persistence of 245, there were differences in the rates of elimination and in the tissue levels. There was enhanced metabolite retention in the muscle, skin, and adipose tissue of older animals which suggested an age-related decrease in tissue clearance. The large volume of adipose tissue in these older Sprague-Dawley rats could in part explain this observation. In general, there were few changes in decay rates from tissues or in biliary excretion. Age had a greater effect on the disposition of the persistent 245 than on the metabolizable 236. Thus, changes in body composition seemed to play a major role in age-related changes in the distribution and excretion of polychlorinated biphenyls.

A survey of generic drug legislation and geriatric pharmacotherapy: opinions of those who generate the literature

Eighty-three authors who had published papers within the last five years on pharmacologic therapy in aged humans were surveyed by written questionnaire and their responses analyzed. The survey sought opinions on the scientific, clinical, and social context of legislation on drug product selection (generic legislation) and its relationship to geriatric pharmaco-therapeutics. The majority of respondents: 1) were generally unaware of the content of the clinical or scientific opinion offered on the subject of drug product selection as part of the legislative process; 2) felt that potential cost savings for elderly people was a factor in advancing this legislation; 3) wrote prescriptions so that product substitution could occur despite their ambivalence about such substitutions and about the knowledge of pharmacist and physician concerning product substitution and drug equivalence for the elderly. Clinical pharmacologists and geriatricians, however, were less likely than other respondents to permit substitution. The implications of current opinions and practices regarding drug product selection for geriatric patients are discussed.

Pharmacokinetics of valproic acid in young and elderly subjects

The disposition of valproic acid was studied following single dose intravenous administration in seven young male volunteers aged 20-35 years and six elderly male in-patients aged 75-87 years. Following administration of 400 mg sodium valproate, blood samples were collected for 48 h and valproic acid concentrations analysed by enzymatic immunoassay. The median elimination half-life was 7.2 h in the young subjects but 14.9 h in the elderly patients (P less than 0.01). However, clearance did not differ significantly between groups, the values for young and old being 0.69 and 0.58 1/h respectively. The prolonged half-life resulted from a greater volume of distribution in the elderly. The median values (1/kg) for young and old were 0.13 and 0.19 respectively (P less than 0.01). These pharmacokinetic changes are unlikely to be of clinical importance.

Pharmacokinetics of ketoprofen in the elderly

Pharmacokinetic constants of ketoprofen (Orodis, Profenid) were determined in 10 young adults (24.9 +/- 1.3 years) and seven elderly patients (86.3 +/- 2.4). Following oral administration of a 150 mg dose of ketoprofen, no difference in tmax was observed between the two groups. However, compared with younger subjects elderly patients showed a significant increase in t1/2,z (2.72 +/- 0.22 vs 1.77 +/- 0.16 h; P less than 0.01) and AUC (70.4 +/- 6.4 vs 29.13 +/- 2.02 mg l-1 h; P less than 0.001), a non-significant reduction of Vd/F per kg bodyweight (0.145 +/- 0.016 vs 0.213 +/- 0.028 l kg-1) and a decrease in total clearance CLT/F (0.037 +/- 0.002 vs 0.071 +/- 0.004 l h-1 kg-1, P less than 0.05). These results suggest that the glucuroconjugation of ketoprofen is slowed down by age.

Reduced clearance of triazolam in old age: relation to antipyrine oxidizing capacity

Thirty-three healthy male and female volunteers aged 21 to 87 years received a single 0.5 mg oral dose of triazolam. Plasma triazolam concentrations were measured in multiple samples drawn during 24 h after the dose. Mean triazolam elimination half-life was not significantly different between young and elderly men (3.0 vs 4.6 h), nor between young and elderly women (2.7 vs 3.2 h). However, apparent oral clearance of triazolam was significantly reduced in elderly as compared to young groups of both sexes, leading to higher peak plasma concentrations and increased total area under the curve. Values of half-life and clearance of antipyrine, a low-extraction hepatically oxidized compound, were poorly correlated with those of triazolam (r = 0.34 and 0.44, respectively), suggesting different mechanisms controlling age-related changes in clearance of these two hepatically oxidized drugs.

Geriatric hypertension

Hypertension in the elderly is a frequent occurrence and is associated with an increase in cardiovascular complications. Therapeutic drug intervention in diastolic-systolic hypertension is both safe and effective in decreasing cardiovascular morbidity and mortality. Convincing evidence supporting the value of therapeutic intervention in isolated systolic hypertension is not yet available. At present, selection of specific antihypertensive drugs remains empirical because of insufficient controlled trials in elderly hypertensives. Antihypertensive agents should be initiated in smaller dosages and titrated upward slowly with particular care in avoiding orthostatic hypotension. Above all, lifestyle modification should be kept to a minimum and special attention should be given to the patient's quality of life while on drug treatment.

Determinants of the pharmacokinetics of antithrombotic drugs

This review describes a variety of factors which determine the pharmacokinetics of antithrombotic drugs, viz., elimination by hepatic and/or renal clearance, plasma protein binding and drug disposition in the geriatric population. An understanding of biotransformation of acetylsalicylic acid and sulfinpyrazone is critical to understanding their usefulness as antithrombotic agents. Acetylsalicylic acid is rapidly hydrolysed to salicylic acid in the body and the latter may be eliminated by five different routes. Two of the biotransformation processes involving salicylic acid are readily saturable. For this reason, salicylate concentration increases more than proportionately with an increase in dose. Acetylsalicylic acid, but not salicylic acid, acetylates cyclo-oxygenase resulting in its inactivation. It is important in pharmacokinetic studies to measure plasma levels of both acetylsalicylic acid and salicylic acid. Biotransformation of sulfinpyrazone involves oxidation to the sulfone and reduction to the sulfide. The sulfide has marked antiplatelet activity. Dipyridamole undergoes hepatic biotransformation to a monoglucuronide which is eliminated by biliary and fecal excretion. Sulfinpyrazone, dipyridamole and salicylic acid are highly bound to plasma proteins. Since binding diminishes with age, one must expect therapeutic and toxic effects at lower plasma drug concentrations in the geriatric population. Other factors to be considered in the geriatric group are altered distribution, diminished glomerular filtration rate, and diminished oxidative biotransformation.

Carcinogenesis and aging

Figure 2 illustrates a suggested mechanism of carcinogenesis. This scheme takes into account the effect of carcinogens at different integration levels: subcellular, tissue, and organism. Any of these levels may be age dependent. Age-associated changes in the activity of enzymes responsible for activation and inactivation of carcinogens, and variations in concentrations of lipids and proteins contributing to the transport of carcinogenic agents into cells, may play an important role in the modifying effect of age on carcinogenesis. The effects of age-associated changes in DNA repair need clarification. However, they are thought to exert a permissive influence on the age-associated rise in tumor incidence. It seems that proliferative activity of target tissues is the important modifying factor of carcinogenesis. Age-related changes of regulation at tissue and organism levels are also powerful factors in carcinogenesis modification. Age-dependent changes in the neuroendocrine system provide conditions for metabolic immunodepression and promotion of carcinogenesis. On the other hand, carcinogens per se (especially chemical and radiological) may intensify aging processes in the organism. Normalization, by drugs, of age-associated shifts requiring synthetic and energetic changes of a transformed tumor cells, and of immunological shifts, may exert both antitumor and geroprotective effects.

Reduced single-dose clearance of clobazam in elderly men predicts increased multiple-dose accumulation

The rate and extent of accumulation of clobazam and its major metabolite, desmethylclobazam, during multiple dosage with clobazam were evaluated in 4 similarly sized groups of young male, young female, elderly male, and elderly female volunteers. Subjects received single 10mg doses of clobazam daily for 22 consecutive days. Plasma levels were measured during and after the period of dosage. Compared with the young male subjects, elderly males had slower rates of clobazam accumulation and washout, higher steady-state plasma levels, and lower steady-state clearance. Accumulation of desmethylclobazam also was slower and more extensive in the elderly male group. Among females, however, age-related kinetic differences did not approach significance. Among all subjects, pharmacokinetic variables for clobazam determined in a previous single-dose study were highly consistent with the multiple-dose pharmacokinetic profile. Single-dose vs post-multiple dosage half-life, single-dose vs steady-state clearance, observed vs predicted accumulation ratios, and observed vs predicted steady-state plasma concentrations were all highly correlated, with regression line slopes close to unity. Thus, reduced single-dose clearance of clobazam in elderly men leads to slower and more extensive accumulation during multiple dosage. The single-dose pharmacokinetic profile of clobazam is highly predictive of drug behaviour during repeated dosage, suggesting that clobazam kinetics are dose- and concentration-independent within the range studied, and that self-induction or inhibition of clearance is not evident during 3 weeks of dosage.

Physiologic changes in old age: relation to altered drug disposition

Current knowledge of the effects of aging on drug disposition is reviewed. Although definitive studies are not always available, based on present evidence it appears that: 1) drug absorption is not impaired in the elderly; 2) drug distribution in the elderly may be altered by significant changes in the lipid/lean body mass ratio; 3) Phase I (non-synthetic) biotransformation reactions of the liver appear to be much more profoundly affected by aging than are Phase II (synthetic) reactions; 4) age-related effects of biotransformation can be different even for compounds that are very similar and undergo the same types of reactions. Important parameters of drug metabolism are also discussed, such as the need to use total clearance, rather than half-life, in assessing pharmacokinetics.