Driving Under the Influence of Cannabis: A Framework for Future Policy

Marijuana is the most widely consumed illicit substance in the United States, and an increasing number of states have legalized it for both medicinal and recreational purposes. As it becomes more readily available, there will be a concurrent rise in the number of users and, consequently, the number of motor vehicle operators driving under the influence. This article examines the cognitive and psychomotor effects of cannabis, as well as current policy concerning driving under the influence of drugs. The authors performed a MEDLINE search on the epidemiology of cannabis use, its cognitive and psychomotor effects, and policies regarding driving under the influence of drugs. Twenty-eight epidemiological studies, 16 acute cognitive and psychomotor studies, 8 chronic cognitive and psychomotor studies, and pertinent state and federal laws and policies were reviewed. These search results revealed that marijuana use is associated with significant cognitive and psychomotor effects. In addition, the legalization of marijuana varies from state to state, as do the laws pertaining to driving under the influence of drugs. Marijuana is a commonly found illicit substance in motor vehicle operators driving under the influence of drugs. Current evidence shows that blood levels of tetrahydrocannabinol do not correlate well with the level of impairment. In addition, although acute infrequent use of cannabis typically leads to cognitive and psychomotor impairment, this is not consistently the case for chronic heavy use. To establish the framework for driving under the influence of cannabis policy, we must review the current published evidence and examine existing policy at state and federal levels.

Lumbosacral Radiculopathy: Inciting Events and Their Association with Epidural Steroid Injection Outcomes

Objective

Low back pain is the leading cause of worldwide disability, with lumbosacral radiculopathy accounting for over one-third of these cases. There are limited data on the relationship between etiologies and lumbosacral radiculopathy, and it is unknown whether specific causes predict treatment outcomes.

Design, Setting, and Subjects

This study explores patient-reported etiologies for lumbosacral radiculopathy in a chronic pain clinic between January 2007 and December 2015 and examines whether these causes affected epidural steroid injection outcomes.

Methods

We reviewed the medical records of 1,242 patients with lumbosacral radiculopathy who received epidural steroid injections. The recording of an inciting event was done contemporaneously based on note templates. A positive outcome following an epidural steroid injection was defined as ≥30% pain relief sustained for six or more weeks without additional intervention. Factors associated with epidural steroid injection outcome were analyzed by multivariable logistic regression.

Results

Fifty point seven percent reported an inciting event, and 59.9% of patients experienced a positive epidural steroid injection outcome. The most commonly reported causes were falls (13.1%), motor vehicle collisions (10.7%), and lifting (7.8%). Individuals with a herniated disc (56.3%) were more likely to report a precipitating cause than those with stenosis (44.7%) or degenerative discs (47.8%, P = 0.012). An inciting event did not predict treatment outcome. Factors associated with negative treatment outcome included opioid consumption (odds ratio [OR] = 0.61, 95% confidence interval [CI] = 0.39–0.95, P = 0.027), secondary gain (OR = 0.69, 95% CI = 0.50–0.96, P = 0.030), and baseline pain score (OR = 0.90, 95% CI = 0.84–0.97, P = 0.006). The number of levels injected was associated with a positive outcome (OR = 2.72, 95% CI = 1.28–6.47, P = 0.008).

Conclusions

Reported inciting events are common in patients with lumbosacral radiculopathy but are not associated with outcome following epidural steroid injection, and their occurrence is not always consistent with the purported mechanism of injury.

Comparisons of beta-adrenergic blocking properties of S- and R-timolol in humans

In animals, the R-enantiomer of timolol causes a significant reduction in intraocular pressure but had only 1/80 the activity of the S-enantiomer at extraocular receptors. The beta 1- and beta 2-adrenoceptor blocking properties of orally administered R- and S-timolol were compared in a double-blind placebo controlled trial in two groups of healthy men. Each subject in group A (n = 6) received placebo, 1 and 3 mg S-timolol and 25 and 75 mg R-timolol in random order, group B (n = 5) received placebo, 0.5, and 1 mg S-timolol and 3 and 10 mg R-timolol. In both groups, R- and S-timolol comparably inhibited isoproterenol-induced increases in heart rate (P < .05), forearm blood flow (P < .05, except at 3 micrograms/minute of isoproterenol after the R-doses in group B), and finger tremor (P < .05) in comparison with placebo. The findings for the R-enantiomer in this study were unexpected based on the animal studies and previous studies that demonstrated marked differences in beta blocking effects of other beta-blockers in which the R-enantiomers were less inhibitory.

The antihypertensive response to lisinopril: the effect of age in a predominantly black population

After a 2-4 week no-treatment period, 24 patients (12 young, age 29-45 yr.; 12 elderly, age 65-81 yr.; 20 black, 4 white) with an untreated sitting diastolic blood pressure between 91-120 mm Hg received the nonsulfhydryl angiotensin converting enzyme inhibitor, lisinopril for three weeks in a singleblind, parallel group comparison. Patients who did not achieve goal blood pressure with the initial low-dose (10 mg/day) were treated with a high-dose regimen (40 mg/day) for three weeks. In those who remained incompletely responsive, hydrochlorothiazide 25 mg/day was added for four weeks in an attempt to normalize blood pressure (less than or equal to 90 mm Hg). Low-dose lisinopril monotherapy produced comparable reductions in the mean systolic and diastolic blood pressures (approximately -15/-8 mm Hg in both younger and older patients). Increasing the dose produced a slightly greater fall in mean blood pressures which normalized the blood pressure in five of six elderly patients unresponsive to the lower dose; addition of hydrochlorothiazide normalized three of the five remaining subjects from both groups who were unresponsive to high dose lisinopril. Lisinopril administration resulted in a rise in plasma renin activity and a fall in plasma aldosterone concentrations which were similar in both groups and which returned over time toward the baseline. The drug was well tolerated, producing one episode of symptomatic hypotension following the addition of hydrochlorothiazide to lisinopril monotherapy. Lisinopril alone or in combination with hydrochlorothiazide produces favorable antihypertensive effects in both younger and older predominantly black, low-renin patients with essential hypertension.

Pathophysiology of hypertension in older patients

More than half of the United States population over 65 years of age has essential hypertension. In 1984, there were 10 million elderly hypertensive persons and this number will reach 25 million in the near future. These patients are at high risk for congestive heart failure, stroke, heart attack, and dissecting aneurysm. Successful reduction of blood pressure can lower these risks considerably, but rational treatment depends on understanding the complex pathophysiology of hypertension in older patients. In fact, treatment that does not take into account the combined effects of aging and hypertension on the cardiovascular system and the kidneys may do more harm than the hypertension itself. Among the prominent age-related cardiovascular changes are stiffening of the arterial tree, with or without a contribution from atherosclerosis. This reduces arterial compliance and increases afterload, resulting in the left-ventricular hypertrophy seen in old age and leading to a progressive rise in systolic pressure. There is considerable shrinkage of the kidneys, due primarily to loss of glomerular and tubular tissue in the cortex, along with sclerosis of the glomeruli and formation of tubular diverticula. Arteriolar changes lead to reduced renal blood flow, the shunting of blood around the glomeruli, and thus a reduction in glomerular filtration rate. Renal water and electrolyte excretion are changed, making homeostasis more difficult to maintain, and the renin-angiotensin system is altered, helping to blunt the kidneys' response to pressure changes. Essential hypertension superimposed on all the foregoing effects exacerbates them. Peripheral resistance is usually markedly elevated in older hypertensive persons, which increases afterload directly.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of food on the absorption of enteric-coated aspirin: correlation with gastric residence time

The Heidelberg capsule is an indigestible indicator of gastrointestinal pH, which was used to evaluate the relationship between gastric residence time (GRT) and variability in aspirin absorption from enteric-coated tablets. In a crossover study, eight healthy subjects (four men and four women) received an enteric-coated aspirin (648 mg) together with a Heidelberg capsule while fasting or with food (breakfast, followed 4 hours later by lunch). Salicylic acid and salicyluric acid concentrations in plasma and urine were measured by HPLC. The mean (+/- SD) GRT was significantly delayed by food (0.8 +/- 0.5 vs. 5.9 +/- 3.3 hours; P less than 0.005). The mean (+/- SD) lag time (TL) and time to peak concentration (expressed as salicylic acid equivalents) were markedly prolonged after the fed regimen (2.7 +/- 0.8 vs. 8.9 +/- 3.7 hours [P less than 0.005] and 8.3 +/- 2.9 vs. 13.8 +/- 4.5 hours [P less than 0.025]). For the combined data from the fasting and fed evaluations, an excellent correlation existed between TL and GRT of the capsule (TL = 1.0 GRT + 1.95; n = 16; r = 0.94; P less than 0.0001). Women demonstrated greater delays in GRT and TL than did men. The delay in aspirin absorption from an enteric-coated tablet is directly related to its GRT, which is gender related and greatly affected by food.

Geriatric clinical pharmacology

Age-related physiologic changes may significantly alter drug disposition and dynamics in the elderly. This is especially important for cardiovascular drugs, because they are used with such high frequency in the geriatric population. Alterations in the pharmacokinetics and pharmacodynamics of several drugs used to treat cardiovascular disease have been demonstrated in the elderly. Knowledge of these alterations may aid in more rational prescribing of cardiovascular drugs in the geriatric population.

Clinical pharmacology of enalapril

Enalapril is administered as the ethyl ester of the potent angiotensin converting enzyme (ACE) inhibitor enalaprilat. As such, it is 60% absorbed and 40% bioavailable as the active species. Absorption is not affected by food. Serum concentrations are proportional to dose, less a small drug residue apparently bound to the enzyme. The half-life for accumulation is approximately 11 h. The drug is eliminated by the kidney without further metabolism. Maximum inhibition of plasma ACE occurs 2-4 h after administration and persists for more than 24 h with clinical doses. ACE inhibition is associated with increases in plasma renin and angiotensin I levels, decreases in angiotensin II and aldosterone concentrations and reduction in blood pressure. All of these events are closely correlated when analysed statistically. The clinical and haemodynamic effects of these actions are addressed in other papers.

In summary: satellite symposium on central alpha-adrenergic blood pressure regulating mechanisms

This symposium reviewed the fundamental principles, pharmacology, and clinical pharmacology of central alpha-adrenergic blood pressure regulating mechanisms. Fundamental principles Arterial baro- and chemoreceptor signals reach the nucleus of the tractus solitarius (NTS) via vagal and glossopharyngeal afferents. The NTS communicates with sympathetic preganglionic neurons in the spinal cord via centers and tracts in the medulla, pons, and hypothalamus that include an alpha-adrenergic inhibitory network. Descending tracts emphasized in this symposium originate in the C-1 epinephrine cells of the medulla, B-1 and B-3 serotonin cells of the medulla, and A-5 norepinephrine cells of the pons. Transmitters involved are norepinephrine, epinephrine, serotonin, glutamate, and gamma-aminobutyric acid (GABA). Catecholamine enzymes share protein domains in their primary structures and may be coded by linked or single genes. New methods of purifying and locating alpha- and beta-receptors have been developed. Pharmacology Methyldopa, clonidine, and clonidine-like drugs lower blood pressure by stimulating postsynaptic alpha 2-receptors in a brain stem inhibitory network, which down-regulates these receptors. Alpha 1-receptors were found to be higher in normotensive than in hypertensive rats and were increased in the latter by methyldopa administration. Alpha 2-receptors were found to differ in various tissues, which permits the development of highly selective agonists and antagonists. Although alpha-methylnorepinephrine is probably the principal metabolite of methyldopa, alpha-methylepinephrine and alpha-methyldopamine may also contribute. The site of action usually is identified as the NTS. Possible roles for the descending tracts were suggested. Clinical pharmacology Methyldopa, clonidine, guanfacine, and related drugs lower blood pressure principally by CNS mechanisms but peripheral actions may also contribute.(ABSTRACT TRUNCATED AT 250 WORDS)

Methyldopa does not alter the disposition of digoxin

To investigate whether methyldopa alters digoxin disposition, eight healthy subjects received methyldopa titrated to 250 mg t.i.d. or placebo in a double-blind, cross-over manner for 16 consecutive days, with 0.25 mg intravenous digoxin coadministered on day 5 and 0.25 mg oral digoxin on days 9 to 16. Digoxin concentrations in plasma and urine were measured by RIA. Although assay sensitivity did not allow an adequate assessment of serum AUC(0-infinity) after intravenous administration, mean digoxin AUC(0-24) was 10.2 +/- 3.5 and 10.0 +/- 1.8 ng/ml X hr with placebo and methyldopa, respectively (P greater than 0.05). Mean urinary excretion after digoxin with or without methyldopa treatment was 0.204 +/- 0.34 and 0.197 +/- 0.38 mg, respectively. The mean steady-state serum concentrations of oral digoxin (AUC(0-24)/zeta) with and without methyldopa were 0.65 +/- 0.2 and 0.62 +/- 0.3 ng/ml, respectively. These data revealed no significant differences (P greater than 0.05) for various parameters with power of greater than 0.8 to detect meaningful differences of approximately 30 per cent. Thus, methyldopa did not alter digoxin disposition in healthy subjects, and a pharmacokinetic interaction in patients is unlikely.

Overview: the role of angiotensin-converting enzyme inhibitors in cardiovascular therapy

Angiotensin-converting enzyme (ACE) inhibitors favorably modify control mechanisms that are disturbed in hypertension and congestive heart failure, principally, but perhaps not exclusively, through reduction in angiotensin II levels. Pharmacodynamic actions are vasodilation, increased sodium excretion, and lowering of blood pressure. Investigations with captopril and enalapril in the treatment of hypertension indicate efficacies comparable to each other and to current step 1 and 2 agents. Enalapril is more potent than captopril and has a longer duration of action. The hemodynamic mechanism of action is reduction in peripheral vascular resistance. Addition of a diuretic potentiates blood pressure lowering and proportion of patients responding. When used in congestive heart failure, ACE inhibitors exert a balanced vasodilator effect on arterial and venous beds and do not induce tachycardia or fluid retention. Cardiac output is increased whereas systemic vascular resistance, central pressures, and systemic blood pressure are reduced acutely and chronically. Although captopril is associated with certain side effects, possibly resulting from the sulfhydryl group in its structure, this profile has not been encountered thus far in clinical investigations with enalapril. The effects of ACE inhibitors on the natural histories of hypertension (independent of blood pressure lowering) and congestive heart failure are yet to be determined.

Relationships among timolol doses, plasma concentrations and beta-adrenoceptor blocking activity

1 We investigated the relationships among dose, plasma concentration and beta-adrenoceptor blockade after single and repeated doses (0.5-20 mg) of timolol and placebo in six normal men. 2 Maximal suppression of exercise-induced tachycardia (bicycle ergometry) was dose-dependent and greater at 2 than at 6 h after dosing; activity up to 12 h was evident on the last dosing day. 3 Attenuation of exercise-induced tachycardia was strongly correlated with the timolol dosage over the 0.5 to 5-10 mg range. 4 A plasma timolol concentration of 27 ng/ml was associated with maximal suppression of exercise-induced tachycardia. 5 Suppression of exercise-induced tachycardia and areas under the plasma concentration-time curves did not differ significantly on the first and last dosing days.

Pharmacology of enantiomers and (-) p-OH metabolite of indacrinone

Indacrinone, a racemic mixture, is a loop-blocking diuretic with effects on uric acid elimination that differ from those of furosemide. A series of studies in healthy men was undertaken to characterize the pharmacologic activity of the positive (+) and negative (-) enantiomers (E) of indacrinone and its (-) p-OH metabolite, (-) MET. All subjects were on sodium- and potassium-controlled diet; each experiment was similar in design and included placebo and positive controls. Oral (-)E and (-)MET exerted dose-related natriuretic and diuretic effects; intravenous doses of (-)E were more effective than (-)MET. The effects of (-)E and (-)MET on serum uric acid were the same as those reported with indacrinone. After (-)E, both (-)E and generated (-)MET appeared to contribute to the natriuresis. (+)E induced dose-related decreases in serum uric acid up to 24 hr after dosage; at the higher doses of (+)E, the hypouricemic effects were of the order of those after 500 mg of probenecid. Thus, indacrinone is a novel loop diuretic with enantiomers and a (-)MET, each of which has a different pharmacologic profile.

Three new long-acting converting-enzyme inhibitors: relationship between plasma converting-enzyme activity and response to angiotensin I

Three new angiotensin converting-enzyme inhibitors were given orally to 20 men in single doses ranging from 1.25 to 40 mg. Two of them induced comparable marked inhibition of both the blood pressure response to exogenous angiotensin I and plasma converting-enzyme activity. Onset of action was relatively slow, but 21 to 24 hr after drug plasma converting-enzyme activity was still clearly reduced. The third was less active. There was a close correlation between blood pressure response on administration of angiotensin I and plasma converting-enzyme activity. There were no adverse effects. These new drugs are interesting because of their long duration of action. The measurement of plasma converting-enzyme activity seems useful for monitoring efficacy of converting-enzyme blockade and compliance to therapy.

Effect of orally administered probenecid on the pharmacokinetics of cefoxitin

To characterize the effect of orally administered probenecid on the pharmacokinetics of cefoxitin in healthy male volunteers, we administered to one group of six subjects 2 g of cefoxitin by intravenous (i.v.) bolus either alone, with 1 g of probenecid concomitantly, or when 1 g of probenecid was administered 1 h previously by using a crossover design. Likewise, we administered to a second group of six subjects 2 g of cefoxitin intramuscularly (i.m.) together with 1 and 2 g of probenecid. Probenecid increased the mean terminal half-life and the area under the serum cefoxitin concentration-time curve (AUC0-24) and decreased renal clearance, but did not alter the volume of the central compartment or the total urinary recovery of i.v.-administered cefoxitin; pretreatment with probenecid produced a greater increase in cefoxitin AUC0-24 and a constant decrease in renal clearance compared to concomitant probenecid. The AUC0-24 after i.m.-administered cefoxitin was greater after 2 g than 1 g of probenecid; the AUC0-24 after i.v.-and i.m.-administered cefoxitin was similar after 1 g of probenecid was given concomitantly. Cefoxitin AUC0-24 was increased further when 1 g of probenecid was given before i.v.-administered cefoxitin or when 2 g of probenecid was given with i.m.-administered cefoxitin. The effect of probenecid was related to both timing and dose.