Use of Nystatin to Eliminate Spontaneous Revertants in Yeast

Studies of induction of suppressor mutants may be obscured by revertants already present in the treated population. Such revertants, which appear as a minority of prototrophs among auxotrophs, can be eliminated by pretreatment with nystatin before application of the mutagen. Treatment with nystatin, under the proper conditions, decreased the frequency of prototrophs about 30-fold. This is sufficient for studying induced mutation at frequencies close to the spontaneous frequency.     

Artificial Infections of Pneumocystis carinii in the SCID Mouse and their Use in the In Vivo Evaluation of Antipneumocystis Drugs

A model for the in vivo evaluation of antipneumocystis drugs has been developed in SCID mice infected intratracheally with cryopreserved mouse-derived Pneumocystis carinii. The development of a highly reproducible fatal P. carinii pneumonia occured within 10 weeks (mean survival time ± SEM = 72.2 ± 1.2 days). Continuous administration of dexamethasone (2 mg/liter in the drinking water) exacerbated the rate of onset of severe P. carinii pneumonia (mean survival time ± SEM = 63 ± 1.3 days) in SCID mice. The number of cysts per g of lung homogenate (homogenate counts) were maximal with an inoculum of 20,000 cysts at 6 weeks post infection. Homogenate counts correlated with infection scores (graded assessments of immunofluorescent cysts on lung impression smears) suggesting that infection scoring accurately and rapidly reflects the severity of P. carinii pneumonia in SCID mice. These studies led to the development of a drug screening protocol in which Pneumocystis-free female SCID mice (20–25 g) were started on dexamethasone 7 days prior to IT inoculation with a single dose of 20,000 cysts. Drugs were evaluated either for: a) prophylaxis (continuously from day 1 post infection) or b) treatment (from day 21 post infection) until day 42 post infection, when all mice were killed and infection scores determined. Co-trimoxazole (at 250 mg sulfamethoxazole + 50 mg trimethoprim/kg/day) given in the drinking water was found to be highly effective in both the prophylaxis and treatment of mouse P. carinii pneumonia. Co-trimoxazole remained very effective in the prophylaxis P. carinii pneumonia in the SCID mouse at 125 mg sulfamethoxazole + 25 mg trimethoprim/kg/day p.o. and showed some enhancement of efficacy over sulfamethoxazole alone at 125 mg/kg/day p.o., suggesting limited synergy between sulfamethoxazole and trimethoprim. The results presented provide confirmation of the usefulness and predictability of the model.     

Government Regulations and the Use of Drugs

I have tried to trace the new drug development pattern from 1766, when Withering obtained his medical degree, to the present.The role of governmental authority as defined by the 1962 Kefauver-Harris amendments to the 1906 law and the subsequently issued regulations has been summarized. Four phases of testing in man have been detailed.Something of the scientific or research capability of the pharmaceutical industry has been presented.It is concluded that in the period of over two hundred years of medical education in the United States, the university hospital has become more and more the focus of medical research, teaching and practice in the community. The safety and effectiveness in the use of drugs in the future will depend upon the liaison and rapport of the industry physicians, government officials and the university hospital teacher-clinical investigators (phase 1 and 2) in designing the most critical studies of the safety and effectiveness of new drugs.Whether the medical profession as we know it will participate more in the future than has been possible since 1962 in mass clinical trial (phase 3) before new drug approval by governmental authority remains to be seen.The final approbation or disapproval of a drug after NDA approval (phase 4) will continue to be in the hands of the participating physician as long as he can establish scientifically that the drug is the best possible agent for him to use in healing the sick and comforting the dying.     

Dangers in the Use of Some Potent Drugs

The chief dangers reported with some common drugs are reviewed. Hazards of antibiotic therapy include: the increasing incidence of sensitization to penicillin with occasional anaphylactic reactions; aplastic anemia with chloramphenicol, and the poor tolerance of infants for chloramphenicol; staphylococcal enterocolitis; unnecessary “prophylactic” use of antibiotics. Thiazide diuretics may precipitate potassium depletion, skin reactions, pancreatitis, blood dyscrasias, gout, diabetes mellitus and hepatic coma. Reserpine can increase gastric acidity, induce mental depression, and when used with digitalis lead to ventricular premature beats. Hydralazine may aggravate angina pectoris, cause tachycardia, and bring about a syndrome resembling disseminated lupus erythematosus. Guanethidine may result in loose stools, impotence, and postural hypotension. Hazards of phenothiazines include jaundice, parkinsonian states and tremors, convulsions, hypotension, and blood dyscrasias. The butanediols have numerous side effects including gastrointestinal, cutaneous and hypotensive reactions. Prolonged corticosteroid therapy introduces a new danger in surgical treatment. The progesterone-like drugs may induce masculinization of the female fetus.